Meteorology Flashcards
Most visible weather phenomenon occurs in the _____
Troposphere
The troposphere goes from ___ up to ~___ also known as the _____
MSL (mean sea level)
~11km (36,090ft)
Tropopause
Temparature decreases at a rate of ___ per 1,000ft (__ per 100m) up to a hight of ___. This is known as the _____ _____
1.98°C
0.65°C
Lapse rate
___ of water vapour is in the troposphere
90%
___ of total mass of air is in the troposphere
75%
ISA Sea level pressure
1013.25Hpa
29.92InHg
760mmHg
ISA Sea level temp
+15°C
ISA Density
1.225Kg/m³
ISA temp 11-20km (36,090 - 65,000ft)
-56.5°C
The composition of air:
78% Nitrogen
21% Oxygen
1% Other Gases
The closer to the poles you are, the _____ the tropopause, at an altitude of aprox. __ -__km
Lower
8 - 10km
The closer to the equator you are, the _____ the tropopause, at an altitude of aprox. __ - __km
Higher
16 - 18km
The closer to the poles you are, the _____ temperature is at the tropopause, aprox. __ to __°C
Higher
-40 to -50°C
The closer to the equator you are, the _____ temperature is at the tropopause, aprox. __°C
Lower
-75°C
Summer tropopause height at Latitude 30°
16km (52,000ft)
Winter tropopause height at Latitude 30°
16km (52,000ft)
Summer tropopause height at Latitude 50°
12km (38,000ft)
Winter tropopause height at Latitude 50°
9km (29.00ft)
Summer tropopause height at Latitude 70°
9km (29,000ft)
Winter tropopause height at Latitude 70°
8km (26,000ft)
Folds in the tropopause are due to
large air masses
ISA = __ - ((Alt/__) x _)
ISA = 15 - ((Alt/1000) x 2
If the actual temperature is warmer than ISA, the deviation is _____
Positive
If the actual temperature is colder than ISA, the deviation is _____
Negative
The Stratosphere extends from the _____ , up to
about ___
Tropopause
50km (164,040ft)
The Stratosphere holds __ of the atmospheres gases
19%
The Stratosphere contains the_____ ______, at __ - __km
Ozone layer
15 - 35km (49,200 - 114,829ft)
The ozone layer _____ UV radiation and emits _____ _____ _____
Absorbs
Long wave radiation
Between 20km and the stratopause, temperature _____ to __
Rises
0°C
The _____ is between the stratopause and __ - __km
Mesosphere
80 - 90km (262,470 - 295,280ft)
You can find ____ but not _____ in the lower stratosphere
Clouds
Turbulence
The _____ between the stratopause and the mesopause falls from __ to __
Temperature
0°C to -90°C
Above the mesopause, you will find the _____ which reaches a height of aprox. ___
Thermosphere
700km
Temperature in the thermosphere _____
Increases
In the thermosphere, you will find the _____ between aprox. ___ - ___
Ionosphere
85 - 600km
Potential difference (v) between the Earths surface and Ionosphere is ___ - ___
250 - 500kv
°C to °F
(°C x 1.8) + 32
°F to °C
(°F - 32) / 1.8
°C to K
+273
°F boiling point
212°F
°F freezing point
32°F
K boiling point
373k
A _____ records temperature over time and plots it on a graph
thermograph
A _____ _____ records surface temperature and humidity, must be placed __ - __ _________
Stevenson Screen
1 - 2m above the ground.
A radiosonde records 3 things:
every __
Air temperature
Humidity
Pressure
1.3 seconds
A radiosonde can reach a hight of ___
35km
Insolation
Amount of solar radiation absorbed per unit area over time
The Earth is tilted on an axis of
23.5°
In January, the Earth is _____ from the sun
91 million miles
In July , the Earth is _____ from the sun
95 million miles
The earth spins
anti-clockwise
Summer solstice
21st June, Northern hemisphere closest to the sun at 23.5°N - the tropic of cancer
Winter solstice
21st December, Southern hemisphere closest to the sun at 23.5°S - the tropic of Capricorn
Spring & Autumn Equinox
23rd March & 23rd September, Sun at same angle as equator.
Conduction
The transfer of heat by physical contact
Convection
The transfer of heat through the vertical
movement of air
Advection
The transfer of heat through the horizontal movement of air
Sublimation
Direct change of a vapour to solid, or solid to vapour
In the day, thick cloud = _____. No cloud = _____
Cooler
Warmer
At night, thick cloud = _____. No cloud = _____
Warmer
Cooler
Inversion
Temperature increasing with height
In the day, wind = _____. No wind = _____.
Cooler
Warmer
At night, wind = _____. No wind = _____.
Warmer
Cooler
_____ reduces non-linearly with height, due to the _____ distribution of the mass of air
Pressure
Non-linear
Colder then ISA, the _____ dense the air
More
Warmer the ISA, the _____ dense the air
Less
Natural inversions
form over night
Fog is caused by the temperature _____ enough to condense the _____ _____ into _____ _____
Cooling
Water vapour
Water droplets
At the bottom of a valley, visibility can be _____ and aircraft performance is _____ due to _____ air.
Poor
Better
Denser
When air is subsiding and diverging it is a _________
High pressure system
The greater the _____ of overlying air, the _____ the atmospheric pressure
Mass
Greater
Pressure reduces by ___ per ___ up to ____
1hPa
27ft (8m)
20,000ft
Low pressure areas are known as
Depressions (lows)
High pressure areas are known as
Anticyclones (highs)
Whenever a pressure variation exists, the _____ created driving the air from high to low _____ is called the ________
Force
Pressure
Pressure gradient force (PGF)
The PGF is the _____ _____ driving the flow of air and _____ the wind speed
Primary force
Determines
Trough lines
Areas of disturbances
Barometric pressure can be measured by 2 devices:
A mercury Barometer
A Aneroid Barometer
What is the QFE?
The isobaric surface pressure at the airfield reference point
What is the QNH?
The barometric pressure measured at the reporting stating which has be mathematically adjusted to MSL using the airfields elevation.
QNH = ___ +- (Elevation/___)
QNH = QFE +- (Elevation/27ft or 8m)
There is a __ height difference for every __ of ISA deviation
4%
10°C
Height
The indication above ground level, normally the height above an aerodrome QFE reference point.
Altitude
The indication above MSL
Flight levels use the pressure setting of
Mean Sea Level (1013pHa)
When the altimeter is indicating a reading lower than the true altitude it is
Over reading
When the altimeter is indicating a reading heigher than the true altitude it is
Under-reading
Cold air: _____ altitude < _____ altitude
True
Indicated
Warm air: _____ altitude < _____ altitude
Indicated
True
The barometric lapse rate
27ft per 1hpa
To determine the IA change use the equation
IA change (ft) = Difference in hPa x 27ft
Most dangerous - “____ to ____, look out below”
High
Low
Most dangerous - “____ to ____, don’t be bold”
Hot
Cold
Equation to calculate Temperature Error Correction
((ISA Devation/10) x 0.04) x altitude
OR
(4 x (Altitude/1000)) x ISA devation
Equation to calculate ISA Deviation
15 - ((alt/1000) x 2)
If an aerodrome elevation is given in the question
It must be taken into account
Due to the _____ effect, _____ occurs over the crest of high terrain, causing air speed to _____, and _____ and _____ to decrease.
Venturi Convergence Increase Pressure Temperature
In controlled airspace, controllers assign levels to ___ flights to provide _____ _____.
IFR
Terrain Clearance
Controllers have no responsibility for the _____ _____ for ____ aircraft.
Terrain Clearance
VFR
In temperatures warmer than ___, FL separation _____
ISA
Increases
In temperatures colder than ISA, FL separation _____
Decreases
What is the definition of Density ? And what is ISA density at sea level
Measure of a mass of air within a given volume.
1.225 Kg/ m3
Under ISA, 1/2 and 1/4 of MSL density occurs at what altitude?
