Meteorology

Question 1

Constituents of gas in atmosphere

Answer 1

Nitrogen: 78%
Oxygen: 21%
Argon: <1%
CO2, ozone (O3) etc.

Question 2

Percentage of water vapour in atmosphere

Answer 2

0.001% to 4%
Averages less than 1%
NOTE: This isn’t included in the usual breakdown of atmosphere which is based on DRY air

Question 3

Temperature changes in stratosphere

Answer 3

Constant up to 20km
Increases up to -15C at 50km
Decreases from 51km again (stratopause)

Question 4

Reason for increase in temperature with altitude in stratosphere

Answer 4

O2 breaks down into 2 O molecules by absorbing UV light (<240nm wavelength), which is exothermic.
Single O’s join with other O2 to form ozone (O3).
O3 absorbs UV light (<290nm wavelength) to breakdown into O2 and O, again exothermic.

Question 5

Tropopause definition

Answer 5

Point where temperature stops falling with altitude increase (taken as rate of fall going below 0.61C per 1000ft - 2C per 1km)

Question 6

What factor impacts tropopause height and temperature?

Answer 6

Temperature depends on height, the higher it is the more temperature is lost before reaching it.
Height is determined by surface temperature, high surface temp (equator) leads to higher altitude (thus high surface temp leads to low tropopause temp).

Question 7

Typical tropopause heights and temperatures

Answer 7

53,000ft (16km) at equator, -75C.
36,000ft (11km) at mid-lat, -56C.
26,000ft (8km) at poles, -45C.

Question 8

Tropopause heights summer & winter
- Latitudes 30, 50, 70

Answer 8

Summer Winter
30deg: 16km 16km
50deg: 12km 9km
70deg: 9km 8km

Question 9

Mesosphere, thermosphere and exosphere altitudes

Answer 9

Mesosphere: 50km to 85km
Thermosphere: 85km to 600km
Exosphere: 600km to 10,000km

Question 10

Mesosphere and Thermosphere features

Answer 10

Mesosphere: Meteors are burned up by the thickness of atmosphere here
Thermosphere: Absorption of high energy UV and X-rays leads to increasing temperature with altitude around -120C at base to 2000C at top.

Question 11

ISA
- MSL temp, pressure, density
- lapse rates

Answer 11

• MSL temp 15C
• MSL pressure 1013.25 hPa
• MSL density 1.225kg / m3
• Lapse rate 1.98C / 1000ft to 36k
• Constant temp up to 20km
• Temp increase 1C / 1km to 32km

Question 12

Pressure levels by altitude

Answer 12

30000’ 300
18000’ 500
10000’ 700

Question 13

Altitude of:
- 50% of MSL pressure
- 50% of MSL density
- 50% of weight of atmosphere below

Answer 13

18,000ft: 50% pressure
20,000ft: Half weight of atmosphere
22,000ft: 50% density

Question 14

Altitude of 25% MSL density

Answer 14

40,000ft

Question 15

Barograph

Answer 15

Aneroid type pressure capsule connected to rotating drum which draws a line over time as pressure increases and reduces

Question 16

Equation for (H), height change in feet per hPa

Answer 16

H = (96 x T) / P

T = Temperature in Kelvin
P = Pressure in hPa

Question 17

Height change per hPa under ISA at:
MSL, 20000’, 40000’

Answer 17

MSL = 30 feet per hPa
20000’ = 50 feet per hPa
40000’ = 100 feet per hPa

Question 18

Diurnal pressure variation

Answer 18

1hPa typically but up to 3hPa in tropics.
Needs to be considered as part of assessment of pressure changes over time.

Question 19

QFE (Field Elevation)

Answer 19

Pressure setting to give zero elevation at HIGHEST point on airfield.
If touchdown point is significantly lower you may be given a touchdown QFE.

Question 20

QFF

Answer 20

Similar to QNH (nautical height) but converts QFE to MSL using actual temperatures rather than ISA temperatures to establish true MSL pressure at a location which is relevant to meteorological charts.
Note - QNH gives correct airfield elevation when at the airfield.

Question 21

QFF vs QNH when temp is higher than ISA and airfield above sea level

Answer 21

If warm and > sea level:
QNH > QFF
Flips if cold, both flip if below sea level.

Question 22

QNE

Answer 22

NOT a pressure setting. This is the height on altimeter at touchdown point if standard pressure setting (1013) is set.
Used for high elevation airfields where QFE is too low to set in altimeter.

Question 23

Risk of ground collision when heading to high or low pressure

Answer 23

Altimeter will over-read if heading into low pressure risking ground collision.
Think about what would happen if you adjusted to the correct pressure setting (turn down to the lower pressure setting, indicated altitude would fall).

Question 24

Density altitude
- description
- calc

Answer 24

The altitude at which observed air density would be found in an ISA standard atmosphere.
Or, pressure altitude adjusted for ISA temperature difference (@120ft per C)

Question 25

Effect of temperature of air column on pressure readings

Answer 25

In cold air pressure changes more quickly with altitude, i.e. the column of air between two pressure points is compressed. Thus higher risk of ground collision if heading into very low temperatures as altitude will over-read. [Not an issue for traffic avoidance as all aircraft the same, but separation will reduce]

Question 26

Impact of latitude on density at low and high altitude

Answer 26

At surface density is higher near the poles as surface temp is colder. At high alt (50000') however, the opposite is true, as higher equator temp leads to lower fall in pressure with height.

Question 27

Specific Heat

Answer 27

The number of calories required to raise temperature of 1g of a material by 1C. This is 1 for water (1 calorie raises 1g by 1C), but less for most materials (ice 0.5, rock 0.25).

Question 28

Latent heat of water (ice to water, water to steam)

Answer 28

80 calories for fusion (melting) 540 calories for evaporation

Question 29

Depression weather - Cloud, prec, vis, temp, wind

Answer 29

Cloud - extensive (including vertically) Prec. - Intermittent or continuous, light to heavy Visibility - Good unless in rain Temp. - Brings colder air in summer, warmer in winter Winds - Strong

Question 30

Anticyclone weather (summer) - Cloud, prec, vis, temp, wind

Answer 30

Cloud - None Prec. - None Visibility - Moderate (haze) Temp - Variable Wind - Light

Question 31

Anticyclone weather (winter) - Cloud, prec, vis, temp, wind

Answer 31

Cloud - Low stratus Prec. - Drizzle Visibility - Poor (mist/fog likely) Temp - Warm Wind - Light

Question 32

Cold anticyclones

Answer 32

Permanent overs the poles Temporary in other places (e.g. Siberia) due to surface cooling (aka Cold Pool). Cold land cools air which becomes dense, high pressured and creates an inversion. Above 500mb level get low pressure.

Question 33

Cold pool/drop - Cause - Conditions - Identification

Answer 33

Cold air BREAKING AWAY FROM A COLD FRONT or the polar region. Convective weather due to instability, lots of rain and TS in afternoon due to insolation in the day. Can be identified using isohypse charts at 500hPa level, surface charts will NOT show.

Question 34

Polar air outbreaks - description - season - locations

Answer 34

Outbreaks of cold polar air into tropical air. Typical in WINTER, in both USA and China (very cold continental air to the north).

Question 35

Warm anticyclones

Answer 35

In subtropical regions (e.g. Azores) where Hadley cell air from equator descends along with air from Ferrel cell from temperate regions. Creates a high pressure area on the surface AND above 500mb level. Recall warm air column has pressure levels further spaced out, so warm column over a high pressure area has to give high pressure at high altitude too.

Question 36

Blocking anticyclones

Answer 36

Quasi-stationary Typically warm anticyclone 50-70N Persist in an area, blocking Eastwards flow of fonts.

Question 37

Anticyclone vs cyclone (depression) size and speed

Answer 37

Anticyclones around 1500NM - slow, depressions around 300NM - quick (fast moving and lifecycle)

Question 38

Col

Answer 38

Level pressure area between 2 highs and 2 lows Look out for "flat pressure area"

Question 39

Col weather

Answer 39

Generally settled, calm winds Summer - Thunderstorms common due to calm winds allowing heating to start convection Winter - Poor visibility, fog due to calm winds

Question 40

Trough - Description - Weather

Answer 40

Trough is an extension of a low pressure area with sharp V shaped isobars causing windshear. Get unsettled weather, clouds and precipitation.

Question 41

Subsidence

Answer 41

Vertical down draught of air

Question 42

Celcius to farenheit

Answer 42

32 - 212 C = (5/9) * F - 32

Question 43

Radiosonde - description - RoC

Answer 43

Radar reflector (GPS lately) attached to balloon which can be tracked to detect wind speed @ altitude. 1,200ft RoC up to 65,000 to 115,000ft height

Question 44

Insolation

Answer 44

Heating of surface by solar radiation

Question 45

Nature of solar radiation

Answer 45

Short wave radiation, passes through atmosphere and warms up surface

Question 46

Nature of radiation from earth

Answer 46

Longer wave radiation than solar, can be reflected back by cloud

Question 47

Clouds absorbing or reflecting radiation from sun and earth

Answer 47

Clouds REFLECT solar radiation into space. Clouds ABSORB infra-red radiation from Earth, although they re-radiate some back again.

Question 48

Conditions for maximal diurnal variation of surface temp

Answer 48

Calm winds (reduces mixing of lower and upper layers of air) and clear skies.

Question 49

Times of minimum and maximum temperature with clear sky over continent

Answer 49

Min temp 30 mins after sunrise Max temp about 2 to 3pm

Question 50

Saturation Vapour Pressure (SVP)

Answer 50

This is the water vapour pressure at which air is saturated with water pressure and water will no longer evaporate. It changes with temperature, the higher the temperature, the higher the energy level in water molecules and more water vapour pressure required to prevent them evaporating.

Question 51

Warm or cold air holds more water vapour?

Answer 51

Warm air holds more. Thus reach saturation as air rises, cools, and can support less water vapour

Question 52

Absolute humidity

Answer 52

Grams of water vapour per metre 3 of air

Question 53

Specific Humidity

Answer 53

Grams of water vapour per kg of air

Question 54

Humidity mixing ratio (HMR)

Answer 54

Grams of water vapour per kg of DRY air. This remains constant as the air rises up until saturation point.

Question 55

Saturation mixing ratio (SMR)

Answer 55

Max amount of water vapour a unit mass of dry air can support at a given temperature

Question 56

Relative Humidity (RH)

Answer 56

HMR / SMR

Question 57

Humidity ratios as temperature changes

Answer 57

Measures of water vapour content (mixing ratio, absolute humidity, specific humidity) don't change, but saturation levels (saturation mixing ratio) increase with temperature, so relative ratios (relative humidity) will decrease.

Question 58

Saturation at below zero temperatures (in terms of partial pressure and temperature)

Answer 58

Partial pressure of water for saturation for ice is less than partial pressure for saturation for water, therefore when saturation is reached below zero, water vapour sublimes to ice (hoar frost). [To remember, increasing water vapour pressure reaches lower ice limit first and gets pushed into ice] In terms of dew point/frost point, frost point > dew point. [falling OAT reaches frost point before dew point]

Question 59

Limitations on dew point

Answer 59

Dew point can't be greater than the temperature of the air parcel

Question 60

Psychrometer

Answer 60

Aka "dry bulb & wet bulb hygrometer". Wet bulb thermometer has wet muslin around it, if air is not saturated there will be evaporation which draws heat and therefore cools the thermometer. Difference between wet and dry thermometers indicates humidity.

