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Temperature
Chapter 3
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3.1 For the Record: Air Temperature
Data
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For the Record: Air-Temperature Data
 Basic calculations:
 Daily mean  Monthly mean
 Average of 24 hourly  Average of daily means
readings  Annual mean
 Daily temperature range  Average of monthly means
 Difference of daily  Annual temperature range
high and low  Difference of highest and
lowest monthly mean
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For the Record: Air-Temperature Data
Isotherms:
 Lineconnecting equal temperature
 Generally there is a 5° to 10° temperature
change per unit of difference
Closely spaced isotherms indicate rapid
temperature changes
Wider spaced isotherms indicate a more
gradual rate of change
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3.2 Why Temperatures Vary: The
Controls of Temperature
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Why Temperatures Vary: The Controls
of Temperature
Controls of temperature:
 Differential
heating of land and water
 Ocean currents
 Altitude
 Geographic positioning
 Cloud cover and albedo
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3.3 Land and Water
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Land and Water
Why do they cool differently?
Water is mobile.
 Temperatures rise and fall slower on water than
on land.
Land is opaque.
 Heat is absorbed only on the surface.
Specific heat is three times greater for water
than land.
Evaporation is greater over water.
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3.4 Ocean Currents
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Ocean Currents
 At the water surface energy is passed from moving
air to the water through friction. The drag exerted
by winds blowing steadily across the ocean causes
he surface layer of water to move.
 Minor horizontal movements of surface water are
closely related to the circulation of the atoms,
which in turn is driven by the unequal heating of
earth by the sun.
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12. +Ocean Currents
The transfer of heat by winds and ocean
currents equalize these latitudinal energy
imbalances
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3.5 Altitude
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Altitude
Temperatures decrease with altitude.
The atmosphere is thinner at higher altitudes.
Higher altitudes produce a greater daily
temperature range.
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3.6 Geographic Position
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Geographic Position
Windward coast
 Costal location where prevailing winds blow from the
ocean onto the shore
Leeward coast
 Costal location where prevailing winds blow from
land toward the ocean
Mountains can cut off the ocean winds and give
cities more continental temperatures
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Geographic Position
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3.7 Cloud Cover and Albedo
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Cloud Cover and Albedo
More clouds cause lower surface temperatures
during the day, but warmer temperatures at
night.
A high albedo reduces surface temperature.
 Clouds have high albedos, so incoming solar
radiation gets bounced back to space. So by
reducing incoming solar radiation, day temps
will be lower than if clouds were absent.
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Cloud Cover and Albedo
Snow acts like clouds
 Sunny days are cooler because energy the land
would have absorbed and used for heating the
air is reflected and lost.
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3.8 World Distribution of
Temperatures
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World Distribution of Temperature
There is a smaller temperature range at the
equator.
There is a larger temperature range at higher
latitudes.
Interiors of continents have a higher
temperature range.
Coastal regions have a smaller temperature
range.
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World Distribution of Temperature
There are also latitudinal shifting of
temperatures caused by seasonal migration of
the sun
 Look at colors on figures 3.18 and 3.19
Isotherms in Southern Hemisphere are much
more regular than in Northern Hemisphere.
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Figure 3.18 pg. 78
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Figure 3.19 pg. 78
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3.9 Cycles of Air Temperature
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Cycles of Air Temperatures
Daily temperature variations:
 Primary control of the daily cycle of air temp is
earth’s daily rotation causing periods of light and
dark.
 At noon time incoming rays exceed outgoing equal a
surplus for a few hours. When the input is no longer
exceeds the rate of energy lost by Earth the
temperature falls.
 Vary by seasons.
 Vary with cloud cover.
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Cycles of Air Temperatures
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Cycles of Air Temperatures
Magnitude of daily temperature change:
 At mid and low latitudes, a high sun angle
results in a large variation throughout the day.
 At higher latitudes, a low sun angle results in
lower temperature variations.
 Windward coasts have small variations.
 Inland areas have larger variations.
 Temperature change depends on the amount of
cloud cover and water vapor.
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Cycles of Air Temperatures
Annual temperature variations:
 Highest and lowest mean temperatures do not
coincide with maximum or minimum incoming
solar radiation.
 In the northern hemisphere, August has the
highest mean temperature, while June has the
highest incoming solar radiation.
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3.10 Temperature
Measurements
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Temperature Measurement
Mechanical thermometers:
 Liquidin glass
 Maximum thermometer—mercury
 Minimum thermometer—alcohol
 Thermograph—bimetal strip
Electrical thermometers:
 Thermistor—electrically resistant at different
temperatures
 Very fast
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Temperature Measurement
Instrument shelters:
 White box
 Louvered sides
 Over grass
 1.5 m above ground
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3.11 Temperature Scales
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Temperature Scales
Fixed points:
 Ice point
 Ice melts
 32° F, 0° C, 273 K
 Steam point
 Water boils
 212° F, 100° C, 373 K
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Temperature Scales
°F = (1.8 x °C) + 32
°C = (°F-32)/ 1.8
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3.12 Heat Stress and Wind Chill
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Heat Stress and Wind Chill: Indices of
Human Discomfort
Apparent temperature is the temperature a
person perceives.
Heat stress is caused by high temperature and
high humidity.
 Sweat does not evaporate from body.
 Feels hotter
 Heat stress index
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Heat Stress and Wind Chill: Indices of
Human Discomfort
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Heat Stress and Wind Chill: Indices of
Human Discomfort
 Wind chill is the cooling power of moving air.
 Evaporates moisture
 Cools body thus feel colder
 Wind chill chart
 Calculates how the wind and cold feel on human
skin
 A calm sunny winter day feels warmer because the
warm feeling is caused by the absorption of direct
solar radiation by the body
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Heat Stress and Wind Chill: Indices of
Human Discomfort
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