22000 FT and 40000 FT
Density in the atmosphere is affected by
Pressure
Temperature
Humidity
The density decreases with altitude, but at a ______-______ rate. It reduces more quickly at ________ altitudes. Mimicking the pressure lapse rate with height.
Non-linear
Lower
What are the 4 main steps of the hydrological cycle
Evaporation, Condensation, Precipitation, Run-off
On average there’s approx. ___% of water vapour in the atmosphere. But it can vary from 0 to ___% . 90% of the water vapour is found in the __________
1, 5, troposphere
Humidity mixing ration tells you how much water vapour is actually in the air, it is measured in ____ of water vapour per ____ of dry air
Grams, Kilograms
g/Kg
Humidity mixing ratio won’t change unless……
You add/ remove water vapour
Saturation mixing ratio is the ______ amount of water vapour that can be in the air for a given temperature
Maximum
Warmer air can potentially ‘______’ more water vapour than colder air
Hold
Saturation mixing ratio ______ with increasing altitude and decreasing temperature. Whereas humidity mixing ratio ______ ______ constant as altitude increase and pressure and temperature decrease
Decrease
Stays constant
The ratio between the amount of water vapour that the air is holding and the maximum amount of water vapour that air can hold is called?
Relative humidity
At constant pressure, relative humidity is affected by……
Amount of water vapour
Temperature
Assuming pressure is constant throughout a clear day, what is the RH like to be _______ 30 mins after sunrise and ______ 2-3 hours after noon.
Greatest
Least
The close the ambient air temperature is to the ______ ______ temperature, the higher the humidity
Dew point
Formulas for relative humidity, using temperature and dew point
RH % = 100 - (5x (T - Td))
% difference between the dry bulb temperature and wet bulb temperature is equal to?
Relative Humidity
What is the DALR?
How does it change with height?
Dry adiabatic lapse rate
3 degrees per 1000 FT/ 1 degree per 100 m
What is SALR?
And how does the temperature vary with height?
Saturated adiabatic lapse rate
1.8 degrees per 1000 FT / 0.6 degrees per 100 m
A parcel of saturated or dry air is said to ________ ________ if it is cooler than the environment. it will sink back down to its original level even when forced to rise
Absolutely stable
ISA ELR is?
2 degrees per 1000 FT / 0.65 degrees per 100 m
When an air parcel is rising and subsiding along the saturated adiabatic lapse rate, the RH must ______ ______, until ______ ______ is removed from the parcel.
Remain constant (at 100%).
Water vapour
The ______ the saturated air, the ______ it cools, because warmer saturated air holds ______ moisture than cold saturated air,
therefore ______ condensation will take place when it is cooled, but more ______ ______ will also be released.
Warmer, slower, more, more, latent heat
The SALR increases ______ with height
Exponentially
Low pressure systems are known as
Cyclones or depressions
Low pressure are always accompanied by _____ and _____
Cloud
Precipitation
Low pressure systems have isobars that are _____ _____ than other systems.
Closer together
In Low pressure systems, air flows _____ in the Northern Hemisphere and _____ in the Southern Hemisphere
Anti-clockwise
Clockwise
As air rises, it _____, causing water vapour to _____ and _____ _____ with possible _____
Cools
Condense
Form clouds
Precipitation
With your back to the wind in the Northern Hemisphere, the low pressure system is to your _____
Left
Small scale low pressure systems can be ___ to ___NM across and usually occur over _____
1 to 20NM
Land
Large scale low pressure systems can be ___ to ___NM across
300 to 1000+NM
Small scale warm, lows can _____ during the day over land masses in _____.
Develop
Summer
Warm lows are low pressure systems in which the _____ is _____ than the surrounding environment
Core
Warmer
Warm lows can produce 3 things:
Heavy rain
Thunder Storms
Flash Floods
Large thermal lows usually form over land in summer where the _____ is present
Inter-tropical Convergence Zone (ITCZ)
In July the ITCZ is in the _____ hemisphere and ranges from latitudes ___ to ___
Northern
15-20°N
In January the ITCZ is in the _____ hemisphere and ranges from latitudes ___ to ___
Southern
0-20°S
When the ITCZ moves it affects local _____ _____ and has a large effect on the _____
Tropical winds
Inland Water warm depressions can form over _____ in winter, when colder air over _____, moves over warmer _____ or _____.
Water
Continents
Seas
Lakes
Small but intense maritime meso-scale cyclones that form in in winter, by cold polar or arctic air advected over relatively warmer water.
Polar lows
Low pressure systems in which the entire core is colder than the surrounding environment
Cold lows
Cold lows can produce 5 things:
Snowfall Thunderstorms Heavy rain Floods Windshear
Cold depressions are typically _____ _____ and move with medium airflow at _____ to _____ft.
Frontal depressions
2,000 to 3,000ft
A low-pressure area which forms in the lee of mountains
Orographic Depression
With a strong wind blowing at approx. ___ towards a mountain range at, the wind will tend to blow _____ ___ _____ of the mountain rather than _____ ___ _____
90°
Around the side
Over the top
Isobaric troughs indicate
An area of low pressure going into another system
Trough lines indicate
Areas of stronger surface convergence
High pressure systems are also known as
Anticyclones
An anticyclone is
an area of relatively high surface pressure.
Air is _____ in a high pressure system
Subsiding
As the air _____ it warms due to _____ and so cloud formation is _____, causing the weather to usually be settled with only _____ amounts of cloud cover
Subsides
Compression
Inhibited
Small
High pressure systems can be up to ____NM and are _____ _____ _____
1500NM
Slow moving systems (quasi-stationary)
Warm highs
High pressure systems in which the entire core is warmer than the surrounding environment
Pressure levels are pushed _____ in the core due to excess air in the upper troposphere as the warm air _____
Higher
Rises
Warm High pressure systems can produce 4 things:
Heatwaves
Drought
Poor air quality
High pollen count
High pressure areas are associated with _____ _____
Light winds
High pressure systems usually occur around
30°N/S
Cold highs
High pressure systems in which the entire core is colder than the surrounding environment
In high pressure systems air flows _____ in the Northern Hemisphere and _____ in the Southern Hemisphere
Clockwise
Anticlockwise
Due to the colder, _____ air, the pressure levels bulge _____ at higher altitudes
Heavier
Downwards
Cold High pressure systems can produce 6 things:
Droughts Frosts Snowfall Mist/Fog Low level cloud Poor air quality
Cold anticyclones are permanently found over the _____ know as _____ _____.
Poles
Polar Highs
Blocking high
Highs that can become stronger in summer, pushing lows around them
Blocking highs are _____ and between __ and __
Quasi-stationary
50° and 70°
Ridges are indicated by _____ extending out from the area of _____ pressure
Isobars
High
Cols
An area of relatively high pressure shown on a synoptic chart, situated between two areas of higher pressure and low pressure
Flat-Pressure Patterns
An area clear of isobars
The 3 cells from the poles to the equator
Polar cell
Ferrell cell
Hadley cell
The polar cell ranges from the latitudes ___ and ___
90°
60°
The Ferrell cell ranges from the latitudes ___ and ___
60°
30°
The Hadley cell ranges from the latitudes ___ and ___
30°
0°
At 90° you can find _____ pressure
High
At 60° you can find _____ pressure
Low
At 30° you can find _____ pressure
High
At 0° you can find _____ pressure
Low
Warm high pressure regions:
Azores high, 1020hPa, (all year)
Pacific high, 1020hPa (all year)
Cold high pressure regions:
Siberian high, 1035hPa (Jan)
Canadian high 1020hPa (Jan)
Warm Low pressure regions:
North Australian low, 1005hPa (Jan)
Asian low, 1000Hpa (July)
North American low, 1010hPa (July)
Cold Low pressure regions:
Icelandic low, 1000hPa (Jan)
Aleutian low, 1000hPa (Jan)
Icelandic low split, 1010hpa (July)
Density
Measure of a mass of air within a given volume (kg/m3 or gm/m3)
As altitude increases, density _____ at a _____ rate
Decreases
Non-linear
In ISA conditions atmospheric density is at 3/4 of MSL at _____, 1/2of MSL at _____ and 1/4 of MSL at _____
10,000ft
22,000ft
40,000ft
If pressure decreases, the mass of air within the same given volume _____
Decreases
More humid air is _____ _____ than than dry air
Less dense
In cold air density decreases ______ with height than warm air.
quicker
Equation for pressure difference:
PA diff = 120ft x ISA temp devation
If colder, it will be a ______ pressure difference. If warmer, it will be a _____ pressure difference.
