Meteorology Flashcards
1
Q
Where is Water Vapour the Greatest?
A
In the lower parts of the atmosphere due to gravity
2
Q
The Troposphere
A
30,000ft above the poles
60,000ft above the equator as it is hotter
3
Q
The Tropopause
A
Top section of the troposphere
Convection weakens
4
Q
Isothermal Layer
A
Temperature stays the same
5
Q
Stratosphere
A
An isothermal layer at which the temp stays constant at -56.5 degrees celcius according to ISA conditions
6
Q
Atmospheric Pressure
A
A force that exerts in all directions
7
Q
Pressure Systems
A
Measured in hPa above MSL
8
Q
Isobars
A
Lines of equal pressure
9
Q
Horizontal Pressure Gradient
A
Air will flow from a high to a low
At night sea= warmer, day land = warmer
Earth moves from west to east
High pressure systems move anticlockwise in the southern hemisphere
10
Q
Atmospheric Density
A
ISA: 1.225kg/m^3
11
Q
Heating processes in the Atmosphere
A
Solar radiation/insolation
Conduction and Convection
Advection
12
Q
Solar Radiation/Insolation
A
Short wave
Electro-magnetic radiation
Long wave terrestrial radiation from the heated Earth
Air is warmest near to the Earth
13
Q
Conduction and Convection
A
Conduction: by touch
Convection: rising air
14
Q
Advection
A
Sea breeze
15
Q
Factos Affecting Atmospheric Temperature
A
The Seasons Specific Heat Capacity The Colour and Reflectivity Diurnal Temperature Variations Effect of Cloud Effect of Wind Effect of Costal Proximity
16
Q
Specific Heat Capacity
A
More energy required to heat water than air, however water has a higher heat retention
17
Q
The Colour and Reflectivity
A
Snow = 90% Forrest = 5-10%
18
Q
Diurnal Temperature Variations
A
Hottest time of day = 3pm
Coldest time of day = just after sunrise
Large amplitude at in-land stations
19
Q
Effect of Cloud
A
Overcast days are cooler
Overcast nights are warmer (blanket effect)
Cloudless night are cooler as nothing to stop terrestrial radiation
20
Q
Effect of Wind
A
Mixing of different air masses moderates the overall temp
21
Q
Effect of Costal Proximity
A
Cool sea breeze cools a hot summers day and vice versa at night
22
Q
Large Scale Atmospheric Circulation
A
Subsidence causes areas of high pressure
Convection causes areas of low pressure
23
Q
Associated Weather Systems with Atmospheric Circulation
A
Equatorial/monsoonal trough
Sub-tropical ridge
Sub-polar low/polar front
24
Q
Equatorial/Monsoonal Trough
A
Complex low pressure systems
Singapore (bad weather)
25
Sub-Tropical Ridge
High pressure systems
26
Sub-Polar Low/Polar Front
Complex, intense low pressure systems
27
Water in the Atmosphere
Solid to vapour: sublimation
| Vapour to solid: deposition
28
Latent Heat and Temperature
Add heat: solid to vapour
29
Humidity
How much water is in the air
30
Relative Humidity (RH)
How much water is in a parcel of air
Ability of the air to hold moisture
Saturation: cloud formation/visible moisture/100% RH: dew point
RH depends on air temperature
31
Relative Humidity and Temperature
Warm air holds more water vapour than cold air
Relative humidity increases when air temp decreases to reach dew point = 100% RH
RH = actual water vapour/max water vapour for temp x 100%
32
Atmospheric Stability (RH)
Depends greatly on the % RH and temp vs dew point relationship
33
Temperature Inversions
Temp increases as height increases
34
Types of Temperature Inversions
Radiation
Subsidence
Frontal
35
Radiation Inversion
Cloudless night and light winds
Ground surface cools rapidly overnight
Temp increases with height in low level (generally)
36
Subsidence Inversion
Requires a high pressure system
Cold air subsides and warms rapidly adiabatically (adiabatic process)
Warm air above, cold air near surface (4,000 - 8,000ft AGL)
37
Frontal Inversion
Cold dense air forces the warm air upwards
38
Effects of Temperature Inversions
Turbulence
Pollution/dust/salt may be trapped under the inversion layer and decrease visibility
Decreased aircraft performance after take-off as flying into warmer air section
