Meteorology Flashcards
(464 cards)
1
Q
What climate zone is the UK situated in?
A
Temperate
2
Q
Characteristics of a temperate zone
A
Hot and warm summers, drier than other seasons
3
Q
Where does the atmosphere extend further into space?
A
Around the equator
4
Q
Two reasons for atmosphere being more extended at equator than poles?
A
Earth’s rotation
Greater heating at equator
5
Q
Thickness of atmosphere is proportional to
A
Temperature
6
Q
In ISA, what atltitude is the tropopause at?
A
30,000ft
7
Q
Aircraft fly mostly in what atmosphere subdivision?
A
Troposphere
8
Q
What lies between the Earth’s surface and the stratosphere?
A
Troposphere
9
Q
The trophosphere’s relation to temperature?
A
Proportional
10
Q
Temperature in the stratosphere is..?
A
Constant
10
Q
Troposphere’s characteristics at the poles?
A
Colder and shallower
11
Q
Approx. what temp is the stratosphere?
A
-57 degrees Celsius
12
Q
What substance in the air is critical for life on earth?
A
Water Vapour
13
Q
In ISA, temp decreases at what rate?
A
2 degrees celcius per 1000ft gained
14
Q
Name of lines on pressure maps connecting areas of similar pressure
A
Isobars
15
Q
Variation of pressure with horizontal distance is called…
A
Pressure gradient
16
Q
Impact on aircraft performance on humid damp days is due to
A
Higher proportion of water molecules in air reduces overall air density
17
Q
Regular pressure variations owing to daily heating and cooling effects of the sun is called
A
Semi-diurnal variation of pressure
18
Q
What kind of barometer is used in aircraft altimeters?
A
Aneroid
19
Q
Altimeter reading 0ft at sea level would read what altitude if the pressure drops 10hPa?
A
300ft
20
Q
Sun’s radiation strikes polar regions at what kind of angle?
A
Oblique
21
Q
Transfer of heat energy from one body to another is called..
A
Diabatic process
22
Q
When heat is neither added or removed from a system, it is called..
A
Adiabatic process
23
Q
Expansion and compression of gases experience what kind of heat process?
A
Adiabatic process
24
Relationship between temperature and radiation wavelength
The higher the temperature of the body, the shorter the wavelength of the radiation
25
Convection describes
Process by which warm air rises into the atmosphere and carries its heat energy with it
26
Why does warm air rise?
It is less dense than the surrounding air
27
Advection follows what other diabatic process?
Convection
28
Advection describes
Horizontal motion of air replacing air that has risen due to convection
29
What has a higher heat capacity? Water or land
Water
30
Because water has a higher heat capacity than land, land does what?
Heat and cool more quickly than water bodies
31
ELR stands for
Environmental Relapse Rate
32
What describes the process of temperature change from altitude increase in the real world?
ELR
33
What is the DALR?
Dry Adiabatic Lapse Rate
34
DALR equates to
3 degrees celcius reduction for each 1000ft climbed
35
If water vapour condenses in a discrete parcel of air, what will happen?
The parcel of air will cool at a lower rate
36
What is the SALR?
Saturated Adiabatic Lapse Rate
37
SALR occurs when?
Parcel of air cools at a lower rate than DALR due to water vapour condensing and latent energy being released
38
Stable atmosphere occurs when...
ELR is less than SALR and DALR
39
Stable atmosphere means air has what tendency?
To return back to its origianl position if displaced
40
Stable atmosphere's typical weather
Clear skies, fog, stratus
41
Unstable atmosphere occurs when
ELR is greater than SALR and DALR
42
Unstable atmosphere means air has what tendency?
Rise if displaced
43
Unstable atmosphere's typical weather
Cumulus and cumulonimbus cloud
44
Conditional instability occurs when
ELR is less than DALR but greater than SALR
45
Conditional instability means
Dry, unsaturated air is stable. Moist, saturated air is unstable
46
In what conditions do temperature inversions occur?
Low wind and clear nights
47
At night, cooling air not mixing with higher altitude warmer air results in...
Temperature inversion
48
Approximately what degrees is the Earth tilted at from the vertical?
23 degrees
49
Why does warm tropic air move towards higher latitudes?
The air cannot rise higher due to stratospheric isotherm
50
What generally happens to cool air over the poles?
It sinks
51
General circulation consists of how many main cells?
3
52
What is the equatorial trough?
A band of low pressure at the earth's surface in the tropics
53
What is the process by which surface air will move towards an area of low pressure?
