Weather - Geography Form 1
Gadgets such as a radiosonde carries a balloon up to 12 km above the ground with weather instruments that records temperature and pressure.
Satellites are also used recording and transmitting weather records and photographs of clouds and movement of cyclones.
Traditional weather prediction is done by studying vegetation and the behaviour of animals and insect.
By the end of the session you should be able to ;
a) define weather
b) state weather elements
c) expain the conditions necessary for setting up a weather station.
d) use instruments to measure weather elements.
e) analyse and interprete data on weather conditions
f) describe the structure and composition of the atmosphere
g)explain the factors influencing weather
Various weather elements combine to produce certain weather conditions. these inlude;
Sunshine which is light and heat from the sun
Temperature - Hotness or coolness of a place
Humidity - Moisture particles
Precipitation - All forms of moisture, such as rain, snow, or hail.
Atmospheric pressure - weight of the atmosphere upon the earth
Winds - Moving air
Measurement of weather elements
Different instruments are used to measure and record elements of weather.The table below shows the elements of weather and the corresponding measuring instrument.
A Weather station
By the end of this lesson you should be able to;
- describe a weather station
explain the conditions for setting up an ideal weather station
- describe the Stevenson's screen
- identify the instruments kept in the Stevenson's screen
- Weather station
A weather station is an area set aside and fitted with the necessary instruments for measuring, reading, observing and recording weather elements.
Conditions necessary for setting up a weather station
The space must be open to allow free flow of air
The success of the weather station depends on proper management and maintenance of records. There must be a trained person to maintain the following records
A graphical record book
Within the station a container for keeping some weather measuring instruments is built. This is the Stevenson screen.
The Stevenson Screen
By the end of the session you should be able to;
describe the Stevenson Screen
identify the instruments kept in the Stevenson Screen.
The Stevenson screen
The Stevenson screen is a wooden box raised on four stands.
It houses thermometers and the hygrometer
The screen has louvered sides to allow the free air circulation.
Has open slots for air circulation at the base.
The roof has double boards to reduce the direct absorption of heat from the sun
It is painted white both inside and outside to reflect heat and light avoiding undue influence on air temperature.
The stands are usually metallic to withstand rotting or attack by termites
The box should be raised 1.2metres so that the heat from the ground does not influence air Temperature.
Provides shelter for delicate instruments for reliable and accurate records.
For further understanding of weather elements, more information is provided on each of the elements
By the end of the session you should be able to explain factors that influence different weather elements.
Factor influencing Temperature
Temperature over the earth's surface will differ due to the following factors that influence atmospheric insolation and radiation.
- Length of day
- Distance from the water bodies
- Ocean currents
- Cloud cover
Latitudes are imaginary lines on the earth's surface. They are parallel to the Equator. It is the angular distance of any point on the earths surface North or South of the equator which is 0 degrees.
There are 180 degrees lines of Latitudes, 90 degrees N and 90 degrees S of the equator. The temperature decreases with increasing latitude. this means that as you move towards the poles the temperature becomes lower.At 90 degrees N and 90 degrees S there is permanent Ice.
This variation can be explained using this diagram which stresses these facts.
The angle at which the rays strike the earth's surface determines the temperature. At the equator the rays are at/near right angles and therefore hotter than areas further away where the angle of the suns rays become acute to making the area much colder.The surface covered by equal suns rays reaching the surface of the earth increases away from the equator.The smaller area at the equator therefore receives more heat than further away.The atmosphere through which the rays pass is thinner at the equator and wider further away. A lot of heat is lost through the wider atmosphere. Areas around the equator are hotter than areas on latitudes that are away from the equator.
The length of Day
The longer the day the more hours of insolation. (Ammount of heat recieved from the sun).
This raises the air temperatures.
The shorter the days, the lower the insolation.
This lowers the air temperature. For instance, when the sun is over head in June at the Tropic of Cancer, the days are longest in the Northern hemisphere.
Altitude refers to the height of the land above sea level. The height of the land varies from the high mountains to the low coastal plains. Temperature drop or decrease as altitude increase.
The rate of temperature decrease with increasing altitude is known as lapse rate which is 0.65 degrees Celcius/100 metres of ascent or 6.5 degrees c /1000 metres of ascent.
Aspect means the direction that a slope faces to or away from the sun.
Aspect influences Temperature where certain slopes in hilly areas receive direct rays of the sun and are warmer than the slopes that are shielded by hills and receive indirect rays. Aspect is felt mainly in high and mid latitudes (away from the equator)
Wind is moving air. The winds are cold or warm depending on their origin.Winds from cold places lowers temperature of the areas they blow over while those from hot areas the winds raises the temperature.