Negative
Positive
There is __% of water vapour in the atmosphere
1%
Warm, air can hold _____ water vapour than cold air.
More
The HMR (Humidity mixing ratio) tells you:
How much water vapour is actually in the air measured in g/kg (or kg/kg)
The HMR’s value won’t change unless you _____ or _____ water vapour from the air:
Add
Remove
The MR is constant as altitude _____ and pressure and temperature _____
Increases
Increase
The SMR (Saturation mixing ratio) is:
the maximum amount of water vapour that can be in the air at a certain temperature, measured in g/kg (or kg/kg)
The SMR _____ with increasing altitude and decreasing temperature
Decreases
Relative humidity equation:
RH% = (HMR/SMR) x 100
At a constant pressure the RH is affected by the:
Amount of water vapour
Temprature
The RH is
The ratio (%) between the amount of water vapour that the air is holding, and the maximum amount of water vapour that the air can hold.
The RH is greatest ____________ and weakest ____________
30 mins after sunrise
2-3hrs after midday.
The closer the ambient air temperature to the dew point temperature, the _____ the humidity and the further away the ambient air temperature to the dew point temperature, the _____ the humidity
Higher
Lower
The dew point
The temperature, to which the air must be cooled for it to become saturated and start to condense
Equation to calculate RH with the dew point:
RH% = 100 - (5x (T - TD)
A Psychrometer is used to determine 3 things:
Temprature
RH%
Dew point
Adiabatic
A process that occurs without the transfer of heat or matter with the surroundings
DALR
-3°C per 1,000ft (-1°C per 100m )
SALR
-1.8°C per 1,000ft (-0.6°C per 100m)
In the tropics SALR can be _____ and in Polar regions it can be _____
- 4°C per 100m
0. 9°C per 100m
Absolute stability is when
ELR < Both DALR & SALR (they subside)
Absolute instability is when
ELR > Both DALR & SALR (they rise)
Conditional stability is when
DALR (Subsides) > ELR > SALR (rises)
Neutral Stability is when
ELR = DALR or ELR = SALR
If cooled from below, the air is _____, if warmed from below, the air is _____.
Stable
Unstable
Clouds form when the invisible water vapour in the air, _____ onto microscopic nuclei, becoming ___________ or __________
Condenses
Visible water droplets
Ice crystals
Cumulus clouds from through _____ when the atmosphere is _____
Convection
Unstable
A front is where ____________, here _____ air rises over _____ air.
2 air masses meet
Warmer
Colder
On a warm front you can find:
Stratus and Cirro clouds
On a cold front you can find:
Cumulus clouds
A cold front is _____ lifting and moves _____.
Steeper
Faster
The quicker a front is moving, the ______ _____ the uplift.
More instense
Unstable orographic uplift is when air is forces to rise by _____ and _____. The air then continues _____.
Mountains
Convects
Upwards
Stable orographic uplift is when the _____ effect takes place. _____ takes place decreasing the _____ _____. Air then _____ on the lee side.
Foehn
Precipitation
Dew point
Descends
Convergence is when
Two air masses coming from different directions meet and are forced to rise.
Turbulent layers are formed by
Air blowing over solid objects such are buildings, trees and hills.
Turbulent layers tend to form up to a depth of about
2,000-3,000ft
If the _____ _____ is reached within the turbulent layer, _____ will form at the top of the layer
Dew point
Cloud
Inversions cause an increase in _____ and _____ the upward growth of cloud by preventing further _____
Stability
Limit
Convection
Oktas leves: Few - Scattered (SCT) - Broken (BKN) - Overcast (OVC) -
1 - 2
3 - 4
5 - 7
8
Cloud base
The height of the base of the cloud is measured above ground level in ft. measured by a Ceilometer
Cloud base equation:
Cloud Base Height ft = Temp. − Dew Point X 400
The height above the ground or water of the base of the _____ layer of cloud below _____ covering more than _____ the sky
Lowest
20,000ft (6,000m)
Half
Vertical visibility is used
When the sky is obscured by precipitation, and cloud details cannot be assessed but information on vertical visibility is available.
High level clouds: name group
Cirro
High level clouds: Polar altitudes
3-8km (10,000 - 25,000ft)
High level clouds: Temperate altitudes
5-13km (6,500 - 23,000ft)
High level clouds: Tropical altitudes
6-18km (20,000 - 60,000ft)
Mid level clouds: name group
Alto/Nimbo
Mid level clouds: Polar altitudes
2-4km (6,500 - 13,000ft)
Mid level clouds: Temperate altitudes
2-7km (6,500 - 23,000ft)
Mid level clouds: Tropical altitudes
2-8km (6,500 - 25,000ft)
Low level clouds: name group
Status/cumulo
Low level clouds: Polar altitudes
0-2km (0-6,500ft)
Low level clouds: Temperate altitudes
0-2km (0-6,500ft)
Low level clouds: Tropical altitudes
0-2km (0-6,500ft)
Cumulonimbus clouds can range from _____ to very _____ levels
Low
High
Cirrus clouds tend to look
Curly/feathery/wispy
Stratus clouds tend to look
Flat, wide and layered
Nimbus clouds tend to be
Rain bearing
Cumulus (Cu)
Base height: 1,200-6,000ft - low level
Detached, generally dense with sharp outlines
Sunlit white, base dark.
Mainly water droplets, little precipitation
Stratocumulus (Sc)
Base height: 1,200-7,000ft - low level
Grey/white
Little precipitation
Composed of water droplets
Stratus (St)
Base height: 0 - 1,500ft - low level
Grey cloud layer
Drizzly precipitation
low temperatures
Cumulonimbus (CB)
Base height: 1,000-5,000ft - low level Heavy dense cloud Reaches extreme heights Base dark, water droplets + Ice crystals Large raindrops, snow & hail
Altostratus (As)
Base height: 8,000 - 17,000ft - mid level Greyish cloud sheet Great horizontal extent thin water droplets + ice crystals
Nimbostratus (Ns)
Base height: 1,500-10,000ft - low/mid level Grey cloud layer Thick, blocks out sun covers wide area Great vertical extent Water droplets Produces precipitation
Altocumulus (Ac)
Base height: 7,000-17,000ft - mid level
White,
small, detached but frequent
water droplets
Cirrus (Ci)
Base height: 17,000-35,000ft - high level
White detached clouds
Small Ice crystals
Silky
Cirrostatus (Cs)
Base height: 17,000-35,000ft - high level Transparent, whitish cloud smooth appearance Very wide Small Ice crystals
Cirrocumulus (Cc)
Base height: 17,000-35,000ft - high level
white patch layer
grains and ripples
Ice crystals
Species - Humilis (hum)
flattened, never produce precipitation
Coulds - Cu
Species - Medicoris (med)
moderate vertical extent, no precipitation
Clouds - Cu
Species - Congestus (con)
Strongly sprouting, great vertical extent, bulging upper part, may produce perciptation.
Clouds - Cu
Species - Fractus (fra)
small, ragged edges, rapid changes
Clouds - Cu, St
Species - Lenticaularis (len)
Shape of lense/almond, elongated, well defined outlines.
Clouds - Sc, Ac, Cc
Species - Castellanus (cas)
turrets rising vertically, horizontal base, evident when seen from side.
Clouds - Sc, Ac, Ci
Species - Virga
Trails of precipitation which does not reach earths surface, attached to under surface of cloud
Clouds - Sc, Cb, As, Ns, Ac, Cc
Species - Calvus (cal)
Sprouting of upper parts are flattened, whitish mass without sharp outlines.
