Workbook Flashcards
1
Q
What percent of the atmosphere is nitrogen?
A
78%
2
Q
What percent of the atmosphere is oxygen?
A
21%
3
Q
What is the percent of other (argon etc) gases in the atmosphere?
A
1%
4
Q
What percent of water vapour is in the atmosphere that gives us ‘weather’?
A
4%
5
Q
What are the atmospheric constituents that vary?
A
Water vapour, CO2 and solid particles like dust and ash
6
Q
What role does CO2 play in the atmosphere
A
CO2 (greenhouse gas) plays a large role in absorbing Earth emitted heat and so warming the atmosphere. This is known as the greenhouse effect
7
Q
What role does ozone play in the atmosphere
A
Ozone (O3) provides a protective layer in the lower stratosphere. As ozone absorbs the suns UV radiation it warms and heats the atmosphere above it (Stratospheric inversion)
8
Q
What role do solid particles play in the atmosphere
A
Solid particles suspended in the atmosphere play a major role in the formation of clouds
9
Q
Describe the troposphere
A
The troposphere is the lowest layer. It extends from the surface upwards and where it ends is called the tropopause. The troposphere is defined as being an area where there is a reduction of approx 2°C in temp with every 1,000 foot gain in altitude. Where this temperature reduction stops is where the end of the troposphere is – the tropopause
10
Q
How is the atmosphere divided
A
The atmosphere is divided into layers based on change of temperature with a gain in height
11
Q
Describe the tropopause
A
At the tropopause, the temperature remains the same with a gain in height. This is an example of an isothermal layer
12
Q
Where does most of the weather occur
A
As the troposphere is the layer closest to the Earth’s surface, the troposphere contains almost all atmospheric moisture and this is where most significant weather occurs
13
Q
Describe the stratosphere
A
Above the tropopause is the stratosphere where temperature increases with a gain in height. This is due to the ozone layer being located in the stratosphere
14
Q
The tropopause
A
The tropopause is where temperature stops decreasing with a gain in height and instead remains the same with a gain in height. The altitude and temperature at where this occurs varies around the Earth
15
Q
Is the tropopause hotter or colder over the equator?
A
As the tropopause is highest over the Equator, it is therefore coldest over the Equator
16
Q
Is the tropopause hotter or colder over the poles
A
As the tropopause is lowest over the Poles, it is therefore warmest over the Poles
17
Q
Why is the tropopause higher over the equator
A
The reason the tropopause is higher over the Equator compared to the Poles is because of differences in air density
18
Q
What is air density
A
Air density is a measure of the amount of air molecules within a given volume of air. Air density is primarily affected by two variables, temperature and pressure
19
Q
Why is a column of air taller in warm air and shorter in cold air
A
Temperature is a measure of heat energy (kinetic energy) contained within a body. If air has a high temperature, the air molecules will have high kinetic energy, bounce off one another and take up space. This will therefore reduce the amount of molecules within a given volume and therefore reduce air density. If air has a low temperature, the air molecules will have low kinetic energy, will not bounce off one another as much and take up less space. This will therefore increase the amount of molecules within a given volume and therefore increase air density. If the volume is not fixed, warm air will cause a column of air to expand and cold air will cause it to contract
20
Q
What is pressure
A
Pressure is a measure of the ‘weight’ of a column of air above a point. If air pressure is high, the force exerted by the atmosphere on a given volume will be high so more air molecules will be packed into that given volume therefore increasing density. If air pressure is low, the force exerted by the atmosphere on a given volume will be low so less air molecules will be packed into that given volume therefore decreasing density
21
Q
What density and temperature will increase and decrease aircraft performance
A
For the highest air density a combination of low temperature and high pressure is best. This will improve aircraft performance. If temperature is high and air pressure is low air density will be low and this will reduce aircraft performance
22
Q
Why is the tropopause different heights at the poles and equator
A
The difference in temperature between the Poles and Equator is the reason for different tropopause heights. At the Poles the air is cold so contracts. This reduces the height of the tropopause. At the Equator the air is warm so expands. This increases the height of the tropopause
23
Q
Describe temperature
A
Temperature is simply a measure of heat contained in a body. When the temperature rises it is due to the “hot plate effect” where the sun heats the earth and the warm air then begins to rise
24
Q
Heat radiation
A
All bodies emit heat radiation. This energy is in waves. The wavelength is affected by the amount of energy. High energy, has a short wavelength, low energy has a long wavelength. The sun emits short wavelength, high energy solar insolation. The Earth emits long wavelength, low energy terrestrial radiation
25
Solar insolation
The Earth only receives solar insolation during the day however it is constantly emitting terrestrial radiation. When there is more solar insolation than terrestrial radiation there is a net energy gain so temperatures increase. When there is more terrestrial radiation than solar insolation there is a net energy loss so temperatures decrease. This provides the basis for the ‘energy budget’ which gives an average global temperature of 15ºC at sea level
26
What percent of solar radiation reaches the earths surface
Not all incoming solar insolation reaches the Earth’s surface. Only around 45% reaches Earth with the rest being reflected, absorbed or scattered by the Earth’s atmosphere
27
The greenhouse effect
The Sun’s energy heats the Earth from below by conduction. Warm air then rises heating the rest of the atmosphere through convection. Carbon Dioxide and water vapour absorb outgoing terrestrial radiation and contribute to atmospheric heating. This is known as the ‘greenhouse effect’. If the amount of carbon dioxide in the atmosphere is increased this will enhance the greenhouse effect and increase global temperatures
28
The suns angle of inclination
Near the Equator the sun’s energy is spread out over a small area and so is concentrated and this gives higher temperatures. Near the poles, due to the greater angle of inclination of the sun, the energy is spread over a larger area and so is not as concentrated
29
What is albedo
Albedo is a measure of an object’s reflectivity. If reflectivity is high, Albedo will be high. Objects with high albedo reflect incoming solar insolation rather than absorbing it
30
What is specific heat
Specific heat is a measure of the energy required to heat a substance by 1ºC. If a substance has high specific heat then it requires a lot of energy to increase its temperature. It will therefore not heat up as fast
31
What is specific heat capacity
Specific heat capacity is a measure of how well a substance retains its heat. If it has a high specific heat capacity it will retain its energy well and therefore not cool down as fast
32
Maximum temperatures-diurnal variation
Maximum temperature will occur just after incoming solar insolation is at its greatest as it takes time for this energy to heat the Earth. The maximum temperature therefore occurs in the early afternoon
33
Minimum temperature-diurnal variation
The minimum temperature occurs at the time where there has been the longest amount of time where outgoing terrestrial radiation is greater than incoming solar insolation. This occurs just after sunrise
34
What affects diurnal variation
- Specific heat of the surface
- Specific heat capacity of the surface
- Wind
- Cloud cover
35
How does wind affect diurnal variation
Wind increases the mixing between warm and cold air. This reduces the maximum temperature and means the minimum temperature will not be as cold. This therefore reduces the diurnal variation
36
How does cloud cover affect diurnal variation
Cloud cover reflects back incoming solar insolation therefore reducing the amount that reaches the surface. It also creates a ‘blanketing effect’ trapping outgoing terrestrial radiation therefore meaning the minimum temperature will not be as cold. Cloud cover therefore reduces diurnal variation
37
What are inversions?
Inversions are where the temperature increases with a gain in height. Dust and pollutants are trapped below an inversion giving poor visibility below and inversion and good visibility above
38
What is isothermal
Isothermal are where the temperature stays the same with a gain in height. They have similar characteristics to an inversion. The tropopause is an example of an isothermal
39
What is atmospheric pressure
Atmospheric Pressure is a measure of force per unit area exerted by the weight of the column of air above the area. In nature, air travels from areas of high pressure to areas of low pressure. Variations in pressure over a horizontal distance results in surface winds and types of weather experienced at the surface
40
At what rate does pressure decrease as height increases
As height increases, pressure decreases. Pressure decreases at an exponential rate
41
What is atmospheric pressure measured in
This force is measured in hectopascals (hPa), millibars or inches of mercury (inHg)
42
Pressure variations with height
To understand how pressure changes with height, imagine an infinitely high column of air extending from sea level. The closer you are to the surface the more air molecules there are above you and therefore there is a greater mass of air acting down upon you. The higher you go the ‘thinner’ the air becomes
43
The aneroid barometer (measures air pressure)
An aneroid barometer works on the principle of sealed capsules that expand and contract based on the air pressure. This contraction drives a needle which is calibrated to indicate air pressure. An altimeter works on this principle and uses 3 capsules for its 3 needles. This method gives air pressure in millibars or hectopascals (hPa)
44
The mercury barometer (measures atmospheric pressure)
A mercury barometer works on the principle of air pressure exerting a force on a reservoir of mercury. If the air pressure increases, this causes the mercury in a tube to rise. The amount that it rises or falls is calibrated to give air pressure. Using this method, air pressure is given in inches of mercury (inHg)
45
Does cold or warm air have a greater pressure lapse rate
because pressure reduces much more rapidly in a cold column of air, cold air has a greater pressure lapse rate than warm air.
