Temperature and its distribution

Heat and temperature. Heat is the movement of molecules in a substance; temperature measures, in degrees, how hot or cold a thing or place is.

Factors controlling temperature:

• Latitude: temperature follows the insolation received.
• Altitude: the air is heated from below, so temperature generally falls with height. The normal lapse rate is 6.5°C per 1,000 m.
• Distance from the sea: the sea heats and cools slowly, land quickly. Places near the sea have smaller temperature swings, helped by land and sea breezes.
• Air masses and ocean currents: warm air masses and warm currents raise coastal temperatures; cold ones lower them.
• Local aspects.

Isotherms are lines joining places of equal temperature. Broadly they run parallel to the latitudes.

January: the bends are greatest, especially in the northern hemisphere with its large land areas. Isotherms bend north over the oceans and south over the continents. The Gulf Stream and North Atlantic Drift warm the North Atlantic; over Europe, and even more over the Siberian plain, temperatures drop sharply. Along 60° E, the mean January temperature is -20°C at both 80° N and 50° N. January means are over 27°C over equatorial oceans, over 24°C in the tropics, 2°C to 0°C in middle latitudes and -18°C to -48°C in the Eurasian interior.

• In the southern hemisphere, with more ocean, isotherms are smoother and nearly parallel to the latitudes: 20°C, 10°C and 0°C follow about 35° S, 45° S and 60° S.

July: isotherms run generally parallel to the latitudes. Equatorial oceans are over 27°C; over 30°C is found over the subtropical land of Asia, along about 30° N. The 10°C isotherm runs along 40° N and 40° S.

Annual range (difference between the mean temperature of the warmest and coldest months): highest, over 60°C, in north-eastern Eurasia because of continentality; lowest, about 3°C, between 20° S and 15° N.

Example (new): two towns at the same latitude, one on the coast and one far inland, may have the same yearly average temperature, yet the inland town has hotter summers and colder winters: land swings, sea steadies.