Lesson 12, Topic 5
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# Temperature

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Temperature is the degree of hotness or coldness of a body, in this case, the atmosphere. It is commonly measured in Celsius or Fahrenheit. The Sun is the source of heat on Earth and directly affects the temperature.

### Measurement of Temperature using a Thermometer:

A thermometer is a narrow glass tube filled with mercury or alcohol. It works based on the principle that mercury and alcohol expand when heated and contract when cooled. The unit of temperature readings is either Celsius/Centigrade (°C) or Fahrenheit (°F). On a Centigrade Thermometer, freezing of water occurs at 0°C whereas the boiling point of water is 100°C. While on a Fahrenheit Thermometer, water freezes at 32°F and the boiling point of water is 212°F.

When measuring the Temperature of the Atmosphere (or air), it is important to obtain the reading exclusive of the heat of the sun’s intense radiation. To ensure the readings obtained are accurate, thermometers used for taking the Atmospheric Temperature are placed in a shelter known as the Stevenson Screen. A Stevenson Screen is a box-like shelter or enclosure, placed 4ft (or 1.2m) above the ground to protect metrological instruments against precipitation and direct heat radiation from outside sources, it has holes or spaces which allow air to circulate.

With the readings or recordings of a Thermometer, it is possible to convert from one scale to another. That is, convert readings from Celsius/Centigrade to Fahrenheit and vice-versa.

Calculating Temperatures:

To measure the maximum and minimum temperatures of the day, a combined maximum and minimum thermometer is used.

Mean Daily Temperature:

The maximum and minimum temperatures for the day are added together and then divided by two (2).

For example

Maximum Temperature = 27℃

Minimum Temperature = 24℃

The Mean Daily Temperature = $$\frac{27^oC \: + \: 24^oC}{2} = \frac{51^oC}{2} \\ = \scriptsize 25.5^oC$$

Mean Monthly Temperature:

This is the sum of the daily mean temperatures for one month divided by the number of days in the month.

For example, if the mean daily temperatures in February (in a leap year) are;

Summing up these values give 678℃, then divide by 29 because there are 29 days in February during a leap year.

= $$\frac{678}{29}$$

= 23.4℃

Mean Annual Temperature:

The sum of the mean monthly temperatures is divided by the number of months in a year, that is, 12.

For example, the mean figures for the respective months of a particular year are given below.

Total temperature of the year = $$\frac{\sum T}{12}$$

= $$\frac{340^o C}{12} \\ \scriptsize = 28.3^oC$$

Diurnal / Daily Temperature Range:

The Diurnal/Daily Temperature Range is the minimum temperature of the day subtracted from the maximum temperature of that same day. For example, if the;

Maximum Temperature of the day is 31℃

Minimum Temperature of that same day is 29℃

Diurnal/Daily Temperature Range = 31℃ – 29℃ = 2℃

∴ 2℃ is the Diurnal or Daily Temperature Range.

Annual Temperature Change:

Annual Temperature Change is the difference between the mean temperature of the hottest month and the mean temperature of the coldest month. For example, if the hottest month in Lagos is April with a mean temperature of 27.5℃ and the year’s coldest month is August with a mean temperature of 24.5℃.

Maximum Mean Temperature = 27.5℃ | Minimum Mean Temperature = 24.5℃

Annual Temperature Range = 27.5℃ – 24.5℃ = 3℃

∴ 3℃ = Annual Temperature Range

Annual Temperature:

Annual Temperature or Total Annual temperature is the summation of the mean monthly temperatures from January to December of that year. For example, using the data in the table above;

41+30+21+25+10+40+48+35+25+30+20+15

= 334℃

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