Clouds - CB
Species - Capillatus (cap)
Upper portion is fibours/striated stucture, shape of anvil or plume. accompanied by shower/thunderstorm.
Clouds -CB
Low base cloud types:
Stratus (St)
Stratocumulas (Sc)
Cumulus (Cu)
Cumulonimbus (CB)
Middle base cloud types:
Altocumulus (Ac)
Altostratus (As)
Nimbostratus (Ns)
High base cloud types:
Cirrrus (Ci)
Cirrocumulus (Cc)
Cirrostratus (Cs)
When water vapour first condenses onto a _____, the water droplet has an average diameter of approx. _____
Nuclei
0.02mm
The Bergeron-Finderson theory:
- If parcels of air are uplifted to a sufficient height in the troposphere, the dew-point temperature will be very low, and minute ice crystals will start to form.
- The supercooled water droplets will also freeze on contact with these ice nuclei.
- The ice crystals subsequently combine to form larger flakes which attract more supercooled droplets.
– This process continues until the flakes fall back towards the ground.
– As they fall through the warmer layers of air, the ice particles melt to form raindrops
– However, some ice pellets or snowflakes might be carried down to ground level by cold downdraughts.
The Coalescence theory:
- Applies to warm clouds
- They contain water droplets of many differing sizes, which are swept upwards at different velocities so that they collide and combine with other droplets
– When the droplets have a radius of approx. 3mm, their movement causes them to disintegrate, forming a fresh supply of water droplets
– This theory allows droplets of varying sizes to be produced
Drizzle (DZ)
Fine drops of water very close to one another that falls from a cloud.
Diameter 0.2-0.5mm
terminal velocity = 4m/s
Rain (RA)
Precipitation of drops of water that falls from a cloud.
Diameter 0.5-0.6mm
Terminal velocity = 9m/s
Freezing Precipitation (FZRA/FZDZ)
Forms ahead of warm fronts,
Starts frozen, melts, falls through air <0°C, freezes upon contact with a surface.
Snow (SN)
Solid precipitation of ice crystals, singly or stuck together, that fall from a cloud.
Falls upto 2°C, heaviest when -2°-0°C
Largest flakes can be >25mm (adv. >4mm)
Sleet
Melting snow or mix of rain and snow,
above 2°C
Snow grains (SG)
Precipitation of very small opaque white particles of ice that falls from a cloud.
diameter <1mm
between -10°-0°C
Do not bounce
Diamond Dust
Precipitation that falls from a clear sky in very small ice crystals, often so tiny that they appear to be suspended in the air.
Diameter 100μm (micrometer)
Snow pellets
Precipitation of white and opaque ice particles that falls from a cloud.
Diameter <5mm
Brittle, easily crushed
Bounce when hit ground
Small Hail (GS)
Diameter <5mm
Hail (GR)
Hailstones form when a nucleus, collects cloud droplets or drops of rain as it repeatedly rises and falls, through a cloud From CB clouds Can be found up to 45,000ft as large as 100mm at 10,000ft Diameter 5-50mm
Ice Pellets (PL)
Precipitation of transparent ice particles that falls from a cloud.
They fall into a sub-cloud layer of warm air where the snowflakes melt or partially melt, and then fall into a cold layer of air, where they freeze and reach the ground as frozen precipitation
Diameter <5mm
Bounce when hity the ground
Light: DZ, RA and SN
N/A,
<2mm/hr,
<0.5cm/hr
Moderate: DZ, RA and SN
Some run-off,
2-10mm/hr
0.5-4cm/hr
Heavy: DZ, RA and SN
> 1mm/hr
10mm/hr
4cm/hr
Continuous -
Lasts over 1 hour
Intermittent -
Continuous with breaks
Showers -
Short lived
The 3 fundamental requirements for thunderstorms
Instability at least 10,000ft above the freezing level
An adequate supply of moisture
A trigger to start uplift
Air movement that can cause thunderstorms:
Convective
Frontal
Orographic
Convergence
Features of a Convective TS:
Uplift trigger is usually thermal uplift cause by surface warming.
Most common in summer
Maximum in the early afternoon
Most server TS
Features of a frontal TS:
Occur where a cold air mass undercuts a warm air mass and forces it upwards Ahead of the cold front More common in winter Fastest moving TS
Orographic TS formation:
Orographic convection forms large CB clouds due to unstable air accelerating the convection process
Single cell TS are made up of a single _____ cloud, that develops into a _____ and then into a _____ before dying away.
CU
CB
Thunderstorm
Features of single cell TS:
Small
Brief
Weak
Grow and start to die within an hour
The initial stage of single cells has updraughts of around _____, it is fed with _____ _____ _____ and can reach the tropopause. This stage lasts _____
30m/s, 60kts, 5000-6000ft/min
Warm moist air
15 - 20 mins
The mature stage of single cell TS, updraft are now at _____ and downdrafts are caused by _____ and reach approx. _____. This stage can last _____
50m/s, 100kts, 10,000ft/min
Precipitation
2,000ft/min
15-30mins
The 9 hazards of a TS:
Rain Hail Ice Turbulence Windshear Lightning Static electricity Pressure Visibility
When rain strikes the aircraft is has a _____ and _____ momentum. It can also cause a _____ moment if it impacts unevenly.
Downward
Rearward
Pitching
Rain increases the airframe’s _____ and produce _____
Mass
Drag
Turbine engines have a limit on the amount of ______ they can ingest.
Water
+RA can cause pressure sensing ____________
Instrument errors
It should always be assumed that where there’s a thunderstorm, there is _____.
Hail
The higher the ______ _____, and the ______ the moisture content of the air mass, the stronger the convective activity and the damaging hail.
Lapse rate
Greater
Airframe ice is likely in cloud or rain at a temperatures below _____
0°C
You can get ______ turbulence inside CB & TS
MOD - SEV
Clear Air Turbulence (CAT), occurs __________.
Severe turbulence can also be encountered several thousand feet _____ active thunderstorm clouds
Outside the cloud
Above
Windshear conditions occur with thunderstorms where there are _____ _____. As the cold downdrafts reach the ground, the air is forced to spread out, up to _____ ahead of the TS and up to _____. Can reach speeds of _____ changing at _____.
Gust fronts 25-30km 6000ft 80kts 90°
Windshear can be indicated by _____ clouds or _____ clouds.
Shelf
Roll
Downbursts
Highly concentrated and powerful downdraughts
of air caused by precipitation at the top of the cloud, drawing cold, dense down with it as it falls.
Microbursts:
3,000-4,000ft/min
Less than 5 mins
Less than 5km across
Macrobursts:
More than 5 mins
More than 5km across
As high as 11,800ft
Wet Microburst / Macrobursts:
Downdraft from a Micro/Macroburst is started by
precipitation and is often marked by a column of
+RA
Dry Microburst / Macrobursts:
If the air below the cloud base is dryer, the rain can
evaporate. Evaporation will cool the descending air,
making it denser and even more powerful
Lightning is a sudden _____ _____ on a large scale. Caused by _____ and _____ water droplets producing a build up of _____ _____.
Electrical discharge
Rising
Falling
Static electricity
Lighting discharges at a heat of _____ and travels up to _____ with a current around _____
5000K
140,000mph
30,000Amps
Lighting can cause:
Holes in the airframe
Temporary blindness
Noise Induced Hearing Loss
Errors with instruments
_____ _____ is another form of electrical discharge and it appears as a _____ glow around the windscreens and external parts of the aircraft. A high voltage differential of min _____ required
St Elmo’s fire
Blue/violet
100kv
St Elmo’s fire can cause:
Very occasionally cracked windscreens
Errors with navigational aids such as ADF
Noise on high and medium frequency radio bands
Dissipating is where:
Down draughts becoming stronger than the updrafts.
The cloud base rises due to adiabatic warming of sinking air, causing evaporation and the cloud can spread into Sc/St
Multi-cell thunderstorms are more_____ than single cell. New updrafts form along the _____ _____ of rain cooled air. Individual cells usually last ______ , while the whole system can last _____.