46
Surface variation with time and position
Uneven heat distribution throughout the Earth’s surface creates uneven densities and therefore uneven surface pressure. These differences in surface pressure over a horizontal distance trigger the transport of air over a horizontal plane – this called wind
47
What is pressure gradient
In nature air will always flow from high pressure to low pressure, an example is a balloon being blown up and then let go. The rate at which the air flow moves (the wind speed), will depend upon the pressure gradient which is dependent on:
- The difference in pressures between the pressure systems (pressure differential)
- The distance between the pressure systems
48
What are isobars
Isobars are lines that join areas of equal barometric pressure. The closer the isobars are, the greater the pressure gradient and therefore the stronger the winds. Closer isobars are created when either the pressure differential increases or the distance between the high and low pressure is reduced
49
Explain a depression/low pressure system
A depression is another name for a low pressure system where in the Southern Hemisphere the winds move around in a clockwise direction. A low has the lowest pressure in the centre of the system and increasing pressure outwards. Winds associated with a depression are generally strong and thus a strong pressure gradient will exist in a low
50
What is a trough
Is a system that extends from the centre of a low pressure system. Pressure increases either side of the axis while weather inside the trough is similar to that of the parent low. The shape of the trough is usually V shaped and maybe associated with a front
51
Explain an anti-cyclone/high pressure system
An anti-cyclone is another name for a high pressure system where in the Southern Hemisphere the winds move in an anti-clockwise direction. A high is generally associated with fine weather and light winds, indicating a weak pressure gradient
52
What is a ridge
As a trough is an extension of a low, a ridge is the extension of a high. Once again, similar weather can be expected with a ridge to that of the parent high. Thus the weather is often fine and clear. A ridge often forms as an egg shaped wing with fairly rounded curves. Pressures are always lower either side of the axis of the ridge
53
What is a col
A col is a system that exists between two lows and two highs. The pressure gradient within a col is almost non-existent and it is difficult to predict whether the high or the low will be the predominant system. Often hazy and poor visibility conditions can be expected and due to the weak pressure gradient, light and variable winds exist
54
What is the international standard atmosphere? (ISA)
The atmosphere is a constantly changing and dynamic body with many variables. It was therefore necessary to establish a global average. The International Standard Atmosphere is the solution (ISA) ISA is based on measurements at Mean Sea Level (MSL)
55
What is the ISA average sea level temperature
+15 degrees
56
What is the ISA average temperature lapse rate
2 degrees/1,000ft (1.98)
57
What is ISA average sea level pressure
1013.25hPa
58
What is ISA average pressure lapse rate
1hPa per 30ft
59
What is the height of the tropopause
36,090ft
60
What is the temperature of the tropopause
-56.5 degrees
61
Define condensation nuclei
Small particle such as salt, carbon, soot or dust etc for water vapor to condense onto
62
Define super saturation
Where there is a lack of Condensation Nuclei, water vapour cannot condense.
63
What is latent heat
Latent heat is the extra energy required or released when a substance changes state. It does not affect the temperature of the substance however it will warm or cool the surrounding environment depending on whether latent heat is released or absorbed. The measurable change in temperature of the surrounding environment is called ‘sensible heat’
64
What is relative humidity
Relative Humidity is the ratio of the weight of water vapour in a given volume of air (absolute humidity) to the maximum weight of water vapour that the same volume can actually hold at the same temperature (saturation content), expressed as a percentage
65
Dew point
A dew point is a temperature at which a parcel of air saturates under constant pressure. It is important to note that dew point is a temperature not a height
66
What happens when a parcel of air reaches its dew point
When a parcel of air reaches its Dew Point, relative humidity is 100%. Cooling beyond this will result in the air no longer being able to hold additional moisture so it will condense forming visible moisture – cloud
67
What happens when relative humidity changes temperature
The relative humidity will change with a change in temperature. The warmer the air the more water vapour can be held before the air saturates, so with an increase in temperate RH decreases. This is the reason why the air feels so wet near the equator and so dry at the poles
68
What is the only thing that affects dew point
The dew point temperature is only affected by the actual water content of the air (absolute humidity).
69
What factors affect the rate of evaporation
The four main factors that affect the rate of evaporation are temperature, relative humidity, air pressure and wind
70
How does temperature increase the rate of evaporation
An increase in temperature will increase the air’s ability to hold moisture therefore increasing evaporation
71
How does relative humidity affect rate of evaporation
If relative humidity is low, then the air is not holding what it can potentially hold. This will increase the rate of evaporation
72
How does air pressure affect rate of evaporation
If air pressure is low then there is more room within a given volume of air to contain the vapour. Low air pressure increases the rate of evaporation
73
How does wind affect rate of evaporation
Wind increases a moisture sources exposure to dry air, therefore increasing the rate of evaporation
74
What factors will cause maximum evaporation
for maximum evaporation the air will be warm, dry, windy and have a low air pressure
75
Calculating relative humidity
R elative Humidity (%) = 100-5
| Difference between Temperature and Dew Point
76
Wet bulb/dry bulb (measuring atmospheric moisture content)
One thermometer is wrapped in a muslin rag which is soaking in a reservoir of water. If the air is dry, the rate of evaporation will increase and so water will evaporate from the reservoir. As latent heat is absorbed during evaporation, temperature drop will be shown on the thermometer wrapped in the muslin rag
77
Hair hydrometer (measuring atmospheric moisture content)
This works on the principle of measuring the length of hair. If the atmosphere is moist, then the hair will absorb moisture and expand. The length of the hair is then calibrated to give atmospheric moisture levels
78
Hydrometer (measures atmospheric moisture content)
This measures the density of air to give atmospheric moisture. Water vapour is less dense than dry air. The greater the moisture content, the lower its density. This is important to note as this means moist air will reduce aircraft performance
79
Describe stability of air
Stability of air is its ability to return to its original position after being disturbed by an external force. Stability in weather refers to the vertical movement of air and whether this movement is rising upwards or subsiding downward. It is by this stability that we can determine what type of cloud we will get, whether it will rain or not and even the temperature we might expect
80
What are airs tendencies if there stable, unstable or neutrally stable
Air that is stable will return to its original position after being disturbed by an external force. If air is unstable it will continue to move away from its original position. If the air stays in its new position and neither moves towards nor away from its original position, it is neutrally stable
81
What is a lapse rate
A lapse rate is the temperature decrease with a gain in height
82
What is adiabatic cooling
When air rises it’s pressure drops causing it’s volume to expand. This expansion requires energy so the temperature of the parcel of air decreases. This is called adiabatic cooling
83
What is adiabatic warming
When air subsides it’s pressure increases causing it’s volume to contract. This contraction releases energy so the temperature increases. This is called adiabatic warming
84
What is the environmental lapse rate (ELR)
Temperature decreases with a gain in altitude. The rate at which the temperature decreases varies day to day but for a standard set of conditions the temperature lapse rate is given as 2°C/1000 ft. So this tells us that on a “standard day” for every 1000ft we gain in altitude it will get colder by 2°C. The ELR is the temperature change with height of the ambient surrounding environment. The ELR can change
85
What is the dry adiabatic lapse rate (DALR)
Air that is less than 100% water is known as Dry Air. When forced to rise, dry air will cool. If forced to descend it will warm. This is known as the dry adiabatic lapse rate or the DALR. Dry air cools/warms at 3°C/1000ft. The DALR is constant and does not change
86
What is the saturated adiabatic lapse rate (SALR)
Air that is 100% relative humidity is known as Saturated Air. When forced to rise or descend, saturated air cools/warms at a different rate to dry air. This is known as the saturated adiabatic lapse rate or the SALR. Saturated air cools/warms at 1.5°C/1000ft. The SALR is constant and does not change
87
What are the two factors that determine whether air is stable or unstable?
- The temperature lapse rate of the surrounding ambient air (the ELR)
- The temperature lapse rate of the rising air (DALR for dry air or SALR for saturated air)
88
When the ELR is less than the DALR is air stable or unstable?
Stable
89
When the ELR is more than the DALR is air stable or unstable?
Unstable
90
When the ELR is less than the SALR is the air stable or unstable?
Stable
91
When the ELR is more than the SALR is the air stable or unstable?
Unstable
92
For an ELR that is less than 1.5 degrees/1000ft
* Both Dry and Saturated air is stable
| * ABSOLUTE STABILITY
93
For an ELR which is between 1.5/1,000ft and 3/1,000ft
* Dry air is stable, Saturated air is unstable
* Stability therefore depends on whether or not the parcel of air is dry or saturated
* CONDITIONAL STABILITY
94
For an ELR greater than 3/1,000ft
* Both Dry and Saturated air is unstable
| * ABSOLUTE INSTABILITY
95
What are clouds
In simple terms cloud is defined as suspended water in liquid droplet or solid ice crystal form. So when ever cloud is present, at some stage, water vapour has condensed (i.e. changed from a gas to a liquid state). For this condensation process to occur, air must contain Condensation Nuclei. These can be small hydroscopic particles of dust, salt or smoke which have a suitable surface for water to form on
96
What characteristics are clouds determined by
Shape
Vertical extent
Altitude
97
Formation of clouds
For clouds to form, air must rise. By whatever method air is lifted, the type of cloud that forms will depend on whether that air is STABLE or UNSTABLE
98
What methods can clouds form
Convective rising - heating of the earth’s surface or of the upper air
Orographic rising - due to significant terrain (i.e. mountain ranges) Mechanical lifting - due to small hills and buildings
Frontal lifting - cold dense air undercutting less dense warm air.
99
If rising air is stable, what type of clouds will form
If the rising air is stable this air will tend to form Stratiform type cloud. This is a layer cloud with small water droplets. Turbulence is generally light in these clouds as the air is stable and not rising
100
If rising air is unstable, what clouds will form?
If the rising air is unstable it will most likely form Cumuliform cloud. This is a heaped cloud with large water droplets. Turbulence can be moderate to severe in these clouds due to air rising from its instability
101
What are the three types of high clouds (17,000ft+)
Cirrus (Ci)
Cirrostratus (Cs)
Cirrocumulus (Cc)
102
What are the two middle clouds (7,000-17,000ft)
Altostratus (As)
| Altocumulus (Ac)
103
What are the six low clouds (7,000ft and below)
```
Stratus (St)
Cumulus (Cu)
Stratocumulus (Sc)
Towering Cumulus (Tcu)
Cumulonimbus (Cb)
Nimbostratus (Ns)
```
104
Cirrus (CI)
The most ethereal looking of all the main types, Cirrus clouds are also the highest, and are composed entirely of ice crystals. These typically fall through the high winds of the upper troposphere to appear as delicate, celestial brush strokes, called fallstreaks. This species of Cirrus, known as uncinus, has a hooked appearance, which indicates that the winds up at the cloud level are particularly strong. These clouds can indicate the presence of a Jet Stream or the approach of a warm front
Icing: no risk
Turbulence: light to moderate
Precipitation: none
105
Cirrostratus (CS)
Cirrostratus is composed of ice crystals. As it is so high it is very cold so its moisture content is very low. For this reason it is thin meaning the sun can still be seen through it. Often sunlight can be refracted by the ice crystals creating a halo around the sun.
