SME
Grade 12 Science · Earth & Space Science
The atmosphere: structure, air pressure, wind and severe weather
Use this for “It is 20 °C at the ground. What is the temperature 8 km up?” with the lapse rate of 6.5 °C/km.
Diagram
In the troposphere the air cools about 6.5 °C for each km up: −32 °C at 8 km.
This is an example. Type your own values to start a new problem.
T (°C)
=
T₀ (°C)
−
6.5
°C/km
×
h (km)
Formulas
T
=
T₀
−
6.5
×
h
−32 = 20 − 6.5 × 8
Assumptions
•
Air is 78 % nitrogen and 21 % oxygen.
•
The troposphere cools about 6.5 °C per km up to about 11 km.
•
Above that, ozone in the stratosphere absorbs the Sun’s UV and warms the air.
Step-by-step
WE KNOW
T₀ = 20 °C, h = 8 km
FIND
temperature at h (T)
Step 1 · Find temperature at h (T)
Use T = T₀ − 6.5 × h
Take off 6.5 °C for each km of height.
T
=
20
−
6.5
×
8
T
=
20
−
52
T
=
−32
°C
Check
Put the numbers back in. Both sides should match.
−32 = 20 − 6.5 × 8 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
Refresh
More problem types
Highs, lows and the pressure gradient
Use this for “A 1,024 hPa high and a 996 hPa low are 700 km apart. What is the pressure gradient, and which way does the wind blow round the low?”
Relative humidity
Use this for “Air holds 6 g of water vapor per kg and could hold 15 g. What is its relative humidity?”
The height of a cloud’s base
Use this for “The air is 24 °C with a dew point of 12 °C. How high is the cloud base?”
How a hurricane grows and dies
Use this for “Put the stages of a hurricane in order. Why does it weaken over land?”
Which air mass is it?
Use this for “Which air mass brings hot, humid summer weather to the southeastern United States?”