Convergence
54
What is the process by which surface air will move outwards from an area of high pressure?
Divergence
55
What temp is absolute zero?
-273 degrees celsius
56
The transfer of heat by the horizontal motion of an air mass is called?
Advection
57
The transfer of heat by the vertical motion of an air mass is called?
Convection
58
What is wind?
Horizontal flow of air across the Earth
59
Wind Velocity is the combination of what?
Wind direction and wind strength
60
A wind changing in a clockwise direction is doing what?
Veering
61
A wind changing in an anti-clockwise direction is doing what?
Backing
62
Wind caused by rotation of the Earth is called
Coriolis force
63
Geostrophic wind results from what...
Balance between coriolis force and pressure gradient force
64
Increasing latitude does what to the relative motion of earth
Reduces the easterly motion of the earth
65
The Earth's rotation has what effect on the relationship between the Earth and a parcel of air
It will lag behind the easterly motion of the parcel of air
66
Observer's experience of the coriolis force
Wind is deflected to the right
67
Coriolis effect increases with
Airflow
68
Coriolis effect cannot occur without
Airflow
69
Why is the Coriolis effect greater away from the equator?
Changes in latitude cause more significant changes in the difference of easterly movement
70
In the northern hemisphere, the Coriolis effect deflects the wind to the..
Right
71
Leftward deflection of wind by Coriolis effect occurs where?
Southern hemisphere
72
Geostrophic wind's relationship to isobars
It flows parallel to the isobars
73
Best sentence to describe the formation of geostrophic wind
The pressure gradient force gets the air moving and the Coriolis effect turns it to the right
74
Geostrophic wind parallel to isobars has the low pressure on what side?
Left
75
Buys Ballot's Law is...
Standing with your back to the wind in the northern hemisphere, the low pressure will be on your left
76
Flying from high to low pressure (in Northern Hemisphere) is indicated by what?
Right starboard drift, as the wind is from the left
77
Right starboard drift (in Northern Hemisphere) indicates what?
Flying from high to low pressure
78
Flying from low to high pressure (in Northern Hemisphere) is indicated by what?
Left drift
79
Left drift (In Northern Hemisphere) indicates what?
Flying from low to high pressure
80
In the NH, wind flows in what direction round a high?
Clockwise
81
In the NH, wind flows in what direction round a low?
Anti-clockwise
82
In the NH, wind flowing clockwise indicates a what?
High pressure
83
In the NH, wind flowing anti-clockwise indicates a what?
Low pressure
84
Wind blowing around a low experiences what process?
Pressure gradient force is greater than the Coriolis force
85
Wind blowing around a high experiences what process?
Coriolis force is greater than the pressure gradient force
86
Surface wind is usually measured at what height
30 ft
87
Why is wind usually less strong at the surface compared to higher levels?
Earth's surface exerts friction
88
Friction causes surface wind to what?
Weaken in strength and back in direction
89
In general, the more unstable atmospheric stability is results in what effect to surface wind
It backs less and is more similar to the 2000ft wind
90
Why is windspeed greater around a high compared to an equally-spaced-isobar low?
Coriolis force increases with wind speed
91
Diurnal can be thought of as another word for..?
Daily
92
Roughly speaking, what altitude does the top of the boundary layer occur? (And frictional/thermodynamic effects become negligible)
2000 to 3000 feet
93
What part of the day does mixing of wind layers reduce?
Night
94
What happens to wind at night?
Slacks and backs
95
Why does sea breeze occur on sunny days?
Land heats more quickly than the sea
96
Light winds + convection near water =
Sea breeze
97
Vertical extent of a sea breeze is usually what?
1000 to 2000 feet
98
Why does sea breeze cause visibility problems?
It may bring cool, moist air over land
99
When does sea breeze occur?
Day
100
When does land breeze occur?
Night
101
Basics of a land breeze?
Land cools quicker than the sea, cooler land air replaces rising warm sea air
102
What kind of heat transfer causes air to cool during clear, cloudless nights?
Conduction (due to ground becoming cool because of terrestrial radiation)
103
In what land type does katabatic wind occur?
Mountainous
104
What causes katabatic wind?
At night, cool air flows down mountain slopes creating wind blowing into valleys
105
What two kinds of wind occur exclusively in mountains/hills?
Katabatic and Anabatic
106
What causes anabatic wind?
Warm air rises up a mountain slope
107
Why is anabatic wind weaker than katabatic wind?
Air flowing upwards is opposed by gravity
108
Cumulonimbus clouds's up/downdraughts can extend how far into clear air around them?