Common
Leading edge
30-60 mins
Hours
The weather Multi-cell’s produce is _____ _____ than a single-cell
More severe
Squall lines can be _____ _____ long but only _____ wide. The gust fronts can be felt _____ ahead.
Hundreds of miles
16-32km
50-60km
Mid-latitude squall lines:
Usually form in the warm air mass, ahead of & parallel to the cold front
Tend to move from west to east with the westerly situations
Tend to pass quickly with the cold front
Most common over large continental areas,
Tropical squall lines:
Structurally very similar to mid-latitude squall lines, but because the tropopause is higher in the tropics, they are generally taller
Tend to move from east to west with the Trade Winds
Most last 1-2 days
GR rarely occurs due to the warmer tropical air masses
Mesoscale Convective System (MCS):
Collection of thunderstorms that act as a system and they can last more than 12 hours (normally 1-2 days)
They can be round or linear in shape, and include systems such as:
Tropical storms
Squall lines
Polar lows
Mesoscale convective complexes
Supercells are the _____ common type of TS, but have the _____ severe weather. They can last for _____
Least
Most
Hours
Supercells have a contains a deep and persistent rotating updraft (approx. 8000-10,000fpm), called a _____
Mesocyclone
Single cells need:
Moderate to strong speed and directional wind shear between the surface up to about 20,000ft
‘A tornado is a _____, violently _____ column of air that extends from the base of a _____ to the ground’
Narrow
Rotating
Thunderstorm
They are the _____ _____ of all atmospheric storms
Most violent
Tornadoes are most likely in __________ and occur between the times _____
Late Spring/early Summer
16:00 - 21:00
Once a TS has formed, if the winds increase strongly with height, the TS updraught may begin to _____. Downdraughts within the supercell storm help to concentrate the rotation and to bring it down
to ______ ______.
Rotate
Lower levels
Speed of a tornado’s horizontal movement:
20-40kts
Wind speeds in funnel:
200kts
Life span:
up to 30mins
Average diameter:
100-150m
Water spouts are:
Tornadoes over water
Tornadoes are measured on the _____ scale which is based on the funnel wind speed and damage it incurs.
Fujita
A Funnel Cloud:
This is a rotating column of air, often a violent whirlwind, indicated by the presence of an inverted cone-shaped cloud, extending downwards from the base of a Cb, but not necessarily reaching the surface.
You can anticipate each type of thunderstorm through what 4 things:
Pre-flight weather briefs
Observation in flight
Meteorological information (charts, reports, etc.)
Information given by ground and airborne weather radar
If using weather radar avoid the thunderstorm by:
Below 20,000ft - 10NM
Above 20,000ft - 20NM
In VFR or no radar available, avoid TS by at least
10 miles
Dust devils:
Small, rotating columns of air that occur when one piece of ground heats up faster than the ground surrounding it on a hot, calm, dry day
Dust devils have an average height of _____ and width of about _____
650ft
10-100ft
Tropical revolving storms must have oceans with a temp. of ______ and are at least _____ deep.
26.5°C
50m
TRS cannot form within ___ of the equator and usually form between the latitudes of _____
5°
10 - 20°
The 4 stages of TRS development:
Tropical disturbance
Tropical depression
Tropical storm
Tropical Revolving storm
Tropical disturbance:
A discrete tropical weather system of apparently organized convection - generally 200-600km (100-300NM) in diameter
Tropical depression
The maximum sustained wind speed is up to 33kts
Depressions have a closed circulation.
Tropical storm
The maximum sustained surface wind
speed ranges from 34kts to 63kts
Convection is more concentrated near the center
Tropical Revolving storm:
Windspeeds >64kts eye is 20-50km in diameter Fastest winds are at the "eye wall" - up to 175kts Vertical winds up to 43kts averiging 500km in diameter
The wind speeds are the top speeds sustained for at least _____ at _____ above the surface and are compares to the _____ Scale
1min
10m
Beaufort
TRS travel:
<15kts
East to West and then curve Northwards, away from the Equator, before turning East again
Hurricanes:
North America
May - Nov
Cyclones:
Central Asia + Oceania
N. Hemisphere: Apr - Dec
S. Hemisphere: Oct - May
Typhoons:
East Asia
April - Jan
Easterly Waves
Generated by an instability in the African Easterly Jetstream, causing troughs to extend out and away from the ITCZ, towards the sub-tropical high pressure belt to the North Move east to west April - October between 5-15° Wavelength 2000 - 25000km last 3-4 days travel at 18-36km/h
Approximately __ easterly waves per week travel from Africa to _____ _____ during hurricane season
2
North America
Only __ out of ___ easterly waves survive to develop into gale-force tropical storms, or full-fledged hurricanes.
9
100
___ of the Atlantic tropical storms and minor hurricanes originate from easterly waves.
60%
Nearly ___ of the intense (or major) hurricanes have their origins as easterly waves. _____ easterly waves become a TRS
85%
1 in 5
Ice can:
Add drag Reduce thrust Increase stall speed Reduce lift Add weight to the aircraft Block pitot tubes and static vents
Airframe icing is caused by an aircraft with airframe temperatures ___, striking a _____ _____ _____
<0°C
Supercooled water droplet (SCWD)
SCWDs can exist in clouds from __ to __. For every __ below 0°C, only ___ of a droplet will freeze
instantly on impact
0° to -40°C
1°C
1/80
Large SCWD’s need:
Great vertical depth of cloud
Small SCWD’s need:
Shallow vertical depth of cloud
Rime Ice
Formed when small SCWDs freeze on contact with a surface which is <0°C
Freeze almost instantly creating a mixture of tiny ice particles and trapped air.
Rough, crystalline and opaque / milky in colour
Brittle
Accumulates slowly (>20mins)
Clear Ice
Formed when large SCWDs start to freeze on contact with a surface which
is <0°C
Do not freeze instantly on contact with the aircraft surface but freeze gradually as they flow back across the surface, leaving a smooth, hard, glossy, and transparent covering of ice
Heavy and difficult to see and to remove with de-icing methods,
Accumulates quickly (<20mins)
How to avoid freezing precipitation:
TOGA and climb
Descend
Turn back
Mixed ice is the blending of _____ _____ and _____ _____
Rime ice
Clear ice
_____ _____ is the most common form of icing
Rime Ice
Hoar frost
When a surface <0°C comes into contact with moist air, the water vapour turns directly into ice by sublimation
Hoar frost occurs when:
When an aircraft has been parked overnight in temperatures <0°C.
When an aircraft flies from temperatures <0°C, into warm moist air, such as in descent, or climbing through a temperature inversion layer, or flying through a front
Hoar frost can reduce lift by _____
10-15%
Packed snow can be mixed with _____ _____ and can contribute to the accumulation of
_____ _____ _____.
Liquid water
Hazardous frozen deposits
At faster speeds _____ SCWDs collide with the airframe,
More
Kinetic heating
Airflow causes a rise in the temperature of the airframe due to compression and friction (Rise = (TAS / 100)2)
Total Air Temperature (TAT) indication includes the temperature rise due to _____ _____ and is therefore used to indicate the possibility of _____.
Kinetic heating
Icing
The bigger the stagnation point -
The less moisture hits the wing, less ice.
Carburettor icing is caused by
sudden temperature drop due to fuel
vaporisation and the reduction in pressure at the carburettor Venturi
Carburettor icing can occur in _____ _____ and at tempratures up to ___.
Clear air
25°C
When information on the dew point is not available…
You should always assume a high relative humidity.
Visibility definitions:
“The greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background”
or
“The greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against an unlit background.”
Ground visibility
‘The greatest known distance at which objects can be seen by an observer under conditions of normal daylight observation’
Prevailing visibility
‘The greatest visibility value, observed in accordance with the definition of “visibility”, which is reached within at least 1⁄2 the horizon circle or within at least 1⁄2 of the surface of the aerodrome. These areas could comprise contiguous or non-contiguous sectors.’
Prevailing visibility should be measured ___ above the runway and updated every __ seconds.