Question 61

Wet bulb temperature

Answer 61

This is NOT dew point, but in-between dew point and OAT.

Question 62

Calculating cloud base - Based on wet bulb lapse rate

Answer 62

Wet bulb falls at SALR (1.8C per 1000ft), so wet bulb rate (proxy for dew point) and unsaturated air "close in" on each other at (3-1.8 =) 1.2C per 1000ft. Don't need to know dew point lapse rate info, just that it does fall with altitude like the other temperatures.

Question 63

Calculating cloud base (i.e. condensation level) based on surface temp & surface dew point

Answer 63

Cloud base in ft = (surface temp - surface dew point) x 400

Question 64

Hair hygrometer

Answer 64

Tool that uses length of a human hair to measure humidity.

Question 65

Diurnal variation of dew point

Answer 65

Dew point doesn't vary through day/night

Question 66

Calculation for relative humidity from temperature and dew point

Answer 66

RH = 100 - 5 x (temp - dew point)

Question 67

Latent heat at different temperatures

Answer 67

More latent heat energy is released/absorbed when temperature is higher

Question 68

Diabatic vs adiabatic

Answer 68

Diabatic involves movement of heat energy. Adiabatic is due to changes in pressure

Question 69

DALR

Answer 69

Dry Adiabatic Lapse Rate 1C per 100m 3C per 1000ft

Question 70

SALR @ low level, mid latitudes

Answer 70

Saturated Adiabatic Lapse Rate 1.8C per 1000ft

Question 71

SALR @ altitudes & latitudes

Answer 71

Cold air holds less water vapour so less latent energy, SALR tends towards DALR. So high altitudes & polar low level can reach 3C per 1000ft. Equatorial low level get down to 1C per 1000ft.

Question 72

Effect of additional moisture on stability

Answer 72

Increase in moisture affects dew point, or alternatively increases mixing ratio. This reduces the altitude increase required before dew point (or saturation mixing ratio) are reached. Thus DALR changes to SALR at a lower altitude, lower lapse rate increases likelihood of layers where ELR > lapse rate, thus instability.

Question 73

Stability of a layer of air

Answer 73

We consider the ELR of a layer of air, which can be any value, as compared to the DALR/SALR of a pocket that might enter that layer. Thus high lapse rate means unstable, as an unsaturated or saturated pocket of air entering it will be unstable.

Question 74

Blue thermal

Answer 74

A rising column of air with no cloud. Requires absolute instability so that a rising pocket of very dry air is unstable at DALR (perhaps due to convection or orthographic lifting). Used by gliders.

Question 75

Inversion in turbulent lee area

Answer 75

Moist air in stable atmosphere (so low ELR) with high winds to create the turbulent layer in lee of hills. Initially temperature profile is ELR, but turbulence causes some air to rise and some to fall, which will happen at DALR. Over time temperature profile changes to match DALR within the layer (surface is warmer, top of layer is cooler) creating an inversion above the turbulent layer.

Question 76

Calculation for temperature inversion at top of turbulence layer

Answer 76

((DALR - ELR) x Height of turbulent layer) / 2 [all in 1,000ft, i.e. DALR in per 1,000ft, height of turbulent layer in thousands of feet]

Question 77

Vertical windshear - description - units

Answer 77

Change in windspeed with change in height. Knots per 100 ft

Question 78

Horizontal windshear

Answer 78

Change in windspeed with movement in horizontal plane Knots per 1000 ft

Question 79

Low level windshear

Answer 79

Up to 1600ft.

Question 80

Severity ratings for windshear

Answer 80

Light: 0-4kt per 100ft Moderate: 5-8kt per 100ft Strong: 9-12kt per 100ft Severe: >12kt per 100ft

Question 81

Determinants of friction layer height - Terrain roughness - Wind speed - Stability

Answer 81

Terrain roughness: more rough => more vertical deflection => higher layer Wind speed: more deflection @ higher windspeed => higher layer Stability: Stable air resists vertical movement => lower layer

Question 82

Types of turbulence in friction layer (2)

Answer 82

Convection from thermal currents Frictional/mechanical turbulence

Question 83

Diurnal changes in friction layer and turbulence

Answer 83

Thermal effects in the daytime create instability and increase depth of friction layer. At night only mechanical turbulence. However surface cooling at night can lead to low level inversions, with light winds below and stronger winds above, causing windshear at the inversion.

Question 84

Turbulent vs Laminar boundary layer

Answer 84

In a laminar boundary layer (1000 to 1500ft) each "slice" of the boundary layer slides over each other easily so windspeed reduces significantly to very low close to the ground. When the boundary layer is turbulent (2000ft thick), these layers mix and so the higher slices lose speed more quickly and lower layers retain more speed. Only very close to the ground does speed fall significantly (i.e. below the 10m anenometer).

Question 85

Driver of boundary layer being turbulent or laminar

Answer 85

Boundary layer turbulence created by thermal disturbance and mechanical (e.g. hills) disturbance. So laminar layers expected over smooth cold surfaces, turbulent over rough hot surfaces.

Question 86

Time of day of greatest thermal turbulence

Answer 86

1500 - same as highest temp

Question 87

More turbulence in stable or unstable atmosphere?

Answer 87

Link to thermal turbulence, less stability increases turbulence.

Question 88

Definition of cloud

Answer 88

Hydrometeor consisting of minute particles of liquid water or ice (or both) suspended in the atmosphere, usually not touching the ground.

Question 89

Conditions for mountain waves (standing waves, lee waves)

Answer 89

- Wind direction perpendicular to mountain range +/- 30 deg - Wind speed at summit >15kt (30kt over large mountains) - Wind speed INCREASING with altitude up to troposphere, but direction constant - Stability around summit altitude (strongest if inversion)

Question 90

Lenticular clouds - description - altitude - cloud type

Answer 90

Formed above mountain tops and at crests of mountain waves in downwind direction. Can be found up to and ABOVE tropopause. Ragged edges => turbulence. In the altocumulus family (altocumulus lenticularis)

Question 91

Rotor (or roll) clouds

Answer 91

Formed under crests of strong waves downwind of the ridge. Strongest rotor formed under first wave, level with or slightly above ridge crest.

Question 92

Cap clouds

Answer 92

Form on the mountain ridge, may be blown down lee slope by strong winds.

Question 93

Visibility of mountain wave clouds

Answer 93

Might be obscured by other clouds, or might not appear if air is dry, but the waves are still present.

Question 94

Advice for mountain waves

Answer 94

Cross mountain ranges at 90 degrees, don't fly parallel and downwind. Don't fly through rotor zone. Allow height clearance = height of ridge. Avoid low altitude flight on lee side and high altitude flight downwind.

Question 95

Turbulence in troughs and ridges

Answer 95

Wind follows isobars so ridges and especially sharp edged troughs create a lot of horizontal windshear. Mostly concerned with upper level troughs and ridges where wind strength is higher.

Question 96

Frontal windshear/turbulence

Answer 96

Wind direction changes abruptly at a front, thus windshear/turbulence, particularly cold front as speed can change significantly. On approach to land this can be dangerous.

Question 97

Turbulence that pilots should report

Answer 97

High level (> FL150) clear air turbulence (i.e. not associated with cumuliform cloud or thunderstorms). Report time, location, level, intensity and aircraft type

Question 98

Turbulence intensity (ICAO) - IAS - G force - control

Answer 98

Light: <0.5g changes @ CoG (5-15ks IAS change) Medium: 0.5 to 1g changes @ CoG (15-25kts IAS change), positive control at ALL times Severe: >1g changes @ CoG (25+ IAS change), MOMENTARILY out of control

Question 99

Jet stream turbulence location

Answer 99

Turbulence related to jet streams is around the boundaries due to windshear. Strongest near to or just below jet axis on the cold air (low pressure) side.

Question 100

Barometric error (altimetry)

Answer 100

Altimeter errors caused by wrong pressure setting on subscale

Question 101

Temperature error (altimetry)

Answer 101

Altimeter errors caused by temperature being different to ISA. Colder than ISA means true altitude is lower than indicated.

Question 102

Calculation to adjust altimeter for temperature error

Answer 102

0.4% per degree C e.g. 5,040ft mountain clearance 20C below ISA. 7040 * 0.4% * 20 = 563ft [NOTE: Add 1,000ft (or 2,000ft in mountains) to an elevation figure, but NOT to a minimum safe altitude figure!]

Question 103

Consequence of temperature error on decision height/altitudes

Answer 103

Need to be adjusted when temperature more than 15C below ISA [increase by 0.4% per deg C]

Question 104

Wind vector indicator meaning

Answer 104

Question 105

Relevance of direction wind vector triangle/dashes point

Answer 105

Towards low pressure

Question 106

Gust

Answer 106

Needs to be at least 10kts over stable wind speed

Question 107

Squall

Answer 107

A sudden increase in wind speed (often along with change in direction), lasting a minute or more, can cover a large area.

Question 108

Squall line

Answer 108

Narrow band of active thunderstorms Indicated by sudden gusts and distinctive "ROLL CLOUD"

Question 109

Gale

Answer 109

Sustained wind speed over 33kts or gusts over 42kts.

Question 110

Equipment for measuring surface wind

Answer 110

10m above surface level Wind vane detects direction Anemometer (3 spinning half cups) measures speed

Question 111

Pressure Gradient Force (PGF)

Answer 111

Force creating wind from high pressure to low pressure areas, with wind speed related to spacing between isobars. This determines wind strength.

Question 112

Coriolis Force (CF)

Answer 112

Causes wind to veer in NH, back in SH. Force relates to windspeed (i.e. windspeed due to pressure gradient force) and latitude (minimal within 5deg of equator).

Question 113

Formula for CF

Answer 113

CF = 2 x w x rho x V x sin(theta) theta = angle of latitude w = angular rotation of earth (15 deg per hour)

Question 114

Formula for windspeed - effect of air density and latitude on windspeed (geostrophic)

Answer 114

In geostrophic wind coriolis force balances PGF so: PGF = 2 x w x rho x V x sin(theta) => V = PGF / (2 x w x rho x sin(theta)) Thus air density and latitude decrease windspeed, so fastest winds at high altitude and low latitude FOR THE SAME PRESSURE GRADIENT.

Question 115

Creation of geostrophic wind

Answer 115

Initially wind moves in direction of PGF and coriolis forces starts acting on it 90 degrees to the right. As the net wind direction turns to the right the coriolis force keeps turning to be 90 degrees to the right of wind. This continues until the coriolis force is in opposite directions to PGF (so wind direction 90 degrees right of PGF), when the two forces balance and wind maintains its speed and direction.

Question 116

Geostrophic wind definition

Answer 116

Created by combination of pressure gradient force and coriolis force. - Above the friction layer - Latitude > 15 degrees - Pressure situation not changing rapidly - Isobars straight and parallel

Question 117

Gradient wind - Cause in exam questions

Answer 117

Occurs when isobars are curved. Combination of pressure gradient force, coriolis force and centrifugal force. [If question refers to surface, likely FRICTION is the answer, otherwise CURVATURE OF ISOBARS]

Question 118

Impact of centrifugal force on wind speed

Answer 118

Coriolis force is based on wind speed so adjusts to the combination of PGF and centrifugal force. So around a low when centrifugal force opposes PGF, coriolis force is lower and windspeed is lower. Around a high the centrifugal force acts with PGF, coriolis opposes and windspeed is higher. [FOR QUESTIONS WHERE ISOBAR SPACING IS THE SAME - LOW SPEED ROUND LOW, HIGH ROUND HIGH]

Question 119

Isolobaric effect

Answer 119

Wind blowing across isobars (high pressure to low pressure) when pressure is changing significantly. In other words, when pressure is changing a lot the geostrophic wind will be adjusted by an additional force from high to low.