Inversion layers generally indicate a stable atmosphere as they restrict air parcels from rising and above the layer becomes smooth
39
Classifications of Turbulence
Light: small effect on attitude and altitude
Moderate: significant effect and variation in IAS
Severe: large abrupt changes with short periods of uncontrollability
Extreme: practically impossible to control, possible structural damage
40
Types of Turbulence
Thermal
Mechanical/Frictional
Wake
41
Thermal Turbulence
Due to solar radiation, frontal activity and inversions
Temp differences in the air masses cause thermals, thunderstorm activity, frontal lines and horizontal wind shear
May display as a large temp vs. dew point split
42
Mechanical/Frictional Turbulence
Up to 2000-3000ft AGL
Friction over the ground surface due to strong winds
Depends on the type of obstruction and windspeed
43
Pilot Actions
Accurate airspeed control
Increase approach speed
Consider 'reduced flap' landing
Use best turbulence penetration speed (Vb)
Find the shortest way out
Visualise airflow around obstructions to minimise surprise
Beware of vortices downwind of obstructions
44
Wake Turbulence
Take-off before their take-off point and touch down after their touch-down point and make a steeper climb and descent
Wind and turbulent air will disrupt wingtip vortices
Generally vortex sinks at +/- 500ft/min
45
Windshear
Sudden change in wind speed and/or direction over a short distance resulting in a speed variation bigger than 10kts
46
Low Level Windshear
Below 1600ft AGL
47
Windshear on Approach
Overshoot: sudden increase in headwind
Undershoot: sudden decrease in headwind
48
Pilot Actions in Windshear
Accurate speed control
Control/capture IAS while maintaining the approach path
Increase approach speed
49
The Adiabatic Process
Rising air cools due to expansion
50
Adiabatic Lapse Rates
Dry Adiabatic Lapse Rate (DALR) = 3 degrees celcius/1000ft, when it reaches its dew point it will use the Saturated Adiabatic Lapse Rate = 1.5 degrees celcius/1000ft (never changes)
51
Cloud Base
Where a parcel of air reaches dew point or condensation
| The bottom of any amount of cloud
52
Atmospheric Stability
Ability of the air to resist any upsetting tendency
Depends on the ELR: ELR < 1.5 degrees celcius/1000ft = stable
: ELR > 3 degrees celcius/1000ft = unstable
53
Cloud Classifications
```
High Level
Mid Level
Low level
Stratus
Nimbostratus
Cumulonimbus
```
54
High Level Cloud
```
Cirrus (Ci)
Base above 18,000ft
No precipitation as forms ice crystals
Cirrocumulus (Cc)
Cirrostratus (Cs) - can create halo
Reduces surface temp as prevents sun rays from increasing temp significantly
```
55
Middle Level Cloud
Alto
Base 8,000 - 18,000ft
Altocumulus (Ac)
Altostratus (As)
56
Low Level Cloud
```
Base below 8,000ft
Cumulus (Cu)
Stratus (St)
Stratocumulus (Sc)
Nimbostratus (Ns)
```
57
Stratus Cloud
Cloud ceiling very low
Cloud base often ragged/diffuse
Poor visibility (VFR flying difficult)
58
Nimbostratus
Expect heavy continuous rain
| Risk of icing, moderate rime ice
59
Cumulonimbus
CB
| Great vertical development
60
Reporting Cloud Cover
```
Few = 1-2 oktas
SCT = 3-4 oktas
BKN = 5-7 oktas
OVC = 8 oktas
NSC = no significant cloud
NSW = no significant weather
```
61
Cloud ceiling
The height AGL of cloud described BKN or OVC
62
Precipitation
Drizzle, rain, showers, hail, snow, virga
63
Intensity of Precipitation
Light (-)
Moderate
Heavy (+)
64
Continuity of Precipitation
Showers: short duration and differing intensity, often associated with convective cloud (Cu + CB)
Intermittent: with short breaks
Continuous: layer type cloud, longer than an hour without breaks
65
Virga
Falling moisture that evaporates before reaching the ground
| Strong downdraught underneath
66
Pressure Gradient
Is the initiating force
| Initiates movement of air from a high to a low
67
Wind
The horizontal movement of air
68
Isobar Spacing