20nm
109
High pressure systems do what to temp inversions?
Detach them from the surface
110
What cloud formation occurs in the lower lee side of a mountain during mountain wave?
Rotor cloud
111
In the tropics, pressure gradients are usually...
Weak
112
Why is the Coriolis force very weak in the tropics?
The distance of isobars from the earth's axis remains constant
113
What wind system dominates in the tropics?
Pressure gradient force
114
What are used instead of isobars in the tropic systems?
Streamlines and isotachs
115
What do streamlines indicate?
Wind direction
116
What do isotachs indicate?
Areas of equal wind strength
117
Outdraughts in a tropic area come from where?
High pressure areas
118
Indraughts in a tropic area come from where?
Low pressure areas
119
What do vertical gusts do to an aircraft's performance?
Increase its angle of atttack
120
During turbulence, why is it good practice to hold the attitude, not the altitude?
Avoid using the elevator excessively to not over-stress the airframe
120
121
Mountain wave occurs during what system?
High pressure
122
ATC wind reports are relative to..?
Magentic north at the airfield
123
Metereological reports on wind direction use what relative indication?
True North
124
A parcel of air moving in line with the pressure gradient force will experience Coriolis acting at what angle to its motion?
Perpendicular
125
Wind that flows around curved isobars is called the..?
Gradient wind
126
In the northern hemisphere, the mean surface wind direction compared to the gradient wind direction will...
Back
127
In what pressure system is vertical motion more upward?
Low pressure because the atmosphere is unstable
128
Lenticular cloud is a good indication of..?
Mountain wave and severe turbulence
129
What are the four forms of cloud?
Cirriform
Cumuliform
Stratiform
Nimbus
130
High-level cloud has what minimum base?
20,000 feet
131
Why does high-level cloud look fine and spideery?
Usually formed in coldest region of troposphere asice crystals rather than water particles
132
Description of cirriform
Fibrous
133
Description of cumuliform
Heaped
134
Description of stratiform
Layered
135
Description of nimbus
Rain-bearing
136
Clouds: cirru/cirro denotes what kind of cloud?
High-level
137
Stratus means what?
Layer
138
Cirrus means what?
High
139
Middle-level cloud occurs in what altitude range?
6,500ft to 20,000ft AMSL
140
What is virga?
Rain that does not reach the ground
141
Virga occurs in what kind of air?
Dry or warm air
142
Why does virga not reach the ground?
It evaporates or sublimes first
143
Alto- denotes what?
Middle-level cloud
144
Clouds: fractus denotes what?
Stratus or cumulus shreds below nimbo/alto-stratus
145
Clouds: castellanus is what?
Cumuliform clouds that are turret-shaped
146
Castellanus indicates what?
Unstable atmosphere
147
When water changes state, its transferred heat energy is known as..
Latent Heat
148
What does humidity measure?
The amount of water vapour present in the air
149
A saturated parcel of air means it has __% humidity?
100%
150
Relative Humidity Equation
RH = Vapour Pressure/Saturation Vapour Pressure
151
What factor determines how much water a particular parcel of air can support, regarding humidity?
Air temperature
152
Air temperature is proportional to how much water that air can support?
True
153
Relation between air temperature and saturation
The higher the air temperature, the more water it can support
154
How much water a parcel of air can support is formally known as?
Saturation Vapour Pressure
155
What is the Humidity Mixing Ratio?
Ratio of the mass of watter vapour in a parcel of air to the mass of dry air in the same parcel
156
What happens to the relative humidity of a rising unsaturated parcel of air?
It increases because temperature decreases and cooler air cannot hold as much water vapour
157
Why does rising unsaturated air increase in relative humidity?
Cooler air cannot hold as much water vapour
158
What remains constant in a rising parcel of unsaturated air?
Humidity Mixing Ratio
159
What is the dewpoint?
Temperature at which a parcel of air becomes saturated if it cools
160
What happens to a dewpoint related to moisture?
The moisture in the air, the higher its dewpoint temperature
161
What happens if a parcel of air is cooler than its dewpoint?
Excess wateer vapour will condense as water droplets
162
Two adiabatic ways in which cloud is formed
Mass uplift
Convection
163
Two diabatic ways in which cloud is formed
Advection
Radiation
164
What is the DALR?
3 degrees per 1000ft
165
Why is cooling not as great for saturated air as it continues to rise?
Latent heat is released due to condensation, so cooling is not as great
166
What is the SALR?
Saturated Adiabatic Lapse Rate
167
SALR's relation to DALR?
