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PPL > Meteorology > Flashcards

Meteorology Flashcards

1
Q

What is the Atmoshpere ?

A

The layer of air around the earth

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2
Q

What is the composition of the Atmosphere ?

A

78% Nitrogen , 21 % Oxygene and 1 % of Carbon dioxide ,Water and other gases .

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3
Q

What are the properties of the Atmoshpere ?

A

Compressible, Expansible, Mobile.

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4
Q

What is the weight of the air at sea level ?

A

14.7 PSI or 29.92 “Hg

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5
Q

What are the layers of the Atmoshpere ?

A

The troposhpere ( tropopause at 28000 ft over the poles
and 54000 ft over the equator with -56°C),
The stratosphere,
The mesosphere and the thermosphere.

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6
Q

What is the International Standard Atmoshpere ?

A

It is a common references atmoshepre which doesn’t exists.
1 - Air is a perfect dry gas
2 - Mean Sea Level pressure 29.92 “Hg
3 - Mean sea level temp 15°C
4 - 1.98°C drop per 1000ft altitude increase
5 - The average temp at tropopause is -56.5°C
6 - The mean altitude of the tropopause is 11km

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7
Q

What is the temperature ?

A

The result of molecular agitation. Scale ( °C , °F and °K )

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8
Q

How the atmoshpere is warmed ?

A

The solar rays are the primary source of heat. Their circulation through the atmosphere produce a very small increase of heat in the air. The earth absorb the rays and heats up and then emitting radiations.

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9
Q

What are the phenomena inducing a heating of the atmosphere ?

A

Conduction, Convection, Advection, Mechanical turbulences and Subsidence.

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10
Q

What are the phenomena inducing a cooling of the atmosphere ?

A

Nocturnal radiation, Advection, Expansion.

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11
Q

What is the difference between cold and warm air ?

A

Cold air is dense with a small quantity of humidity

Warm air is less dense with a large quantity of humidity.

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12
Q

What is the relative humidity ?

A

It is the ratio between the quantity of humidity a volume of air contains and the quantity of the humidity needed to saturate this volume.

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13
Q

What is the dew point ?

A

It is the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapour to saturate.

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14
Q

What are the main adiabatic lapse rates per 1000 feet ?

A

Dry : 3°C
Wet : 1.5°C
Dew point : 0.5°C
Dry + Dew point : 2.5°C ( cloud base calculation )

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15
Q

What are the main lifting agents ?

A

Convection, Orographic Lifting, Mechanical turbulence, Convergence and Frontal.

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16
Q

What is the stability of an air mass?

What is the instability of an air mass?

A

Tendency of an air mass to stop raising when it is submitted to a lifting agent.
Tendency of an air mass to keep raising when it is submitted to a lifting agent..

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17
Q

What are the Isobars ?
What is a Ridge of high pressure ?
What is a Trough of low pressure ?

A

Lines of same pressure.
Are joining two adjacent high pressure centers.
Line joining two adjacent low centers of pressure.

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18
Q

What is the horizontal pressure gradient ?

A

Pressure rate of change in function of the horizontal distance.

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19
Q

What is the general movement of the air ?

A

The air will move from the high to the low pressure generating wind.

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20
Q

In the northern hemisphere how the winds are behaving around a high pressure area and a low pressure area ?

A

In a high pressure the wind turns clockwise .

In a low pressure the wind turns counterclockwise .

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21
Q

What is the geotropic wind ?

A

As altitude increases, the resultant of the pressure force and the Coriolis force gives the Geotropic Wind.

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22
Q

What is the effect of friction ?

A

The wind speed is affected by the ground surface friction. In altitude the wind is parallel to the isobars, whereas near the surface wind crosses the isobars .

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23
Q

What is the overall wind circulation on the planet ?

A

The unequal heating of the earth produces a low pressure belt at the equator and a high pressure region at the north pole. In reality there is an accumulation of air ( in altitude) at the 30th parallel, generating a must complex stream path.

24
Q

What are the name of the three cells produced by prevalent winds ?

A

The polar cell ( over the 60° N )The Ferell cell ( between 30°N and 60°N ) and the Hadley cell ( between the equator and the 30°N ).

25
Q

What is the wind gust ?

A

A rapid augmentation of wind speed or drastic change in direction for a short period of time.

26
Q

What is a sea breeze ?

A

As the sea heats less rapidly than the earth (during the Day ) there is a difference of temperature that generate an air stream.

27
Q

What is a Land breeze ?

A

As the land cools less rapidly than the sea ( during the Night ) there is a difference of temperature that generate an air stream.

28
Q

What are the Orographic waves ?

A

When a strong wind flows over a relief a wave is created.

29
Q

What are the Anabatic and Katabatic winds ?

A

Anabatic wind is air moving upslope and Katabatic wind is air moving downslope.

30
Q

What is the Jet stream ?

A

Jet stream is a flat corridor in altitude where wind circulate at very high speed (60 to 250 Kts).

31
Q

What is an air mass ?

A

A large volume of the troposphere with uniform properties of temperature and humidity.

