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ATPL Meteorology > Weather > Flashcards

Weather Flashcards

1
Q

What is fog?

A

Fog is a cloud at ground level through which the visibility is less than 1000mt with a relative humidity near 100%

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2
Q

What is mist?

A

Mist is similar to fog however it has a visibility greater than 1000mt and a relative humidity lower than 100%

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3
Q

When does fog form?

A

When air is cooled below its dew point temperature causing saturation and condensation

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4
Q

What processes may produce fog?

A
  • Radiation

- Advection

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5
Q

How does radiation produce fog?

A

Air close to the ground may be cooled due to radiation. This effect is strongest on cool nights with moist air and an inversion. A light wind up to 6kts will deepen fog as the cool air is mixed through greater depth

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6
Q

When is fog intensity greatest?

A

Usually around dawn when surface temperature is the lowest

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7
Q

What is advection?

A

Warm moist air cools as it flows over a cool surface

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8
Q

When does fog disappear?

A

When either the air temperature is raised above dew point or wind mixes drier air with the fog causing evaporation

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9
Q

What clouds are thunderstorms?

A

Cumulonimbus

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10
Q

What conditions must exist for thunderstorms to develop?

A
  • Unstable conditions
  • Abundant supply of water vapour
  • A lifting mechanism to trigger convection
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11
Q

3 stages of thunderstorm?

A
  1. Cumulus
  2. Mature
  3. Dissipating
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12
Q

When are updrafts present in thunderstorm?

A

Only as the cloud builds (Cumulus stage)

The cloud is warmer than the environment so the vertical development continues

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13
Q

What occurs in the mature stage of a thunderstorm?

A

-Cloud has grown to a great height (some cases over 40,000ft)
-It is now a cumulonimbus cloud with anvil shaped top composed of cirrus cloud and ice crystals
-Precipitation falls generating strong downdrafts (3000ft/min)
Wind shear and severe turbulence

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14
Q

The whispy cirrus anvil is blown flat on top by the wind, what does this indicate?

A

Indicates direction of storm movement

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15
Q

Downdrafts from thunderstorm may cause…

A

Gusts and a temperature drop ahead of the storm. Downdrafts undercutting the warm air at the front of the cloud base may form a roll of cloud which can detach and move ahead of storm

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16
Q

What occurs in the dissipating stage of a thunderstorm?

A

Updrafts die out leaving downdraughts

Rain gradually decreases and cloud breaks up

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17
Q

How long does a typical thunderstorm last?

A

60 minutes

18
Q

How are thunderstorms named?

A

By the mechanism that triggered them

19
Q

What is a frontal or squall line thunderstorm?

A

Formed as a result of instability at the boundary of two air masses

20
Q

What is the most hazardous thunderstorm in aviation?

A

Frontal or Squall line thunderstorm

They are often closely spaced, fast moving with a low base

21
Q

What can be associated with a frontal or squall line thunderstorm?

A

Roll clouds

22
Q

What is an air mass thunderstorm?

A

Tend to be more isolated and form as a result of some other trigger

23
Q

How is a orographic thunderstorm formed?

A

Formed due to orographic uplift of moist unstable air

24
Q

How is a cold stream thunderstorm formed?

A

A cold air stream flows over a warm surface. This generates instability in the lower layers. Thunderstorms can develop if the instability extends through a deep enough layer

25
Q

How are night equatorial thunderstorms formed?

A

Tropical regions cloud tops cool due to radiation at night. This causes unstable conditions and a thunderstorm can develop

26
Q

What are shear thunderstorms named after?

A

Wind shear effect which can increase storm severity

27
Q

How does a shear thunderstorm form?

A

If the vertical development is strong enough the shear may spread the storm out horizontally, reducing the friction between up draughts and downdraughts. This allows higher velocities in the storm. Greater turbulence can result and this is why shear thunderstorms are so dangerous

28
Q

Hazards associated with thunderstorms?

A
  • Heavy rain
  • Hail
  • Icing
  • Electrical interference
  • Lightning
  • Severe turbulence
29
Q

What is the turbulence in thunderstorms caused by?

A

Vertical wind shear between up draughts and downdraughts

30
Q

Where is icing generally concentrated in thunderstorm?

A

Around the middle of storm particularly around freezing level

31
Q

Where is severe turbulence found in thunderstorm?

A

Generally everywhere but also considerable altitude over cloud top

32
Q

Minimum safe altitude above thunderstorm general rule of thumb…..

A

Wind Speed/ 10 x 1000= Minimum safe altitude above thunderstorm

33
Q

Where in thunderstorm is hail most likely encountered?

A

10,000ft to 30,000ft

34
Q

What is a tornado?

A

Funnel shaped cloud extending down from the base of cumulonimbus cloud

35
Q

What are the most violent and destructive disturbances in the atmosphere?

A

Tornadoes

36
Q

What 3 conditions are required before dust storms can form?

A
  • Source of dust
  • Mechanism of uplift
  • Unstable environment to keep the dust aloft
37
Q

What are jet streams?

A

Fats moving narrow currents of air found near tropopause

38
Q

Characteristic of jet stream?

A

Strong horizontal wind shear

39
Q

What speeds can wind reach in jet streams?

A

150kts

40
Q

How are jet streams generated?

A

Advection of upper air in the global circulation pattern and the thermal wind gradients produced by temperature differential over different parts of the earths surface.

41
Q

How are jet streams aligned?

A

Roughly East/ West and are westerly winds

42
Q

What are the two major jet streams in the southern hemisphere?

A
  • Subtropical jet located 30 degrees south latitude
  • Polar front jet located further south at the location of the polar front

Both located around the tropopause

ATPL Meteorology (12 decks)

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