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Gliders Part 2 > Chap 9 Weather > Flashcards

Chap 9 Weather Flashcards

1
Q

What is the composition of air

A

21% oxygen 78% nitrogen

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2
Q

What % of air mass is below 18,000 MSL

A

50%

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3
Q

What is standard P & T at sea level

A

29.92” Hg 59 F
1013 mb 15 C

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4
Q

How much does pressure change with elevation?

A

1” Hg or 0.5 psi per 1000’. This decreases with altitude. Not linear.

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5
Q

Standard temp lapse rate?

A

2 C decrease per 1000’

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6
Q

What are the first 3 layers of the atmosphere?

A

Troposphere - 12 miles at equator 4 miles at poles. Almost all weather occurs here. 1.4 psia & -67 F
Tropopause - upper limit of troposphere. Temp does not decrease with altitude.
Stratosphere - Temp increases with altitude due to UV radiation of the ozone. Ozone layer. Jet stream. Air moves horizontally.

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7
Q

What are the two thermal models?

A

Bubble & Column

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8
Q

What is DALR?

A

Dry adiabatic lapse rate. Temp decreases 3 C for each 1000’ of altitude.

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9
Q

What’s a typical width of a thermal?

A

500 - 1000’

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10
Q

When the lapse rate is (lower/higher) than the surrounding air, the air mass is said to be unstable.

A

Lower

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11
Q

What is an inversion?

A

A layer of warm air on top of cold air. It traps the lower air because it cannot rise.

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12
Q

What are the two ways to increase instability?

A
  1. Heat the ground
  2. Cool air aloft
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13
Q

What is the Saturated adiabatic lapse rate?

A

1.2 C per 1000’

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14
Q

What is a good sign of a thermal?

A

Cumulus clouds. Especially ones that have dark concave bottom.

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15
Q

What are cloud streets?

A

A row of cumulus clouds.

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16
Q

What are characteristics of cloud streets?

A

Can be 50 miles long.
Spacing between streets is 3 x cloud height.
They align with the wind direction.

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17
Q

Distance to remain away from thunderstorms

A

20 miles

18
Q

What type of clouds create thunderstorms?

A

Cumulonimbus. Cb

19
Q

Nature of Cb clouds.

A

Cb clouds create condensation which releases heat causing strong downdrafts.

20
Q

3 stages of Cb clouds?

A

Cumulus to towering cumulus.
Mature stage = Strong downdrafts
Dissipating stage = windshear

21
Q

What is the lifted index?

A

Measure the severity of a thunderstorm.
T grnd - T at 500 mbar (7.3 psia) in C
0 to -2 Weak
-3 to -5 Moderate
< -5 Strong

22
Q

What is the K index?

A

Probability of a thunderstorm.

Above 35 = Numerous thunderstorm
< 20 = No chance

23
Q

Thunderstorms have outflow winds of ? knots lasting for ? minutes?

A

20 - 40 knots for 10 minutes

24
Q

Hails usually occurs under what part of a Cb cloud?

A

Anvil

25
Q

What kind of slopes generate poor slope lift?

A
  1. Short isolated hills (Pilot Mtn)
  2. Shallow slopes
26
Q

What type of slope generate good slope lift?

A
  1. long
  2. 4:1 slope
  3. 500 - 1000’ above valley floor
27
Q

What occurs on the lee side of the slope?

A

Possible downdraft / sink.

28
Q

Slopes should be approached at what angle?

A

30 degrees from perpendicular.

29
Q

During ridge soaring, tow gliders are travelling in opposite direction. Who has the right of way?

A

Glider with the ridge on his right. Ridge- Right - Right of way.
This allows that pilot to turn away from the ridge.

30
Q

During ridge soaring with two gliders travelling in the same direction, which side should the back glider pass the front glider

A

On the ridge side of the front glider. Front glider might make a turn away from the ridge.

31
Q

Where do waves form?

A

They form on the lee downwind side of the mtn ridge.

32
Q

What causes mtn waves?

A

Stable air is pushed up the upwind side of the mtn and sinks on the downwind side. It then oscillates up and down trying to find equlibrium.

33
Q

Name of mtn waves?

A

1st = Primary
2nd = Secondary
All others = Tertiary

34
Q

What are clouds called on top of a mtn ridge?

A

Cap clouds

35
Q

Where do rotors occur?

A

Below a wave

36
Q

What are rotors?

A

Currents circulating vertically beneath a wave.

37
Q

Is there lift above a cap cloud?

A

Yes

38
Q

What type of clouds appear above waves?

A

Lenticular

39
Q

What is the distance between waves?

A

2 - 20 miles

40
Q

How does convergence lift form?

A
  1. Two air masses collide. Cold air mass slides under warm air mass and displaces it upwards.
  2. Above a ridge if wind is blowing from opposite sides of mtn.
  3. In a valley when wind flows downslope from two ridges.
41
Q
A

Gliders Part 2 (8 decks)

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