4. Moisture and Convection

Question 1

Mechanics of evaporation / SVP

Answer 1

Water is heated, molecular activity increases pushing more molecules from liquid to gas into the air. Water Vapour Pressure in the air rises until equilibrium of evaporating molecules and molecules being pushed back into liquid state by increased water vapour pressure is reached. (Saturation Vapour Pressure)

Question 2

what happens to density if humidity increases? (Pressure and temp stay the same)

Answer 2

Density decreases (water vapour molecules have less mass than air molecules)

Question 3

Relative Humidity

Answer 3

(Mass of water vapor / Mass of air) / (Saturation mass of water vapor / mass of air)

(g / kg)

Question 4

Why does frost form before dew at sub-zero temperatures?

Answer 4

The SVP over ice is slightly lower than over water, so it’s easier for water vapour molecules to turn into to ice

Question 5

Wet bulb temperature

Answer 5

Always between OAT > Wet Bulb > Dew Point
All three are the same at Dew Point

Question 6

Average environmental lapse rate

Answer 6

2 degrees C per 1,000ft
6.5 degrees C per 1,000m

Question 7

What is “adiabatic”

Answer 7

Without energy gain or loss

Question 8

Dry adiabatic lapse rate

Answer 8

3 degrees celsius per 1,000ft = 1 degree C per 100m

Question 9

Saturated Adiabatic Lapse Rate

Answer 9

1.8 degrees C per 1000ft = 0.6 degrees C per 100m

Question 10

Absolutely unstable air

Answer 10

ELR > DALR

Question 11

Stable air

Answer 11

ELR < SALR

Question 12

Conditionally unstable air

Answer 12

DALR > ELR > SALR

Question 13

What is the “normal” stability state of the atmosphere?

Answer 13

Conditionally unstable (saturated air tends to rise)

Question 14

Calculation of cloudbase height

Answer 14

Difference between surface OAT and Wet Bulb Temp divided by 1.2 (difference between DALR and SALR) x 1,000 feet