THE ATMOSPHERE

Question 1

What are the four layers to the atmosphere (and pauses)

Answer 1

Troposphere
(tropopause)
Stratosphere
(stratopause)
Mesosphere
(mesopause)
Thermosphere

Question 2

Describe the Tropopause

Answer 2

Temp generally decreases with height in the atmosphere (positive lapse rate), however in the tropopause, located between troposphere & stratosphere, temperature remains constant.
This acts as a ‘cap’, (temp inversion) keeping all wx in the troposphere (bar high energy CBs that can push through briefly).

Question 3

Characteristics of the troposphere?

Answer 3

1. Always in motion
2. Contains 75% of mass of the atmosphere at mid latitudes. 50% of atmosphere is found <5000ft.
3. Temp generally decreases with height (1.98deg/1000ft)
4. Height of 36,089ft on average.

Question 4

How does location/seasons affect the troposphere height?

Answer 4

At equator (greater heating = greater thermal expansion), height is ~56,000ft. At the poles it is ~28,000ft.
In winter, it is colder (less thermal expansion), therefore the height of the troposphere is lower & vice versa in summer.

Question 5

What does troposphere always being ‘in motion’ mean?

Answer 5

horizontal movement of mass: wind
vertical movement of mass: convection, frontal lifting, orographic lifting.

Question 6

Isothermal layer?

Answer 6

Temp remains constant

Question 7

Negative lapse rate?

Answer 7

Temp increases with height, inversion

Question 8

List the percentages of gases in the troposphere

Answer 8

Nitrogen: 78%
Oxygen: 21%
Other: 1%

Question 9

Water vapour volume equator vs poles

Answer 9

4% equator
0% poles

Question 10

Define water vapour

Answer 10

It is the gaseous state of water in the atmosphere. entering through the evapotranspiration process.

Question 11

Define/describe latent heat

Answer 11

Latent heat is released when water vapour changes state to water or ice. The heat released destabilises the atmosphere.
The reverse process of the above (sublimation - evaporation or melting), cools & stabilises the atmosphere.

Question 12

Define Aerosols

Answer 12

Tiny solid particles with a crystalline structure at the molecular level, floating freely in the atmosphere.
sea salt, dust, volcanic ash, smoke etc.

Question 13

Describe the importance and distribution in the atmosphere of aerosols and water vapour

Answer 13

Water vapour and aerosols are the building blocks of all clouds and therefore precipitation.
All water vapour and aerosols originate from the surface of the earth, therefore there is a higher concentration of both at the earths surface, and virtually none above the tropopause.

Question 14

ISA?

Answer 14

International standard atmosphere.
MSL Temp: 15deg C
MSL pressure: 1013.25hpa (2992 inHg)
MSL density: 1.225kg/m3
Temp lapse rate: 1.98deg/1000ft up tp 30,090ft (-56.5 in tropopause)

Question 15

Why do we have ISA?

Answer 15

Prescribes a standard atmosphere that simulates average conditions in mid latitudes. Allows for corrections to be made for deviations away from this (e.g. high DA or hot environments) for aircraft performance etc.