13 Calculating mean temperature and temperature range
The temperature range is the difference between the highest temperature and the lowest temperature. It can be calculated for daily, monthly or annual periods. The lowest temperature is subtracted from the highest temperature for whichever period is being calculated.
Highest temperature – Lowest temperature = Temperature range
The average or mean daily temperature is calculated by adding the lowest and the highest temperature for the day and dividing by two. The mean temperature is also calculated on a monthly and an annual basis.
The mean monthly temperature is calculated by adding the mean daily temperatures and dividing by the number of days in the month.
The mean annual temperature is calculated by adding the mean monthly temperatures and dividing by 12.
Max temp. Min temp.
20 °C
10 °C
0 °C Jan
: Figure 13.26 A maximum and minimum thermometer
Feb Mar Apr May Jun Jul Aug Sep : Figure 13.27 Maximum and minimum monthly temperatures Oct Nov Dec
NUMERACY ACT VITY
Examine Figure 13.27. Can you calculate the mean annual temperature? Calculate the mean summer and winter temperatures also.
Atmospheric pressure
1. Atmospheric pressure is the weight of the atmosphere pressing down on the Earth.
2. The instrument used to measure atmospheric pressure is called a barograph.
A barograph consists of a small container with a moveable top. As the atmospheric pressure rises, the top is pushed inwards. As the pressure decreases, the top pushes back up again. A system of levers connects the top to a pen, which traces atmospheric pressures onto a barogram, located on a revolving drum.
3. The unit of measurement of atmospheric pressure is millibars (mb) or hectopascals.
4. The lines on a weather map that show areas of equal atmospheric pressure are called isobars. 241