Indicates wind strength, blows at right angles to the isobars
Close = strong wind
Far apart = less wind
69
Coriolis Force
```
Deviating force
Air appears to be turning to the left in the southern hemisphere
Less wind = less coriolis force
At the equator: coriolis = 0
At the poles: coriolis = maximum
```
70
Gradient Wind/Actual Wind
PGF + coriolis effect = gradient wind
| Net result or actual wind = winds that flow approx parallel to the isobars
71
Anti-Cyclones/High
Anticlockwise in the southern hemisphere
| Airflow flowing out of a high pressure system
72
Ridge
Extension of a high pressure system
73
Weather in a High Pressure System
Subsiding air is stable and clouds tend to disperse
Subsidence inversion
The clear nights may result in radiation fog or radiation inversion as it is clear and dry
On the coast with higher humidity sheet-like clouds with rain may be present
74
Depression/Low
Clockwise in southern hemisphere
| Air flowing into a low pressure system
75
Trough
Isobars extending out of a low pressure system, forming a valley
76
Weather Associated With a Low
Rising air in a low will cool adiabatically
Cloud tends to form (Large Cu, CB or Ns) with heavy rain and showers
Good visibility
77
Col Area
Area of almost constant pressure between two highs and two lows
Wind light and variable, potential fog
Isobars bending away from the centre
High temps may lead to thunderstorms
78
Backing
Anticlockwise
Decreasing in number
More coriolis effect
79
Veering
```
Clockwise
Increasing in number
Going to the right
Slower wind
More common over land due to more friction
```
80
Surface Friction
Uneven and different types of terrain
Up to 3,000ft AGL
Speed increases with height
Wind direction backs more with height due to coriolis force
81
Difference Between Surface Wind and Gradient Wind
Over land veers approx 30 degrees (surface wind 1/3 of the original speed)
Over water veers approx 10 degrees (surface wind 2/3 of the gradient speed)
82
Diurnal Variation in Wind Direction and Speed
Strongest during the day and veers less
Max approx 3pm (instability of air with convection currents)
Weakest around dawn (air is cool and friction is max)
Day to night: weaker and therefore veers
83
Squall (SQ)
Ahead of convective clouds and CB's
| Outflow of cold air, down-draughts, gust fronts
84
Line Squalls (LSQ)
A band of intense thunderstorms
85
Gust (G)
A sudden increase in wind speed of more than 10kts and lasting for only a few seconds
86
Local Winds on the Coast
```
Sea breeze (daytime)
Up to approx +/- 1000ft and strongest at mid-afternoon
Land breeze (night)
```
87
Thermals
Updraughts (reduce power)
Downdraughts (increase power)
Maintain best rate of climb airspeed after take-off
Temp (Tx) vs dew point (Td) split could indicate possible thermals
Areas of known thermal activity = glider activity
88
Dust Devils
Short lived and localised, a few metres in diameter
Air and surface is dry
Large temp and dew point split
89
Dust Storm
Mod to strong wind, instability, <1000m visibility
| Reduced performance and possible structural damage
90
Katabatic Wind
Night
Land loses heat by terrestrial radiation
Gravity pulls cooler air down the slope
91
Anabatic Wind
Day
Sun heats up the ground and air above, therefore less molecules are present and it begins to rise
Cooler air flows up the slope to replace it
Weaker as upward airflow is opposed by gravity
Supported by sea breeze
92
Requirements for Mountain Waves
Requires a stable layer on top of a mountain with a height of >1000ft with wind coming from right angles at >25kts
93
Mountain Waves
Significant turbulence on the lee side
Can result in lenticular clouds if sufficient moisture is present
Stationary clouds on downwind side
Altocumulus lenticularis
Rotor zone rotors (can have rotor clouds) below the crest
94
The Föhn Effect
Moist air is forced up against a mountain
Cools to dew point and cloud forms
Rain falls on the upwind side, the moisture content reduces and air descends and warms on the lee side with a higher cloud base