Icing: nil
Turbulence: none
Precipitation: none
106
Cirrocumulus (CC)
Cirrocumulus is also composed of ice crystals. Its cold temperature means moisture content and therefore icing is not a risk. It often appears to resemble sheep’s wool
Icing: no risk
Turbulence: light to moderate
Precipitation: none
107
Altostratus (AS)
Altostratus is a mid-level, generally featureless, grey, overcast layer. It is a ‘Tupperware sky’ that often extends over several thousand square miles. Known by some as the boring cloud, Altostratus produces little more than a lingering drizzle or light snow. Once it is thick enough to produce more significant precipitation, it has generally developed into Nimbostratus
Icing: moderate to severe 4-6,000ft above freezing level
Turbulence: light to moderate
Precipitation: light
108
Altocumulus (AC)
This is a mid-level cloud (with bases between 7000ft and 17,000ft), which is typically a layer of joined or separated ‘cloudlets’. As it is lower than the high level clouds it is warmer and will therefore have a higher moisture content. It can be composed of water droplets and ice crystals. Altocumulus is one of the most dramatic and variable of the ten main cloud types, showing more possible species and varieties than any other.
Icing: moderate to severe 6-8,000ft above freezing level
Turbulence: moderate
Precipitation: light- in form of Virga
109
Stratus (ST)
This featureless, grey, overcast layer is the lowest-forming of all the cloud types, having a base that is typically no higher than 1,500ft. Stratus cloud like this that is down at ground level is called fog or mist.
Icing: moderate if above freezing level
Turbulence: nil significant
Precipitation: light drizzle
110
Cumulus (CU)
Cumulus are often described as ‘fair-weather clouds’ because they tend to form on sunny days. When they are small like these, they are the species known as ‘humilis’ (which means ‘humble’ in Latin). Cumulus generally have flat bases and bumpy, cauliflower-shaped tops
Icing: nil significant
Turbulence: light to moderate
Precipitation: none to light
111
Stratocumulus (SC)
In many parts of the world, Stratocumulus is a very common cloud type. It is a low layer, composed of individual or joined-up cloud clumps, known as ‘cloudlets’. Stratocumulus is generally less regular looking than the higher Altocumulus and Cirrocumulus layers of cloudlets. A high Stratocumulus cloud layer like this can be hard to distinguish from a low Altocumulus one. It is Stratocumulus when the base of the cloud layer is lower than 7000ft.
Icing: light to moderate above freezing level
Turbulence: light to moderate
Precipitation: none to light showers
112
Towering cumulus (TCU)
When the fair-weather clouds, known as Cumulus, grow taller than they are wide, they have developed into the largest species, known as ‘congestus’. These tall Cumulus often produce showers and can, if conditions are right, continue to grow into Cumulonimbus storm clouds. These clouds formed from large amounts of unstable air. Up draughts can be strong enough to ‘suck up’ a plane.
Icing: moderate to severe
Turbulence: moderate to severe
Precipitation: moderate showers to heavy showers
113
Cumulonimbus (CB)
This enormous storm cloud, which is often in the shape of a blacksmith’s anvil, can form individually or co-ordinate with neighbours to form ‘multicell’ and ‘supercell’ storms. The cloud is defined as a Cumulonimbus once its summit has changed from droplets to ice crystals, which give the top softer edges. Below a Cumulonimbus, you will see just its dark, ragged underside, which (being so low) appears to cover the whole sky. Cumulonimbus can form thunderstorms and have high moisture content and vast amounts of unstable air.
Icing: severe
Turbulence: severe
Precipitation: heavy showers
114
Nimbostratus (NS)
When people claim clouds are depressing, they’re often thinking of Nimbostratus. This thick, grey, featureless rain cloud gives all the other ones a bad name. Not only does it block much of the Sun’s rays, casting everything in a dim, miserable light, it also produces widespread rain – and lots of it. Nimbostratus generally results from the thickening and lowering of Altostratus clouds.
Icing: moderate to severe
Turbulence: none to light
Precipitation: moderate widespread rain to heavy widespread rain
115
How is cloud assessed
Cloud is assessed in how many eighths of the sky it covers. The term OKTAs is used to describe how many eighths
116
Sky's clear - SKC
0 oktas
117
Few - FEW
1-2 oktas
118
Scattered - SCT
3-4 oktas
119
Broken - BKN
5-7 oktas
120
Overcast - OVC
8 oktas
121
NSC
Nil significant cloud. (Oktas)
| Does not provide info on sky coverage
122
Cloud ceiling
A cloud “ceiling” is the height of the lowest level of cloud obscuring more than half of the sky (BKN or OVC)
123
Cloud base
A cloud “Base” is the height of any amount of cloud (FEW, SCT, BKN or OVC)
124
How is cloud base measured
Cloud searchlight
Ceilometer
Vaisala laser ceilometer
125
How can cloud be dispersed
- Adiabatic warming of subsiding air – warming causes relative humidity to decrease
- Warming of the air through surface conduction and convection
- Warming of air through absorption of solar or terrestrial radiation
- Reduction in buoyancy of air causing subsidence of air
- Mixing of saturated and unsaturated air reducing relative humidity -Precipitation resulting in a reduction in the relative humidity
126
Define wind
Wind is defined as the horizontal movement of air due to the forces acting upon it. Wind speed and direction is expressed as a velocity. Direction is given to the nearest 10° and is expressed as where the wind is coming from. For example a wind from the south is a southerly wind. If, however, the wind is expressed as where it is going, a southerly wind would be a northwards wind
127
Velocity and variation with height of wind
The principle reason for the movement of air is that variations of temperature and pressure cause air to flow. These pressure gradients have their origins in solar insolation. It is affected by cloud, surface (land or water), latitude and season. The sun’s energy is the prime cause of atmospheric motion
128
Backing and veering
If the wind change occurs in a clockwise direction then the wind is said to VEER. If the wind change occurs in an anti-clockwise direction then it is said to BACK. In the southern hemisphere the surface wind backs and increases after sunrise and it veers and decreases after sunset.
129
What is coriolis force
Due to the tilt and rotation of the earth the wind is subject to an apparent deflection force called Geostrophic Force or Coriolis Force (here in NZ).
This Coriolis force causes a deflection to the RIGHT in the NORTHRN HEMISPHERE and to the LEFT in the SOUTHERN HEMISPHERE
130
What is coriolis force proportional too
- The wind speed, the stronger the wind the stronger the turning force
- Latitude, the higher the latitude, the greater the Coriolis force
131
What are the two forces acting on coriolis wind
- Pressure gradient force acting from high to low
| - Coriolis force acting at 90° to the wind towards the high
132
What happens when coriolis force is equal to pressure gradient
When the Coriolis force is equal to the pressure gradient force, isobars will be straight
133
What happens when coriolis force is greater than the pressure gradient force
When the Coriolis force is greater, isobars will curve around the high.
134
What happens when the pressure gradient force is greater than coriolis force
When the pressure gradient force is greater, the isobars will curve around the low
135
What is the friction layer
Due to drag from the Earth’s surface, the wind at the surface is slowed down. The layer of air affected by this drag is known as the friction layer.
136
What is the depth of the friction layer?
The depth of the friction layer is approximately 2000 feet however this varies depending on the amount of surface drag. Over the land, where there is significant terrain, buildings and trees, there is a lot of drag so the friction layer is deep. Over the sea, there is a relatively flat surface so the friction layer is not very deep
137
Will wind speed decrease more over the sea or land
Greater surface drag will slow the wind speed to a greater extent. This means wind speed is decreased to a greater extent in the friction layer over the land compared to the sea.
138
What's the effect of the wind speed slowing down in the friction layer
The effect of the wind speed slowing down in the friction layer is that it causes a reduction in Coriolis force meaning the pressure gradient force is dominant and wind travels across the isobars.
139
Descending into the friction layer
D-descending
V- veers (wind direction)
D-decreases (wind speed)
140
Ascending out of the friction layer
A-ascending out
B-backing (wind direction)
I-increases (wind speed)
141
Amount of wind direction change due to the friction layer
Because the type of surface affects the friction layer, the amount that the wind direction will change will also be different
Land - wind speed decreases by 2/3
- wind direction change 30 degrees
Sea- wind speed decrease by 1/3
- wind direction change 10 degree
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Changes in the friction layer due to density
The affect of the friction layer will also be changed by the density of the air. During the day, air is warm so the air within the friction layer will be less dense. This will mean that it will not slow down the wind by as much and therefore the wind will travel more parallel to the isobars. At night when temperatures are colder, the air becomes denser. This slows the wind speed down to a greater extent and results in wind travelling across the isobars
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What's the effect of the friction layer on pressure systems
As wind speed is slowed down at the surface it results in a decrease in the coriolis force. This causes wind to travel across the isobars from high to low. This has the effect of decreasing the pressure in a high pressure system and increasing the pressure in a low pressure system.
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Effects of the friction layer on a HIGH pressure system
As air moves away from the high at the surface, in a high pressure system there is low level divergence of air. Air subsides within the high to replace the air and there is high level convergence at altitude. As air is subsiding within a high, it warms adiabatically resulting in a decreased relative humidity and therefore clear, generally cloud free, skies.