2.5m
60
The averaging periods should be:
1 min for local routine reports
10 mins for METAR and SPECI
Visibility should be reported in steps of:
50m when <800m
100m when 800m - 5km
1km when 5 - 10km
given as 10km or 9999 when >10km
If visibility is observed from more than 1 location, the _____ _____ is reported first
Touchdown zone
In METAR + SPECI, visibility should be reported as prevailing visibility when …..
Vis is not the same in different directions
lowest vis is diffrent from prevailing vis and
<1500m or
<50% of the prevailing vis and <5000m
Runway visual range (RVR)
“The range over which the pilot of an aircraft on the centre line of a
runway can see the runway surface markings or the lights
delineating the runway or identifying its centre line”
RVR is determined by…
Transmissiometer
Forward-scatter meter
Human observer, by counting no. of visible lights
RVR is reported in reported in m when vis or RVR is _____
<1500m
Assessed at a height of…
2.5m
5m if human observer
Assessed _____ from runway center line
<120m
Observations of touchdown zone should be…
300m along runway threshold
Midpoint -
1000 - 1500m along runway threshold
Visual range shall be reported in steps of:
25m when <400m
50m when 400 - 800m
100m when >800m
R23/p1500 means
RWY 23
Greater than max. valus (1500m)
R23/0400N means
RWY 23
Fluctuating over last 10 mins, avg 400m
R23/1200U means
RWY 23
1200m with an upwards tendency
R23/0750D means
RWY23
750m with a downwards tendency
ILS
Instrument landing system
MLS
Microwave landing system
PAR
Precision approach radar
GLS
Global Navigation landing system
Aerodrome operating minima are expressed in
Terms of visibility and/or RVR and Decision Altitude/height (DA/DH).
Slant visual Range (SVR)
‘The visual range of a specified object or light along a line of sight which differs significantly from the horizontal; for example, the visual range of ground objects or lights as seen from an aircraft on the approach (metre, m).’
Flight visibility
The average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be
seen and identified by night.
Mist (BR) and Fog (FG) are known as
Hydrometeors
Mist limits of visibility and relative humidity
lower limit: 1000m
upper limit: 5000m
RH: >90%
Fog limits of visibility and relative humidity
Lower limit: 0m
upper limit: 1000m
RH: 100%
Radiation fog:
When ground surface cools through radiation, usually at night, cooling air above ground to the saturation temperature.
More common in Autumn/winter
Requites: clear skies, long nights, light winds
Radiation fog is densest __________ due to __________ and goes up to heights of _____
1 hour after sunrise
increase in thermal turbulence
1500ft
Radiation fog is dispersed by
drier air
Increase in wind speeds (>8kts)
Surface heating
Valley fog is caused by
Cool air flowing down the hill (katabatic effect)
Upslope fog is caused by
Air flowing upwards over rising terrain and
adiabatically cooled to its saturation temperature.
Hill fog is
Low cloud covering high terrain
Advection fog is caused by
Relatively warm, moist air moves (advects)
over a cooler surface, and the temperature of the air is cooled to saturation by contact with the cold surface. Requires wind of at least 15kts
can be up to 1000ft thick
Evaporation fog is caused by
cold, stable air moving over a much warmer body of water.
Can be upto 500ft
Frontal fog forms:
In frontal zones when rain falls from warm air into cold, stable air
Up to 200NM and be increase by orographic lifting
Freezing fog FZFG
Occurs at temp <0ºC
Supercoold fog droplets freeze on impact with ground or other objects
All fog below 0ºC is reported as
Freezing fog
Ice fog forms when:
Water vapour, is introduced into the atmosphere and condenses, forming droplets that freeze rapidly into ice
particles.
Ice fog is
Suspension of numerous minute ice particles in the air, reducing the visibility at the Earth’s surface
Observed at high latitudes, usually in clear, calm weather when the temperature is
Shallow fog/mist is
MIFG/MIBR
2m high on land
10m high at sea
Patches is:
BCFG
only with fog
Randomly covering aerodrome where horizontal vis is >1000m, but observer can see parts where there is less.
Partial is:
PRFG
only part of aerodrome is covered by fog
Precipitation can be considered a
Hydrometeor
Low Drifing snow (DRSN)
Snow picked up by wind, <2m
Blowing snow BLSN
Snow picked up by wind, >2m
Lithometeors
A suspension in the air of extremely small (microscopic), dry particles invisible to the naked eye and sufficiently numerous to give the air an opalescent appearance
Haze (HZ)
Blue light is scattered more than red light such that dark objects are seen as if viewed through a veil of pale blue.
HZ and other lithometeors (VA, FU, SA, DU), are reported only when the visibility is _____ (except for low drifting _____ and ______ _____ which are
always reported for operational reasons)
<5000m
Sand
Volcanic ash
Dust/Sand haze (DU/SA)
A suspension in the air of dust or small sand particles, raised from the ground prior to the time of observation by a dust storm or sandstorm.
Low drifting dust/Sand (DRDU/DRSA)
Dust or sand raised by the wind to small heights (<2m), above the ground. The visibility is not sensibly diminished at eye level (eye level is defined as 1.80m above the ground).
Blowing dust/Sand (BLDU/BLSA)
Dust or sand raised by the wind to moderate heights (>2m), above the ground. The horizontal visibility at eye level is sensibly reduced (eye level is defined as 1.80 m above the ground).
Sandstorm (SS)
Need a minimum of 15-20kts to form
sand particles are mostly confined to the
lowest 2m, and rarely rise more than 15m above the ground.
Due to strong winds caused or enhanced by surface heating and tend to form during the day and die out at night.
Dust storm (DS)
Need a minimum of 15-20kts to form
Particles of dust are energetically lifted by a strong and turbulent wind over an extensive area.
A duststorm usually arrives suddenly in the form of an advancing wall of dust which may be kilometres long and is commonly well over 3000m in height.
Smoke (FU)
The suspension in the air of small particles produced by combustion
Reduces horizontal visibility to <5000m
Volcanic Ash (VA)
Atmospheric dust or particles varying considerably in size, originating from active volcanoes.
Smog
A mixture of smoke and fog.
Where significant industrial pollution is present
Horizontal pressure gradient - the steeper the gradient….
The faster the wind is going to be
_____ _____ _____ is what moves air from high to low pressure
pressure gradient force
In the Northern hemisphere, the Coriolis deflects to the _____, and in the Southern hemisphere it deflects to the _____
Right
Left
Coriolis equation:
CE = 2ΩρVsinθ
Ω = speed of earth ρ = air density V = wind speed θ = latitude
Buys ballot law
If an observer stands with his back to the wind, the low pressure system will be on his:
Left in the northern hemisphere
Right in the southern hemisphere.
Gradient wind is the result of what 3 forces
PGF
Coriolis
Centrifugal
Around a high pressure system centrifugal force acts in the _____ direction as the pressure gradient force
Same
Around a low pressure system centrifugal force acts in the _____ direction as the pressure gradient force
Opposite
Global winds from 90º to 0º
Polar Easterlies
Upper Westerlies / Prevailing Westerlies / Variable Westerlies
Tropical Easterlies / NE(or SE) Trades
Surface winds occur below the _____ _____
Friction layer
The friction between moving air and the Earth’s surface will reduce the _____ _____and _____ near the ground and therefore, the wind direction
Wind speed
Coriolis
In the day, the friction lay can reach heights of _____ due to __________
3,000ft
Rising thermal currents
At night, the friction layer drops to __________
1000 - 1500ft
Factors affecting the vertical extent of the friction layer:
Terrain – the rougher the terrain, the deeper the layer
–Wind speed – the stronger the wind, the deeper the layer
Stability – the more unstable the atmosphere, the deeper the layer
In low pressure systems, isobars are _____ _____
Closer together
Over water, the wind speed in the friction layer is ___ that of 2,000ft, at ___
70%
10°
Over land (day), the wind speed in the friction layer is ___ that of 2,000ft, at ___
50%
30°
Over land (night), the wind speed in the friction layer is ___ that of 2,000ft, at ___
25%
45°
Most reports report the wind direction in °, except HTIS or ATC which report it in °
°T
°M
Wind speeds are measued at __ - __ above the ground by a
8 - 10m
anemometer
The avg. observation period is ___ for local routine + ATC, and ___ for METAR + SPECI, which are reported in steps of __°
2 mins
10 mins
10°
When wind speeds are
<0.5m/s (1kt)
Gale force winds:
34-47kts
Storm force winds:
48 - 63kts
Squall
A sudden increase in wind speed often with a change in direction. Lasts for some minutes and can cover a much wider area.
