Temperature

Copyright © 2013 Pearson Education, Inc.

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TemperatureChapter 3


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3.1 For the Record: Air Temperature Data


+For the Record: Air-Temperature Data

Basic calculations: Daily mean

Average of 24 hourly readings

Daily temperature range Difference of daily

high and low

Monthly mean Average of daily means

Annual mean Average of monthly means

Annual temperature range Difference of highest and

lowest monthly mean


+For the Record: Air-Temperature Data

Isotherms:Line connecting equal temperatureGenerally 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


+Why Temperatures Vary: The Controls of Temperature

Controls of temperature:Differential heating of land and waterOcean currentsAltitude Geographic positioningCloud cover and albedo


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3.3 Land and Water


+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


+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.


+Ocean CurrentsThe transfer of heat by winds and ocean currents equalize these latitudinal energy imbalances


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3.5 Altitude


+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


+Geographic Position

Windward coastCostal location where prevailing winds blow from the

ocean onto the shore

Leeward coastCostal location where prevailing winds blow from

land toward the ocean

Mountains can cut off the ocean winds and give cities more continental temperatures


+Geographic Position


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3.7 Cloud Cover and Albedo


+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.


+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


+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.


+World Distribution of Temperature

There are also latitudinal shifting of temperatures caused by seasonal migration of the sunLook at colors on figures 3.18 and 3.19

Isotherms in Southern Hemisphere are much more regular than in Northern Hemisphere.


+Figure 3.18 pg. 78


+Figure 3.19 pg. 78


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3.9 Cycles of Air Temperature


+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.





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.



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


+Temperature Measurement

Mechanical thermometers:Liquid in glassMaximum thermometer—mercuryMinimum thermometer—alcoholThermograph—bimetal strip

Electrical thermometers:Thermistor—electrically resistant at different

temperaturesVery fast


+Temperature Measurement

Instrument shelters:White boxLouvered sidesOver grass1.5 m above ground


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3.11 Temperature Scales


+Temperature Scales

Fixed points:Ice point

Ice melts32° F, 0° C, 273 K

Steam pointWater boils212° F, 100° C, 373 K


+Temperature Scales

°F = (1.8 x °C) + 32

°C = (°F-32)/ 1.8


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3.12 Heat Stress and Wind Chill


+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





Wind chill is the cooling power of moving air.Evaporates moistureCools body thus feel colderWind 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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