physics of dry air

Question 1

true or false:

rain shower/ thunderstorms are caused by moist air rising and cooling

Answer 1

true. rain shower are caused when the moist air rises and cools its temperature, reaching condensation and releases water. the moister the air –> the heavier the rain

Question 2

why studying vertical profiles are important?

Answer 2

• know where clouds form
• study inversion
• pollution dispersion

Question 3

radiosondes

Answer 3

• helium filled weather balloon
• measures atmospheric temperature
• with temperature, humidity, pressure sensors
• with radio and radar to track wind speed and direction
• track with GPS

Question 4

define an air parcel

Answer 4

• a mass of unspecified amount of dry air; can’t be too big
• thermally insulated from the environment (the only way to change T is through change of p)
• no mass mixing with environment
• parcel’s pressure adjusts immediately to environmental p at the same level (if parcel has lower pressure –> less denser –> rises)
• slow movement –> neglect the macroscopic kinetic energy of the parcel (eg. radiation, convection)

Question 5

lapse rate

Answer 5

the rate at which an air parcel changes its temperature as it moves up or down in the atmosphere

Question 6

why increases temp increases pressure

Answer 6

higher temp. provides particles with more energy to move –> expand –> exert a greater force –> higher pressure

Question 7

true or false:

when the parcel has a lower temperature, it rises

Answer 7

false

Question 8

define air pressure

Answer 8

the force exerted by the weight of all the air above, per unit area

Question 9

define hydrostatic balance

Answer 9

The balance of gravity and vertical pressure gradient

Question 10

explain why pressure decreases rapidly in cold air using the hydrostatic equation.

Answer 10

the change of pressure with high is due to (-)density x gravity. as cold air is denser, it has a higher density hence decreases more.

Question 11

for thickness chart, the thickness for warm air is ________ and the cold air is _________

Answer 11

-thicker (as warm air is less dense)
-thinner
The thickness chart can be used to assesscold air advection (thinner) , warm air advection (thicker)

Question 12

trough is associated with ______ air and ridge is associated with _______ air. therefore clouds formed varies with height.

Answer 12

• cold

- warm

Question 13

1st law of thermodynamics

Answer 13

dq=du+dw

Question 14

what is dq=0 in the air parcel

Answer 14

• because we assume there is no mixing of the parcel with the environment and that they are thermally isolated –> no radiation, convection…
• therefore 0 = du + dw. aka: du= -dw

Question 15

given that du = CV Dt (CV= heat capacity), what happens to the temp when work is done to the parcel (compression) by the environment?

Answer 15

parcel–> assume dq=0
as work is done to the parcel, dw= negative, this means dt (du) is positive. as temperature is positive –> temp. increases (warm)
-compression- particles move more- increase in pressure and energy in the parcel compared to the environment –> warmer –> parcel rises

Question 16

given that du = CV Dt (CV= heat capacity), what happens to the temp when work is done by parcel (expansion) to the environment?

Answer 16

parcel–> assume dq=0
as work by the parcel, dw= positive, this means dt (du) is negative. as temperature is negative –> temp. decreases
(cold)
-expansion –> particles move less- decrease in pressure and temp.–> air is cooler –> sinks

Question 17

define adiabatic

Answer 17

A process occurs without or subtracting adding heat to the system

Question 18

differences between isothermal and adiabatic

Answer 18

iso- temp remains constant the whole time despite changes in pressure
adiabat- internal temp changes due to the changes in pressure

Question 19

Dry adiabatic lapse rate equation

Answer 19

-g/Cp

Question 20

define potential temperature

Answer 20

the temperature that a parcel would have if it is compressed/expanded from its existing p and T to a standard pressure.
-eg. what would the parcel resulting temp. be if it is compressed from 800hPa to 1000hPa with an initial temperature of 20C