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Effects of the friction layer on a LOW pressure system
In a low pressure system, air moves towards the centre of a low at the surface, it then rises and cools adiabatically. This increases the relative humidity and when the air reaches saturation it condenses giving cloudy skies. At altitude the air diverges
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Buy ballots law
Buy Ballot’s law states that if an observer were to stand with their back to the wind, in the Southern Hemisphere, the area of low pressure would be on one’s right
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Applying buy ballots law to see if your flying toward or away from a high or low pressure system
Applying Buy Ballot’s law, if you were to stand with your back to the wind, the area of low pressure is to your right. This means that, from the aircraft’s perspective, the area of low pressure is ahead of the aircraft. The aircraft is flying from high to low so if the altimeter is not adjusted, the aircraft’s true altitude would be lower than indicated. As it is flying towards a low pressure system, cloudy skies and increased wind speeds could be anticipated
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Windsock 30 degrees
8kts
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Windsock 45 degrees
15kts
150
Windsock 75 degrees
22kts
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Windsock 90 degrees
25kts +
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Determining windspeed and direction from smoke
Smoke blows in the direction of the wind. The degree to which the smoke is ‘bent over’ can be used to assess wind speed. In nil wind the smoke will rise directly upwards, the smoke will blow horizontally in strong wind
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Determining wind speed and direction from dust
Dust can come from cars travelling on a dusty road or cultivation. Dust acts similar to smoke however it can be confusing as it can show the path of the car rather than the wind direction
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Determining wind speed and direction from aircraft drift and ground speed
The direction in which the aircraft is holding drift can show wind direction and the amount of drift can show strength. Changes to groundspeed can also be used. This must be used with caution as this is the wind speed and direction at the aircraft’s altitude, not what is necessarily on the ground
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Determining windspeed and direction from crops/trees
Wind can form a wave pattern on crops and trees. The direction and strength can be assessed from this
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Determining windspeed and direction from water
Ripples form on water at 90° to the wind. A ‘shadow’ area will form where the bank of the lake shields the water from the wind. This is used to assess wind direction. If foamy ‘whitecaps’ can be seen, this indicates a wind strength greater than 15 knots
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Determining windspeed and direction from wind lanes
Wind lanes are streaks of disturbed water caused by very strong winds. Unlike ripples, these form in line with the wind direction
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Determining wind speed and direction from cloud shadow
Tracking the path of a cloud’s shadow can indicate wind direction and its speed shows the strength of the wind. Caution must be taken however as this indicates the wind at the altitude of the cloud and not necessarily what is on the ground.
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Determining wind speed and direction from local knowledge
If in close proximity to an aerodrome, the duty runway and/or ATIS can be used to assess wind speed and direction
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What is wind shear
Wind shear is a change in wind velocity over a vertical or horizontal distance. This could mean a change in wind speed or direction. A change in the wind will result in a change in the headwind component the aircraft is experiencing. The boundary between layers of air with different winds is known as the shear zone where the winds mix and tumble creating significant turbulence. The narrower the shear zone is, the more sudden the change in wind velocity will be and therefore the greater the winds shear
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What happens to lift when wind shear is encountered
Due to inertia, the aircraft’s groundspeed will initially be slow to react. Therefore, wind shear causes changes in the aircraft’s indicated airspeed resulting in changes to lift production.
- If the aircraft gains lift, it is known as an energy gain or positive wind shear
- If the aircraft loses lift, it is known as an energy loss or negative wind shear.
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What should you do if you encounter wind shear
Vacate the area or;
| Increase power and approach speed
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What happens if you encounter wind shear when approaching an aerodrome
If an aircraft is approaching an aerodrome, positive wind shear can result in overshooting the runway and negative wind shear could result in undershooting the runway.
This is an important consideration as downdraughts from a Cumulonimbus cloud that could be situated between the aircraft and the runway could cause this wind shear.
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What is vertical wind shear
This is a change in wind velocity over a vertical distance and would be experienced by an aircraft climbing or descending
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What is horizontal wind shear
Horizontal wind shear is a change in wind velocity over a horizontal distance and would be experienced by an aircraft in level flight
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What is a sea breeze
During the day the land heats up more quickly than the adjacent sea. The air over the land rises creating a comparatively lower pressure compared to the air over the sea. Air then travels from the area of comparatively higher pressure over the sea to the area of comparatively lower pressure over the land. The air over the land is therefore replaced by the cooler moist air from the sea.
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What are the strengths of a sea breeze
The strength of a sea breeze is greatest when the temperature difference between the land and the sea is at its greatest. This is during Spring and Summer as the sea is still cold from the previous winter and land temperatures are at their hottest. It is at it’s greatest strength in the afternoon when land temperatures are at their hottest. The strength of a sea breeze is, on average, around 10 to 15 knots
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What are the times for sea breezes
The time a sea breeze can be expected is that it starts around 10am and peaks in intensity around 3pm. It stops as the sun sets.
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What are the extents of a sea breeze
Sea breezes can penetrate inland around 25 to 40 kilometres and reach a height of around 2000 to 3000 feet above ground level.
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What cloud is likely to develop with a sea breeze
As moist air is being transported inland and then heated, it is forced to rise. Cumulus cloud can develop and is called Fair Weather Cumulus.
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Can wind shear be present during a sea breeze
If the sea breeze opposes prevailing winds, wind shear can be present
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What is a land breeze
This is the opposite of the sea breeze and is due to the land being cooler than the sea at night, (the sea retains its heat a lot more easily than the land does). Therefore air from over the sea is relatively warm and rises. The cooler air from the land moves in an offshore direction to replace the rising air. Once again the cycle is set up but this time in the opposite direction.
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When do land breezes occur
The land breeze is most common in Autumn as this is when the sea is still relatively warm from the previous summer but land temperatures are decreasing. It occurs at night as this is when the land will be at its coldest
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What's the strength of the land breeze
It is the temperature difference between land and sea which determines the strength of a land breeze. Unlike a sea breeze where the land is much warmer than the sea, the sea is never too much warmer than the land. For this reason, the temperature differential for a land breeze is a lot less creating a much less wind speed of around 3 to 4 knots.
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Is there any cloud associated with a land breeze
As air from the land is not likely to contain much moisture, there is no cloud associated with a land breeze
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What is an anabatic wind
These are mountain breezes caused by the sun heating up the surface of the mountains during the day causing the air to rise. This results in a gentle upslope breeze allowing air to cool adiabatically. These winds are generally weak as gravity opposes.
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What is a katabatic wind
As an anabatic wind flows up a valley the katabatic does the opposite and flows down and out. This is due to the cooling of the mountain surface causing the air to subside down the slopes. It is a night phenomenon however it can persist into early morning
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What is a fohn wind
This may be experienced when a mountain range forms a barrier to the wind flow. The orientation of the mountains determines the direction from which the Fohn wind blows.
The fohn wind is the wind that descends down the Lee side. It is a warm, dry and turbulent wind
(Calculating cloud bases)
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What does a fohn wind require to begin
- A substantial mountain range
- A wind blowing at more or less right angles to the range
- A high moisture content of the approaching air
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What happens if the air doesn't reach its dew point in a fohn wind
If the air does not reach its dew point then will be no temperature difference between the Windward side and the Lee side. For this reason the approaching air must have a high moisture content
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What are mountain waves
Mountain waves are often dramatic weather phenomenon which can affect hundreds of miles of sky and cause severe turbulence under certain conditions
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What are the requirements for mountain waves to occur
- A substantial mountain range
- A wind blowing at right angles to the mountain range
- Wind speed a minimum of 10 to 15 knots at the surface increasing in strength with height
- An unstable atmosphere at low levels to assist air rising, a stable layer at or just above the mountain tops and a slightly unstable atmosphere above the mountain tops
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What are the dangers of mountain waves
Flying in the Lee side is potentially very dangerous as the turbulence in the ‘rotor zone’ can be sufficient to flip an aircraft. Up and downdraughts in the wave can be greater than an aircraft’s ability to climb or descend
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What clouds are associated with mountain waves
In the wave air rises and cools. Once it reaches it’s dew point it condenses forming cloud. It then descends and warms and when it passes through its dew point it ceases being cloud. The cloud therefore forms in the crest of each wave and this cloud is known as lenticular cloud. Lenticular clouds indicate mountain wave conditions
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What is rotor streaming
Rotor streaming is similar to Mountain Waves however the wind speed decreases in strength from the top of the crest. This then acts like a ‘lid’ keeping the wind speed strong and turbulent on the lee side. As there is no wave, lenticular clouds are not associated with rotor streaming however swirling cloud can form from the turbulence experienced in the rotor zone. This cloud is known as rotor cloud. Turbulence will be severe to extreme beneath the mountain peak on the Lee side but above the crest of the mountain the flight conditions will be much less turbulent.
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What is a gust
A gust is a momentary increase or decrease in wind speed and/or direction, which lasts for a few seconds and is due to mechanical turbulence
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What is a squall
This is a rapid increase in wind speed and/or direction, which lasts for a number of minutes and then dies away due to frontal activity. They may be pronounced by the passage of individual cumulus clouds, thunderstorms or by the passage of a frontal system. A squall is defined as an increase in wind speed by 16kts to a minimum of 22kts for greater than 1 minute
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What is a lull
A lull is a DECREASE in wind speed lasting less than a few minutes. Gusts include lulls.
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What is a gale
Average surface wind is greater than 34 knots or gusts are greater than 43 knots.
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What is a hurricane
Average surface wind is greater than 63 knots
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What is a wind gradient
This is the gradual change in wind velocity between the surface and the top of the friction layer
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What is a funnel effect
Wind flow that is forced into a confined space such as Cook Strait or Lyttelton Harbour will speed up, causing strong gusty winds
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What are airmasses
Air masses are large blocks of air which possess similar characteristics in temperature, moisture and temperature lapse rate. Air masses can be classified by describing its temperature and moisture
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Arctic continental (Ac)
Very cold and dry
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Polar continental (Pc)
Cold and dry
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Polar maritime (Pm)
Cold and moist
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Tropical continental (Tc)
Warm and dry
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Tropical maritime (Tm)
Warm and moist
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What are source regions
Regions of the world which give air masses their characteristics are known as source regions. For example, the Southern Ocean is a source region for Polar Maritime air. Australia is a source region for Tropical Continental
200
What is cold advection
Pressure systems transport these air masses to different regions of the world. Where a cold air mass is travelling equator-wards and travelling over warmer surfaces, the air mass will be warmed from below. This is called cold advection. This means that the temperature change with height is greater – or in other words, the ELR has steepened. This will lead to more unstable conditions and if condensation occurs, cumuliform cloud will develop
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What is warm advection
If a warm air mass moves pole-wards, it will be cooled from below. This is called warm advection. The ELR will be shallower and stability will increase. If condensation occurs, Stratiform cloud will develop
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Fronts
The boundary of a moving air mass is where the front is. If it is cold air replacing warm air it is a cold front, if it is warm air replacing cold air it is a warm front
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The extent of a front depends on what?
