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Weather records
Following are some of the weather records that might be kept by individuals. Details are included about the best position for each instrument that will result in relatively accurate and consistent records. Measurements should be taken at least once each day, usually at 9 am.
Rainfall
Rainfall is measured with a rain gauge and recorded in millimetres (mm).
The gauge is usually mounted on a post on relatively flat ground. It should
be in the open, away from trees, buildings and other shelters.
Temperature
Temperature is measured using a thermometer and is recorded in degrees Celsius
(°C).
Maximum-minimum thermometers record the hottest and coldest temperatures experienced
and should be reset on a regular basis. Thermometers are usually mounted on
a post or veranda wall that is shaded all day and out of the rain. At weather
stations, thermometers are placed in a specially designed wooden box called
a Stevenson screen.
Humidity
Relative humidity is measured using a wet bulb thermometer and is recorded
as a percentage (%).
The wet bulb thermometer is placed in a shady position with free flowing air.
The bulb of the thermometer is wrapped in muslin that is kept damp. The temperature
recorded is compared with that of a normal (dry bulb) thermometer and the relative
humidity calculated from a table of figures.
Evaporation
Evaporation is measured with a pan evaporimeter and is recorded in millimetres
(mm).
The pan is placed on the ground in an open area and filled with water to a
set level. Wire mesh is often placed over the pan to stop birds and other animals
drinking the water. The water level is measured daily and adjusted to take
any rainfall into account.
Wind direction
Wind direction is measured using a weather vane or wind sock and is recorded
as a compass direction.
Weather vanes are usually mounted on tall posts or roof tops where they can
catch the prevailing winds. A wind sock is mounted on a tall post beside an
airstrip.
Wind speed
Wind speed is measured using an anemometer and is recorded in knots. One knot
approximately equals two kilometres per hour (1 knot » 2 km/hr).
Anemometers are specialised pieces of equipment usually only found in weather
stations. Wind speeds can be estimated and described using terms such as calm,
light, moderate, strong and gale force.
Air pressure
Air (atmospheric) pressure is measured with a barometer and is recorded in
hectopascals (hPa).
Barometers are usually kept inside and hung on a wall or placed on a sideboard
or cabinet as a feature.
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