Chap 9 Weather

Question 1

What is the composition of air

Answer 1

21% oxygen 78% nitrogen

Question 2

What % of air mass is below 18,000 MSL

Answer 2

50%

Question 3

What is standard P & T at sea level

Answer 3

29.92” Hg 59 F
1013 mb 15 C

Question 4

How much does pressure change with elevation?

Answer 4

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

Question 5

Standard temp lapse rate?

Answer 5

2 C decrease per 1000’

Question 6

What are the first 3 layers of the atmosphere?

Answer 6

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.

Question 7

What are the two thermal models?

Answer 7

Bubble & Column

Question 8

What is DALR?

Answer 8

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

Question 9

What’s a typical width of a thermal?

Answer 9

500 - 1000’

Question 10

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

Answer 10

Lower

Question 11

What is an inversion?

Answer 11

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

Question 12

What are the two ways to increase instability?

Answer 12

1. Heat the ground
2. Cool air aloft

Question 13

What is the Saturated adiabatic lapse rate?

Answer 13

1.2 C per 1000’

Question 14

What is a good sign of a thermal?

Answer 14

Cumulus clouds. Especially ones that have dark concave bottom.

Question 15

What are cloud streets?

Answer 15

A row of cumulus clouds.

Question 16

What are characteristics of cloud streets?

Answer 16

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

Question 17

Distance to remain away from thunderstorms

Answer 17

20 miles

Question 18

What type of clouds create thunderstorms?

Answer 18

Cumulonimbus. Cb

Question 19

Nature of Cb clouds.

Answer 19

Cb clouds create condensation which releases heat causing strong downdrafts.

Question 20

3 stages of Cb clouds?

Answer 20

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

Question 21

What is the lifted index?

Answer 21

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

Question 22

What is the K index?

Answer 22

Probability of a thunderstorm.

Above 35 = Numerous thunderstorm
< 20 = No chance

Question 23

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

Answer 23

20 - 40 knots for 10 minutes

Question 24

Hail usually occurs under what part of a Cb cloud?

Answer 24

Anvil

Question 25

What kind of slopes generate poor slope lift?

Answer 25

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

Question 26

What type of slope generate good slope lift?

Answer 26

1. long 2. 4:1 slope 3. 500 - 1000' above valley floor

Question 27

What occurs on the lee side of the slope?

Answer 27

Possible downdraft / sink.

Question 28

Slopes should be approached at what angle?

Answer 28

30 degrees from perpendicular.

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Where do waves form?

Answer 31

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

Question 32

What causes mtn waves?

Answer 32

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.

Question 33

Name of mtn waves?

Answer 33

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

Question 34

What are clouds called on top of a mtn ridge?

Answer 34

Cap clouds

Question 35

Where do rotors occur?

Answer 35

Below a wave

Question 36

What are rotors?

Answer 36

Currents circulating vertically beneath a wave.

Question 37

Is there lift above a cap cloud?

Answer 37

Yes

Question 38

What type of clouds appear above waves?

Answer 38

Lenticular

Question 39

What is the distance between waves?

Answer 39

2 - 20 miles

Question 40

How does convergence lift form?

Answer 40

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.