Approximately half
168
Approximately, what rate is SALR?
1.5 degrees per 1000ft
169
What primary factor determines the type of cloud formed?
Stability of the atmosphere
170
What are the three kinds of atmopsheric stability when it comes to ELR/DALR/SALR and cloud formation?
Unstable, neutral and stable
171
ELR stuff: when does unstable air occur?
ELR is greater than DALR or SALR
172
ELR stuff: when does stable air occur?
ELR is less than DALR or SALR
173
ELR stuff: when does neutral air occur?
ELR is equal to DALR or SALR
174
In unstable air, clouds and air do what?
Continue to move verticaally after displacement
175
What clouds are typically formed in unstable air?
Cumuliform
176
What clouds are typically formed in neutral air?
Stratiform clouds
177
In neutral air, what happens to the air?
Remains in the position to which it was vertically displaced
178
In stable air, what happens to the air?
Returns to the position from which it was displaced
179
What clouds are typically formed in stable air?
Stratiform clouds or fog
180
When a parcel of air cools to the same temperature of its surrounding environment, it does what?
Stops rising
181
Air flowing over mountains cools and rises in what way?
Adiabatically
182
Why does cloud formed over mountains cease to exist as it descends on the lee side?
Temperature exceeds dewpoints and therefore water vapour vapourises
183
A cloud that forms as a 'cap' over the top of a mountain is known as what..?
Lenticular
184
What factors determine the level at which a cloud bases forms?
Humidity and dewpoint temperature
185
Unstable air over a mountain could yield what cloud?
Cumuliform
186
Stable air over a mountain could yield what cloud?
Lenticularis, stratus or stratocumulus
187
A warmer, drier wind on the lee side of a mountain describes what effect?
Foehn
188
Describe the foehn effect
Cloud forms on windward side of mountain
Air now drier and dewpoint temp less, cloudbase higher on leeward side
Drier and warmer wind on leeward side
189
Why does foehn effect result in drier, warmer air
Dry leeward air descends at DALR, which is a greater rate than the SALR-air on windward side
190
Two large masses of differing temp air meet, what undercuts the other?
The warmer air will be undercut by the cooler air
191
What is the name given to the boundary layer between two air masses?
Front
192
What cloud usually precipitates in a gradual way over a long period?
Stratiform
193
Showers only fall from what clouds
Convective cumuliform clouds
194
Drizzle is usually associated with what kinds of cloud?
Thick, overcast stratus cloud
195
In order of coverage, what are the cloud abbreviations used in METAR and TAF?
SKC, FEW, SCT, BKN, OVC
196
What kind of air has more potential to carry more water before saturation?
Warmer
197
A parcel of air has warmed in contact with the earth's surface. What happens?
It will rise and cool adiabatically
198
Orographic uplift of unstable air is likely to cause what cloud?
Cumuliform
199
Orographic uplift of stable air is likely to cause what cloud?
Stratiform
200
What is the name of visibility between a pilot and the ground?
Slant visibility
201
What makes visibility reduce?
Particles suspended in the air
202
Haze produced by sea salt has what appearance?
Whitish
203
Salt particles from sea spray can attract water vapour (and reduce visibility) at humidity as low as...?
70%
204
Why does flying towards the moon give greater visibility?
Silhouettes of objects can be seen better
205
What does a temp inversion do to convection?
It stops vertical convection currents because of the layer of warmer air above
206
Inversions usually occur during what weather systems?
High pressure
207
Why does smog occur during a temp inversion?
Particles cannot mix throughout the atmosphere so they form a smog
208
Minimum humidity for mist/fog
95%
209
Visibility below 1km is...?
Fog
210
Poor visibility above 1km is called?
Mist
211
What conditions make the formation of radiation fog likely?
Cloudless night
Moist air
Light winds
212
Why are cloudless nights conducive for fog buildup?
Allows surface to cool which cools the air near it
213
Why do light winds help the formation of fog?
Resupply of moisture from the atmosphere to condense on the ground
214
Does the proportion of oxygen reduce with altitude?
No, pressure does
215
What is terrestrial radiation?
Long wave radiation emitted by earth that heats the atmosphere?
216
What usually heats the atmosphere?
Terrestrial radiation
217
Density equation
Mass/Volume
218
What is a trough?
Area of low pressure
219
Weather associated with a trough?
Increasing cloud and risk of precipiation
220
What is a col?
Area of widely spaced isobars between two highs and two lows
221
Weather associated with the col?
Light winds
222
When do altimeters over-read?
