Weather & Climate
We are aware that, the atmosphere envelops us like a blanket. Apart from protecting us from the direct heat and damaging rays of the Sun, the atmosphere also determines the weather of a country.
Weather is the state or condition of the atmosphere, such as hot or cold, cloudy or sunny, over a short period of time, usually a few hours or a day or so. Climate, on the other hand, is the average weather conditions of a region over a number of years. Thus, while the weather of a place may change from hour to hour or from day to day, the climate varies with the change of seasons or from place to place.
There are certain elements that influence both weather and climate, of which air temperature, air pressure, wind, precipitation, humidity and cloudiness are most important.
Air temperature is influenced by heat. Heat is a type of energy, which makes things or objects hot and when it is not there, it is cold. So cold is just absence of heat energy and that's why it is not an energy. For the Earth, the Sun is the primary, and practically the sole source of heat. However, the atmosphere receives only two billionths of the Sun’s energy. This incoming solar radiation is called ‘Insolation’.
Only 19% of the insolation is absorbed by the atmosphere and only 47% is absorbed by the Earth and converted into heat. The Earth, in its turn, releases this energy and warms up the atmosphere by radiation and convection. Summer days are longer than the winter days and hence, the longer periods of daylight during the summer days heat the Earth more. So summer temperatures are high and winter temperatures are low. At dawn, the Sun’s rays are slanting and therefore, the temperature is low. But, as the Sun climbs up the sky, its rays become more and more direct and the temperature keeps on in increasing.
Temperature is the term used to express the intensity of heat. The temperature of air is measured with the help of a ‘Thermometer’, placed in the shade at about 1.2 metres from the ground. A thermometer is a narrow glass tube filled with mercury. It works on the principle that mercury expands when heated and contracts when cooled. However, for the purpose of climatic records, it is necessary to know the highest and the lowest temperature during a given period, such as a day, and for this purpose the ‘Six’s Thermometer is used.
There are certain factors affecting the air temperature, of which latitude, altitude, cloud and rainfall, wind and ocean currents, distance from the sea and the natural vegetation and soil are important.