After completing this lesson, you will be able to answer:
- What is meant by temperature?
- What is air temperature?
- Why the day and night temperatures vary ?
- How maximum and minimum temperatures are measured?
- What is the difference between maximum and minimum thermometers?
What is air temperature?
- Temperature is a measure of the level of sensible heat (temperature measured by a thermometer) of matter, whether it is gaseous (air), liquid (water), or solid (rock or dry soil).
- Air temperature is the intensity aspect of sun's energy that strikes the earth's surface.
- Because the amount of energy from the sun reaching the earth varies from day to day, from season to season, and from latitude to latitude, temperatures also vary.
- The earth as a whole receives a constant flow of radiant short-wave energy from the sun. The earth also radiates long-wave energy to space.
- During the day, the flow of short-wave radiation absorbed exceeds long -wave energy emitted, and the surface temperature increases.
- At no short-wave radiation strikes the darkened side of the earth. But, long-wave energy is still emitted from the surface. Therefore, surface temperatures decrease.
How air-temperature is measured?
- The liquid-in-glass thermometers are used to measure the minimum and maximum temperatures.
- Such thermometers are mounted side by side and read every 24 hours at a specific time. Once read, they are immediately reset.
The alcohol thermometer is usually used for recording minimum temperature
The mercury thermometer is usually used for recording maximum temperature.
An Alcohol thermometer is used to indicate the daily minimum temperatures. A small metal index is inside the glass tube. When the temperature reaches its lowest point, the metal index sinks. When the temperature rises again, the metal index stays at the lowest point and keeps a record of the lowest temperature. After that temperature is read and recorded, the thermometer is reset.
The Mercury thermometer is used to indicate high temperatures. It can record the highest temperature in a time period. There is a constriction just above the bulb of the thermometer that causes the mercury to rise, but when it cools, gravity doesn't allow all of the mercury to fall. The tiny thread of mercury breaks at the constriction at the highest temperature recorded.
This concludes Lesson 4- What is air temperature? - in this Module.
The next Lesson is about air pressure and its measurement.
Select Lesson 5 in Module III from course contents