As the aircraft moves into lower pressure
223
Why do altimeters over-read in lower temperatures?
Density increases
224
Snow generally comes from what clouds?
Cumuliform
225
Most common type of adiabatic change?
Rising air expanding and cooling/sinking air condensing and warming
226
Why is SALR less than DALR?
Condensation releases latent heat energy which reduces the rate
227
What is the ELR like in stable conditions?
Less than 1.5 degrees per 1000ft
228
What is the ELR like in unstable conditions?
Greater than 3 degrres per 1000ft
229
If the ELR is between 1.5°C and 3°C the stability of the atmosphere will depend on...?
The moisture of the air
230
If the air is wet the atmosphere is unstable, whereas if it is dry it is stable. This is known as
Conditional Stability
231
Conditional Stability can be described as what?
Determining the stability of the air by the moisture of the air
232
Air Mass: Arctic Maritime
Wet cold air bringing snow in winter
233
Air Mass: wet cold air bringing snow in winter
Arctic Maritime
234
Air Mass: Polar Continental
Cold, dry, giving clear skies and frost in
winter and cool weather in summer
235
Air Mass: Cold, dry, giving clear skies and frost in
winter and cool weather in summer
Polar continental
236
Air Mass: Polar Maritime
Cold, wet, unstable air giving showers
and thunderstorms
237
Air Mass: Cold, wet, unstable air giving showers
and thunderstorms
Polar Maritime
238
Air Mass: Tropical Continental
Warm, dry air giving hazy and sometimes
dusty days, can be the source of the most
severe thunderstorms over the UK.
239
Air Mass: Warm, dry air giving hazy and sometimes
dusty days, can be the source of the most
severe thunderstorms over the UK.
Tropical Continental
240
Air Mass: Tropical Maritime
Warm, moist, stable air giving stratus,
sea fog and drizzle. This normally clears
inland in the summer.
241
Air Mass: Warm, moist, stable air giving stratus,
sea fog and drizzle. This normally clears
inland in the summer.
Tropical Maritime
242
Warm front: Cloud base
Gradually lowers, 600nm ahead of front at surface
243
Warm front: pressure
Pressure decreases and is stable once front has passed
244
Warm front: temperature
Temp and dewpoint rise
245
Warm front: wind
Veers
246
Warm front: aftermath
Low stratus and drizzle
247
Cold front: speed
Cool air moves more quickly than warmer air ahead
248
Cold front: stability
Rising warm air causes instability
249
Cold front: relation to warm front
Undercuts warm front
250
Cold front: clouds
Cumuliform clouds
251
Cold front: wind
Veers
252
Cold front: temperature
Temp and dewpoint decrease
253
Cold front: pressure
Falls then rises rapidly after front has passed
254
Global circulation results in what characteristics at the equator?
Hot rising air
255
Global circulation results in what characteristics at the poles?
Cold descending air
256
Occluded front: wind
Veers sharply
257
Occluded front: pressure
Drops rapidly then rises rapidly after front has passed
258
A cold occlusion results in what?
Cold front conditions at the surface
259
A warm occlusion results in what?
Warm front conditions at the surface
260
Danger of occluded front
Embedded CB in ST
261
3 conditions required for thunderstorms
Instability, high humidity and trigger action
262
What kind of instability causes thunderstorms?
ELR greater than 4 degrees per 1000ft
263
Three stages of a thunderstorm
Cumulus
Mature
Dissipating
264
Thunderstorms: cumulus stage
Strong updrafts
Rapid vertical growth
265
Thunderstorms: Strong updrafts, rapid vertical growth
Cumulus stage
266
Thunderstorms: mature stage
Updrafts
Severe downdraughts create microbursts, gusts and roll cloud.
267
Thunderstorms: Updrafts
Severe downdraughts create microbursts, gusts and roll cloud.
Mature stage
268
Thunderstorms: dissipating stage
Downdraughts
Precipitation
269
Thunderstorms: downdraughts, precipitation
Dissipating stage
270
How are Mountain Waves denoted in met reporting?
MTW
271
Is the relationship between altitude and pressure linear?
No
272
Moist air is usually associated with what system?
Low pressure system
273
Why does moist air weigh less than dry air?
Water vapour weighs less than dry air
274
Why is moist air related to low pressure systems?
Moist air exerts less pressure on the Earth's surface than dry air
275
What is the main source of heat energy in the atmosphere?
Radiation
276
What is insolation?
Earth's surface being heated by the sun
277
Typical vertical movement in low pressure?