Warm dry wind on the downwind side
95
The Low Level Jet
Strongest in the early morning, prevalent in winter with long cold nights
Strong windshear and turbulence usually below 3,000ft AGL
Located over a plain and to the west of a mountain range
Disperse when the sun heats the surface inversion
High moving to a low but obstructed by mountain ranges
96
Source region of Air Masses
```
Sea (maritime)/land (continental)
By latitude (Tropical/Polar)
Tropical maritime (Tm), Tropical continental (Tc), Polar maritime (Pm), Polar continental (Pc)
```
97
Fronts
Boundary between two air masses of differing temps
98
Cold Front
Cold, dense air will wedge in under the warmer air
When approaching: decreased QNH, bad weather (gusts, squalls, turbulence, fast moving cloud and showers), north-westerly winds, cumulus
After: South-easterly winds, increased QNH, cumulus clouds due to hot air rising with potential thunderstorms, decreased temp
99
Warm Front
Warm, less dense air will slope up against the cold air
Approaching: stratiform low level, nimbostratus, rising air is stable, heavy and continuous rain
After: weather becomes 'fine', increased surface temps
100
Occluded Front
An active and fast moving cold front catches up with the slower moving warm air
The cold air forces the warmest air upwards
Embedded CB: thunderstorms are normally obscured by other types of cloud
101
Quasi - Stationary Front
When 2 air mass systems become stationary and there is practically no horizontal movement
Disturbance from upper air may displace the system
102
Visibility
Greatest horizontal distance at which someone can identify a dark object
103
Factors Affecting Visibility
```
Obscurations
Reported vs flight visibility
Slant visibility
Night and day visibility
Vertical visibility
```
104
Obscurations
Moisture, smoke, dust/sand, pollution, sun
105
Reported vs Flight Visibility
Reported: vis from the ground
Flight: vis from the cockpit
106
Slant Visibility
```
On final (looking at airfield at a slant)
Air to ground vis observed by the pilot from the cockpit
```
107
Night and Day Visibility
Night vis is greater (certain things stand out better)
| Day vis worst at dawn and dusk
108
Vertical Visibility
On top of the airfield
| In hundreds of feet
109
Dew and Frost
Water vapour condensates in the form of dew when sufficient moisture is available during overnight cooling (clear night - max terrestrial)
When temp close to 0 degrees celcius or windy dew can turn to frost
110
Fog
Horizontal vis < 1000m
111
Mist
Horizontal vis equal to or greater than 1000m
112
Types of Fog
Radiation
Advection
Frontal
Steam
113
Radiation Fog
Requires clear nights, high humidity, light wind (>5kts)
Forms late at night or just after sunrise (mixing due to heat)
Insolation (sunrise) causes mixing of the air just above the ground and dissipates as the ground gets warmer
Is thin and evaporates due to the terrestrial heat radiated from below due to insolation or a strong wind and forming of low stratus cloud
114
Advection Fog
Warm, humid air is passing horizontally over a cold surface
| Dissipates by strong winds (>15kts) or reduced humidity, or a change in wind direction
115
Fog Due to Mixing
Radiation = 2-5kts (light wind)
Small or no difference between OAT and dew point
Advection Fog = 10-15kts (stronger wind)
116
Frontal Fog
Cloud forms on the frontal boundary of the warm front
Warm rain causes the colder air below to become saturated
Fog or stratus cloud forms ahead of the frontal line
117
Steam Fog
Forms on top of water (arctic waters)
118
Dangers of Fog
Visibility into sun is greatly reduced
119
Types of Icing
Hoar frost
Clear ice
Rime ice
120
Requirements for Icing
Visible moisture
Freezing temperature
Freezing airframe temperature
121
Hoar Frost/White Frost
Night time cooling close to the ground
Deposits of ice crystals
Negatively affects the aerodynamics of the wings