Question 120

Antitriptic wind

Answer 120

Wind that blows in low latitudes where CF is very small

Question 121

Wind change as surface is approached [Northern Hemisphere]

Answer 121

Day over land: backs 30 deg, 50% windspeed (compared to free stream flow/2000ft) Night over land: back 40 deg, 30% speed Over sea: back 10 degrees, 70% speed [So windspeed at 2000ft in day is twice that over land]

Question 122

Diurnal variation of surface wind

Answer 122

At night friction layer is stable, friction is high so surface effect causes wind to back and slow down relative to high level wind. In the day thermal effects mix the layers more so that effect is reduced, wind speed increases and veers (relative to night time).

Question 123

Diurnal variation of 1500' wind

Answer 123

At night the friction layer can reduce to less than 1500' so now 1500' level is behaving like high level, increased windspeed and veering. In day the friction level rises and ground effect impacts 1500' level, so windspeed reduces and backs (relative to night time).

Question 124

Sea breeze and land breeze - wind speed - distance from coast - height

Answer 124

Sea breeze about 10-15 nm from coast, 10-15kts. Land breeze about 5 nm from coast, 5 kts. Recirculation in opposite direction at about 1000'.

Question 125

Mountain/valley breezes

Answer 125

Thin air over mountains warms quickly in the day, rising and sucking up air from lower valleys. So mountain breeze is uphill in daytime, downhill at night.

Question 126

Katabatic and anabatic winds

Answer 126

Katabatic/anabatic due to cooling/heating of ground/mountains thus falling/rising over mountains. Kata - 10kts, ana - 5kts [Remember KATANA!]

Question 127

Fohn winds

Answer 127

Wind pushes air upwards against mountain, clouds forming on windward side resulting in warmer wind and higher cloud base on leeward side. TURBULENCE expected on lee side.

Question 128

Contour pressure chart

Answer 128

Chart produced for a given pressure level (e.g. 500 hPa), contour lines (isohypse) show relative altitudes of that pressure level.

Question 129

Drivers of isohypse (and pressure levels) at high altitudes

Answer 129

1) Thermal differences - recall that a warmer column of air with a given pressure range will take up more space (i.e. altitude) than a colder column of air. So adjacent areas with different temperatures will create a pressure difference at altitude. 2) The pressure at the surface.

Question 130

Which way do upper winds go relative to isohypses?

Answer 130

Bays Ballots law says in NH winds travel parallel to isohypses, with low numbers on the left (as with isobars).

Question 131

Isotach

Answer 131

Line of equal windspeed, shown as dashed red line on contour pressure charts

Question 132

Cause of winds in upper atmosphere

Answer 132

Thermal differences which cause pressure differences, ultimately coming from surface temperature effects. Thus upper winds referred to as thermal winds.

Question 133

General upper wind direction

Answer 133

Westerly (i.e. West to East) in both hemispheres. From Buys Ballot's, wind blows with low pressure (i.e. low temp) on left in NH, right in SH. Thus equator on the right for NH thermal winds, on the left for SH thermal winds.

Question 134

Easterly upper winds

Answer 134

NOT jet streams Tropical easterlies around ITCZ Polar regions in summer (thermal effects limited so low level winds replicated). [i.e. arctic in June, antarctic in Jan] [Polar Easterlies are NOT jet streams]

Question 135

Jet streams - position relative to tropopause - speed - dimensions

Answer 135

Strongest upper thermal winds JUST BELOW tropopause, >60kts (up to 300kts). Assumed 2000 miles long, 200 miles wide, 2 miles deep. [ratio 1000:100:1]

Question 136

Location of jet stream around fronts

Answer 136

Jet stream will be in the warm part (although appears in cold part from surface level charts due to frontal slope).

Question 137

Subtropical jet streams

Answer 137

Formed by subtropical anticyclones. Permanent but move with seasons as the anticyclones move. NH: 25 to 40 deg in winter, 40 to 45 in summer SH: 25 to 30 deg

Question 138

Polar front jetstreams

Answer 138

Caused by pressure gradient between wTm and cPm on either side of polar front. The only frontal jet stream. Follows polar fronts around the globe but interrupted over Siberia in Winter. Straight lines in SH but land mass disturbs the line in NH. NH: 40 to 65 deg SH: 50 to 55 deg

Question 139

Tropical/equatorial easterly jet

Answer 139

In NH summer between 10 and 20 degrees, due to heated central Asian plateau. Hotter over India than sea at equator so initially heads south, coriolis turns right so EASTERLY jet stream. Runs from South China Sea across India, Ethiopia and sub Sahara. Only 30 to 50kt.

Question 140

Arctic Jet Stream

Answer 140

Boundary of Arctic and Polar air. 60 deg N around USA or 45 to 50 deg N elsewhere. Transient feature during NH winter. Westerly

Question 141

Jet stream altitudes

Answer 141

Equatorial: 50,000ft, 150hPa Sub-tropical: 40,000ft, 200hPa Polar front: 30,000ft, 200hPa Arctic: 20,000ft, 400hPa

Question 142

Jet stream summary - Altitudes - Seasons - Latitude - Wind speed

Answer 142

Question 143

Low level jet stream

Answer 143

Not technically a jet stream. Caused by mass of cold air moving over ground, or intense uneven ground cooling at night. Creates a strong INVERSION, temperature differential causes wind in the warm air above inversion up to 70kt.

Question 144

Clear air turbulence

Answer 144

Caused at boundaries of jet streams. Recall jet stream is on warm air side. Strongest turbulence is in the warm air, but on the cold side of the jet stream, just below the jet stream. [Also mountain waves w/o cloud termed CAT]

Question 145

Indicators of strength of CAT

Answer 145

Curving jet stream (change of direction => windshear) Trough at surface level Conjunction of two jet streams

Question 146

Indicators of jet stream speed

Answer 146

Largest pressure gradients, so boundary between ridge and trough, or low and high pressure systems in proximity would give greatest speeds.

Question 147

Detecting turbulence

Answer 147

Radar reflects liquids and solids, so turbulence related to cloud/rain phenomena can be interpreted. CAT is harder. LIDAR can detect it, but pilot reporting is helpful.

Question 148

Jet streams stronger in summer or winter

Answer 148

Increase in strength in winter due to higher temperature differential.

Question 149

Cloud associated with jet streams

Answer 149

Cirrus cloud can form on the equatorial side, due to corkscrewing of air around the jet stream, rising air on equatorial side (often moist, e.g. tropical front jet stream) leads to cirrus cloud.

Question 150

Cloud ceiling

Answer 150

Height above aerodrome of lowest layer of cloud of more than 4 OKTAS

Question 151

Measuring cloud base by day or night

Answer 151

By day release a balloon and time until it disappears By night shine a searchlight at the cloud base and use alidade (trigonometry) to calculate height.

Question 152

Ceilometer

Answer 152

Uses light or lasers and reflection to determine cloud base height.

Question 153

Cloud height bands

Answer 153

Low: 6,500' Alto: 6500' to 23000' Cirro: 16500' to 45000' [Alto & Cirro lower in polar regions, higher in tropical]

Question 154

Cirrus cloud conditions

Answer 154

Ice crystals No icing (as particles are ice already!) Light turbulence in Cc, no turbulence in Ci/Cs Fair visibility (>1000m)

Question 155

Alto cloud conditions (As, Ac)

Answer 155

Water droplets + ice crystals Light icing Light to Moderate turbulence Fair visibility (<1000m) As: Light to Moderate rain

Question 156

Stratus/Stratocumulus conditions

Answer 156

Water droplets Light to Moderate icing S: No turb, Sc: Light turb Poor visibility (<30m) Drizzle/light rain

Question 157

Cumulus/Cumulonimbus/Nimbostratus conditions

Answer 157

Water droplets + ice crystals Moderate to Severe icing Moderate to Severe turbulence Poor visibility Heavy showers (rain Ns) Cloud base low (low/medium for Ns)

Question 158

Cumulus development stages

Answer 158

[Early stages start in am] Cumulus Fractus Cumulus Humilis (fair weather Cu) Cumulus Mediocris (dark underneath) Cumulus Congestus (towering cumulus) Cn Calvus (rounded tops, no anvil) Cn Capitallis (has an anvil)

Question 159

Altocumulus castellanus (Acc)

Answer 159

Little towers of cumulus clouds forming on a flat cloud layer. Requires considerable instability and can occur before thunderstorm.

Question 160

Turbulence Cloud

Answer 160

Stratiform cloud formed in stable conditions, due to turbulence in the friction layer. Turbulence at surface steepens the lapse rate and thus there will be an inversion above the turbulence cloud.

Question 161

Mammatus

Answer 161

"Breast shaped" cloudbase of Cu/Cb indicating imminent precipitation

Question 162

Convection Cloud

Answer 162

Cumulus type cloud formed by the earth warming the air, which then cools at DALR and forms cloud at dew point (cloud base) up to the point ELR takes over SALR when the cloud top is reached. Only forms over land.

Question 163

Nacreous cloud

Answer 163

Aka "mother of pearl" cloud. Exist in lower stratosphere (20 to 30km) and have a bright shiny appearance due to reflected sunlight.

Question 164

Noctilucent clouds

Answer 164

In mesosphere at 70 to 95km, reflect sunlight, thus the name meaning "night light clouds". Made of ice crystals (potentially from rocket engines).

Question 165

Bergeron Theory (Norwegian or Ice Crystal theory)

Answer 165

Bergeron theory is that precipitation is caused by some water droplets turning to ice, growing in size through sublimation with water vapour and colliding with supercooled droplets. These droplets then become heavy and fall as rainfall or snow depending on temp. Related to the partial pressure of water vapour over ice/water.

Question 166

Coalescence Theory

Answer 166

Assumes a variety of droplet sizes, with larger ones falling faster and uniting with smaller ones, eventually overweight drops fall as drizzle or rain.

Question 167

Likely or initial precipitation at high latitudes or in cloud where water droplets and ice crystals exist

Answer 167

If ice crystals exist in the cloud due to low temperature, partial pressure of water vapour over ice vs water will cause ice crystals to grow relative to water droplets (water droplets may even partially evaporate). Thus initial precipitation is SNOW, which may melt by the time it reaches the ground, depending on temperatures. Ice crystals are NOT hail!

Question 168

Symbols for: - Drizzle - Rain - Snow - Hail - Soft hail (graupel) - Ice pellets

Answer 168

Question 169

Diameters of precipitation types: - Drizzle - Rain - Snow - Hail - Ice pellets

Answer 169

Drizzle: 0.2 - 0.5mm Rain: 0.5 - 5.8mm Snow: 1- 5mm (grains - pellets - flakes) Hail: 5 - 50mm Ice pellets: <5mm

Question 170

What cloud do snow grains fall from?

