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PPL Met > cloud > Flashcards

cloud Flashcards

1
Q

what is OKTA

A

it is the rating system for cloud coverage

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2
Q

1-2 OKTA’S is considered as?

A

Few clouds (FEW)

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3
Q

3-4 OKTA’s is considered as?

A

Scattered Clouds (SCT)

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4
Q

5-7 OKTA’s is considered as?

A

Broken Clouds (BKN)

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5
Q

8 OKTA’s is considered as?

A

Overcast (OVC)

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6
Q

what are two acronyms used for clear skies?

A

Skies Clear (SKC) and Cloud and Visibility OK (CAVOK)

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7
Q

what is a cloud?

A

A cloud is a visible mass of

air containing minute water droplets or ice crystals

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8
Q

what are the 3 families of cloud?

A

cirrus, cumulus and stratus

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9
Q

what does nimbo/nimbus mean?

A

rain-bearing cloud

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10
Q

what does alto mean?

A

middle level

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11
Q

the height at which saturation occurs is called?

A

the condensation level

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12
Q

what causes cloud?

A

As air rises, it is subjected to a steady decrease in pressure which causes it to expand and cool. The rising parcel contains water vapour. With sufficient cooling it will become saturated with water vapour, as its capacity to contain water vapour is reduced on cooling.

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13
Q

what is the cloud limit of low cloud?

A

ground - 6500ft

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14
Q

what is the cloud limit of middle cloud?

A

6500ft - 13000ft

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15
Q

what is the cloud limit of high cloud?

A

13000ft - 25000ft

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16
Q

what does cumulus mean?

A

cloud forming rounded masses heaped on each other above a flat base at fairly low altitude

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17
Q

what does stratus mean?

A

cloud forming a continuous horizontal grey sheet, often with rain or snow.

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18
Q

what does cirrus mean?

A

cloud forming wispy filamentous tufted streaks or ‘mare’s tails’ at high altitude

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19
Q

how are convection clouds formed?

A

Convection cloud forms when the air is heated at the ground producing thermal up-currents.

With continued solar heating, these convection currents become stronger.

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20
Q

What determines the height of a Cumulus cloud top when formed by convection?

A

depends on the stability of the atmosphere. In cases
of extreme instability, the tops can extend as far as
the Tropopause.

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21
Q

if the lapse rate is small and the atmosphere is basically stable what type of convection cloud will form.

A

cumulus

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22
Q

if surface temperatures continue to rise and the lapse rate is steep what type of convection cloud will form?

A

towering cumulus will form and rise until stable air is reached.

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23
Q

during when does convection cloud form the most (over land)?

A

Convection clouds formed as a result of surface heating over land and are most common during the seasons of spring, summer
and autumn

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24
Q

during when does convection cloud form the most (over sea)?

A

Over the sea, Convection cloud develops in the winter months where the sea is warmer than the air.
Since there is little change in sea temperature during the day, these clouds are usually present
both day and night. In coastal regions, Cumulus clouds develop predominantly during
nighttime when a cool land breeze blows above a warmer sea.

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25
Q

how are turbulence clouds formed?

A

high humidity within the turbulence layer,

a sufficiently strong wind speed, at least 8 knots, to create a deep turbulence layer

a stable lapse rate, so that cloud is restricted to the height of the turbulence layer.

26
Q

turbulence is a primary feature of what?

A

primary feature of winds in the surface frictional layer

27
Q

eddy currents caused by irregular up and down currents (turbulence) create what?

A

It creates a uniform humidity mixing ratio and a dry adiabatic lapse rate
throughout the frictional layer

28
Q

what if the air is sufficiently moist in the turbulence layer?

A

air in the upper part of the turbulent layer will be cooled below dew point and a layer of uniform low Stratus cloud will form with a
temperature inversion above.

29
Q

what if the air is sufficiently moist in the turbulence layer but it is unstable?

A

If the air is unstable, the turbulence layer will be much deeper and large Cumulus clouds will develop in sufficiently moist air.

30
Q

what can turbulence clouds at higher levels develop too?

A

Turbulence clouds at high levels may develop into Altocumulus Castellanus.

31
Q

what is the main condition needed for turbulence cloud to form?

A

high relative humidity

32
Q

turbulence cloud is most common when?

A

most common when air originating over subtropical oceans arrives in temperate latitudes.

also found in winter over the Continents, wherever there is a clear difference in air temperatures between regions.

33
Q

what happens to turbulence clouds in summertime normally?

A

Clouds formed by turbulence in the summertime usually clear during the day by surface
heating.

34
Q

how are orographic clouds formed?

A

When an airstream meets an area of rising terrain it is forced to rise and cool adiabatically.

35
Q

what type of orographic cloud will usually form at the top of the hill?
Stable and unstable

A

If the air is stable, Stratus cloud will normally develop at the top of a hill.

If it is unstable, Cumulustype cloud will form on the windward side.

36
Q

where is the orographic effect most noticeable?

A

when a long mountain range lies perpendicular to the wind direction.

Where there are isolated hills, the air can flow around them, and only isolated cap clouds will develop.

37
Q

what is one risk associated with orographic cloud?

A

mountain waves

38
Q

why are mountain waves dangerous?

A

if mountain waves exist, the up-and-down motion may cause clouds to form and reform.

