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.

Fig. 3-19, p. 70

Sprinkler systems can help prevent frost damage to trees through the release of latent heat energy as the water freezes to ice.

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 TemperatureLatitudeTime of yearAltitudeCloud coverLand Water proximity Ocean currentsMean air flowMean Wind speed and directionMountains

Others??

Fig. 3-20, p. 72

In winter the Pacific ocean is warmer at most latitudes than the land areas in United States

Fig. 3-21, p. 72

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. 3-22, p. 73

The daily range in temperature (daytime high – night time low) is smaller as you travel up a very high building.

Fig. 3-23, p. 74

Fig. 3-24, p. 74

Fig. 4, p. 75

On a local level for a given day, temperatures fluctuate drastically from year to year.

Fig. 3-25, p. 76

Extra credit idea. Summarize how heating degree days and cooling degree days are defined and parcticaly used.

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. In the above diagram the direction of the solar collector is adjusted to an average position.