Answer 170

Stratus or fog only, never fall in showers

Question 171

Ice Crystals (precipitation)

Answer 171

Aka Diamond Dust. Very small particles found in polar and alpine regions, forming at below -10C. Sparkle in the sunlight.

Question 172

Hail - how and where it is created

Answer 172

From Cb cloud only, made up of layers around a nucleus. Can fall (gathering moisture) and be lifted back up by an updraft, freezing again. Eventually too heavy, or thrown out of top of cloud. High freezing altitude at equator means they usually melt there before reaching the ground. Not common over sea due to lack of convective strength.

Question 173

Ice pellets

Answer 173

Produced by frozen raindrops (as opposed to hail which has a frozen core). Likely linked to FREEZING RAIN! <5mm [Hail is >5mm]

Question 174

Visibility in rain types - drizzle, rain, snow

Answer 174

Drizzle: 0.5km to 3km Rain: 3km to 5.5km (1km heavy) Snow: below 1km (almost zero for drifting/blowing)

Question 175

Visibility in sand/dust storm

Answer 175

Moderate: 200m - 600m (maybe <200m with sky not obscured) Heavy: <200m

Question 176

Duration of rain

Answer 176

Showers associated with convection cloud (cumulus). Intermittent or continuous with layer cloud (continuous is no break for 60 mins+).

Question 177

Surface temp for snow to reach surface

Answer 177

< 4 deg C

Question 178

Definition of slight, moderate & heavy precipitation

Answer 178

Rain in mm/h, snow in cm/h: Slight <0.5, Moderate 0.5-4, Heavy 4+ Showers <2mm/h, 2-10mm/h, 10+mm/h

Question 179

Basic requirements for thunderstorms

Answer 179

- Lapse rate greater than SALR at least 10,000ft thick and above freezing level (i.e. CONDITIONAL instability) - Sufficient water vapour - Trigger action

Question 180

Triggers for TS

Answer 180

Winter: Frontal uplift Summer: Convection, orographic uplift, convergence (also advection)

Question 181

Frontal type thunderstorms

Answer 181

Frontal type caused by fronts (cold front or occlusion in a depression or trough), usually in Winter, fast moving.

Question 182

Air mass thunderstorm

Answer 182

Occur in daytime over land in summer, thermal convection from heated land.

Question 183

Advection type thunderstorms

Answer 183

Medium level (base around 10,000ft). Can happen day or night, over land or sea, at any time of year.

Question 184

Thunderstorm initial stage - description - time - up draft speed - size

Answer 184

15-20 mins. Small Cu combine and strong up currents (1000 to 2000fpm) draw air from sides and below. Approx 5NM across.

Question 185

Thunderstorm mature stage

Answer 185

15-20 mins. Precipitation starts. Rain/hail causes 2400fpm down currents carrying cold air down. Descending air warms at SALR so accelerates downwards creating gust fronts 13 to 17NM ahead and 6000ft in depth. Up currents remain strong (up to 10000fpm), cloud top rising at 5000fpm. Rising and falling raindrops cause static electricity leading to thunder.

Question 186

Thunderstorm dissipating stage

Answer 186

1.5-2.5 hours. Sporadic showers, extreme turbulence. Cloud extends to tropopause where it spreads out into cirrus and forms an anvil.

Question 187

Movement of thunderstorms

Answer 187

In direction of 10000ft (700hPa) wind, though large and newly developed storms will differ

Question 188

Lightning in Cb

Answer 188

Upper cloud +ve charge, lower -ve, differential causes lightning. Found +/- 5000ft from freezing level, where temp is around 10/-10C.

Question 189

Supercell thunderstorm description

Answer 189

High winds at upper layers separate the updraughts from the downdraughts, thus preventing the usual dissipation method of single cell thunderstorms. Occur around polar fronts typically.

Question 190

Supercell thunderstorm (severe local storms) requirements

Answer 190

Great depth of instability Strong vertical windshear Stable layer between warm upper and cool lower air which is broken down by insolation.

Question 191

Supercell mature stage

Answer 191

Very strong up and down draughts causing violent weather & tornados. Can last several hours.

Question 192

Supercell movement & location

Answer 192

Located over continental land masses generally (e.g. central USA). Move 20 deg to the right of the 18000ft wind (500hPa).

Question 193

Avoidance distance for thunderstorms on radar (by flight level)

Answer 193

0 - FL250: 10NM FL250-300: 15NM FL300+: 20NM Vertical: 5000ft [Visual avoidance - 10NM]

Question 194

Thunderstorm risks

Answer 194

Turbulence Hail (up to 45000ft) Icing (airframe -45 to 0C, carb -10 to 30C) Lightening (within 5000ft of freezing level, temp -10 to +10C) Static (affects radio equipment) Pressure variations Microbursts Water ingestion (in jet engine) Tornadoes

Question 195

Microburst - downdraft speed - windspeed & windshear - size - time

Answer 195

Down currents in cloud and also outwards due to ground impact. c. 3000fpm downwards (up to 6000fpm) and 50kt horizontal (in 2 directions, so up to 100kt windshear) Only 4km horizontal length and last < 5 mins.

Question 196

Dry microburst

Answer 196

If air below the thundercloud is dry, the rain can evaporate before reaching the ground. This absorbs energy, reduces temperature of the air, increasing density and thus the intensity of the microburst effects (windspeed).

Question 197

Detecting downbursts - 2 methods

Answer 197

Detection @ aerodromes where it is a concern for large aircraft. 1) Low Level Windshear Alert System (LLWAS), set of anemometers around airfield @5 to 10NM distance 2) Low frequency doppler radar measures windspeed around aerodrome

Question 198

Tornado - description - size - time

Answer 198

Connected to thunderstorms, caused by opposing vertical airflow movements. Diameter generally less than 150m but can be up to 1.6km. Called funnel clouds if they don't reach the ground (can be embedded within cloud). Last a few mins up to 30 mins.

Question 199

Dust devil

Answer 199

Small whirlwind on hot, sunny afternoons up to 2000ft

Question 200

Action when flying through thunderstorm

Answer 200

Maintain heading, don't turn, this will probably be quickest way out. Don't climb or descend to make up for moves in turbulence. Avoid flying below or above cloud due to down draughts below and growth of the cloud above.

Question 201

Limitation for reporting of fog or haze

Answer 201

Not reported if visibility >5000m

Question 202

Radiation fog - description - time of day

Answer 202

Formed overnight or early morning, with light winds, clear skies, high relative humidity. [Look out for reference to morning or afternoon, maybe advection fog if afternoon?]

Question 203

Unusual instances of radiation fog

Answer 203

Southern Gulf in Winter - cool moist air from sea breeze is cooled overnight over cold earth, fog drifts back out to sea in land breeze. Polar Maritime air winter (NE Europe)

Question 204

Hill (Orographic) fog

Answer 204

Cloud (usually stratiform) with a base lower than the summit of the hills. Can be caused by air being forced up hills, or normal turbulence creating St or Sc cloud.

Question 205

How orographic fog is lifted

Answer 205

A DOWNWIND blowing moist air back down the mountain, below the dew point level. Or potentially solar radiation.

Question 206

Advection fog - description - ideal conditions

Answer 206

Warm moist air (e.g. from water) moving over cold land. Wind speed around 15kt (much greater than 15kt will lift the fog to form stratus cloud) OAT close to dew point is important, but also higher temp means more potential moisture in air so 20/15 more likely than 10/5.

Question 207

Notorious area of advection fog

Answer 207

Over sea around Newfoundland and the Kamchatka peninsula. Several areas where warm and cold sea flows coincide.

Question 208

Steaming fog (arctic smoke) - description - specific conditions

Answer 208

In high latitude areas, requires high level of stability. Cold air (BELOW -10C) from above land moves over warmer sea.

Question 209

Frontal fog

Answer 209

Occurs AT warm front (or occlusion), clears once it passes. Warm front sliding over cold front, warm rain evaporates in drier cold air. Also evaporation of standing water and mixture of saturated air with non-saturated air below. Can form 200nm band ahead of warm front.

Question 210

Freezing fog

Answer 210

With temperatures below 0C air won't sublime due to lack of freezing nuclei, but will freeze on contact with an object. Can also happen when fog forms over 0C and air then cools below 0C.

Question 211

Ice fog - description - cause

Answer 211

Rare occurrence below -40C where warm moist air is introduced to cold saturated air (e.g. due to car engines). Condensation and immediate freezing leads to ice crystals in the atmosphere.

Question 212

Prevailing visibility - description (# candelas)

Answer 212

Based on black object on white background OR 1000 candela white lights on black background. Refers to the visibility around at least half of the horizon circle from aerodrome (except areas <1500m or <5000m and <50% prevailing will be reported additionally [e.g. 1200NE - 1200m visibility in NE direction]).

Question 213

Runway Visual Range (RVR) - Description - When is it reported?

Answer 213

Max distance that a pilot 15ft above runway in touchdown area can see marker boards (day) or runway lights (night) in direction of TO/L. Reported when meteorological optical range (MOR) or RVR <1500m, or if shallow fog is reported/forecast.

Question 214

UK RVR increments

Answer 214

25m from 0 to 400m 50m from 400m to 800m 100m above 800m

Question 215

RVR measurement frequency

Answer 215

Every 30 minutes in regular usage, 15 mins before TO/L in irregular usage.

Question 216

RVR segment reporting

Answer 216

Divided into touchdown, midpoint, stop end. Always report touchdown. If other two are <400m, or <800m AND

Question 217

Is RVR or meteorological visibility better?

Answer 217

RVR is usually better as it is based on bright runway lights.

Question 218

Transmissometer

Answer 218

Transmitter and receiver measure visibility over short distance. Can have 3 at middle and each end of runway.

Question 219

Forward Scatter Visibility Meter

Answer 219

Transmitter and receiver positioned 20 to 50 degrees away from each other, thus senses scattered light reflected. Can assess visibility and also the nature of the particles in the air for more accurate information.

Question 220

Freezing & condensation nucleii

Answer 220

Required in the atmosphere for water to freeze and condense, regardless of temperature of the water. Condensation nucleii are more common, so supercooled (below 0C) water is common.

Question 221

Share of ice crystals and SCWD in temperature bands

Answer 221

0 to -15: Mostly SCWD (large & small) -15 to -40: Mix of SCWD (small) & ice crystals -40 below: Ice crystals only

Question 222

Impact of ice/frost/snow layer on lift surfaces (%)

Answer 222

Thickness and roughness similar to sandpaper can reduce lift by 30% and increase drag by 40%.

Question 223

Clear Ice

Answer 223

Freezing of supercooled water droplet impacting airframe releases latent heat, water drifts back causing thin clear layer of ice. 1/80th of a supercooled water droplet freezes for every degree below zero (80 calories latent heat), rest stays water. Most dangerous form of icing as it builds up quickly, so just below 0C more dangerous than lower temps.

Question 224

What conditions does clear ice form in?

Answer 224

Large supercooled water droplets. Cu/Cb/Ns from 0 to -20C

Question 225

Rime Ice

Answer 225

Small supercooled water droplets freeze instantly, creating white coloured rime ice on the leading edges. Can happen all the way down to -45C, from -23C down only get rime ice.

Question 226

What conditions does Rime ice form in?

Answer 226

Stratiform cloud from 0 to -30C

Question 227

Visiblity of Rime and Clear ice

Answer 227

Rime ice more visible as air gets trapped between frozen droplets. No air trapped in clear ice so not visible (no refraction of light).