Upwards
278
Typical vertical movement in high pressure?
Downwards
279
Drawback to the 'better weather' advantage in high pressure systems?
Lower visibility
280
How is an air mass classified?
Temperature then humidity
281
What causes areas of high and low pressure?
Uneven surface heating (mainly)
282
Why may wind direction and runway headings not match up?
Runways use magnetic, wind uses true north
283
ATC-issued wind direction is given in what format?
Magnetic heading
284
Effect of altitude on wind direction means the bearing of the wind does what?
Reduces the closer to the surface it gets
285
Effect of altitude on wind direction: bearing of the wind reduces because of..?
Coriolis effect reducing
286
Why is there less difference between surface wind and aloft during the day?
More mixing
Coriolis force is stronger so surface wind more aligned with aloft
287
If the surface wind is stronger, what does this do to its relationship with the coriolis effect?
It makes the Coriolis effect stronger (so backs less and veers more)
288
What causes mixing of surface air and aloft winds during the day?
Convection currents
289
Reason for little or no turbulence during the night near the surface?
Smooth deceleration of air between winds aloft and surface wind
290
What is Boyles Law?
At constant temp, volume of gas is inversely proportional to pressure
291
What is Charles Law (gas)
At constant pressure, volume of a gas is directly proportional to its temperature
292
What element/factor of the atmosphere is most significant for aircraft performance?
Air density
293
What is QNE?
Height of an aerodrome threshold at 1013.2hPa
294
What is the name of an air mass that is descending?
Subsidence
295
How does a subsidence cause a temperature inversion?
Descending air warms up and acts as a lid on pollutants beneath it
296
What causes more significant altimetry errors? Temp change or pressure change?
Pressure
297
Why would a moist parcel of air rise?
Water vapour less dense than dry air, it is therefore lighter and so will rise
298
Why are SALR and DALR always the same?
Composition of gases in dry and moist air remains constant
299
If the ELR is above 3 degrees per 1000 ft (DALR), what occurs?
Absolute Instability
300
If ELR results in Absolute Instability, what happens?
Air cools at a lesser rate than surrounding atmosphere
Parcel rises in temperature relative to surrounding air
Due to warmth, its vertical motion accelerates
301
If ELR results in Absolute Stability, what happens?
Parcel of air's temperature cools relative to surrounding air, so sinks again and returns to original place
302
What does pressure do to relative humidity?
High pressure means less water vapour can be accomodated
303
In METAR/TAF temperature readings, what rounding is used?
x.0 - x.4
304
In terms of stable and unstable atmosphere, we can think of what two kinds of respective clouds?
Layered and heaped
305
Why are layered clouds associated with stable atmosphere?
Large scale ascent of air
306
Why are heaped clouds associated with unstable atmosphere?
Localised vertical lifting
307
What cloud produces a halo?
Cirrostratus
308
What are the white streaks on altocumulus?
Virga
309
Rule of Thumb for calculating cloud base formation?
(Temp - Dewpoint) x 400
310
Why do stratiform clouds produce light precipitation?
They have weak vertical currents and little extent
311
Why do cumuliform clouds produce heavier precipitation?
They have large vertical currents due to their larger extent
312
Metar code: SG
Snow Grains
313
Metar Code: Snow Grains
SG
314
Metar Code: GR
Hail
315
Metar Code: Hail
GR
316
Metar Code: PL
Pellets
317
Metar Code: Pellets
PL
318
Metar Code: IC
Diamond Dust
319
Metar Code: Diamond Dust
IC
320
Metar Code: SQ
Squalls
321
Metar Code: Squalls
SQ
322
Metar Code: NIL
No precipitation
323
Metar Code: No Precipitation
NIL
324
Metar Code: MON
Mountainous Regions
325
Metar Code: Mountainous Regions
MON
326
Metar Code: Over Land Regions
LAN
327
Metar Code: LAN
Over Land Regions
328
Metar Code: Over Coastal Regions
COT
329
Metar Code: COT
Over Coastal Regions
330
How is sleet indicated in UK METARS etc?
RASN
331
What does RASN indicate in the UK?
Sleet
332
What is the minimum cloud thickness for rain to occur?
4000ft
333
Why does more light (rising sun) make mist worse for visibility?
More light becomes reflected
334
When is radiation fog most likely?
At dawn when the ground temp is lowest
335
Radiation fog: if the wind is too light (less than 2kt), what happens?
Dew forms instead
336
Radiation fog: if the wind is too strong (>10kt)m what happens?