32
Q

What is the front ?

A

A front is the contact zone between two air masses of different characteristics as it appears on the ground.

33
Q

Can you describe a Warm front ?

A

The slope is shallow. We can encounter Stratus, Nimbostratus , Altostratus , Cirrostratus and Cirrus.
When crossing a warm front the Temperature increases , Dew point increases ( Humidity goes up ) . pressure decrease and then remain stable.

34
Q

Can you describe a Cold front ?

A

The slope is steep. We can encounter Cumulus, Towering cumulus or Cumulonimbus.When crossing a cold front the Temp decreases, The Dewpoint decreases ( humidity reduces ) , The Pressure reduces rapidly before crossing a cold front then increases rapidly after.

35
Q

What correction should we adopt after crossing a front ?

A

Whenever we cross a front ( Warm or Cold, in any direction ) we have to apply a correction to the right.

36
Q

What is the Occlusion ?

A

The Occlusion appears when there is no more trace of warm air on the ground. We call it an occluded Front.

37
Q

What is the Trowal ?

A

The Trowal is the projection on the Earth’s surface of the trough of warm air aloft formed during the occlusion process of the depression.

38
Q

What can we encounter when we fly to a winter Warm front ?

A

When flying through a winter Warm front you can encounter first Snow, then Ice pellets, then Freezing rain and eventually Rain.

39
Q

What is the Frontogenesis ?

A

The temperature gradient increases and isotherms get close to each other.

40
Q

What is the Frontolysis ?

A

The temperature gradient decreases and isotherms spread farther apart.

41
Q

What is the Buy Ballot’s law ?

A

When the wind is at your back, the depression is at your left.

42
Q

What are the requirements for a cloud formation ?

A
  • High relative humidity
  • Presence of condensation nuclei
  • Cooling agents / increase of humidity
43
Q

What is the Coalescence ?

A

The water vapour particles start to agglomerate to each other around a nuclei ( dirt particle in the air ) and become visible.

44
Q

What are the lifting agents generating clouds ?

A

Convection, Orographic, Convergence, Frontal lift and Mechanical turbulence.

45
Q

What are the two types of clouds shape ?

A
  • Stratiform : Horizontal development and sign of stability , light and continue precipitations.
  • Cumuliform : Vertical development and sign of instability, strong and intermittent precipitations.
46
Q

How do we define the sky condition ?

A 
CLR : no cloud
Few : 1 - 2 Oktas
Scattered : 3 - 4 Oktas
Broken : 5 - 7 Okats
Overcast : 8 Oktas
47
Q

How does precipitation forms ?

A
  • Condensation : The air is saturated and becomes visible.
  • Coalescence : The fine particles of water start to agglutinate and increase in size.
  • Precipitation : When their weight becomes sufficient to counter the updraft currents, precipitation starts.
48
Q

What are the types of precipitations ?

A
  1. Drizzle : Fine droplets of water.
  2. Freezing Drizzle : Fine droplets that freeze on contact.
  3. Snow : Agglomeration of ice crystals.
  4. Snow Grain : White opaque grains of ice.
  5. Snow Pellet : Supercooled water droplets collected and frozen on falling snow flakes.
  6. Rain : Water droplets.
  7. Freezing Rain : Water droplets below 0°C for a long period.
  8. Hail : Irregular lumps of ice ( with several layers ).
49
Q

What is Fog ?

A

It is the result of condensation. It can be caused either by cooling off the ambient air passed its dew point temperature or increasing the dew point temperature to the actual ambient temperature by adding humidity.

50
Q

What are the conditions of Fog ?

A

Conditions : High relative humidity, a Cooling process, Condensation nucleus, A light surface wind to maintain water droplets in suspension.

51
Q

What are the types of Fog ?

A

Radiation, Advection, Slope, Evaporation and Frontal.

52
Q

What are the conditions for Thunderstorms to form ?

A

Conditions of thunderstorms : Condensation nucleus, high relative humidity, high instability and presence of a lifting agent.

53
Q

What are the 3 stages of thunderstorms ?

A
  • Cumulus : Instability, pronounced vertical development ( up to 6000 ft/min) , no precipitation.
  • Maturity : Start of precipitations , heavy turbulence ( descending air currents up to 2000 ft/ min ).
  • Dissipation : No more ascending currents, formation of the anvil, the storm loses its energy.
54
Q

What are the dangers of Thunderstorms ?

A

Turbulence, Hail, Lightning, Icing, Rain.

55
Q

What are the two types of Icing ?

A
  • Rime ice : White (opaque ), light and brittle ice accumulates due to small droplets that freeze instantaneously on contact with aircraft surface.
  • Clear ice ( the most dangerous ) : A small part of the large droplets freeze on contact and unfrozen water will expend on a larger surface before freezing , giving a heavy clear coat of ice.
56
Q

What are the conditions for the highest rate of catch ?

A
  • Large super cooled droplets
  • Thin wing
  • High speed
57
Q

What is Virga ?

A

Virga : A precipitation that falls from a cloud but evaporates before reaching the ground.

PPL (9 decks)

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