Question 228

Mixed ice

Answer 228

Combination of clear ice and rime ice which can be experienced in -10 to -15C

Question 229

Icing severity in cloud types

Answer 229

Worst icing requires large super-cooled water droplets just below 0C. Cb, TS: severe/moderate Cu, Sc, Ns: moderate St, Ac, As: light Ci, Cs: nil (trace in Cs) [St could get moderate or even severe with orographic uplift]

Question 230

Very worst icing area

Answer 230

Tropical Cb cloud at temperatures just below 0C. Creates combination of large super-cooled water droplets held up by cumulus cloud, high level of moisture at low levels and the right temperature conditions at high altitude.

Question 231

Rain Ice/Freezing rain

Answer 231

When rain becomes supercooled by falling through an inversion, so common in triangle of cold front underneath Ns clouds of the warm front. Will freeze to form clear ice or rime ice when impacting airframe. Can build up very quickly so climb or descend. [Freezing drizzle also exists]

Question 232

Rain ice (diagram)

Answer 232

Question 233

Hoar Frost

Answer 233

White crystals forming in clear air if airframe is below 0C and ambient temperature lowered to saturation level. Water vapour sublimates (requiring sublimation nucleii, usually inorganic like volcanic dust or soil particles).

Question 234

Situations causing hoar frost (and how serious)

Answer 234

On the ground at night: Must be cleared due to skin friction, obscuring windscreens and affecting radio antennae. In the air if descending from cold region to warm moist air (or up through inversion). Effects not severe, speed up or move to warmer air.

Question 235

Active frost - Description - Conditions

Answer 235

Hoar frost that reforms (obviously more dangerous). Same conditions as hoar frost: - Aircraft skin below 0C (perhaps due to cold soak fuel - very cold fuel close to aircraft skin) - Air temp close to dew point (within 3C) - Dew point < 0C - Either cloudless sky & calm wind (get radiation cooling) or warm front (brings warm, moist air)

Question 236

Ice Crystal Icing (ICI) - description - where it is found - problems caused (2)

Answer 236

Very small ice crystals at high altitude. Can't be detected by radar as particles are too small. Found downwind of TS and convective cloud at high altitude but BELOW the tropopause [OVER FL330] Can cause damage to engines and problems with heated temperature probes (to do with partial melting).

Question 237

Avoiding Ice Crystal Icing (ICI)

Answer 237

Steer clear of area above convective rain clouds by 50NM

Question 238

Ice Water Content (IWC)

Answer 238

grams per m3 of ice in a cloud (high at high levels in convective cloud)

Question 239

Impact of surface/aerofoil shape on icing

Answer 239

Airflow adheres closer to a thinner profile so more icing will occur. Thus thin winged aircraft more affected and also thin surfaces (e.g. tailplane) might get more icing than the main wings.

Question 240

Impact of aircraft speed on icing

Answer 240

Faster speed leads to striking more water droplets, however the kinetic effect of increased speed may offset this. Skin Temp = OAT + (TAS/100)^2 Increase in temp to below 0C can increase icing!

Question 241

Cloud base temperature impact on icing

Answer 241

Higher temperature leads to higher amount of water vapour content. So a cloud with a warm base has more potential for icing at the higher (colder) layers, than a cloud which is cold at its base.

Question 242

Worst Cb layer for icing?

Answer 242

Middle At the top precipitation will be ice, at the bottom temperature is too warm. Supercooled water drops mostly in the 0 to -20C temperature band which is probably in the middle of the Cb.

Question 243

Requirement to report icing

Answer 243

Pilot must report to ATC any experience of unforecast icing, or moderate & severe icing (meaning continuous de-icing or diversion required)

Question 244

Airframe icing severity reports

Answer 244

This is different to the severity for forecasting purposes. Trace: De-icing not necessary unless exposure for > 1 hour. Light: De-icing occasional use removes accumulation, only a problem if over 1 hour exposure. Moderate: Short encounters may become dangerous and de-icing is necessary. Change of heading or altitude may be desirable. Severe: De-icing can't control and diversion is necessary. Immediate change of heading/altitude essential.

Question 245

Piston Engine Induced Icing types

Answer 245

Impact icing (from snow, snow+rain or supercooled water droplets). Only this one affects turbo/fuel injected planes. Fuel icing Carb icing (due to temp drop as fuel evaporates and expansion of air passing through venturi)

Question 246

Most dangerous temp for carb icing

Answer 246

-10 to +25C OR 0 to 15C [Centred around 7.5]

Question 247

Key factors for carb icing

Answer 247

Difference between temperature and dew point, or in other words - relative humidity (100% when temp = dew point). Very worst conditions are temp = dew point = 10C.

Question 248

Jet engine icing

Answer 248

Jet engines often have some degree of convergence (high air velocity, temp and pressure falls) which can cause intake icing. Operating manual will describe the risk and RPM, airspeed (etc.) to avoid (likely to be high RPM and low airspeed).

Question 249

Impact of orographic uplift on icing

Answer 249

Air forced upwards loses heat rapidly at the DALR, thus freezing level falls to lower altitude and icing risk increases. Updrafts support supercooled water droplets so icing more intense above mountains than flat land (orographic intensification).

Question 250

Classification of air masses

Answer 250

e.g. mAc 1) m for maritime, c for continental 2) Equatorial, Tropical, Polar, Arctic 3) c for cold, w for warm

Question 251

Note on stability in air masses

Answer 251

All air masses are stable at source (i.e. get their properties by hanging around for a while in a cold/warm dry/moist area), possibly under an inversion. Air moving to colder land becomes more stable, moving to warmer land becomes less stable. [Note air mass are uniform in horizontal plane, not vertical]

Question 252

Main air mass sources for NW Europe

Answer 252

Constant high pressure areas of polar region (cold) and Azores (warm), plus the temporary high pressure over very cold Siberia in winter. Give rise to 6 air masses: Polar: mAc, mPc, mPw Azores: mTw, cTw (more like North Africa) Siberia: cPc

Question 253

Polar maritime (mPc)

Answer 253

Starts as cold, dry, stable air. Heading over warmer North Atlantic picks up moisture and is heated, becoming conditionally unstable. Winds from NW/W. If sufficient heating (e.g. summer) get convective cloud (Cu, Cb), rain showers, hail, TS. Can also get clear skies (especially at night), good visibility, radiation fog.

Question 254

Arctic maritime (mAc)

Answer 254

Similar to mPc but from North in winter, air is colder so relative heating from beneath is higher and becomes less stable over UK. Cu, Cb and heavy snowfall.

Question 255

Polar continental (cPc)

Answer 255

From Siberia in winter only, very cold and dry, becomes unstable over UK. From over the continent very dry, no precipitation, creates inversion so poor vis. If coming over Baltic/North sea more moist, get Cu and heavy snow showers.

Question 256

Tropical Continental (cTw)

Answer 256

Mostly in summer, warm, dry, stable air. No cloud or precipitation, haze due to stability. Comes from SOUTHERN BALKAN REGION AND NEAR EAST.

Question 257

Tropical Maritime (mTw)

Answer 257

Azores anticyclone - warm, stable, high absolute & relative humidity. Stability and humidity cause low stratiform cloud, poor visibility. In spring advection fog over sea. In summer insolation breaks down the stability giving clear skies or a few Cu.

Question 258

Returning Polar Maritime (mPw)

Answer 258

Polar air moves to the South in Atlantic and approaches UK from W or SW. End up with a mix of mPc and mTw, could behave like either depending on conditions/season.

Question 259

Coldest source of air

Answer 259

Continental Polar (i.e. Sibera). Colder than arctic maritime largely as dry air is colder than moist air.

Question 260

Polar Front

Answer 260

Boundary between polar and tropical air, 35-65deg latitude in NH, 50-55 in SH. In winter mid-Florida to SW UK, in summer Newfoundland to NW UK.

Question 261

Arctic Front

Answer 261

Boundary between arctic and polar air.

Question 262

Mediterranean Front

Answer 262

Boundary between polar continental/maritime air from Europe and tropical continental from Africa. Extends West to East over the Med. Disappears in summer. [Med is LOW pressure, sucks in the SGK winds from Africa]

Question 263

Intertropical Convergence Zone (ITCZ)

Answer 263

The fourth of the main world weather fronts. Separates air masses either side of heat equator, also know as thermal equator or equatorial trough. Created by the trade winds coming from the sub-tropical high pressure zones towards the equator.

Question 264

Polar Front Depressions - creation - pressure aloft

Answer 264

Main cause of UK bad weather, depressions formed in families along the polar front (mPc, mTw). Warm Tropical air pokes into cold air creating the warm sector. The warm air surrounded by cold will rise and make this a depression. Move parallel to the warm sector isobars. Low pressure at high altitude as well as at the ground (unlike warm depressions).

Question 265

Time between polar front "waves" in Europe

Answer 265

A "wave" means the passage of a new front. About 1-2 days between each front (bit more in winter, bit less in summer).

Question 266

Death of polar front depressions

Answer 266

Their energy is fed from the warm air (mTw) to the south (poking into the cold mPc). As occlusion forms the warm sector is pushed out and the depression separates from the mTw air, losing the hot air that gives it energy. Eventually it dissipates.

Question 267

Warm front

Answer 267

Low slope (1:150) rising over cold air, Ci and stratiform cloud types behind the front. Total distance of 400/600nm, rain up to 200/300nm under the lower Ns clouds. Moves at right angles to itself, at 2/3 of the geostrophic interval at the front.

Question 268

Cold front

Answer 268

Steep slope (1:80) forces warm sector air up quickly, forming Cb cloud (& Ns) ahead of it - heavy showers. Low pressure at the front itself (so passing of the front sees pressure fall then rise within the cold air following).

Question 269

Other cloud at warm & cold fronts

Answer 269

Stratus fractus due to high humidity

Question 270

Warm sector conditions

Answer 270

mTw air in the polar depression. Summer: good weather, fair weather Cu Winter: stable conditions, stratiform cloud, drizzle, mist

Question 271

Passing of warm front - pressure - wind direction - cloud - precipitation - temp - visibility

Answer 271

Pressure falls as the centre of the low is approaching you (travelling Eastwards to your north). Sharp veer from S to SW. Cloud increases as it approaches (Ci, Cs, As) then Ns and drizzle as it gets closer. Continuous rain as it passes. Frontal fog as it passes. Temp & dew point rise as it approaches. Reducing visibility.

Question 272

Passing of cold front - pressure - wind direction - cloud - precipitation - temp - visibility

Answer 272

Pressure low point around the front (closest to centre of the low) then increases after passing. Sharp veer from SW to NW. Cu/Cb/Ns cloud, heavy rain or snow showers, thunder/hail possible (air forced upwards steeply by cold front). Temp & dew point fall. Visibility good except in showers.

Question 273

Distance covered by frontal area behind cold front

Answer 273

Warm air at altitude extends back 100-200 NM from surface cold front. Precipitation extends 50-100 NM behind the cold front at surface. [Questions about time taken for weather to clear on passing of cold front]

Question 274

Conditions in cold air behind cold front

Answer 274

Cumulus clouds (cold air aloft gives steep pressure gradient therefore instability). Showers Good visibility

Question 275

Faster or slower cold front more active

Answer 275

Slower cold fronts are more active (wider band of convective clouds and related activity).