- The amount of moisture involved;
- The stability/instability of the rising warm air;
- The slope of the front;
- The speed of the front;
- The contrast in temperature across the front
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What cloud will be present in unstable and stable fronts
Cloud will be of the cumuliform type (heaped), if the air is unstable or if the rate at which it is forced to rise is great. For example, in steeply sloping fronts, such as cold fronts, it is most often found that cumulus cloud including cumulonimbus cloud is involved. Conversely in stable conditions or when the slope is very shallow (as in many warm fronts), the presence of stratiform type cloud is normal
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The cold front
This is where a cold air mass moves to overtake a warmer air mass. Here the cold air is acting like a wedge to force the warm air upward. As the warm air rises it is replaced by the cold air. The cold front has a steep slope and as was said before this results in a fair degree of instability
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How are cold fronts depicted
Blue line with triangles
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Characteristics of a cold front
Moves relatively quickly (20 to 30 knots)
Steep slope forcing warm air to rise quickly – cumuliform cloud
Decrease in surface temperatures
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The warm front
The cold air is still acting like a wedge to force itself under the warmer air, but remember it is the warm air that is moving. If the air approaching is of a stable nature then as the air rises it will likely form a layer of stratiform clouds. If this air is stable at high levels, vertical extent of the cloud will be limited as the air will want to sink back down due to its stability
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Cloud types involved in a warm front
Cloud types present before the front are Cirrus and cirrostratus and can be seen up to 1000km in advance of the warm front. Due to the shallow gradient of the warm front the weather can last for many hours and even days. Precipitation can be persistent and heavy
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How are warm fronts depicted
Red lines with semi circles
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Characteristics of a warm front
Moves 10-15kts slower than cold fronts
Shallow slope forcing warm air to rise slowly – stratiform cloud
Warmer air replacing cold air however due to cloud cover and precipitation, no noticeable change in surface temperature may occur
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Occluded front
An occluded front occurs when one front catches another. This is due to cold fronts travelling faster than warm fronts. The occluded front is usually born from a depression when there are three sectors of air: cold, warm and colder. As warm air is forced to rise, it cools and condenses.
Occluded fronts are shown on charts as lines with triangles and semi-circles on the same side
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What are the two types of occlusion
Cold Occlusion – advancing cold air is colder than the air ahead of the warm front
Warm Occlusion – air ahead of the warm front is colder than the advancing cold air
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What is a stationary front
A stationary front occurs when one front is moving in the opposite direction to another front. They are weak and often represent the remains of a decaying frontal system. There is not a great deal of cloud, wind or weather associated with them
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What clouds are associated with a stationary front
Even though the air masses are not moving, the weather at a stationary front is not the weather that usually occurs under an air mass. Often warm air mixes with cooler air, and could form on both sides of the front. The clouds are pushed upward, cool, and precipitation can occur. This precipitation is usually light but because the front is not moving, it can last for a long time. When a warm front or cold front stalls, or stops moving, it becomes a stationary front. When a warm front or cold front starts moving again, it is once again a warm front or a cold front, and it produces the weather that is typical of it.
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How are stationary fronts depicted
Red semi circles on one side
| Blue triangles on the other side
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How do liquid drops form
For liquid droplets to form, water vapour must condense onto condensation nuclei such as dust, soot or carbon. Similarly, ice crystals can only form around a freezing nuclei
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How can liquid drops overcome buoyancy
For liquid droplets or ice crystals to be heavy enough to overcome the buoyancy of air, they must grow in size. This means that there needs to be a way for them to combine. There are two main processes through which this can occur:
- Bergeron Process – Ice crystal development
- Coalescence – Water droplet development
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What is the Bergeron process
This is where a cloud is below 0°C. Vapour freezes directly onto a freeing nuclei. This process is an example of deposition. More vapour freezes onto this crystal causing it to grow in size
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What is coalescence
This is where water droplets combine around a condensation nuclei. When the droplet becomes big enough, it falls and as it does so, it draws more droplets in behind its wake
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Drizzle
small water droplet less than 0.5 millimetres in diameter
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Rain
water droplets larger than 0.5 millimetres in diameter up to 5 millimetres
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Snow
branched, star shaped ice crystals. Soft to touch
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Sleet
a mixture of rain and snow
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Hail
ball like pieces of ice formed through the crystal being repeatedly thrown aloft in a CB cloud to grow. The more updraughts, the longer it will stay aloft and the greater it will grow.
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Continuous precipitation
from widespread cloud such as stratiform cloud. The cloud is not likely to clear in the short term
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Intermittent precipitation
from widespread cloud such as stratiform cloud. This is where continuous precipitation temporarily ceases
228
Showers
from individual cloud such a cumuliform. In between clouds are periods of no precipitation and clear skies
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Visibility
Visibility means the ability, to see and identify prominent unlighted objects by day and prominent lighted objects by night. It is determined by atmospheric conditions, and expressed in units of metres or kilometers
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How is visibility proportional to transparency
If transparency increases, visibility increases, if transparency decreases, visibility decreases. As transparency is affected by the amount of solid or liquid particles in the air, illumination from the sun or moon has no effect on visibility.
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Visibility range
However if an object is large, brightly lit or contrasts well against a background, its visibility range will increase beyond the prevailing visibility distance. Alternatively if it is a small object, poorly lit or does not contrast against a background, it’s range may be less than the prevailing visibility
Visibility range increased - facing moon + down sun
Visibility range decreases - down moon + facing sun
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What is the visibility of mist (BR)
visibility between 1000m and 5000m
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What is the visibility of fog (FG)
visibility less than 1000m (i.e. 999m and below)
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What is the visibility of sea spray
visibility reduction depends on strength of onshore wind
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Visibility reduction due to solid particles - haze (HZ)
visibility between 1000m and 5000m
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Visibility reduction due to solid particles - Dust storm (DS) / Sand storm (SS)
visibility less than 1000m (i.e. 999m and below)
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Visibility reduction due to rain
Heavy rain- Less than 500m
Moderate rain - less than 10km
Light rain- little effect on visibility
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Visibility reduction due to snow
Heavy snow - less than 100m
Moderate snow- less than 1000m
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Visibility reduction due to drizzle
Heavy drizzle- less than 500m
Light drizzle- less than 3km
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What is slant range
Visibility is measured horizontally but can change if instead it is measured on an angle. This is known as Slant Range
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What is fog
Fog is basically cloud on the ground (usually stratus cloud) with a visibility of less than 1000m. There are two main types of fog and they are classified due to the nature of their formation
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What are the requirements for radiation fog
- High relative humidity
- Unrestricted surface cooling (little or no cloud)
- A light wind, 2-8kts, to promote mixing
- A generally stable atmosphere so that the mixing and cooling are confined to a shallow laye
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When is radiation fog thickest
Radiation fog is usually thickest after sunrise. This is due to the initial excitement of the air molecules due to mixing
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When is radiation fog most common
Radiation fog is most common in anti-cyclonic conditions as these are associated with clear skies (for surface cooling), light winds and a stable atmosphere. It mainly forms at night and thickens in the morning
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Dispersal of radiation fog
Dispersal of radiation fog will generally occur once solar radiation is introduced. The solar insolation warms the surface then the atmosphere, reducing relative humidity. If the solar insolation heats the surface resulting in a steeper ELR, the fog can lift into stratus and stratocumulus. If wind strength increases then dry air will mix with moist air reducing overall relative humidity
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Where does radiation fog form
As radiation fog requires significant surface cooling, this fog only forms over land as oceans do not have significant reductions in temperature.
Radiation fog can be enhanced in valleys as katabatic winds aid in cooling and rivers and streams provide a moisture source
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Requirements for advection fog
All the requirements for the formation of advection fog are generally the same as for radiation fog. Cooling of moist air with mixing will take place. However it is the movement of warm air over a cooling surface that is the difference between the two types. The temperature of the cold surface must be lower than that of the warm air’s dew point
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Advection fog, unlike radiation fog can:
- Can form over the sea
- Requires a surface that is already cold rather than one that is cooling
- Can persist throughout the day
- Does not require anti-cyclonic conditions provided wind strength is not too great
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How is advection fog dispersed
Advection fog is dispersed through a decrease in the moisture content of the moving air or through a change in wind direction. A change in wind direction can either transport the moist air over a warmer surface or increase the mixing of moist air with dry air. This reduces the relative humidity
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Sea fog
moist sea air moves over onto cooler seas
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Cold stream fog
a cold ocean current is surrounded by warmer oceans. Warm air is transported over the cold stream forming fog
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Warm stream fog
a warm ocean current is surrounded by cooler seas. Warm air is transported over to the cooler adjacent seas forming fog
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Frontal fog
caused by saturation of the air at a warm front
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Valley fog
cool air combines with moisture from lakes and rivers
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Steaming fog
evaporated moisture from a relatively warm body of water saturates relatively cool air above (common in winter)
256
Define turbulence
Turbulence is defined as small scale, short-term, random and frequent changes to the velocity of the air
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How can turbulence be made
- Air rising through convection
- Orographic effects (large scale mechanical turbulence)
- Surface obstructions (small scale mechanical turbulence)
- Wind shear
- Aerodynamic effects (wake turbulence)
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Thermal turbulence
Surface heating causes a steepening of the ELR. This makes air unstable and allows it to rise. Rising air then causes turbulence. As the surface is not of a uniform type, surface heating, and therefore thermal turbulence, can be encountered randomly.
