Air Temperature

• Surface Temperature

• Air Temperature

• The Daily Cycle of Air Temperature

• Temperature Structure of the Atmosphere

• The Annual Cycle of Air Temperature

• World Patterns of Air Temperature

• Global Warming and the Greenhouse Effect

Surface Temperature

Surface Temperature

measured

at 1.2

meters (4

feet) above

the ground

surface by

weather

recording

instruments

Figure 3.4, p. 92

Five key factors influence Air Temperature

Insolation - daily and seasonal variations

Latitude - also daily and seasonal variations, and energy deficit

Surface type - albedo of surface as well as surface moisture

Coastal vs. interior location - temperature range is lower at

coasts

Elevation - thinner atmosphere means less greenhouse effect

varies with

time of day

and season

early or late in

the day there

is a deficit

the length of

time for a

surplus also

changes

seasonally

Air Temperature – Daily Cycle of Insolation

Figure 3.3a, p. 91

Air Temperature – Daily Cycle of Net Radiation

when net

radiation is

Positive

(surplus) a

surface gains

heat

when net

radiation is

negative

(deficit) a

surface loses

heatFigure 3.3b, p. 91

daily

maxima and

minima

positive net

radiation

leads to an

increase in

temperature

notice that

there is a

time lag

Figure 3.3c, p. 91

Air Temperature – Daily Cycle of Temperature

Cooler Temperatures - rural areas

transpiration from leaves cools the surface

evaporation from moist soils plus transpiration

= evapotranspiration

Warmer Temperatures - urban areas

water is channeled so surfaces tend to be dry

surfaces are often dark (asphalt)

building materials store heat, and heat is

released from buildings

the heat island tends to persist over night

parks can reduce the heating

desert urban areas often do not exhibit heat islands

since irrigated vegetation may make the city cooler

Air Temperature – The Urban Heat Island

Figure 3.6, p. 94

Temperature Structure of the Atmosphere

atmosphere = gaseous envelope surrounding

the Earth

made up of a series of concentric layers

atmosphere is held down by gravity

most of the atmosphere’s mass is near the

surface

troposphere

bounded by the

tropopause

(~12km)

immediately above

is the stratosphere

in which the

temperature

increases with

altitude and a

prevalence of

ozone absorbs

ultraviolet (UV)

radiation

Temperature Structure of the Atmosphere

Figure 3.9, p. 97

Temperature Structure of the Atmosphere

Figure 3.9, p. 97

Stratosphere is

bounded by the

stratopause

immediately above

is the mesosphere

where

temperatures

decrease with

altitude (bounded

by the mesopause

above)

immediately above

is the

thermosphere

Heat is transferred through the atmosphere by:

Conduction (direct heat transfer from the heated ground surface to the atmosphere)

Convection (heat transfer by warm air moving to colder upper atmosphere)

Advection (heat transfer by warm air mixing with colder adjacent air)

Temperature Structure of the Atmosphere

Temperature Structure of the Atmosphere

The troposphere is the lower most atmospheric layer

temperature

decreases on

average by

6.4˚C per 1000

meters (3.5˚F

per 1000 feet) in

the troposphere

(environmental

lapse rate)

Figure 3.8, p. 96

sometimes

upper air is

warmer than

lower air

(temperature

inversion)

occurs if the

ground cools

overnight

cold air may

flow into an

area

Temperature Structure of the Atmosphere

Figure 3.12, p. 99

Cities in Peru at altitude

generally temperatures drop with altitude

daily temperature range also increases due drier air and less

absorption

Elevation and Temperature

Figure 3.11, p. 98

January Isotherms

Air temperature is warmer at the equator than at the poles, but land and water, ocean currents, and elevation create additional variations.

July IsothermsSouthern hemisphere has fewer land masses and ocean currents that encircle the globe, creating isotherms that are more regular than those in the northern hemisphere. Figure 3.22

World Air Temperature Patterns

1. Temperature decreases from the equator to the poles

2. Large land masses in Arctic and subarctic regions

develop centers of extreme cold

3. Temperatures in equatorial regions are relatively

constant

4. Isotherms over land masses make large seasonal shifts

5. Highlands are always colder than surrounding lowlands

6. Areas of perpetual ice and snow are always cold

The Annual Cycle of Air

Temperature: Net Radiation and

Temperature

Low latitudes have

greater amounts

and longer periods

of surplus energy

High latitudes

experience large

and long periods of

deficit

Figure 3.14, p. 100

land heats and cools

quickly while water

heats and cools

slowly

maritime locations

experience a smaller

annual range of

temperature

(maritime climates)

continental locations

experience a larger

annual range of

temperature

(continental climates)

The Annual Cycle of Air Temperature: Land and

Water Contrasts

Figure 3.15, p. 101

The Annual Cycle of Air Temperature: Land and

Water Contrasts

Figure 3.17, p. 102

World Patterns of Air Temperature

distribution of air

temperatures

shown on a map

uses isotherms

(lines of equal

temperature)

reveal centers of

low or high

temperatures,

and temperature

gradientsFigure 3.19, p. 103

temperatures

decrease from

the equator to

the poles

large

landmasses

located in the

subarctic and

arctic zones

develop

centers of

extremely low

temperatures in

winter

World Patterns of Air Temperature

Figure 3.20, p. 105

Temperatures in

equatorial regions

change little from

January to July

Isotherms make a

large north-south shift

from January to July

over continents in the

midlatitude and

subarctic zones

World

Patterns of Air

Temperature

Figure 3.20, p. 105

highlands are

always colder than

surrounding

lowlands

areas of perpetual

ice and snow are

always intensely

cold

World Patterns of Air Temperature

Figure 3.20,

p. 106

Global Warming and the Greenhouse Effect

p. 110

atmospheric

concentrations

of carbon

dioxide are

currently

increasing at a

rate of 4% per

year

Greenhouse gas

concentrations

• Concentrations have

increased dramatically

since Industrial

Revolution

• Increases since 1750

– CO2 -- 31%

– CH4 -- 151%

– N2O -- 17%

Global Warming and the Greenhouse Effect

Figure 3.24, p. 109

Earth’s

mean

surface

temperature

(1866 –

2002)

Projected temperature

changes

• IPCC (2000) expects global average T rise of 1.4 to 5.8 oC from 1990-2100

– Amount varies with emission scenario and computer model

– Some scientists argue system is not predictable given current knowledge

• Projected warming rate is much larger than observed in 20th century and probably unprecedented in last 10,000 years

• Most land areas will warm faster than global average

The IPCC is the Intergovernmental Panel on Climate Change