39
Q

what can an orographic cloud appear as?

A

a cloud vane caused by severe turbulence on lee side of mountain,

40
Q

what determines the type of orographic clouds formed?

A

depends on the moisture and stability of the air at the base of the hill.

41
Q

how are lenticular clouds formed? And how do they increase in height

A

when the air is stable and winds blow across hills and mountains from the same or similar direction at different heights through the troposphere.

Although it may appear to be stationary, it is in fact constantly dissolving and reforming as the up-and-down currents over the hill.

42
Q

how do eddies contribute to lenticular cloud formation?

A

The eddies created by the airstream climbing the slope can also cause Standing Waves which contribute to the formation of Lenticular cloud

43
Q

what type of cloud form if the surface air is moist but the temperature lapse rate above the high ground stable

A

uniform stratus cloud is likely.

44
Q

what type of clouds form If the air near the surface is moist but unstable

A

thick cumulus cloud

45
Q

how are frontal clouds formed?

A

Frontal clouds form when two air masses of different temperatures meet

46
Q

a warm front associated with stable airflow is associated with fine weather and little cloud. the sloping band of air associated with a front forces air to rise. because of stable airflow what type of cloud is expected to form?

A

cirrus cloud

47
Q

approaching closer to a warm front what happens to the cloud?

A

it thickens and develops into stratus cloud and there may be a belt of precipitation 200 miles ahead of front.

48
Q

what happens when you pass the warm front, what type of cloud is expected?

A

shallow clouds of stratus dispersing

49
Q

In a Cold Front, the region of cold air is moving forward below the region of warm air, forcing
it to rise. The sloping line of a Cold Front is much steeper than that of a Warm Front, creating what type of cloud?

A

more vigorous movement of air, dense Cumulus cloud and heavy precipitation

50
Q

as a cold front approaches what type of clouds are expected?

A

large Cumulus clouds will be clearly visible

Cirrus cloud may develop out of anvils of Cumulonimbus, carried away by strong upper level winds

51
Q

what are the characteristics of cirrostratus cloud (Cs)?

height, appearance,icing,turbulence precipitation

A
  • high level cloud
  • smooth and fibrous - if sun or moon visible halo surrounds it often indication of bad weather coming
  • cloud consists of ice crystals
  • no turbulence or precipitation
52
Q

what are the characteristics of cirrocumulus (CC)

height, appearance,icing,turbulence precipitation

A
  • high level cloud
  • sheep’s wool appearance with small ripples
  • cloud consists of ice crystals
  • no turbulence or precipitation
53
Q

what are the characteristics of Cirrus (Ci)

height, appearance,icing,turbulence precipitation

A
  • high level cloud
  • feather like cloud of pure white, streaky outlines indicate high winds aloft
  • cloud consists of ice crystals
  • no turbulence or precipitation
54
Q

what are the characteristics of altostratus (As)

height, appearance,icing,turbulence precipitation

A
  • middle cloud
  • blue/grey smooth and fibrous, can be thick cos water content high, indication of bad weather coming
  • light to moderate icing and turbulence
  • little to no precipitation
55
Q

what are the characteristics of altocumulus (Ac)

height, appearance,icing,turbulence precipitation

A
  • middle level cloud
  • white/grey larger ripples then As
  • light to moderate icing and turbulence
  • no precipitation
56
Q

what are the characteristics of Stratocumulus (Sc)

height, appearance,icing,turbulence precipitation

A
  • low level cloud
  • grey or white patches, sheets or layers, almost always dark parts composed of rounded masses or rolls
  • no icing or turbulence
  • light drizzle or light showers
57
Q

what are the characteristics of Cumulus (CU)

height, appearance,icing,turbulence precipitation

A
  • low level cloud
  • bright white on sunny side base and dark on shadow side and base
  • above freezing layer, moderate to heavy icing
  • outside cloud ,smooth. between clouds and mountains, moderate.
  • occasional precipitation. well developed
58
Q

what are the characteristics of Cumulonimbus (Cb)

height, appearance,icing,turbulence precipitation

A
  • low to middle level cloud
  • heavy/dense, often associated with thunderstorms. Bright white on sunny day and dark on shadow and base. Anvil at top
  • above freezing layer, moderate to heavy icing
  • moderate up and down draughts
  • hail or rain
59
Q

what are the characteristics of Towering Cumulus (TCU)

height, appearance,icing,turbulence precipitation

A
  • low level cloud
  • heavy/dense, often associated with thunderstorms. Bright white on sunny day and dark on shadow and base.
  • above freezing layer, moderate to heavy icing
  • moderate up and down draughts
  • hail or rain
60
Q

what are the characteristics of Nimbostratus (Ns)

height, appearance,icing,turbulence precipitation

A
  • low to middle level cloud
  • starts at low level and extends thousands of feet up, associated with stable air, very extensive at edges, looks dark and heavy
  • above freezing layer, moderate to heavy icing
  • little to no winds
  • heavy and persistent precipitation
61
Q

what are the characteristics of Stratus (ST)

height, appearance,icing,turbulence precipitation

A
  • Low level
  • grey/blue with fairly level base
  • no icing
  • nil to little turbulence
  • light drizzle
62
Q

What is nimbus

A
  • a dark grey cloud bearing rain.

PPL Met (20 decks)

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