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Mechanical turbulence
Small-scale Mechanical Turbulence is caused by wind striking objects such as buildings and trees. Large-scale Mechanical Turbulence is caused by wind striking terrain such as mountains
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Wake turbulence
Wake turbulence is caused by the rotating vortices extending rearward from the wingtips of aircraft. They are produced when the aircraft is producing lift so therefore they begin from when an aircraft leaves the ground on takeoff to when it touches down on landing.
261
What are wake turbulence vortices proportional to
- Aircraft weight- more weight gives greater vortices’
- Aircraft configuration-clean configuration gives greater vortices’
- Aircraft speed-slower speed gives greater vortices
- Distance behind the aircraft-the smaller the distance the greater the vortices’
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Clear ice
Super cooled water droplets (SCWD) are large and the temperature somewhere between 0° and -15°, only a very small amount of the drop freezes and the rest flows back along the surface. This flowing back of the droplet has the effect of squeezing out most of the air bubbles within the developing ice layer. The result being a solid sheet of glass like ice covering the skin of the wing after a short period of time. This is known as glaze ice or clear ice. It is heavy, adheres strongly and is difficult to get rid of, especially if built up to a high degree. If the water droplet size is small then a smaller amount of water will flow back. Clear ice is most likely from Cumuliform cloud
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Rime ice
Temperature is less than -15° and the freezing of the droplets is almost instantaneous. As a result numerous pockets of air will be trapped within the accumulating ice build up, which gives the ice a milky, opaque appearance. Unlike clear ice, which has a smooth appearance, rime ice is rough and uneven in shape. As it builds up on frontal areas such as leading edges, the aerodynamic qualities will be affected and a close monitoring with active use of de-ice systems is important. Rime ice is most likely from Stratiform cloud
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Hoar frost
Hoar frost occurs when the temperature of the aircraft is below 0˚C and the environmental air is moist but not necessarily saturated. A thin layer of ice forms which adds weight, can affect the aircraft aerodynamics and may impair vision. Hoar frost typically forms on a cold clear night. It can also occur when an aircraft descends from above the freezing level into a moist layer of air. Note that cloud need not be present for hoar frost to form in flight
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Freezing rain
This comes from precipitation falling from the warm sector of a warm front and into the cold sector. As it does so it becomes a SCWD. If an aircraft then flies into the freezing rain, it will be the freezing nuclei and ice accretion will be rapid
266
Icing hazards
```
Increased weight
Decreased lift
Increased drag
Increased stall speed
Decreased angle of climb
Restricted control surface movement
Radio interference
Reduction in visibility from windscreen
Pitot tube / static vent blockage
```
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Anti-icing and de-icing methods
```
De-icing boots
Glycol fluid (reduces freezing temperature)
Heated aircraft surfaces
Heated windscreens
Heated propeller leading edge pads
Flying below the freezing level
Carburettor heat
Ground based equipment
```
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What is an inversion
An inversion is where temperature increases with a gain in height. As it is an example of a very shallow ELR, they are associated with stability and hence they act like lid preventing air from rising. This causes dust and pollutants to be trapped below an inversion. Therefore poor visibility is experienced below the inversion and good visibility above. If different winds are experienced above and below the inversion, wind shear can be present. As temperature increases with a gain in height and pressure decreases, air density rapidly decreases causing a reduction in aircraft performance. There are many different types of inversion
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Ground/radiation inversion
A radiation inversion is formed when the ground cools on a clear night cooling the air just above the ground. The air above is still relatively warm from the day before. This means that temperature will increase with a gain in height
270
Turbulence inversion
A turbulence inversion begins as a radiation inversion. After sunrise, mixing is enhanced. A parcel of air at the surface is colder than a parcel of air above it. The cooler parcel at the surface is forced aloft causing it to cool and become even colder. The warmer air aloft is forced downwards causing it to warm. There is now very warm air at the surface and very cold air aloft. This creates a very steep ELR. This steep ELR does not ‘match’ the normal ELR at a higher altitude and in between is an inversion. Due to air rising, if it is moist, cumulus cloud can form however they will not rise higher than the inversion
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Subsidence inversion
Subsidence inversions form in high pressure systems where air is subsiding. At lower levels, air is more dense and cannot subside as fast as air at altitude diverging slowly at the surface. When air descends it warms adiabatically. As the rate of subsidence is greater at altitude, it can warm to a higher temperature than the slower subsidising air at the surface. This creates an inversion
272
Frontal inversion
Frontal inversions are created by warm air rising over cold air such as that found in a warm front
273
How is carburettor icing caused
the reduction of temperature when air is de-pressurised, and the drop in temperature when fuel is vaporised
274
What are the temperatures for carburettor icing
The dangerous outside air temperature limits are accepted to be approximately +25°C to -15°C
275
What is the a thunderstorm
Thunderstorms are defined as one or more electrical discharges, manifested by a flash of light (lightning) and a sharp rumbling sound (thunder)
276
What are the requirements for a thunderstorm
An atmosphere which is unstable through a deep layer
An adequate supply of moisture
A ‘trigger’ action which causes air to rise
A mechanism of electrical discharge
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What are the three different types of thunderstorms
Convective (thermal) thunderstorms – caused by heated air rising
Orographic thunderstorms – caused by air rising due to terrain
Frontal thunderstorms – caused by colder more dense air forcing warm air to rise
278
What are the main hazards of flight through a thunderstorm
```
Turbulence (instability of air)
Wind shear
Hail
Icing
Lightning
```
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What is a tornadoe
Thunderstorms are associated with tornadoes which are a rotating funnel of air being ‘sucked’ up by the thunderstorm. Strong instability is required for such a vast amount of air to be forced upwards. They can be caused by strong wind shear near the cloud which rotates around a horizontal axis and is then drawn into the base of the cloud. The axis then becomes vertical. Pressure decrease within the core of a tornado is extreme. This can cause buildings, with a relatively high pressure inside, to explode as a tornado passes overhead. The pressure drop results in adiabatic cooling causing condensation and therefore the tornado can be seen
280
What happens in the growing stage of a thunderstorm
This is where all the draughts are upwards and a very unstable condition exists. Massive amounts of moisture are carried aloft some of which turn to ice as the freezing level is passed
281
What happens in the mature stage of a thunderstorm
Once the vast amounts of moisture have been carried aloft, there comes a point where even the greatest amounts of up draught are not enough to support the weight of the moisture. Thus a torrent of moisture descends and often at a high rate. Up and down draughts are felt and this can be classed as wind shear, (abrupt changes in wind velocity). As the down draughts of the thunderstorm hit the ground they have no option but to spread out horizontally. This highspeed squall of wind is known as the gust front.
282
What happens in the decaying stage of a thunderstorm
Updraughts within the particular cell cease so that a generally descending motion takes place. Turbulence and gusts decrease and in the absence of other cells at different stages, the high level stratiform cloud settles resulting in the thunderstorm slowly disappearing.
283
Why should extreme caution be exercised when flying at low levels in the presence of a thunderstorm
In both the mature and decaying stage of the thunderstorm the downdraughts can be severe enough for aircraft to be forced down if flown below the base of the cloud. Thus extreme caution must be exercised when flying at low level in the presence of thunderstorms or Cumulonimbus (Cb).
284
New Zealand typographical effects
New Zealand’s mountains lie at almost right angles to the prevailing westerly winds. The orographic rising, causes a wet West Coast and drier East Coast. There will usually be more cloud associated with the West Coast when these winds prevail, and more turbulence on the East Coast of both islands due to the associated mountain waves that are formed
285
What happens before a cold front
```
Pressure drops
Wind veers and increases
Temp is steady and warm
Cloud included CS, SC,AC
Precipitation is uncommon
Visibility is fair
```
286
What happens during a cold front
```
Pressure rises
Wind backs
Temperature drops
Cloud TCU, CU, possibly CB
Precipitation can be heavy showers and hail
Visibility is poor in showers
```
287
What happens after a cold front
```
Pressure rises
Wind decreases slowly and steadily
Temperature is cool and steady
Cloud isolated CU
Precipitation is showers
Visibility good outside of showers
```
288
What happens before a warm front
Pressure falls
Temp is steady or slightly decreases
Wind beer and slight increase
Cloud CI, CS, AS, ST, SC and maybe Cb if unstable
Precipitation light rain turning persistent and heavy
Visibility poor in rain
289
ARFOR
Degrees true
| AMSL
290
ROFOR
Degrees true
| AMSL
291
SIGWX, wind/temp charts
Degrees true
| AMSL
292
TAF
Degrees true
| AGL
293
METAR / SPECI / TREND
Degrees true
| AGL
294
ATIS
Degrees magnetic
| AGL
295
BWR / PIREP / AIREP
Degrees magnetic
| AMSL or AGL
296
Automatic weather information broadcast (AWIB)
AWIB is similar to ATIS in that it is a broadcast of aerodrome meteorological and operational information. They are however not certificated by CAA and the information is often sourced from automatic weather station so there is no assurance of their reliability or accuracy. When flying, the broadcast may have to be triggered by use of the aircraft’s transmitter
297
Basic weather reports (BWR)
AWIB is similar to ATIS in that it is a broadcast of aerodrome meteorological and operational information. They are however not certificated by CAA and the information is often sourced from automatic weather station so there is no assurance of their reliability or accuracy. When flying, the broadcast may have to be triggered by use of the aircraft’s transmitter
298
What may a BWR contain only
- Wind direction in degrees magnetic
- QNH
- Temperature
- Weather conditions and cloud cover
A BWR does not supersede a METAR or TAF.