Lull
A sudden decrease in wind speed
Sea/Land breezes only occur where…
there is little or no pressure gradient
Sea breezes are caused by
A temperature difference between warm land and a cooler adjacent sea
As the day goes on, sea breezes:
Increase in speed
Veer in NH, back in SH by approx 20- 30°
Goes further inland/out to see
At mid latitudes, sea breezes are
around 20 -30 kph
10 - 15 miles either side of coastline
Land breezes are caused by:
temperature difference between cooler land and a warmer adjacent sea
Anabatic winds:
Light winds that blow up a mountain side due to insolation, during the day in calm weather
Valley winds
Air flowing into and through a valley due to low pressure
Katabatic winds
wind that carries high density air from a higher elevation down a slope under the force of gravity, occurring at night
Mountain winds
Air flowing through/leaving the valley due to high pressure
Valleys and mountain winds are prone to the _____ effect
Venturi
Mistral
South France cold, often violent + dry \+50kts Blows through the valley of the Rhône River to the Mediterranean. effecting Sardinia, Italy Accompanied by clear, sunny weather
Bora
The Balkans + Italy
In winter/Spring
70-100kts
Blowing on the north Adriatic coast and north Italian
plains
It forms when a high pressure lies over Central Europe and a low pressure area over the Mediterranean
Lasts many days, clouds + heavy rain
Mountain Waves formation:
Occur when an air mass blows over a mountain range,
Must have:
Stable air at ridge, slightly less stable air above and below
An increasing wind velocity with altitude and wind velocity >15kts near mountaintop level
Wind direction staying roughly the same with height and within 30° of the perpendicular to the ridge line
Mountain waves may extend _____ _____ with an average wave length of approx. _____
50 - 100NM downwind
5NM
Mountain waves can extend
_____ in the Rockies
_____ in the Andes
300NM
500NM
Detection of mountain waves:
Lenticular clouds
Rotor/roll clouds
Cap clouds
To avoid mountain waves:
Cross at an angle of 30 - 45°
Jet Steam
a strong narrow current, concentrated along a quasi-
horizontal axis in the upper troposphere or in the stratosphere, characterised by strong vertical and lateral wind shears and featuring one or more velocity maxima
Speed of jet stream must be
> 60kts
Jet steam ratios
Depth:width:length
1:100:1000
All year jet streams:
Polar Front jet steam (polar - tropical air masses)
Sub-tropical jet stream (tropical - equatorial air masses)
The arctic jet stream is
winter only
Equatorial jet stream is caused by
Summer heating of India and coastal regions of Africa, flows from east to west
The Polar and Sub-tropical jets are strongest in the _____ due to….
Winter
greater temperature differences between the respective air masses
The ‘Jet Core’ always occurs at the point of _____ _____ _____, and it is always in the _____ air mass, just below tropopause
maximum pressure gradient
Warm
Maximum windshear and CAT is also always in…
warm air, on cold air side of core, level with and slightly below the core
Jet stream are _____ away from the cold front and _____ away from the warm front
50 - 200NM
300 - 500NM
Climbing up through a warm front to jet stream – wind _____
Climbing up through a cold front to jet stream – wind _____
Veers
Backs
Flying above the Jet Core:
You are in the Stratosphere
The air above the cold sector is slightly warmer than the air above the warm sector
On this track the OAT would steadily decrease
Max. CAT will be where the isotachs are closest
Flying at the level of the Jet Core:
The temperature would only change slightly
Wind speed would increase as you flew into the jet stream and you would reach max. CAT
No turbulence in the jet core
The wind would decrease on the way out as you fly into the warm air
Flying below the Jet Core:
The temperature would increase slightly in the cold air and would increase quickly as you cross into the warm air
The temperature would continue to increase through the warm air
Highest wind speeds would be just after crossing the frontal layer
Isotach
Line connecting points of equal wind speed
Isotherm
Line connecting points of equal temperature
Jet stream clouds -
Cirrus
Isohypes
Line of equal windshere
Low level jet streams:
Due to great temp. difference between air masses or low level inversions
500 - 5000ft
70kts
Windshear
change in headwind or tailwind sustained for more than a few seconds, that results in changes to the lift of the aircraft
Gust
The extreme values of wind direction and speed between which the wind has varied during the last 10mins
Turbulence is caused by
a rapid irregular motion of air
Wind shear and turbulence can be found in areas of:
Rough surfaces Relief Inversions Cb and TS Unstable atmospheric layers
Wind shear and turbulence can cause
Airspeed + AoA fluctuations
Structural fatigue and possible damage
The response of aircraft to wind shear depends on:
Type of aircraft
Phase of flight
Scale of the wind shear relative to aircraft size
Intensity and duration of the wind shear encountered.
Information used to avoid turbulence/windshear:
Weather reports and forecast
Routine or Special Pilot’s reports
Visual observation
On-board predictive wind shear system
Buildings near the runway can…
cause the wind flow to divert around them, resulting in the surface wind varying along the runway.
If hills near a runway are low…
Range unable to divert the low-level wind flow and so the wind blows vertically downward towards the runway
If hills near a runway are high…
Range able to divert the low-level wind flow and the surface wind may be funnelled along the range
Windshear/turbulance can be caused by:
katabatic flow fohn wind rotors (mountain winds) fronts land/sea breeze friction layer inversions thunderstorms - downdrafts, gust fronts, micro/macrobusts wingtip vortices
Types of turbulence:
Convective Orographic Mechanical Frontal Clear air (CAT)
MOD TURB:
mod changes in aircraft attitude/altitude small variations of airspeed accelerometer readings of 0.5 - 1g difficulty in walking in cabin loose objects move about
SEV TURB:
Abrupt changes in attiude/altitude
large variations of airspeed
accelerometer readings of >1g
Violent in cabin
the 4 temperature groups
Arctic (A)
Polar (P)
Tropical (T)
Equatorial (E)
the 2 humidity groups
Maritime (m)
Continental (c)
Maritime journey:
A track predominantly over the sea, will increase the
moisture of the air mass, particularly in its lower layers
Land journey:
A track predominantly over the land keeps the air mass dry
Cool journey:
A warm air mass moving over a cooler surface is cooled from below and becomes stable in low layers
Warm journey:
A cold air mass moving over a warmer surface is warmed from below and becomes unstable in low layers
Weather fronts
When a warm air mass meets a cold air mass, they will mix with each other, but only in a relatively thin layer, due to temperature and density differences
The thin mixing layer is known as the _____ _____ and is __ - __ wide at the surface
Transition zone
3 - 5km
creation of fronts
Frontgenesis
destruction of fronts
Frontolysis
Arctic front:
Only tends to occur in winter
The arctic front separates the colder arctic air to the north, from the warmer polar air to the south
Greenland to Northern Norway (70N), but drops down over Iceland
Polar front:
Effects the UK all year
In the UK, the polar front usually separates warm moist air from
the tropics and cold, relatively dryer air from polar regions
Winter: Between Florida and SW UK (30-50N)
Summer: Between Newfoundland / Nova Scotia and Scotland (60N)
Mediterranean Front:
Forms in winter
The low-pressure systems along the Mediterranean front can develop storms, even small Hurricanes known as ‘Medicanes’
With the sand from North Africa, the RA can fall in a red colour
The local Mediterranean winds converge towards these low-pressure systems
Stationary Front (Quasi)
when a cold air mass and a warmer air mass first meet, or when a front stops moving (stalls), or moves very slowly over the surface (<4kts)
Neither air mass has enough force to move or replace the other, but the air
in each airmass can still move along the front
Stationary Front cause (if air is dry)
Clear to partly cloudy, with no precipitation
Stationary Front cause (if air is humid)
Clouds can form and precipitation can fall
Can cause flooding if the precipitation falls continuously over an
area for several days
Formation stage 1 - Origin + Infancy:
The depression starts as a small wave or ‘buckling’ along the front.
