Keeping Weather Records And Instruments-Rainguage
There are ways in which weather records and instruments can be kept.They are as follows:
1. Measurement of rainfall: Rainfall including other forms of precipitation is measured by an instrument called rain-guage. A rain-guage consists of a metal funnel that leads to a glass bottle which is enclosed within a copper cylinder. The funnel is connected to an inner container where the water is collected. There is also a measuring jar which is used for measuring the rain water.
How rain-guage is used
The rain guage is installed 30 cm above the ground level to avoid water splash. Rain that falls each day is collected in the glass jar. The rain water enters the inner container or glass jar through the funnel. The rain guage is placed in an open space free from any water splash entering the funnel. Then the rainwater that falls in the inner container is emptied each day and measured in the calibrated measuring jar or it can be read directly from the glass jar. The total rainfall for each month is added to get the monthly rainfall which is added at the end of the year to get the total rainfall for the year.
how to use rainfall data
- For agricultural purposes
- For calculation of mean annual rainfall
- To determine the characteristics of rainfall
- For calculation of monthly mean annual rainfall
- For educational purposes
- For planning military operations
- For air and sea navigation
2) Measurement of temperature:
The temperature of a place is measured by an instrument called thermometer. The thermometer is a narrow glass tube filled with mercury and alcohol. I t works on the principle that mercury and alcohol expand when heated and contract when cooled. The temperature is commonly recorded in centigrade or fahrenheit scale. The freezing point for centigrade scale is zero degree centigrade while that of the boiling point is 100 degree centigrade and thst of the fahrenheit is 212
Geographers are interested in a shade temperatures which is the temperature of the air to exclude the intensity of the sun’s radiant heat. For you to get accurate record,you must keep the thermometer in a standard shelter called the stevenson screen to protect them from the effects of radiant heat. The stevenson screen can be a wooden box raised above the ground to a height of 4ft or 1.2m
3) measurement of wind:
Wind has direction and speed.The direction of wind is measured with an instrument called Wind Vane while the speed of the Wind is also measured with a different instrument called Anemometer.
Wind vane is made up of two parts –
a) The narrow or vane on the top,which is free to move with the prevailing wind.
b) The stationary part which consist of a frame and four compass points.
The vane or narrow points to the direction from which the wind is blowing so that the wind is named from the direction it blows. For example south west wind blows from south west direction.
Wind vane is located in an exposed position so that tall buildings and trees will not deflect the wind direction.
The anemometer consists of three or four semi circular cups attached to the end of horizontal spokes mounted on a high vertical spindle. As the wind blows,the cups rotates.The higher the speed of the wind,the greater the speed of the cups.
4) measurement of pressure:
The instrument used in measuring atmospheric pressure is called Barometer.Pressure is measured in unit of force called millibars. The normal atmospheric pressure shows a reading of 760mm(76cm) or 1013 millibars. A reading of 790mm is regarded as high pressure while 700mm is regarded as low pressure.
Mercury barometer consists of a beaker in which a glass tube is dipped;both contains mercury. Another instrument used in measuring pressure is the aneroid barometer.But a modified aneroid barometer is used in aeroplanes is called Altimeter.