Question 276

Effect of mountains on passing warm & cold fronts.

Answer 276

Warm front can trap cold air on windward side of mountains, forcing warm air higher so longer term precipitation on windward side, less on leeward. Cold front gets extra lift from mountains so again, lots of activity on windward side, less on leeward.

Question 277

Movement of fronts - speeds in kt - in terms of geostrophic wind speed

Answer 277

Warm front around 15kt, cold front 20kt. Speed <5kt means stationary front. Winds will blow along the front rather than over it (so 180kt windshear at the front). Warm front 1/3 to 2/3 of geostrophic wind, cold front over 2/3.

Question 278

(Quasi) Stationary front weather

Answer 278

Wide area of cloud (predominantly on cold side) with varying levels of precipitation (showers).

Question 279

Polar Front upper winds

Answer 279

Jet streams parallel to fronts as driven by thermal differences. One 400nm ahead of warm front, parallel to it, from NW. One 200nm behind cold front, parallel to it, from SW. In the warm sector will be parallel to isobars (i.e. similar to geostrophic).

Question 280

Wind directions around polar front depression

Answer 280

Question 281

Triple point

Answer 281

Or occlusion point, the point where the cold front catches up with the warm front.

Question 282

Warm or cold occlusion

Answer 282

Depends on relative temperatures of the cold areas (ahead of warm front and behind cold front). If air behind warm sector is warmer than air ahead of warm sector, it's a warm occlusion.

Question 283

Identify warm vs cold occlusion on a chart

Answer 283

See if it follows the shape of the cold front or warm front that it connects to

Question 284

Description of occlusion cloud

Answer 284

Whether warm or cold occlusion, warm sector gets pushed up off ground. Cumulus cloud ahead of cold front is forced upwards so get Ac or Cb (hail, TS). Occurs towards the end of depression lifecycle so moves slowly, bad weather can hang around.

Question 285

Occlusion types in Europe in winter/summer

Answer 285

Get cold occlusions in summer, warm occlusions in winter in Europe. Due to land warming/cooling the air in front.

Question 286

Lifecycle of polar front/mid-latitude depression

Answer 286

4-7 days

Question 287

Orographic (lee) depression

Answer 287

Air flow redirected around sides of mountain range causes low pressure on lee side. Creates convective conditions on the lee side.

Question 288

Three possible weather conditions around orographic depressions

Answer 288

1) Dry stable air leads to Fohn effect, warm, clear & dry weather lee side. 2) Moist unstable air creates Cu and Cb with showers, thunderstorm and hail possible over mountain and the lee depression. 3) Cold front approaching the mountain range when it breaks over will be above warmer air in the depression, increasing the convective, unstable effect. Line squalls, heavy showers, TS, hail. e.g. Northern Italy over Alps

Question 289

Thermal depression

Answer 289

Surface air is heated causing convection, creating a low at the surface and cyclonic winds. Get Cu, Cb (hail & TS), heavy showers, moderate/sev turb and good visibility outside showers. Lots of types (monsoon, polar air, inland water, TRS, NOT tornados).

Question 290

Monsoon low

Answer 290

A large thermal low developed over continents in summer which dominates weather patterns.

Question 291

Polar Air Depressions (Polar low)

Answer 291

Formed when Arctic Maritime air is lifted on a large scale as it moves south over warmer seas. Gives Cu, Cb, heavy showers and secondary cold fronts. Like TRS, lose power over land. NOT the same as polar front depressions. ONLY formed over water

Question 292

Inland Water lows

Answer 292

In winter, cold air (e.g. Siberian cPc) over warm lakes or inland seas (Caspian, Black, Mediterranean) can create convection and depressions.

Question 293

Summer thermal lows over land

Answer 293

Surface heating can cause thermal lows over land in summer, causing TS or widespread rain if conditions are unstable. Over land OR (rarely) water

Question 294

Tropical Revolving Storms (TRS) - Description - windspeed - Size - Time

Answer 294

aka hurricanes. Thermal depressions over warm tropical oceans with sustained wind speeds over 33kt. Designated tropical cyclone if sustained wind speed over 63kt [NO LONGER A TRS!, max TRS windspeed 63kt!] 270 NM (500km) diameter Heavy rainfall Tornados may be faster, but only last for minutes, TRS last for a couple of weeks.

Question 295

Formation of TRS - general - specific example in atlantic

Answer 295

Formed from complexes of thunderstorms. Gain moisture from warm waters which condenses releasing latent heat, exacerbating the depression and the convergence, leading to more condensation & latent heat. Atlantic - Easterly waves coinciding with SE trade winds

Question 296

Airflow around TRS

Answer 296

Cyclone (anti-clockwise in NH) rotation at lower levels around the depression, changes to high pressure and opposite rotation at highs where the air is expelled (divergence). Some air flows back into the eye and down from the top level.

Question 297

Requirements for TRS

Answer 297

5 to 25 latitude (coriolis too low <5, sea too cold over 25) Ocean temp over 26C Sufficient depth of water to provide energy Minimal shear otherwise storm topples Instability in atmosphere

Question 298

Origins of TRS

Answer 298

Mainly from the Intertropical Convergence Zone (ITCZ) or from equatorial easterly atmospheric waves (originating in North Africa).

Question 299

Movement and life of TRS - direction and speed of movement - death

Answer 299

Driven West by the easterly trade wind belt at 10-20 kts. Get turned away from equator by coriolis force, losing energy as they move over colder seas or over land.

Question 300

TRS eye - description - size

Answer 300

10-20 NM wide, lowest pressure and calmest conditions. Air forced up by the storm descends in the centre. Adiabatic heating causes clouds to evaporate. It rose at SALR creating clouds and descends at DALR in the column, so relatively warm. Walls of the eye are the fastest winds.

Question 301

TRS stages

Answer 301

1) Tropical Disturbance: Area of low pressure, rising air giving towering Cu, releasing latent heat. Winds light. 2) Tropical Depression: Stronger depression and cylonic circulation, driven by divergence at altitude. Cb forms. Winds up to 33kt. 3) Tropical Storm: Continues to strengthen, subsidence in eye develops, no cloud there. Wind 33kt to 63kt. 4) Tropical Cyclone: (or hurricane, typhoon dependent on location) Wind speeds >63kt

Question 302

How to avoid a revolving storm

Answer 302

Heading towards a low if you experience rightward drift, so turn (either direction) until you get leftward drift - then you must be going away from the low.

Question 303

Most dangerous quarter of TRS

Answer 303

Fastest wind speeds on the half furthest from equator as cylonic windspeed direction (anti-clockwise) same as TRS movement (Westwards). So front-right quarter in NH is the most dangerous zone.

Question 304

Seasonality of TRS

Answer 304

Driven by high ocean temperatures so occur when ITCZ is passing through an area.

Question 305

Examples of global TRS - frequencies and season

Answer 305

Typhoon: NW Pacific, most active region (16 a year) mostly at sea, mostly Jun-Nov (never Feb-Mar) Hurricane: N Atlantic (6) and NE Pacific (9) (i.e. USA), Jun to Nov Cyclones (NH): Indian Ocean (12) mainly autumn/spring Cyclones (SH): SW Pacific (Australia) (Willy-willy) (9), SH summer

Question 306

Forecasting TRS path

Answer 306

Cannot ACCURATELY forecast TRS path

Question 307

TRS sizes (degrees lat)

Answer 307

Small: 2-3 degrees lat Medium: 3-6 degrees lat Large: 6-8 degrees lat V Large: 8 degrees+

Question 308

Secondary Depression - description - where is it likely to form

Answer 308

Secondary area of low pressure nearby a "primary" low. Can eventually form another primary low or simply act as a disturbance in normal flow. Sometimes more active than the primary depression. Likely to form on the COLD FRONT.

Question 309

North American Tornados - size - time of day - cause - season

Answer 309

100m in diameter, between 1400 and 2200 (peak at 1700) in central USA. High level cold air from West rises over Rockies above warm moist unstable air from Gulf of Mexico. Localised reduction of pressure (20 to 200hPa) and high wind speeds in vortex (300kt) cause high level of damage. Spring & summer.

Question 310

West African Tornados

Answer 310

Line of thunderstorms moving from East to West between March and November. Associated with passage of ITCZ. Example of Easterly wave. NOT similar to NA tornados.

Question 311

Idealized Circulation

Answer 311

Consideration of weather and airflow patterns based on a simplified spherical earth entirely sea with only earths rotation to consider (no tilt). Get trade winds at equator and air cells along latitude (Hadley, Ferrel, Polar). Air cells produce anticyclone at subtropical level where hadley and ferrel meet.

Question 312

Trade winds - Description - Latitudes

Answer 312

Winds NEAR equator curve towards West (Easterly winds). So wind direction NE in NH and SE in SH. The main low level winds between sub-tropical high pressure belt and the equatorial low pressure region. Note: Primarily 10-20 degrees N or S

Question 313

Koeppens - Geiger Climate Zones - By degrees latitude

Answer 313

0-20: A) Tropical rain forest (wet), tropical monsoon (seasonal), tropical savannah (dry) 20-35: B) Sub-tropical and mid-latitude steppe and desert (dry) 40-70: C) Wide variety including Mediterranean, humid sub-tropical. Classified based on wet/dry and seasonality. 50-70: D) Sub-arctic climate (hot summer, cold winter) 70+: E) Snow climate (polar)

Question 314

Earth tilt and impact on savannah regions weather

Answer 314

23.5 degrees tilt The wet equatorial climate zone moves into the "summer" hemisphere, creating high rainfall in savannah regions in summer and dry trade winds in winter.

Question 315

Impact of land mass on idealised circulation weather

Answer 315

Minimal in SH as less land, but big effect in NH due to Asia & North America. In Winter the Rockies in NA and Himalayas in Asia block flow so gets very cold in NA and Northern Asia. No barrier below UK allows some warming from equator direction. Less contrast in summer, warm air from gulf of mexico and warming of large land masses makes NA & Asia warm, UK more static.

Question 316

Impact of land mass on idealised circulation weather - Diurnal variation

Answer 316

Larger land masses have bigger impact from heating of the sun so more diurnal variation. Diurnal difference peaks at 15C in middle of Africa, NA, some other areas in middle of continents. Over seas goes below 5C.

Question 317

Impact of land mass on idealised circulation weather - Freezing altitudes

Answer 317

Generally gets higher over landmasses due to heating of the land. Around 16000ft over equator, but up to 18000ft over parts of the land, so hail from thunderstorms melts before reaching land. Less variation further north.

Question 318

Global pressure spots - January

Answer 318

Equatorial low pressure zone to the south of geographic equator. Sub-tropical high's over oceanic areas either side of equator. Travelling low pressure systems at latitude 40 to 60 N are interrupted by high pressure over very cold large land masses (Siberia & USA).

Question 319

Global pressure spots July

Answer 319

Equatorial low pressure zone to the north of geographic equator. Sub-tropical highs below including Australia, and some ocean areas in NH. Over land in NH (e.g. Asia) warming of land creates lows instead of sub-tropical high. Sub-tropical high strong around Azores and pacific ocean.

Question 320

Main global surface winds (4)

Answer 320

Westerlies at temperate latitudes (40-60), especially strong in SH where land doesn't interfere. Trade winds (tropical easterlies) at equator. Monsoons, seasonal winds caused by cooling/heating of land masses in winter/summer. At poles strong Easterlies (although westerly in summer over N Atlantic & Pacific).