Low cloud forms instead
337
Radiation fog: the wind speed is directly proportional to...?
Cloud base
338
Radiation fog: rule of thumb for wind speed and cloud base
8kts = 800ft, 10kts = 1000ft etc
339
Why is radiation fog more likely to occur in autumn?
Diurnal temp variation is greatest
340
When is diurnal temp variation greatest?
Autumn
341
Metar Code: FU
Smoke
342
Metar Code: Smoke
FU
343
Metar Code: Fog
FG
344
Metar Code: FG
Fog
345
Metar Code: Mist
BR
346
Metar Code: BR
Mist
347
Metar Code: BL
Blowing
348
Metar Code: Blowing
BL
349
Metar Code: SA
Sand
350
Metar Code: Sand
SA
351
Metar Code: MI
Shallow
352
Metar Code: Shallow
MI
353
Metar Code: PR
Banks
354
Metar Code: Banks
PR
355
Metar Code: BC
Patches
356
Metar Code: Patches
BC
357
Metar Code: SS
Sandstorm
358
Metar Code: Sandstorm
SS
359
Metar Code: PO
Dustdevils
360
Metar Code: Dustdevils
PO
361
Metar Code: UP
Unidentified Precip
362
Metar Code: Unidentified Precip
UP
363
What unit of measurement is used for visibility?
Metres
364
CAVOK refers to clouds not below...?
5000ft
365
Does CAVOK mean no cloud at all?
No, just none below 5000ft
366
2 main causes of low pressure systems
Unstable air rising
Air being less dense due to water vapour
367
What type of front moves the fastest?
Cold
368
What is a stationary front?
Where warm air and cold air reside next to eachother
369
Why do occluded fronts result in prolonged rain and poor visibility?
The fronts are slower moving
370
Why does severe weather occur in a trough?
Increased mixing and lifting forces where isobars are closer together
371
High pressure systems are known as what?
Anti-cyclones
372
Why are winds usually slack in a high pressure system?
Isobars are widely spaced
373
Col in summer typified by what?
Moist air and little movement (wind)
374
Col in winter typified by what?
Little movement (wind) can cause low cloud and poor visibility
375
What happens to the cloud base as a warm front approaches?
It lowers
376
Why does icing occur even if an aircraft flies into above-zero water droplets?
The airframe may be sub-zero and will freeze the droplets
377
In what form does ice begin as in the icing process?
Large super-cooled water droplets
378
What is rime ice?
Impact ice
379
How is rime ice formed?
Water droplets impacting the air frame
380
How is clear ice formed?
Water droplets flow backward over air frame after rime ice formed
381
Why is clear ice formation so dangerous?
Reaches parts of aircraft unprotected by anti-ice systems
382
What type of icing is typically seen on the ground structures?
Hoar frost
383
How is hoar frost formed?
Sublimation
384
How does hoar frost form on an aircraft?
Aircraft cooled by flying through cold air mass
Aircraft enters warm air and sublimation occurs
385
Does hoar frost form in clouds?
Not always
386
What icing occurs when a warm front meets a cold air mass?
Freezing rain
387
How does freezing rain form in fronts?
Super-cooled droplets fall from warm air into cool and instantly freeze
388
Carb Icing: what happens to fuel/air as it passes through the venturi?
Pressure reduces
Dewpoint reduces
Air's water condenses
Fuel evaporation reduces air temp further due to energy required
389
Why is carb ice more likely on warm days?
Warm air has the ability to hold more moisture
390
What is the dominant factor in causing carb icing?
Humidity
391
Why does the engine sometimes run more roughly after carb heat has been applied?
Ice melts into water which enters the system
392
Why is rime ice opaque?
It is trapped air
393
Rime ice is trapped air. This gives it what characteristic?
Opaque
394
What are the optimum conditions for a thunderstorm to form?
Hot humid atmosphere
395
For thunderstorms, when is TCU used instead of CU?
When a thunderstorm is taller than it is wide
396
What causes lightning and thunder in a thunderstorm?
Air current friction
397
What direction does a thunderstorm's anvil point?
In direction of wind aloft
398
Thunderstorms: during the dissipating stage, what causes the updrafts to reduce?
Falling precipitation
399
Thunderstorms: during the dissipating stage, why does a flat top occur?
Temperature inversion
400
Thunderstorms: when the anvil becomes well-defined, what does this indicate?
Dissipating stage and end of the cells life
401
How does a supercell occur?
When winds aloft move precipitation away from the up-draughts
402
How is a supercell self-sustaining?