299
Pilot reports
Pilot reports (PIREP) are reported on domestic flights. They are reported to the nearest Air Traffic Service (ATS) whenever severe weather is encountered. This may lead to a SIGMET being issued. A PIREP must be made when wind shear is encountered or Volcanic Ash is observed
300
What information can be gathered from synoptic charts
```
Sea Level air pressure (QNH)
Pressure gradient and therefore wind speed
Wind direction
Approaching fronts
Weather patterns
```
301
What are the limitations of synoptic charts
- Synoptic charts are unable to depict localised weather phenomenon
- Cannot give specific weather details
302
NZST
12 hours ahead of UTC
303
NZDT
13 hours ahead of UTC
304
Daylight saving dates
25th September - 2nd April
305
The altimeter
An altimeter is a type of aneroid barometer. Using its subscale, many different indications can be used. The subscale can be calibrated in millibars (hPa) or inches of mercury (inHg). If the subscale is wound upwards, the reading on the altimeter will increase. If the subscale is wound downwards, the reading on the altimeter will decrease. When using millibars, 1 hPa is equivalent to 30 feet
306
QNH
QNH is the most commonly used setting. If QNH is set on the altimeter, the altimeter will read feet above mean sea level. For example if an aircraft is on the ground at an aerodrome with an elevation of 300 feet, the altimeter will read 300 feet
307
How can you obtain QNH
- Meteorological reports can be used or,
| - If the aircraft is on the ground, aerodrome elevation can be set on the altimeter and the subscale will give QNH
308
QFE- height above a datum
QFE is usually only used if operating at one aerodrome. It is used to give height above aerodrome level. If an aircraft is on the ground and QFE is set, the altimeter will read 0 feet. The danger of using QFE is if flight was to be undertaken over an area of a different elevation, the aircraft’s height above ground level could not be easily determined. In this case, reset QNH
309
How to obtain QFE
Set the altimeter to read 0 feet when on the ground and read QFE off the subscale or,
Take the ground elevation, divide that by 30 (as 1 hPa = 30 feet) and subtract from QNH
310
How to obtain pressure altitude
Take difference between QNH and 1013
Multiply by 30
Subtract from aerodrome elevation (if QNH higher than 1013)
Add to aerodrome elevation (if QNH lower than 1013)
311
How to obtain QNE
Set 1013 on the sub scale
312
From high pressure to low pressure
Read high, be low
313
From low to high pressure
Be low read high
314
Flying through places of different temperatures
As temperature has an effect on pressure lapse rate, it will affect true altitude. The same mnemonic can be used when flying between two regions with different temperatures. A ten degree deviation from ISA is equivalent to a 4% change in true altitude
315
Liquid to vapour
Evaporation
316
Vapour to liquid
Condensation
317
Ice to liquid
Melting
318
Ice to vapour
Sublimation
319
Liquid to ice
Freezing
320
Vapour to ice
Deposition
321
What changes of state require latent heat
Evaporation, melting, sublimation
322
Which changes of state release latent heat
Condensation, freezing, deposition
323
What process warms the air particles touching the earths surface
Conduction
324
What effect does conduction have on air temperature
Conduction heats the air particles that are in direct contact with the earths surface
325
How does convection affect the earths temperature
When air is warmed it rises and expands, and through the process of convection, transfers heat to the higher levels in the atmosphere
326
What is conduction and convection
A warm earths surface warms air particles in touch with the surface through conduction. When air particles have been warmed they expand and rise and through convection warm higher layers of air
327
When air temperature reduces
Relative humidity goes up
| Dew point is not affected
328
When air temperature goes up
Relative humidity goes down
| Dew point is not affected
329
When vapour content increases
Relative humidity goes up
| Dew point goes down
330
When vapour content decreases
Relative humidity goes down
| Dew point goes down
331
When temperature increases and vapour content decreases
Relative humidity goes down
| Dew point goes down
332
When temperature goes up and vapour goes up
It becomes impossible to state what happens to relative humidity.
It depends on which factor is stronger.
Dew point can be determined though, it increases because water content is increased.
Same principle apply when temperature goes down and vapour content goes down
333
What is divergence
Divergence at high level associated with low level convergence causes slow widespread ascent of air over a large area generally causing cloud development by adiabatically cooling the air as it ascends
This occurs in a low pressure system when surface convergence and high level divergence cause large scale rising
334
What is convergence
Convergence at high level associated with low level divergence causes slow subsidence of air over a large area inhibiting cloud development by adiabatically warming air as it descends
335
What happens during a warm front
```
Pressure fall arrested
Temperature slight increase
Wind backs
Cloud types - ST,NS may have CU,SC or CB
Precipitation may change to drizzle
Visibility very poor
```
336
What happens after a warm front
```
Pressure steady or slight rise
Temperature steady
Wind steady
Cloud - low level may persist
Precipitation occasional rain or drizzle
Visibility fair, poor in drizzle and rain
```
337
How is NZ climate influenced by its latitude
NZ lies between 34S and 47S.
The northern part is subtropical while the remainder is temperate
The country lies at the northern edge of the mid-latitude westerlies, causing the winds to prevail from the west
338
How do the oceanic surroundings influence NZ's climate
With NZ being surrounded by oceans, temperatures generally have small fluctuations through the year and moisture content is high
339
Describe the characteristics of a NW wind in New Zealand
Brings warm moist air travelling over cooling surfaces
They tend to sink and become stable with layer type cloud
The west coast will have low cloud levels and rain or drizzle
Eastern areas will be mainly fine but with turbulent conditions
340
Describe the main characteristics of a SW wind in New Zealand
Blows behind a cold front producing showers on the west coast, and fine but turbulent conditions on the east coast.
The weather coast will have smooth flying conditions and good visibility outside of showers
341
Describe the characteristics of a SE wind in New Zealand
Not common in NZ
They bring strong winds and rain to the east coast, and produce fine dry weather on the west coast.
The east coast has unstable conditions where cumuliform cloud is produced
342
When planning a flight around the Southern alps, what considerations need to be made in regards to weather conditions
The conditions need to be throughly researches and understood through the use of meteorological data, and also local knowledge.
If the pilot is inexperienced they are urged to seek a check flight with a local company. Significant fuel should also be carried
343
What reports are in ft AMSL
AFFOR, SIGMETS
344
What reports are reported in ft AGL
TAF, TREND, METAR, METAR AUTO, SPECI, ATIS
345
Which reports directions are in degrees magnetic
Spoken, ATIS, BWR
346
BC
Patches
347
BR
Mist
348
DR
Low drifting
349
FU
Smoke
350
GR
Hail
351
GS
Small hail
352
MI
Shallow
353
MS
Minus
354
PL
Ice pellets
355
PO
Dust and sand whirls
356
/
Weather not detected due sensor temporarily inoperative
| Used in METAR AUTO only
357
///
Cloud is detected (unable to determine TCU/CB)
| Used in METAR AUTO only
358
////
Visibility not reported
| Used in METAR AUTO only
359
Why would a SIGMET be issued
Provide information on observed or forecast hazardous weather conditions
360
When is a SIGMET issued
As required, valid for 4 hours (6 for volcanic ash and tropical cyclones)
Reviewed after 3 hours of when further info is available
NZZC and NZZO
361
What is an AFFOR for
Area forecasts are forecasts for a specific region. They are intended for domestic VFR and IFR flights below 10,000ft
The 17 AFFOR areas are designated by a two letter code
362
When are AFFOR's issued
0530-0610 and 1130-1210 local time
363
What is a TAF
A TAF is an aerodrome forecast provided for a specific aerodrome presented in a code
364
What is a TREND
A forecast, valid for 2 hours, attached to the end of a METAR or SOECI (nzwp, nzoh) and METAR AUTO (nzaa,nzwn,nzch)
Stating any significant changes from those described, while the TREND is valid it supersedes the aerodrome TAF
365
When is a TAF and TREND issued
NZAA, NZWN, NZCH 2300,0500,1100,1700 UTC
Other aerodromes 0230-0430, 0930-1015, 1400-1445 local time
366
How long are TAF's and TRENDS valid for
Date/time specified on reports in UTC
367
What area are TAF's and TRENDS for
8km of the aerodrome reference point
368
What is a METAR
A routine meteorological report, complied manually, provided for a specific aerodrome, and presented in a code
369
What is a METAR AUTO
A routine meteorological report provided by an automatic weather station (AWS) for a specific aerodrome, also presented in code
370
What is a SPECI
A SPECI is a METAR issued outside of the routine issue time of a METAR (nzwp, nzoh, nzmf only)
371
When is a METAR issued
Hourly, on the hour
372
When is a METAR AUTO issued
Every half hour for 24 hours a day
373
When is a SPECI issued
When required and will have issue time other than on the hour
SPECIs is not issued at metar auto aerodromes
374
Direction in METAR, METAR AUTO and SPECI
Degrees true, when direction varies by 60degrees or more, the extreme directions are given, separated by a V e.g 260V330
375
What is an ATIS
The ATIS is a continuous plain language broadcast of the current conditions at an aerodrome, on a discrete frequency
376
When is an ATIS issued
Irregularly, when conditions change or deteriorate
377
UTC calculations
UTC. NZST. NZDT
| 0000. 1200. 1300
378
What is a BWR
Basic Weather Reports (BWR) are spoken reports of weather. These can come from a variety of sources. When these reports come from an Air Traffic Service, they can be used with confidence and wind direction will be given in degrees magnetic. If not provided by an ATS, they may lack accuracy.
