A. Earth-Atmosphere System

• the Earth-atmosphere energy system is in a state of balance; i.e., 100 units of energy come into the system, and 100 units leave.

• the earth and atmosphere must return to space as much energy as they take in - otherwise the earth's average surface temperature would change

• the budget: 100 units of insolation

20 units ...... absorbed by clouds and the atmosphere

50 units ...... absorbed at the earth's surface

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70 units .........radiated back to space by the Earth-Atmosphere system

• the earth maintains a delicate balance between incoming and outgoing energy, and essentially there is no yearly gain or loss of total energy, thus the average temp of the earth remains fairly constant from year to year.

• in contrast, the Earth's surface receives a surplus of energy, while the atmos. exhibits a deficit

• the daily variation in air temperature is controlled (primarily) by insolation

• when insolation exceeds outgoing longwave, the air temperature rises; when outgoing longwave exceeds insolation, the temperature falls

• as insolation input decreases toward sunset, the energy lost (longwave) exceeds the energy input (insolation) - temps begin to drop

• (the warmest time of the day occurs not at the moment of maximum insolation (solar noon), but at the moment when a maximum of insolation is absorbed)

• the warmest time of the day thus occurs 3-4 hours after solar noon - lag between peak insolation & maximum temperature

A. Introductory Concepts

Temp. Definition:

• a measure of the average speed of the atoms and molecules that comprise air. (higher temps correspond to faster average speeds.)

• air temperature is measured on a regular basis from thermometers mounted in an "instrument shelter"
• these shelters, keep the thermometer from direct sunlight, and allow for a free flow of air
• max and min temperature thermometers are usually mounted in the shelter as well

Daily Mean Temp = (max + min) / 2

Daily Temp Range = (max - min)

Monthly Mean Temp = sum of the daily means/ # days in month

Annual Mean = average of 12 montly means

Annual Temp Range = diff. between highest and lowest montly mean temp

Defn: any factor that causes air temperature to vary from place to place and from time to time

(1) Latitude:

• insolation receipt is the most important influence on temperature variations

• recall that direct insolation is more concentrated (provides more heating) than oblique insolation; and the equatorial areas are the only latitudes to receive direct insolation;

• thus, there is a decrease in insolation/ heating/temperature from the equatorial regions northward and southward toward the poles

• from the equator poleward: continually warm; seasonally variable; always cold

recall: temperature decreases w/ht. in the troposphere. why?

• the distance from the heat source (the ground) increases;

• and the air becomes less dense (thinner) w/ht., & thus it's ability to absorb and radiate energy lessens w/ht.

• average temps are lower

• nightime temps (minimums) are lower

• diurnal temperature ranges are greater

• UV component is greater - sunburn hazard

cloud type, height, and thickness determine how insolation is reflected

• low thick clouds have albedo of ~ 90%

• high, thin (ice crystal) clouds have albedo of ~ 50%

• clouds are moderating influences on temp - they produce lower daily maximum temps & higher nightime minimums

• clouds result in slightly lower Earth-atmos. system temperatures

• more moderate (less extreme) temperature patterns are associated with water bodies vs. land masses

continental (continentality) - stations that lack the temperature-moderating effects of large water bodies - they exhibit a greater range of diurnal and annual temperatures than maritime locations

what causes these differences?

Land-Water Temperature Controls:

• Evaporation:

• Transmissibility:

over land, the energy is concentrated and contained in the top most layer, & thus higher temps are achieved there

• Specific Heat:

• mixing (movement):

influence the temperatures of adjacent land masses - Gulf Stream & Japan Current produce milder temps for Eastern U.S. & Japan

Example: - Marine (Vancouver) vs. Continental (Winnipeg) Location:

Vancouver (Marine Location) has a smaller annual and daily temperature range than Winnipeg (Continental Location)

"Isotherms" - connect locations having the same temperature - show temp patterns

Highlights:

January: isotherms trend zonal; S. Hemisphere; hottest temps/coldest temps are over the landmasses; coldest temps are in NE Siberia - clear, dry, & calm.

July: (winter now in S. Hemisphere, but since there is more ocean area in S. Hemisphere it has milder winters than N. Hemisphere); warmest temps found in N. Hemisphere deserts - clear skies, dry air & land, & strong insolation.

Range : (recall that a combination of daylength and angle of insolation determine heating);

• an equatorial station - which experiences little variation in daylength and sun angle throughout the year- has a small annual temp range
• a mid-latitude station - which experiences a greater variation in daylength and sun angle throughout the year- has a larger annual temp range
• thus: the annual temperature range increases with an increase in latitude
• since a continental lecation vs. a marine location experieinces hotter summers and colder winters, the annual temperature range increases with an increase in continentality;
• e.g., Yakutsk, Siberia = 62.2 C (112 F) range