Chapter 3: Air Temperature

1
Chapter 3 Air Temperature

• Daily temperature variations
• The controls of temperature
• Air temperature data
• Air temperature and human comfort
• Measuring air temperature

2
Daily Temperature Variations
Record high T 58 C or 136 F (Libya) Record
low T -89 C or -129 F (Antarctic)
3
Daytime Warming

• Thermals calm wind condition
• forced convection strong wind
• water vapor effects

• Cumulus clouds are markers of convection.

4
Nighttime Cooling

• radiational cooling
• nocturnal inversions

• Inversions tend to occur on
• clear, calm, dry nights
• strong winds would mix
• air
• clouds or water vapor would
• absorb longwave radiation

5

Stepped Art
Fig. 3-2, p. 57
6

Fig. 3-5, p. 60
7
Cold Air Near the Surface

• inversions
• thermal belts

• Drainage winds cold air that slides downhill.

8
Protecting Crops from the Cold Night Air

• orchard heaters
• wind machines
• Freeze Ta below
• freezing for a long
• enough time
• To protect small
• plants
• Use straw, cloth,
• or plastic bag
• to cover

9
The Controls of Temperature
10
The Controls of Temperature

• Latitude control daylight period and solar
  radiation
• land and water distribution water moving
• ocean currents
• elevation
• specific heat energy needed to raise T of 1 kg
• air by 1 K

• Average weather conditions in the interior of
  large continents are much different than average
  conditions in coastal areas.

11

January sea level Ta
Fig. 3-8, p. 64
12

July sea level Ta
Fig. 3-9, p. 64
13
Air Temperature Data
14
Daily, Monthly and Yearly Temperatures

• diurnal temperatur range Tmax Tmin
• large range occurs for dry, clear sky
  over desert
• clouds and humidity effects reduce daytime T but
  increase nighttime T
• proximity to large bodies of water
• Urban heat island
• annual temperature range
• max monthly T -- min monthly T

15

Fig. 3-11, p. 65
16

What is normal T (30-yr average) for a particular
day (March 15 over southwestern U.S.)?
Figure 2, p. 69
17
The Use of Temperature Data

• heating degree-days daily mean T below 64oF
• cooling degree-days daily mean T above 65oF
• growing degree-days daily mean T 1 degree above
  base T

18
Air Temperature and Human Comfort

• Human body stabilizes its T primarily by
  converting food
• into heat (metabolism)
• The stronger the wind, the faster the bodys heat
  loss
• High winds in below-freezing air can remove heat
  from exposed
• skin so quickly that the skin may actually
  freeze (called frostbite)
• Dry heat perspire to feel cool heat and
  humidity feel hotter

19
Air Temperature and Human Comfort

• wind chill index

Shaded area frostbite could occur in 30 min or
less
20
Measuring Air Temperature
While T is as high as 500oC in the upper
atmosphere of 300 km, astronauts still feel very
cold. Why?
21
Measuring Air Temperature

• liquid-in-glass thermometers mercury or alcohol
• maximum and minimum thermometers
• Infrared sensor or radiometer
• Electrical thermometers
• instrument shelters

22

Precip, wind, T/Td, rain type, lightning, cloud
base, freezing rain, visibility