Supply of moist air is present
403
What causes a thunderclap?
Sudden massive expansion of air around lightning bolt due to sudden increase in temperature
404
A sudden massive expansion of air around lightning bolt due to sudden increase in temperature causes what?
Thunder
405
What instrument will give unreliable readings in the vicinity of a thunderstorm?
ADF
406
Why does the ADF give unreliable readings near a thunderstorm?
Lightning has a broad Radio Frequency spectrum
407
Rule of thumb for thunderstorm distance
5 second delay between thunder and lightning = 1nm distance
408
What factor determines a thunderstorm's direction?
Winds aloft, not surface winds
409
Do thunderstorms travel in the prevailing surface wind direction?
No
410
Thunderstorms tend to be severe above what dewpoint?
20 degrees
411
412
A plane flying towards a depression will experience what? (In the NH)
Starboard drift
413
What moves faster across the earth? Highs or lows?
Lows
414
Why do clouds form in a depression?
Rising air is cooled
415
Why is visibility good in low pressure?
Vertical motion of air carries away suspended particles
416
What kind of visibility is associated with a low?
Good
417
What is a V-shaped extension of isobars from a depression called?
Trough
418
A trough on a chart resembles what?
V-shaped extension of isobars
419
A trough carries which two key factors for the development of CBs and storms?
Unstable air and rising air due to low level convergence
420
In a trough, what is a major risk associated with observing a cloud formation?
CBs may be embedded within other cloud (such as stratiform)
421
An aircraft flying towards an anticyclone will experience what?
Port drift
422
What is the stability of subsiding air?
Very stable
423
Subsiding air in an anticyclone means the air is what…?
Very stable
424
What causes mountain waves and windshear to exist on the outskirts of an anticyclone?
Temperature inversion combines with stronger winds
425
Temperature inversions and strong winds on the outskirts of an anticyclone can produce what?
Windshear and mountain wave
426
U-shape extension of isobars from a high is called what?
Ridge
427
What is the anticyclone equivalent of a trough?
Ridge
428
Venturi effect means high pressure, low speed becomes what when constricted?
Low pressure, high speed
429
Where can the venturi effect exist in the air?
Mountain wave
430
Mountain wave venturi effect results in what?
Wind aloft speeds increase, pressure decreases
431
Venturi effect in mountain wave has wgat effect on safe flight?
Altimeter may over-read due to lower pressure
432
Icing: what cloud is specifically risky for icing in mountain flying?
Lenticular clouds
433
European Air Circulation: winter pressure
Low pressure in Atlantic, High in continent
434
European Air Circulation: winter jet stream
More southerly than usual
435
European Air Circulation: summer pressure
High pressure in Atlantic
436
European Air Circulation: high pressure in Atlantic summer is known as what?
Azores HIgh
437
When does an Azores High usually occur?
Summer
438
Which air mass is generally responsible for snow over the UK?
Arctic Maritime
439
Arctic Maritime is an air mass that can bring what event in the UK?
Snow
439
'Continental' in air mass description denotes what
Dry, and therefore stable
440
F215 provides weather for what vertical space?
Ground to 10,000ft
441
Typical F215 forecast validity?
9 hours
442
F215 terminology: phenomenon coverage >50%
Frequent
443
F215 terminology: phenomenon coverage 25-50%
Occasional
444
F215 terminology: phenomenon coverage <25%
Issolated
445
F215 chart provides info on what in the UK?
Significant weather
446
Significant weather in the UK is forecasted by the Met Office in what publication?
F215
447
F214 chart provides info on what in the UK?
Spot wind and temperatures
448
F214s are issued every...hours?
6 hours
449
What two probability codes are used in the UK for TAFs?
PROB30 and PROB40
450
In a TAF, PROB30 is generally understood as...?
Might happen
451
In a TAF, PROB40 is generally understood as...?
Will happen
452
For METARS, NOSIG means what?
No significant change during the two hours after observation time
453
For METARS, NOSIG has what time forecast
2 hours
454
Infra-Red satellite shows what?
The temperature of clouds
455
In IR-satellite, how is temperature indicated?
The lighter the colour, the lower the temperature
456
VOLMET broadcasts METARs or TAFs?
METARs
457
How is VOLMET broadcast?
On VHF continuously
458
Where does the tropopause begin at the equator?
18km (60,000ft)
459
Where does the tropopause begin at the poles?
9km (30,000ft)
460
What weather conditions might be associated with a Col in the winter months in the UK?
Low Cloud, light winds, Poor visibility (possibly even fog)
461
