TEMPERATURE

WORLD DISTRIBUTION OF TEMPERATURE :-

Isotherms: There is a convenient method of showing the distribution of temperature over the earth or over large areas of the earth. This is done by means of maps employing isotherms. The word "isotherm" means equal heat. Isotherms are imaginary lines drawn on a map, joining places having the same average temperature for a specified period, supposing them to be at sea level. It means that the isotherms show the average temperature of that place as it would be, if the place were at sea level.

January and July Isotherms: In most of the Atlas's, the isotherm maps show January and July temperatures as they represent the extremes of heat and cold for the Northern and Southern Hemispheres. In the Northern Hemisphere temperatures are lowest in January and highest in July. Similarly in the Southern Hemisphere temperatures are highest in January and lowest in July.

MAIN FACTORS CONTROLLING THE CLIMATE OF A REGION :-

1. Latitude: Latitude or distance from the equator controls the length of the day and night at different seasons of the year. It is evident from the fact that the duration of daylight goes on increasing in summer in the Northern Hemisphere as one goes from the equator towards the pole.

2. Altitude: Altitude affects the climate in several ways. As we go higher up a mountain there is a decrease in temperature. This rate of decrease is not uniform. It varies with time of day, season and place. The average decrease of temperature upward in the troposphere is about 6°C per km above sea level. This rate of fall of temperature with height is referred to as normal lapse rate.

3. Distance from the Sea: This factor modifies the influence of latitude to a great extent. The sea has a moderating influence on the climate of coastal area due to the phenomena of land and sea breezes. Places which are situated far away from the influence of the sea have a large range of temperature.

4. The Direction of Mountain Ranges: The direction of Mountain ranges makes a great difference to the climate of country. Mountains may shield a region from the influence of a cold (or warm) wind and thus 'create a difference in temperature between places otherwise similarly situated.

5. Ocean Currents: Warm Ocean currents tend to make the climate of the neighboring coast lands warmer than it would otherwise be. Parts of coastal Europe are very warm in January as compared with the normal for their latitudes. London on Latitude 51°N is quite warm while New York on Latitude 40°N is very cold although it is nearer the Equator. The former is kept warm by the North Atlantic Drift while the latter is affected by the cold Labrador Current. The effect of the current is more marked when the wind blows from the sea to the land. Winds blowing over warm currents pick up moisture and bring much rain. This accounts for the heavier rainfall on the West European coast lands where the prevailing westerlies blow from the sea to the land.

6. Prevailing Winds: When a wind blows more frequently from one direction than from any other, It is called a prevailing wind. A win.d from the the sea lowers the summer temperatures
and raises the winter temperatures. If winds blow from the lands, they are generally dry.