Question 321

Intertropical Convergence Zone (ITCZ) weather [time of day of relevance?]

Answer 321

Generally unstable conditions, extensive Cu, Cb and TS (especially at MIDDAY). In stable conditions instead get As and Ns and continuous rain. Severe turbulence and icing.

Question 322

Width of ITCZ

Answer 322

25nm to 300nm, no well defined frontal surface.

Question 323

El Nino

Answer 323

Normal pattern is cold water blown West from Peru to far east, warming as it goes. Every 3 to 7 years El Nino means the cold water goes deeper, so far east is colder and Pacific is warmer, disrupting weather patterns. El Nina is when Pacific is colder than normal.

Question 324

Monsoon definition

Answer 324

When trade winds blow towards continental lows, or from continental highs.

Question 325

3 Monsoons

Answer 325

NE monsoon in Asia from Siberian winter high, cold dry air over continental Asia, heavy rain & TS where it crosses ocean. NW monsoon is continuation of NE monsoon which backs as it crosses equator and heads to Australia. SW monsoon caused by SE tradewinds crossing equator and veering to SW, taking heavy rain over south Asia (big impact on aviation).

Question 326

West African Monsoon

Answer 326

This is the SW monsoon in summer when ITCZ is north of the equator. SE trade winds veer to SW over equator, very unstable and moist creating convection and heavy rain up to the ITCZ. After summer they get pushed south by ITCZ and replaced by harmattan, dry NE winds on other side of ITCZ.

Question 327

Easterly Wave - description - where is activity relative to the trough?

Answer 327

Trough of low pressure in NH only, originating in Africa from 5 to 20 deg lat, moving towards Caribbean (over Atlantic). Usually about 50 a year, similar to TRS but not as severe, can develop into TRS. Caused by disturbance in the low pressure line (parallel isobars) along ITCZ. Activity in REAR of trough.

Question 328

Westerly Wave

Answer 328

Interconnected warm front and cold front bands (associated with polar fronts) moving west to east creating a wave pattern.

Question 329

Chinook wind

Answer 329

Fohn wind over the Rockies to the east. From southern Colorado up to Mackenzie basin, can create a rise of 20C in 15 minutes. Blows for several days and can clear snow on the eastern side of rockies.

Question 330

Mistral wind

Answer 330

Valley wind through Rhone valley (between Masif central and alps). High pressure over central France, low pressure over Gulf of Genoa during winter. Temps well below zero, turbulent flying conditions and 40 to 75kts.

Question 331

Bora wind

Answer 331

Katabatic wind. Cold, dry NE wind down mountains from central Europe over adriatic (high pressure central Europe, low over adriatic). Strongest in winter (70kt, gusts up to 100kt)

Question 332

Mediterranean winds

Answer 332

Blow out of winter high pressure region over Sahara and Northern Africa. Hot & dusty southerly winds, usually spring time lasting about a day. Can reach southern Europe and pick up moisture (stratus, drizzle fog). Scirocco - Algeria Ghibli - Libya Khamsin - Egypt SGK - ALE [strong goat kick Ale]

Question 333

Pampero wind

Answer 333

Burst of cold polar wind from W/SW/S on the pampas in south Brazil/Argentina/Uraguay. Common in the southern hemisphere winter.

Question 334

Harmattan wind

Answer 334

Winter wind in line with trade winds (NE towards ITCZ) from Sahara over West Africa. Cool and dusty, reducing visibility below 1000m. Dust can get to 10,000ft or more.

Question 335

Doldroms

Answer 335

Occur where ITCZ coincides with the equator. Winds turned as the coriolis forces when crossing the equator, being heated from beneath, creating light and variable winds and lots of convective activity (Cb, TS).

Question 336

Horse latitudes

Answer 336

30 degrees N/S Slack winds, no rain, around subtropical highs

Question 337

Mesoscale convective system - description - size - shape

Answer 337

Thunderstorm regions found in ITCZ area. Mesoscale convective complex is a convective system with 100,000sq km cloud tops below -32C and 50,000sq km with temp below -52C. Eccentricity <0.7 so fairly round in shape. Long lived and form overnight.

Question 338

Cold Air Outbreaks in tropics (ITCZ)

Answer 338

Pampero in Argentina summer and Blizzards in North America. Cold air (from antarctic or canada) pushes into warm, moist air at ITCZ. Big temperature differential form a low pressure area, with strong storm winds and significant snowfall.

Question 339

NW Africa weather

Answer 339

Below 20 degrees N, get SW monsoon in summer and Harmattan in winter (NE trade winds). Above 20 degrees N get winter wet season (polar lows, wind from canaries) and NE trade winds in summer.

Question 340

NW Africa advection fog

Answer 340

In the area above ITCZ (changes from summer to winter) offshore winds towards Canaries can create advection fog, which can be blown back onto land by sea breeze.

Question 341

Equatorial double rains

Answer 341

Mostly in East Africa (Nairobi). ITCZ passing over the equator in Spring and Autumn. Especially North going rains in Spring, bring the "long rains" fed from Indian ocean. South going rains from dryer areas but still bring 25% of annual rain.

Question 342

North Atlantic weather - Winter

Answer 342

Cold air from NA high moves SE over sea and encounters warm gulfstream waters of NA east coast, creating the western end of the polar front. Azores High ensures the depressions move NE towards UK (from SW Florida to SW UK). Iceland statistical low caused by the trailing end of the depressions.

Question 343

London vs New York winter

Answer 343

London further North but where London gets dry cold air from Siberia, New York gets cold continental flow going out over warmer sea, becoming unstable, then bringing snow back over land.

Question 344

North Atlantic weather - Summer

Answer 344

Everything moves north, inc. Azores high and Iceland low. Temperature differences reduced so polar front, jet stream (etc) intensity reduced. Polar front between Labrador/Newfoundland and Scotland/Norway. Advection fog over cooler seas. Hurricans and Easterly waves closer to equator.

Question 345

NW Europe weather - Winter

Answer 345

Polar front depressions move from Atlantic to Russia, bounded between mountains of Norway and the alps. Get some E/NE dry winds from Siberian high, mostly Westerly winds though. Lots of cloud and precipitation.

Question 346

NW Europe weather - Summer

Answer 346

Polar front further north and less strong. Lots of local depressions due to insolation, which creates the dominant cloud being Cu/Cb type and heavy showery precipitation.

Question 347

Mediterranean weather

Answer 347

Hot summers, warm wet winters Much less than 700mm annual rain.

Question 348

Arabian weather

Answer 348

Winter: Siberian high can impact the area, crossing med to pick up moisture and create instability (Cu, Cb, TS) in North. Summer: Baluchistan low over rocky Baluchistan due to insolation, passing thermal equator so very hot

Question 349

Crachin

Answer 349

In Hong Kong from Jan to Apr as ITCZ moves far to south, air comes from the warm Kurosiwo sea over seasonally cool HK waters. This creates advection fog, low stratus drizzle and gloomy conditions in HK for this period.

Question 350

Singapore to Tokyo via Hong Kong weather

Answer 350

Summer: Typhoons, SW monsoon Winter: NE monsoon, Crachin Hong Kong Both monsoons convective TS type weather

Question 351

Australia weather

Answer 351

Winter (local): Polar front depressions over south, SE trade winds in north, subtropical jet stream above Summer: Tropical cyclones North side (W and E), convective activity in N due to ITCZ

Question 352

Nairobi region weather

Answer 352

ITCZ transits create long rains in spring and short rains in autumn.

Question 353

ICAO weather domains (altitude)

Answer 353

Low level: SFC to FL100 Medium level: FL100 to FL250 High level: FL250 to FL630

Question 354

Polar orbiting satellites

Answer 354

Inclined @ 99deg to Equator, take 1h42 to orbit earth at 820 to 870km height covering 1500nm wide band. Any point on globe experiences a southbound pass in morning, northbound in afternoon.

Question 355

Geostationary satellites

Answer 355

Stationary over equator at 36000km. Less clear definition towards poles can be corrected with computer processing.

Question 356

METAR

Answer 356

Meteorological Aerodrome Report Half hourly report of current weather conditions at an aerodrome

Question 357

Wind measurement basis: - Local reports - ATS units - METARs - SPECIs

Answer 357

Local & ATS: Average of last 2 mins METAR & SPECI: Average of last 10 mins

Question 358

METAR: "220V300"

Answer 358

Appears after wind information indicating variability of wind direction, if this is more than 60 degrees.

Question 359

METAR visibility - 2 special values

Answer 359

Four digits for metres of visibility. "9999" means over 10km "0000" means less than 50m

Question 360

METAR RVR - format - point measured at - value over what time

Answer 360

After visibility, state runway in use then RVR if either visibility or RVR are less than 1500m. eg "R30/1100" Note: Refers to RVR at touchdown point, not average of the 3 points. Note: Lowest value in last 10 mins

Question 361

METAR RVR - codes

Answer 361

"R30/P1500": RVR > 1500m (i.e. plus) "R30/M0050": RVR < 50m (i.e. minus) If RVR increases by 100m in last 10 mins add "U" at end, if decreases add "D", if no trend add "N" Can have two figures separated by "V" if significant variation in last 10 mins.

Question 362

METAR weather codes "+" "-" " " "VC"

Answer 362

"+": Heavy "-": Light " ": Moderate "VC": In the vicinity (within 8km)

Question 363

METAR weather codes "MI" "BC" "BL" "SH" "TS" "FZ" "PR" "DR"

Answer 363

"MI": Shallow (<2m above ground) "BC": Patches "BL": Blowing "SH": Showers "TS": Thunderstorms "FZ": Freezing (supercooled) "PR": Partial (covering of aerodrome) "DR": Drifting

Question 364

METAR precipitation codes "DZ" "RA" "SN" "IC" "PL" "GR" "GS" "UP" "PY"

Answer 364

"DZ": Drizzle "RA": Rain "SN": Snow "IC": Ice Crystals "PL": Ice pellets "GR": Hail "GS": Small hail (<5mm) "UP": Unknown precipitation "PY": Spray

Question 365

METAR obscuration codes "BR" "FG" "FU" "VA" "DU" "SA" "HZ"

Answer 365

"BR": Mist (vis 1000 to 5000m) "FG": Fog (vis <1000m) "FU": Smoke "VA": Volcanic Ash "DU": Dust "SA": Sand "HZ": Haze

Question 366

What is obscuration?

Answer 366

Something blocking vision that is NOT precipitation (e.g. haze, mist, sand)

Question 367

METAR other codes "PO" "SQ" "FC" "SS"

Answer 367

"PO": Dust/sand whirls "SQ": Squall "FC": Funnel cloud (tornado) "SS": Sandstorm/duststorm

Question 368

When is TS included in METAR?

