Thermometers are kept in a shelter that has plenty of ventilation to get a true reading of air temperature. Direct sunlight hitting the thermometer would make it read unrealistically high. Thermometers are usually 5 to 6 ft above the ground.

On a calm afternoon the ground and air near the ground may have temperatures much higher than recorded by the thermometer.

When the wind picks up the air mixes and so the difference in temperature between the near surface air and air higher up is reduced.

The maximum temperature is reached during the time of day when the incoming solar energy matches the outgoing longwave (terrestrial) energy. In the diagram this occurs at 4 PM. So the maximum temperature does not occur at the same time as the maximum sunlight.

On a calm evening the ground and air near the ground may have temperatures much colder than recorded by the thermometer. The ground radiates away energy much better than does the air.

When the wind picks up the air mixes and so the difference in temperature between the near surface air and air higher up is reduced.

Orchard heaters help prevent frost damage to trees.

Mixing the air with large fans helps prevent frost damage to trees.

Figure 3.19 A coating of ice protects these almond trees from damaging low temperatures, as an early spring freeze drops air temperatures well below freezing. Sprinkler systems can help prevent frost damage to trees through the release of latent heat energy as the water freezes to ice. Fig. 3-19, p. 70

Controls of Temperature Before looking at the next slide, try to list as many physical features that might influence the temperature and precipitation of a region like western WA.

Controls of Temperature Latitude Time of year Altitude Cloud cover Land Water proximity Ocean currents Mean air flow Mean Wind speed and direction Mountains Others??

Figure 3.20 Average air temperature near sea level in January (°F). In winter the Pacific ocean is warmer at most latitudes than the land areas in United States Fig. 3-20, p. 72

Figure 3.21 Average air temperature near sea level in July (°F). In summer the Pacific ocean is cooler at most latitudes than the land areas in United States. Also comparing this slide with the previous, the difference (or range) in temperature between summer and winter is larger for land areas than for oceans Fig. 3-21, p. 72

Figure 3.22 The daily range of temperature decreases as we climb away from the earth’s surface. Hence, there is less day-to-night variation in air temperature near the top of a high-rise apartment complex than at the ground level. The daily range in temperature (daytime high – night time low) is smaller as you travel up a very high building. Fig. 3-22, p. 73

Figure 3.23 Monthly temperature data and annual temperature range for St. Louis, Missouri, a city located near the middle of a continent and Ponta Delgada, a city located in the Azores in the Atlantic Ocean. Fig. 3-23, p. 74

Figure 3.24 Temperature data for San Francisco, California (37°N), and Richmond, Virginia (37°N)—two cities with the same mean annual temperature. Fig. 3-24, p. 74

On a local level for a given day, Figure 4 The high temperature measured (for 30 years) on March 15 in a city located in the southwestern United States. The dashed line represents the normal temperature for the 30-year period. On a local level for a given day, temperatures fluctuate drastically from year to year. Fig. 4, p. 75

Figure 3.25 Mean annual total heating degree-days in thousands of °F, where the number 4 on the map represents 4000 (base 65°F). (Data from U.S. Department of Commerce) Extra credit idea. Summarize how heating degree days and cooling degree days are defined and parcticaly used. Fig. 3-25, p. 76

Figure 3.26 Mean annual total cooling degree-days in thousands of °F, where the number 1 on the map represents 1000 (base 65°F). (Data from U.S. Department of Commerce) Fig. 3-26, p. 76

1st Thermometer. Galileo invented a rudimentary water thermometer in 1593 which, for the first time, allowed temperature variations to be measured.

Maximum thermometer for reading the maximum temperature during a 24 hr period.

Minimum thermometer for reading the minimum temperature during a 24 hr period.

A thermograph. These are becoming obsolete through the deployment of computer data loggers

Between roughly 35 N and 35 S Earth receives more sunlight than it radiates back to space via longwave radiation. Poleward of these latitudes Earth receives less sunlight than it radiates back to space via longwave radiation. The surplus and deficit are balanced by energy transport in the atmosphere and oceans.

The angular position of direct sunlight changes throughout the year The angular position of direct sunlight changes throughout the year. In the above diagram the direction of the solar collector is adjusted to an average position.