the weather station
a weather station is a place where the elements of weather - temperature, humidity, pressure, wind direction and velocity, cloud cover and sunshine are measured and recorded as accurately as possible.
the stevenson screen is a wooden box standing on four legs at a height of about 120cm. the screen is built so that the shade temperature of the air can be measured. the sides of the box have slats (louvers) to allow free entry of air, and the roof is made of double boarding to prevent the sun's heat from reaching the inside of the screen. insulation is further improved by painting the outside of the screen white so as to reflect much of the sun's energy.
instruments kept inside the stevenson screen include a maximum and minimum thermometer and a wet- and dry- bulb thermometer (hygrometer). instruments placed outside the stevenson screen include a rain gouge, a wind vane to determine wind direction, and an anemometer to assess wind speed.
rain gouge is kept well clear of trees and buildings so that only raindrops falling directly from the sky enter the funnel of the gauge. use to measure rainfall and it's consist of a cylindrical copper container.the gauge is placed in an open space so that no runoff from trees or buildings or other object can get into the funnel. the other case is sunk into the ground to prevent the sun's heat from evaporating any of the rain collected in the glass jar.
measurement of air pressure
pressure varies with temperature and altitude, and the instrument that measures pressure is called barometer with millibars of the unit.
a mercury barometer consists of a hollow tube from which the air is extracted before the open end is placed in a bath of mercury. when the pressure of the mercury in the tube balance the pressure of the air on the exposed mercury, the mercury in the tube stop rising.
an aneroid barometer is an instrument that consist of a small metal cylinder which is a vacuum chamber. a barograph is an aneroid barometer which continuously records for one week.
measurement of wind direction and velocity
the speed of the wind is measure by an anemometer, which consist of three or four metal cups fixed to metal arms that rotate freely on a vertical shaft. the number of rotations are recorded on a meter to give the speed of the wind in km/hour.
measurement of temperature
temperature is measured using thermometer. a continuous temperature reading is given by a thermograph.
maximum thermometer
maximum temperature is obtained by reading the scale at the end of the index which was in contact with the mercury.
minimum thermometer
the daily or diurnal temperature range is found by subtracting the minimum temperature from the maximum and minimum.
How is relative humidity measured?
wet- and dry- bulb thermometers are used to measure relative humidity.
Recording the weather
clouds
climate associated with tropical rainforest and hot desertsa weather station is a place where the elements of weather - temperature, humidity, pressure, wind direction and velocity, cloud cover and sunshine are measured and recorded as accurately as possible.
the stevenson screen is a wooden box standing on four legs at a height of about 120cm. the screen is built so that the shade temperature of the air can be measured. the sides of the box have slats (louvers) to allow free entry of air, and the roof is made of double boarding to prevent the sun's heat from reaching the inside of the screen. insulation is further improved by painting the outside of the screen white so as to reflect much of the sun's energy.
instruments kept inside the stevenson screen include a maximum and minimum thermometer and a wet- and dry- bulb thermometer (hygrometer). instruments placed outside the stevenson screen include a rain gouge, a wind vane to determine wind direction, and an anemometer to assess wind speed.
rain gouge is kept well clear of trees and buildings so that only raindrops falling directly from the sky enter the funnel of the gauge. use to measure rainfall and it's consist of a cylindrical copper container.the gauge is placed in an open space so that no runoff from trees or buildings or other object can get into the funnel. the other case is sunk into the ground to prevent the sun's heat from evaporating any of the rain collected in the glass jar.
measurement of air pressure
pressure varies with temperature and altitude, and the instrument that measures pressure is called barometer with millibars of the unit.
a mercury barometer consists of a hollow tube from which the air is extracted before the open end is placed in a bath of mercury. when the pressure of the mercury in the tube balance the pressure of the air on the exposed mercury, the mercury in the tube stop rising.
an aneroid barometer is an instrument that consist of a small metal cylinder which is a vacuum chamber. a barograph is an aneroid barometer which continuously records for one week.
measurement of wind direction and velocity
the speed of the wind is measure by an anemometer, which consist of three or four metal cups fixed to metal arms that rotate freely on a vertical shaft. the number of rotations are recorded on a meter to give the speed of the wind in km/hour.
measurement of temperature
temperature is measured using thermometer. a continuous temperature reading is given by a thermograph.
maximum thermometer
maximum temperature is obtained by reading the scale at the end of the index which was in contact with the mercury.
minimum thermometer
the daily or diurnal temperature range is found by subtracting the minimum temperature from the maximum and minimum.
How is relative humidity measured?
wet- and dry- bulb thermometers are used to measure relative humidity.
Recording the weather
clouds
- high clouds are usually composed solely of ice crystals and have a base between 5500 and 14,000m (cirrus-white filaments,cirrocumulus-small ripped elements, cirrostratus-transparent sheet often with a halo)
- medium clouds are usually composed of water droplets or mixture of water droplets and ice crystals, and have a base between 2000 and 7000m (altocumulus,altostratus,nimbostatus)
- low clouds are usually composed of water droplets, though comolonimbus clouds include ice crystals, and have a base below 2000m (stratocumulus,stratus,cumulus,cumulunimbus)
the main characteristics of the climate in tropical rainforests include :
1. hot conditions - generally above 26*C- throughout the year
2. high levels of rainfall,often over 2000mm
3. a lack of seasons - the temperatures are high throughout the year
4. the different between daytime and night-time temperatures
5. rainfall is mainly convectional and many fall on as many as 250 days each year
6. cloud cover varies
7. the presence of clouds tends to reduce the amount of heat that is lost at night
8. the humidity is high, and relative humidities of 100% are often reached in the late afternoon
9. wind speeds within the forest are reduced by the large numbers of trees present
hot desert characteristic :
1. very hot days and cold nights, caused by the lack of cloud cover
2. low and irregular amounts of rainfall, which lack any seasonal pattern
3. low levels of humidity for much of the year
4. warm dry winds, sometimes causing sandtorms
Factors affecting climate
Latitude
at the equator the overhead sin is high in the sky, so high-intensity insolation is received.
proximity to the sea
the specific heat capacity is the amount of heat needed to raise the temperature of a body by 1*C.
Ocean currents
the effect of ocean current on temperatures depends upon whether the current is cold and warm.
Altitude
air temperature decreases with increasing altitude.this is because air under the grater pressure of lower altitudes is denser and therefore warmer.
Winds
the effects of the winds on temperature depends on the initial characteristics of the wind
Cloud cover
cloud cover decreases the amount of insolation reaching the surface by reflecting some of it.
Pressure
in low pressure systems air is rising. it may rise high enough to cool,condense and form clouds and rain.
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