379
What must a BWR contain only
Wind direction in degrees magnetic
QNH
Temperature
Weather conditions and cloud cover
380
What is an AWIB (automatic weather information broadcast)
AWIB is similar to ATIS in that it is a broadcast of aerodrome meteorological and operational information. They are however not certificated by CAA and the information is often sourced from automatic weather station so there is no assurance of their reliability or accuracy. When flying, the broadcast may have to be triggered by use of the aircraft’s transmitter
381
What is a PIREP
Pilot reports (PIREP) are reported on domestic flights. They are reported to the nearest Air Traffic Service (ATS) whenever severe weather is encountered. This may lead to a SIGMET being issued. A PIREP must be made when wind shear is encountered or Volcanic Ash is observed
382
How is an occluded front depicted
Purple with semi circles and triangles on the same side
383
How many volcanic ash advisory centres are there
9
384
What does air in a high do
Subsides (goes down)
385
What does air in a low do
Rises, hence usually associated with cloud
386
What is wind strength directly proportional to
The pressure gradient
387
What is pressure gradient
The difference in pressure per horizontal distance
388
Is pressure gradient a force
Yes pressure gradient is a force, it always acts at right angles to the isobars and always from high to low
389
If QNE is set on your altimeter what will it read
1013.2 it will read pressure altitude
390
What is QNH
Altitude above MSL
391
What wave length is solar radiation
Short wave, high frequency energy
392
When is rate of evaporation best
Warm, dry, pressures low and wind is blowing
393
Vapour to ice and vice versa
Vapour to ice - deposition
| Ice to vapour - sublimation
394
What's the process of a drop in temp on dp and RH
When temperature decreases, RH goes up and when dew point is reached, saturation occurs. If temperature reduces further, condensation takes place
395
Which reports contain temperature and dew point
METARs and SPECIS
396
What is the fundamental cause of wind
Unequal solar radiation received
397
What determines the circulation around a pressure system
The strengths of pressure gradients and coriolis force determine the circulation around pressure systems (H and L)
398
What is wind that blows parallel to isobars called
| When PG and CF are equal
Geostrophic wind
399
What is the wind called when is blows along curved isobars, anticlockwise or clockwise (H and L)
A gradient wind
400
What happens to wind in the friction layer over the sea
Wind direction changes 10 degrees and wind speed reduces 1/3rd
401
What happens to wind in the friction layer over land
Wind direction changes 30 degrees and wind speed reduces 2/3rd
402
What happens when an aircraft descends through a shear zone which has lighter wind
The IAS will reduce, angle of descent will steepen and its rate of descent will increase
403
Where do PG and CF act in lows and highs
Pressure gradient is a force acting towards the centre of a low and coriolis force acts towards the centre of a high
404
Cloud in stable saturated air
Stratiform, little - no precipitation, droplet size small, precipitation drizzle or rain, if temps below freezing, snow
405
Cloud in saturated unstable air
Cumuliform, turbulence, large drop size, showers and hail cloud is of great vertical development
406
What is thermal rising
Unstable
| The hotter the surface and the drier the air the higher the cumulus cloud base and vice versa.
407
When is sea breeze strongest in the year
Spring
408
When is land breeze most common
In autumn
409
What cause gusts
Terrain
410
What causes squalls
Weather systems
411
Mountain waves
- lenticular clouds
- unstable low levels, stable layer at or above mountain tops, less stable or slightly unstable above the inversion
- rotor action on downwind side below height of the mountains
- strong down draughts on lee side
412
Rotor streaming
- decrease wind speed above mountain height
| - below mountain height in lee side, very turbulent
413
What does the vaisala laser ceilometer measure
Cloud base by echo
414
What cloud will form from slow widespread ascent if the air is unstable
Cumuliform
415
What cloud will form from slow widespread ascent in stable air
Stratiform
416
What cloud can showers only fall from
Cumuliform
417
What does the vaisala detector sense
Visibility
418
On a flight towards a warm front, what should you do?
Icing is a risk, descend, vacate the area
419
An aircraft is holding port drift in the Southern Hemisphere, if the altimeter setting is not adjusted:
True altitude will be lower than indicated
420
High level divergence results in what?
Subsidence of air
421
What should you do if wind shear is suspected
Increase power and approach speed
422
Dispersal of advection fog is most likely from?
The moisture content of the approaching air reduces
423
In SW winds :
The east coast gets rain, cumuliform cloud and funnelling through Wellington
424
What are frontal inversions associated with
Warm fronts
425
What is the ELR
A measurement of temperature of the stationary atmosphere taken at different heights
426
What are frontal thunderstorms likely associated with
Cold fronts
427
What are gust fronts associated with
Thunderstorms
428
What happens to visibility in anticyclonic conditions
Visibility decreases due to weak pressure gradients
429
When is radiation fog most common in the year
Autumn and winter
430
What conditions is radiation fog usually met
Anticyclonic conditions, clear skies, widely spaced isobars (light winds), and subsidence (which enhances stability)
431
When can frontal fog form
Occasionally develops when a warm front travels across the country
432
What is advection
Horizontal transport
433
What cloud is mainly in polar depressions
Cumulonimbus
434
What does a steep ELR indicate
Unstable conditions
435
What are the requirements for a thunderstorm
- atmosphere which is unstable through a deep layer
- an adequate supply of moisture especially from low levels
- a trigger action that causes air to rise
- a mechanism than provides electrical discharge
436
When is thermal turbulence at its max and min during the day
Minimum around dawn
| Maximum around 2pm
437
When does the anvil occur during a thunderstorm
At the end of the mature stage, made form stratiform (consisting of ice crystals)
438
What does QNH read
Altitude above MSL
439
What does QFE read
Atmospheric pressure above a given datum
440
What does QNE read
1013 set, reads pressure altitude
441
Where can heat type thunderstorms form
Over ocean areas
442
Frontal thunderstorms
Cold fronts
2-3 hours max
Occasionally squall lines come before a cold front
443
Clear ice
0 to -15
Cumulus cloud
Worst in first 6-8000ft above freezing level
444
Rime ice
```
Temp of droplets less than -15
Stratiform cloud (altostratus)
```
445
Hoar frost
Formed through deposition process
| Scrape off with plastic scraper or zig zag rope along wingtip
446
Freezing rain
Frontal and inversion situations
| Warmer air above, below freezing below
447
When is ice accretion worst
Due to water content is worse in summer than winter
448
Is ice build up worse in tropical or polar regions
Worse in tropical above freezing level
449
Is ice build up faster in slow or fast flight up to 250kts
Faster speeds=faster accretion up to 250kts
450
Where does throttle icing accumulate
Throttle butterfly
451
Where doe refrigeration icing accumulate
When fuel vaporises in the Venturi
452
Where is a shear zone usually found around a CB
Shear zone often formed by the gust front ahead of CB cloud and below its base
453
When is the friction layer most dense
Around dawn, turbulence is worst
454
Which way do wake turbulence vortices go
Clockwise from left wing
Anticlockwise from right wing
Which creates wake turbulence
455
What speed and weight will increase vulnerability to wind shear and turbulence
The slower it's airspeed, the lighter the aircraft the more vulnerable it is
456
What time of year is carb icing most common
Autumn, winter and early spring
457
What happens to your angle of descent, IAS and rate of descent when meeting a shear zone on approach to land
The angle of descent steepens, the IAS reduces and the rate of descent increases
458
Where can low level wind shear be expected
- descending into a dense friction layer (dawn)
- descending into a cold zone (airfield snow covered)
- descending into lee of sand dunes when a sea breeze blows
- descending into low level where winds lighter or blowing in a different direction
- ascending/descending through a sea breeze boundary
459
When are the effects of turbulence lessened
At reduced air speed
460
Which was is it wise to track over mountains
It is wise to track across the mountains at an oblique angle so that, should a strong down draught force the aircraft down, it only requires a small heading change to turn away from the mountains
461
How far can wake turbulence travel in calm conditions
Can affect areas within approx 750m from the centreline of the runway
462
Which airframe is not subjected to UV desegregation
Metal
463
When vortices of air increase
There is convergence
464
When vortices of air decrease
There is divergence
465
Cirrocumulus
Sheeps wool
466
Cirrostratus
Halo from sun
| Indication of approaching bad weather
467
Cirrus
Indication of high winds aloft
468
Altostratus
```
Blue/grey
High water content
Ice above FL
Light precipitation
In mountainous terrain precipitation can be heavy may include snow or sleet
```
469
Altocumulus
White/grey
Broken patches occasionally
No precipitation
470
Nimbostratus
Stable air
Heavy,persistent rain
Poor visibility
Contains large amounts of water
471
Stratus
```
Grey/blue
Vertical 1-2000ft
When thin, halo from sun
Usual from early morning mixing when low level inversion forms
Turbulence
Light drizzle
Reduced visibility
-mechanical rising
```
472
Stratocumulus
```
Grey/white patches with dark patches
Usually from early morning mixing within the friction layer
Light turbulence at base
Light showers, drizzle
Visibility good
Often along coastlines with low base
Common in anticyclonic conditions
-mechanical rising
```
473
What's the difference between CB and TCU
TCU has no anvil
474
Cumulus humilis (fair weather cumulus)
```
Caused by thermal and orographic rising
Precipitation not common for mid latitudes
Heavy showers in tropics
Tops at an inversion
Turbulence
No turbulence above inversion
Smooth air
-convective rising
-unstable orographic rising
```
475
Stratiform
Stable orographic rising
476
What type of cloud is smooth and fibrous and often covers large areas of the sky as well as being an indication of approaching bad weather
Cirrostratus
477
Cloud will form when a rising parcel of air
Is cooled below DP temperature
478
What will cause the formation of steaming fog?
An increase in surface temperature
479
How does gravity affect katabatic winds
Gravity helps to pull the higher level dense air down the valley.
480
An aircraft is flying south in a westerly wind. Where is the high pressure system?
In front of the pilot
481
What causes the formation of steaming fog?
Evaporation into cool air that becomes saturated quickly and condenses.
482
What is Virga
Liquid drops or ice crystals that evaporate before making contact with the surface of the earth
483
What type of cloud is most likely to cause the formation of rime ice?
What type of cloud is most likely to cause the formation of rime ice?
484
How is the earth’s atmosphere warmed when the air particles are in contact with the ground?
Conduction
485
When will cloud, dew, or fog always form
When the water vapour in the air condenses
486
How does the adiabatic process affect anabatic winds?
The adiabatic cooling of the rising air helps to oppose the upwards flow.
487
How does frontal lifting affect cloud types and stability
Cold fronts produce cumuliform cloud. Warm fronts produce stratiform cloud