122
Rime Ice (Airframe Icing)
- 10 to -20 degrees celcius
Small super cooled water droplets (freeze on impact)
Opaque in colour due to air spaces between frozen droplets
123
Clear Ice (Airframe Icing)
Large drops of freezing rain
Cumuliform or nimbostratus cloud
The drop flows backwards on the cold surface before it freezes
No air trapped inside the ice and is therefore transparent and difficult to see
124
Dangers of Icing
Can impact prop, windscreen, engine intakes, antennae
Increased weight, decreased lift, increased drag, decreased thrust (prop icing), decreased vis, blocked pitot tubes, may restrict control surfaces, reduced braking action on the runway
125
Warm Fronts and Icing
Rain falling from the warmer air through the colder air may become severe clear ice
Flying into a lowering cloud base due to a warm front may present you with severe icing conditions
126
Conditions for a Thunderstorm
Humidity (abundance of moisture)
An ELR of >3 degrees celcius/1000ft (unstable atmosphere)
Lifting force (eg. orographic, convection, convergence, frontal activity, etc)
127
Stages of a Thunderstorm
1. Growing/Cumulus
2. Mature
3. Dissipating
128
Growing/Cumulus Stage of a Thunderstorm
Lots of up-draughts
| No precipitation
129
Mature Stage of a Thunderstorm
```
Up and down-draughts causing turbulence
Lightening
Possible hail
Wind shear
Gust front can cause roll clouds
Precipitation
Anvil at the top
Wind change 180 degrees = runway change
```
130
Dissipating Stage of a Thunderstorm
Mainly down-draughts
Continuous precipitation until cloud is empty
Storm moves in direction of the anvil
131
Orographic Storm
Day or night
Humid air is forced to rise over an obstruction
Air continues to rise after condensation
132
Lightening
Faulty ADF and compass readings
| Temporary effect on night vision of the pilot
133
Down-Draughts Due to Cloud
Strong underneath
Fly through the areas which are brightest with increased visibility
Eg. Virga
134
Microbursts
Often associated with CB's (severe wind shear)
Very strong downburst with a small diameter (10km)
Airflow spreads out near the ground
135
4 Stages of Tropical Cyclones
1. Formative (eye forming)
2. Immature (strong winds)
3. Mature (gale force winds)
4. Decaying (die out to rain depression)
136
Formative Stage of a Cyclone
Start with a low pressure system in an area approx 5 - 15 degrees South
Develop in tropical oceans with water > 28 degrees celcius
<1000 hPa
137
Immature Stage of a Cyclone
Pressure gradient near centre too steep to plot
Winds light and variable inside the eye
Strong winds > 120kts around the eye with CB
138
Mature Stage of a Cyclone
Surface pressure approx 950 hPa
Strongest wind in left forward quadrant
NS with spiral bands of Cu and CB
139
Decaying Stage of a Cyclone
Die out or become rain depressions once they move inland or move towards the colder pole (water temp < 26 degrees celcius) or beyond 15 degrees South
Over land: colder and drier air, increased surface friction
Widespread rain may continue for several days
140
Tornado
Over land
Massive convergence with sharply inclined isobars
Rotating twist due to differing winds that become a spiral
Exposed to cold and warm air
Massive super-cell thunderstorm < 300m in diameter
Wind speeds up to 200kts
141
Funnel Cloud
Tornado which does not touch the ground
142
Water Spouts
Over water touching the surface
143
Aerodrome Forecast
TAF
| TTF - 3 hours
144
Area Forecast
GPWT
| GAF
145
Reports
SPECI, METAR, ATIS
146
Advices
Sigmets, airmets
147
Aircraft
Aireps: from the pilot
148
Aerodrome Categories
Cat A, B, C, D
Cat A: Issued 6 hourly validity 24 hrs
Cat B: Issued 6 hourly validity up to 18 hrs
149
TAF
True wind direction
AGL
5nm radius of the aerodrome
Statement of expected conditions
150
Tempo
< 1hr or less than 1/2 the forecast time (60 mins HLD fuel)
151
Inter
Less than 30 mins (carry 30 mins of fuel)
152
Dew Point Temp Difference
Small: humid
Large: dry air needs to rise