Answer 368

Thunder heard in last 10 minutes

Question 369

Cloud types specified in METAR

Answer 369

Cb: Cumulonimbus TCu: Towering Cumulus

Question 370

CAVOK requirements

Answer 370

- Visibility >10km - Cloud base >MAX(5000ft, MSA) - No Cb or TCu - No significant weather in vicinity (e.g. RERA)

Question 371

METAR temperature - depiction - rounding

Answer 371

Temperature and dew point as 2 digits with "/" in between. If negative use "M". e.g. "10/M02" -> 10C, dewpoint -2C Temperatures rounded UP (+0.5 up to +1, -0.5 up to 0)

Question 372

METAR pressure information

Answer 372

QNH reported with "Q" followed by four digits, rounded DOWN. In USA inches of mercury reported with the letter "A" (e.g. 29.89 as A2989)

Question 373

METAR "RE"

Answer 373

"RE": Recent - in the last hour e.g. "RETS" thunderstorm in last hour

Question 374

METAR "WS"

Answer 374

"WS": Windshear Could specify a runway number or "ALL RWY"

Question 375

METAR "TREND" "BECMG" "TEMPO" "NOSIG"

Answer 375

"TREND": Valid for 2 hours FROM TIME OF OBSERVATION "BECMG": Changes becoming permanent "TEMPO": Less than one hour and less than half the time period "NOSIG": No changes expected in next 2 hours

Question 376

METAR runway state - Structure of code

Answer 376

Contaminated: "RXX/ABCCDD" "RXX": Runway no or 88 for all, or 99 message repetition "A": Type of deposit "B": Extent of contamination "CC": Depth of deposit "DD": Friction/braking coefficient

Question 377

METAR runway state - Type of deposit

Answer 377

0: Clear & dry 1: Damp 2: Wet 3: Rime/frost 4: Dry snow 5: Wet snow 6: Slush 7: Ice 8: Compacted/rolled snow 9: Frozen ruts/ridges /: Not reported (e.g. being cleared)

Question 378

METAR runway state - Extent of contamination

Answer 378

1: 10% or less 2: 11%-25% 5: 26%-50% 9: 51%-100% /: Not reported (e.g. being cleared)

Question 379

METAR runway state - Depth of deposit

Answer 379

00 to 90: mm of coverage 91: not used 92: 10cm 93...98: 5cm increments 99: Depth not reported, runway not operational //: Not significant or measurable

Question 380

METAR runway state - Friction/braking coefficient

Answer 380

28: 0.28 friction coefficient 35: 0.35 friction coefficient 91: Braking poor 92: Braking medium/poor 93: Braking medium 94: Braking medium/good 95: Braking good 99: Figures unreliable //: Not reported

Question 381

METAR "SNOCLO"

Answer 381

Closed due to contamination

Question 382

METAR "SPECI"

Answer 382

"An aviation selected special weather report" Special report due to significant change in conditions (improvement or deterioration) "SA" at beginning indicates METAR, "SP" indicates SPECI (not always there) Will include all parameters updated to time of the SPECI, not just the change.

Question 383

METAR & SPECI vs Met Report & Special

Answer 383

In both cases SPECI/special means an updated version due to changing conditions. METAR/SPECI is for "general public", i.e. wider audience over VOLMET (for example) Met Report/Special is for "local public", i.e. ATIS for people at the aerodrome

Question 384

TAF "NSC"

Answer 384

No significant cloud Means no cloud below 5000ft or sector altitude, no Cb or TCu, but CAVOK not appropriate.

Question 385

TAF "TX" "TN" "AMD"

Answer 385

"TX": Maximum temperature "TN": Minimum temperature "AMD": Amendment

Question 386

Answer 386

Question 387

Answer 387

Question 388

Answer 388

Question 389

Answer 389

Question 390

- FRQ - OCNL - ISOL Which one is "well separated"?

Answer 390

FRQ: Frequent, spatial coverage greater than 75% of area OCNL: Occasional - WELL SEPARATED, maximum spatial coverage of 50 to 75% ISOL: Isolated, less than 50% of area

Question 391

Form 215/415 abbreviations: BLW BTN CIT CLD COR COT LAN LCA LSQ

Answer 391

BLW: Below BTN: Between CIT: Near or over large towns CLD: Cloud COR: Correction COT: At the coast LAN: Over land LCA: Locally LSQ: Line squall

Question 392

Form 215/415 abbreviations: LV SEV SFC VAL VRB VSP WRNG WS WSPD

Answer 392

LV: Light & Variable SEV: Severe SFC: Surface VAL: Valleys VRB: Variable VSP: Vertical speed WRNG: Warning WS: Windshear WSPD: Wind speed

Question 393

Reasons for SIGMET

Answer 393

TS/TSGR (only OBSC, EMBD, FRQ or SQL) Heavy hail Tropical cyclone Freezing rain Severe turbulence Severe icing Severe mountain waves Heavy sand/dust storm Volcanic ash cloud

Question 394

AIRMET

Answer 394

Lower level weather warnings (usually FL100, could by FL150+ in mountainous regions)

Question 395

Reasons for AIRMET

Answer 395

SFC wind > 30kt SFC VIS < 5000m TS/TSGR (incl. ISOL, OCNL) Mountain obscuration (MT OBSC) Moderate Icing, turb or MTW BKN/OVC cloud <1000ft Cb or TCu (ISOL, OCNL or FRQ)

Question 396

First 4 letters of SIGMET represent

Answer 396

Name of the air traffic services controlling unit

Question 397

SIGMET abbreviations NC OTLK STNR TC VA WKN

Answer 397

NC - No Change OTLK - Outlook STNR - Stationary TC - Tropical Cyclone VA - Volcanic Ash WKN - Weakening

Question 398

Which agency prepares SIGMET and AIRMETs?

Answer 398

Meteorological WATCH office

Question 399

AIRMET & SIGMET validity time

Answer 399

4 hours

Question 400

Frequency for VOLMET

Answer 400

Locally on VHF Globally on HF

Question 401

VOLMET code

Answer 401

Uses plain language

Question 402

VOLMET update frequency

Answer 402

30 minutes

Question 403

VOLMET content - 3 standard - 2 potential

Answer 403

METARs, SPECIs & TRENDs Potentially also TAFs and SIGMETs

Question 404

ACARS

Answer 404

Ground air link with weather information, to pass general warnings, SIGMETs, ATIS for destination

Question 405

When are ATIS broadcasts updated?

Answer 405

When aerodrome or weather info changes, or 30 minutes

Question 406

Where else are ATIS messages broadcast other than a VHF channel?

Answer 406

VOR and potentially through ACARS

Question 407

In-flight weather briefings (2)

Answer 407

Can arrange pre-flight a special in-flight enroute weather service with relevant Meteorological Authority. Also get a diversion briefing from ATC unit if required to divert into area you don't have weather info for, will include SIGMET and AIRMET warnings.

Question 408

AIREP

Answer 408

Report from pilot on weather (PIREP in USA). Can be handed in at end of flight as written report. AIREP SPECIAL (or ARS) reported immediately in case of: Mod/Sev turb or icing Sev MTW TS (OBSC, EMBD, WDSPR or SQL) Heavy dust/sand storm Volcanic ash

Question 409

Sections of a special AIRREP

Answer 409

1) Aircraft identification, position, time, level 2) n/a 3) Meteorological info

Question 410

AMDAR

Answer 410

Aircraft Meteorological Data Relay System that automatically transmits weather data from aircraft to WAFCs

Question 411

GAMET

Answer 411

Plain language general aviation forecast for low level flights in an area.

Question 412

Timing of MSL pressure charts

Answer 412

Data taken every 6 hours from midnight. MSL charts published 4 hours later. 24 hour forecast charts published 5 hours after the observation (e.g. 5am for midnight data), covering the next 24 hours.

Question 413

Weather chart symbols - Fronts at surface and above surface - Quasi-stationary fronts - Convergence line - Trough axis - Ridge axis

Answer 413

Question 414

Significant weather chart timing

Answer 414

Prepared 24 hours in advance of a time period 3 hours each side of the synoptic times (0000, 0600, 1200, 1800).

Question 415

Upper wind and temperature charts - How is temperature information displayed?

Answer 415

Number next to the wind symbol is temperature, assumed negative (has "+" or "PS" preceding if positive).

Question 416

Interpreting airborne weather radar

Answer 416

Large areas of red might not be an issue, just warm moist areas of rain. Having the different colours close together however indicates sharp updrafts at the edge of a cell, more risk of turbulence. Round shapes less concerning than fingers, hooks, U-shapes and scalloped edges.

Question 417

Use of satellite imagery

Answer 417

To locate frontal systems, not areas of precipitation (radar better for this).

Question 418

Gridded forecast

Answer 418

Produced by the World Area Forecast Centres (WAFC) [Washington/Kansas & London/Exeter] using Numerical Weather Prediction (NWP) models. Produce 3d gridded forecasts including temp, humidity, wind, tropopause height, Cb, turb & icing - NOT jet streams.

Question 419

Low Drifting Sand/snow/dust definition

Answer 419

Below 6ft/2m (visibility above eye level not affected) AKA "Shallow", "MI" in code (eg MIFG)

Question 420

Sand diameter and wind speed required to impact visibility

Answer 420

0.08 to 0.3mm 20kt

Question 421

Virga - description - what does it indicate?

Answer 421

Rain which evaporates before reaching ground. Typical of microbursts under TS. INDICATION OF WINDSHEAR

Question 422

White areas on IR satellite image

Answer 422

High cloud is bright white, lower cloud is darker, warm land is very dark. If IR is bright white and visual image is not "whispy" that means cloud tops are high and not cirrus, so possibly TCU/Cb.

Question 423

Cloud to cloud vs intra cloud lightning

Answer 423

Cloud to cloud is between 2 different clouds, intra-cloud is inside a single cloud

Question 424

Frequency of windshear alert updates

Answer 424

Every minute until they drop below 15kt

Question 425

Pressure level variation flying across mountain ridge in strong winds

Answer 425

Question 426

World Area Forecast Centre responsibilities

Answer 426

Significant weather forecasts Upper air forecasts

Question 427

Sublimation Deposition

Answer 427

Sublimation: Solid to gas Deposition: Gas to solid

Question 428

0 degree altitude (isotherm) altitude - polar regions - temperature regions - tropics

Answer 428

Polar: Ground Temperate: Ground in winter 10,000ft in summer Tropics: 15,000ft in winter 17,000ft in summer

Question 429

Stormscope

Answer 429

Device that identifies thunderstorms via electrical discharges (useful for embedded Cb)

Question 430

Purpose of merging gridded forecasts with pilot reports

Answer 430

Improve situational awareness

Question 431

Increase or decrease airspeed in turbulence

Answer 431

DECREASE - to avoid damage to airframe But be careful of stall risk!

Question 432

How does aircraft initiate lightning

Answer 432

Builds up charge by flying through electrically charged air, can initiate a lightning discharge itself.

Question 433

What maintains the global potential (electricity) difference between ionosphere and ground?

Answer 433

Thunderstorms around the globe

Question 434

St Elmos fire

Answer 434

Static discharge, doesn't affect instruments or anything else, occurs on sharp edges (wipers, pitot tube)

Question 435

Which cloud type has a halo?

Answer 435

Cs

Question 436

Geographical location of fastest jet stream

Answer 436

Japan

Question 437

How to get out of rain ice?

Answer 437

Do a 180

Question 438

What percentage of all gas and all water is in the troposhere?

Answer 438

75% of gas 90% of water

Question 439

Bays Ballots Law

Answer 439

In NH, low on the left (when going with the wind)

Question 440

Vertical visibility - steps and limit in metres & feet

Answer 440

100ft steps to 2000ft 30m steps to 600m

Question 441

Where does doppler radar measure turbulence?

Answer 441

Thunderstorms, picks up precipitation.