Measurements of Weather and Climate

Measuring and Recording Air Temperature
Temperature is a very important element of climate and weather.
The instrument for measuring temperature is the thermometer, which is a narrow glass tube filled with mercury or alcohol.
It works on the principle that mercury expands when heated and contracts when cooled.
On thermometers, temperatures are marked in two ways.
In °F. (Fahrenheit)
Freezing-point is 32°F. and the boiling-point is 212°F.
2. In Centigrade °C. scale is preferred.
Its freezing-point is 0°C. and its boiling-point is 100°C.
These two scales are interconvertible
C = (F – 32 )𝟏𝟎𝟎/𝟏𝟖𝟎="(F – 32 )" 𝟓/𝟗 𝑭=𝒄(𝟏𝟖𝟎/𝟏𝟎𝟎)+𝟑𝟐= 𝒄(𝟗/𝟓)+𝟑𝟐
Mean daily temperature: it is calculated by adding the maximum and minimum temperature of the day and dividing the sum by 2.
Daily (diurnal) range of temperature: it is the difference between the daily maximum and daily minimum temperature.
Mean monthly temperature: is determined by adding together the daily averages and the dividing the number of days in a month.
Mean annual temperature: it is calculated by adding the mean monthly temperatures and dividing the sum by 12.
Annual range of temperature: it is the difference between the temperatures of the hottest and coldest months.

Measuring and Recording Rainfall
Rainfall is measured using a rain gauge.
Rain gauge is usually anchored in the ground with the top of the gauge around 30cm above the ground surface to ensure that rain splash does not affect the results.
The depth of the rain in millimeters can be read from the side of the container at least once a day (usually at 9:00a.m).
A records is kept of the amount of rain (if any) which has fallen during the past 24 hours.
At the end of a month the daily amount rainfall records are added together and this gives, of course, the total amount of rainfall for that month.
Mean monthly rainfall: it is calculated by adding all the amounts of rainfall on daily basis for the month and dividing the sum by the number of days of the month.
Total annual rainfall: it is calculated by adding the amounts rainfall of the 12 months.
Mean annual rainfall: it is calculated by adding the annual amounts of rainfall for 35 years and dividing the sum by the number of those years.

Measuring and Recording Air Pressure
Air is made up of a number of mixed gases and has weight.
This weight exerts a pressure on the earth’s surface which varies from place to place and from time to time.
This force that presses on the surface of any object can be fairly accurately measured.
The instrument for measuring pressure is a barometer.
The unit more commonly used for measuring pressure is called millibar and millimeter.
At sea level, the mercury column is 1013.25 millibars, or 760 mm.


Measuring and Recording Wind Speed
Wind speed can be measured using an anemometer.
The anemometer should be held at arm’s length, above the head so that the cups can rotate without any interference.
Measuring and Recording Wind Direction
Wind direction is reported by the direction it is blowing from, according to the compass.
Wind blowing from the west is travelling eastwards so is called a westerly wind, not an easterly wind.
Wind direction is often observed using a wind vane.