The air to the south of the front is warm tropical air
The air to the north of the front is cold polar air
Formation Stage 2 – Maturity
The pressure around it falls, leading to closer isobars
This causes stronger winds and, the wave / ‘buckle’ in the front to be much more pronounced
There will be distinct warm and cold fronts being formed as the warm air is pushed towards the north and the colder pushed towards the south
Warm front:
Warm air is advancing and rising up over cold air. moves at 2/3 of the wind at 2,000ft (avg. 10 -20kts)
Warm-frontal surface:
Shallow - 1:100 - 1:300
Cold front:
Cold air is advancing and pushing underneath warmer air. Moves at speed of wind at 2,000ft
Cold-frontal surface:
Steep - 1:50 - 1:100
An occluded front (occlusion - stage 3), is formed when
a cold front catches up with a warm front because the cold front is moving faster than a warm front and convergence takes place at the fronts and the warm sector of a PFD
In a occlusion:
The warm sector is lifted from the surface of the earth, becomes smaller and is reduced to a trough line known as the line of occlusion
Warm occlusion
The air ahead of the occluded front is colder than the air behind
More common in winter
The cloud and precipitation will be ahead of the surface occlusion
Cold occlusion
The air behind the occluded front, is colder than the air ahead
More common in summer
The cloud and precipitation will be a narrow band over the whole surface occlusion
Stage 4 – Death
The frontal system dies as all the warm air has been pushed up from the surface and all that remains on the surface is cold air
The occlusion dies out as temperatures are similar on both sides of the
front known as Cyclolysis
Each section of a front moves at _____ to itself
90 ̊
A frontal system moves in the direction of the _____ _____ blowing _____ to the isobars inside the warm sector, at approx. _____ of the geostrophic wind speed (_____kts)
Geostrophic wind
parallel
80%
15-25kts
The time between Polar waves is approx. _____ in Europe
1 - 2 days
Each PFD generally takes _____ to pass over the UK
9 - 12 hours
There is a sharp change in the direction of the isobars at the front approx. ____. The isobars always turn to orient themselves towards the area of _____
pressure
20°
Low
Windshear characteristics on a cold front:
A vigorous cold front poses the greater risk but through a shorter period
The cold front surface can stop briefly and then jump several miles, bringing very sudden gusts and wind shear
Windshear characteristics on a warm front:
The effect will be ahead of it and will be more
prolonged.
Temporary Cold Anticyclones
Occur between polar front depressions and provide a respite from polar front weather.
They are of significantly higher pressure than lows either side of it.
Secondary Lows
Can be found behind the cold front of the primary depression.
Can be more intense than the main depression as the flow to the west of the low center is from the pole towards the equator = highly unstable
Secondary lows move around the main depression _____ in the northern hemisphere
Anticlockwise
Freezing levels in January
Equator - 16,000ft
40°N/S - 10,000ft
60°N/S - 0ft
Freezing levels in July
Equator - 18,000ft 40°N - 16,000ft 40°S - 8,000ft 60°N - 8,000ft 60°S - 0ft
Temperature difference is greater in the _____ hemisphere due to __________
Northern
Greater land mass
Doldrums
Around the equator (5°N-5°S)
Intense surface heating causes the air to warm and rise
straight up rather than blow horizontally, resulting in little or no wind
Horse latitudes
At the subtropical high pressure belts (30°N/S)
Near vertical downwards motion causes little or no wind at the surface
Clear skies but with possible poor visibility due to haze and inversions
Roaring, Furious & Screaming
Due to temperature variations and a greatly reduced amount of friction over the southern oceans near Antarctica, wind speeds can reach very fast speeds
Roaring 40’s
Furious 50’s
Screaming 60’s
Monsoons
Characterised by a dramatic seasonal change in the
direction of trade winds
Cause dry/wet seasons
When crossing the ITCZ:
NE trade winds become ___ trades winds
SE trade winds become ___ trade winds
NW
SW
January monsoons:
Oct - Apr NW. Africa, India & Eastern Asia: - large areas of high pressure - dry air to south of tropics - cool dry season - NE monsoon
N. Australia:
- large areas of low pressure
- warm rainy season
- NW monsoon
July monsoons:
Apr - Oct NW. Africa, India & Eastern Asia: - Large areas of low pressure - warm rainy season - SW monsoon
N. Australia:
No monsoon in winter
Polar outbreak
The movement of a cold air mass from its source region towards the equator bringing cold weather and strong winds.
Pampero
Outbreak of cold, dry polar air blowing towards the N/NE across the pampa of Argentina and Uruguay
Sometimes RA/TS
Most common Oct - Jan
Southerly Buster
Outbreak of cold, polar air behind a trough of low pressure crossing SE Australia, manifesting itself as a strong, dry southerly wind which causes rapid falls of temperatures (10°C)
Most common Oct- Feb
Cut-off low
Closed upper-level cold low, which has become
completely displaced (cut-off) from the westerly situation
Can remain stationary for days
Occasionally moves westward, opposite to the prevailing flow
Unsettled weather (in summer TS)
Cold-Air drop
Slow moving cold low pressure in the central
troposphere between 10,000ft and 30,000ft
Normally occur in august/winter, and their diameters are approx. 2000km
Their direction and speed of movement is difficult to forecast
Lifespan of several days
El Nino (ENSO) - Neutral
Trade winds blow from east to west across the surface of the tropical Pacific Ocean
Brings warm moist air and warmer surface waters to the western Pacific and keeps the central Pacific cool
Warm sea temp. in W. Pacific cause CB, RA
Dry air then travels east before descending over the cooler eastern tropical Pacific
El Nino
Every 3-4 years
Easterly trade winds weaken/reverse
Allows the Pacific to warm in central + eastern areas
N + S America suffers HVY RA, floods and extream temps.
Australia, NZ, Philippines + Indonesia have droughts
La Nina
every 2 - 7yrs Easterly trade winds strengthen Warm water pushes to far west tropical pacific Australia, HVY RA, floods S america experiences droughts.
Koeppen 5 zones
A. Equatorial Zone / Tropical Rain Climate
B. Arid Sub-tropical Zone / Dry Climate
C. Temperate Zone / Mid-Latitude Climate
D. Snow Zone / Sub-arctic Climate / Disturbed
Temperate Climate / Boreal
E. Polar Zone / Snow Climate / Tundra Climate / Cold Desert
A. Equatorial Zone - Tropical rain forest:
0° - 10° Lowest diurnal/annual temp. variation Max. 30 - 35°C, Min 20 - 25°C Highest annual rainfall on earth No dry season Always under influence of ITCZ
A. Equatorial zone - Savannah:
10° - 20°
lowest diurnal/annual temp. variation
20° - 30°C
1 rainy season in summer
B. Arid zone - Desert:
20° - 35°
Hot in summer, large daily/seasonal variation
Dry, no wind or cloud
High evaporation
B Arid zone - Steppe:
30° - 35°
Hot in summer, large variation in temp.
Dry, no wind or cloud
Slightly higher rainfall (still very little)
C. Temperate zone - Warm:
35° - 40°
18 - -3°C
Summer - Hot + Dry
Winter - Cool + Wet (Rain <700mm)
C. Temperate zone - Cool:
40° - 65° 18 - -3°C Little season variation Generally wet + windy Predominantly westerly winds
D. Snow zone:
40° - 65°
avg. temp <0°C (can be up to 60°C in peak summer)
Cool + Dry
Mostly high pressure
E. Polar Zone:
65° - 90°
<10°C
Cool + Dry
Mostly high pressure
