The term wind refers to air which is moving horizontally across the earth. Temperature is the major contributor to the creation of wind. The temperature of the air produces the various atmospheric pressures which are associated with the production of winds. The uneven distribution of the sun’s heat over land and sea is the major cause of these variations in the temperature and pressure of the air. The area surrounding the equator receives most of the light and heat of the sun, while the poles receive very little. This in return causes the heat from the warmer latitudes to shift towards the poles resulting in a complex circulation of air in earth’s atmosphere. Highs and low pressure areas are the result of the difference in the thermal properties of land and air. As the temperature of a region becomes unstable, warmer air will rise and flow over colder, heavier air. The Coriolis affect can modify these winds immensely.
There are four major types of winds, the prevailing winds, local winds, seasonal winds, and cyclonic or anti-cyclonic winds. These winds are associated with seven major wind belts. Three of these belts are located in northern hemisphere, another three are located in the southern hemisphere, and seventh belt is the area surrounding the equator which is known as the doldrums. The zonal winds in each hemisphere are referred to as the westerlies, the house latitudes, and the easterlies (or the trade winds.)
The Prevailing, Cyclonic & Anti cyclonic Winds
The doldrums belt is a low pressure area which lies on both sides of the equator to about ten degrees latitude. This area receives most of the light and heat of the sun and so the air around the doldrums is hot and humid. This region is typically known as the tropics. The horse latitudes are at about thirty degrees to the north and south of the equator. The light variable surface winds of this belt are associated with high pressure. The deflection of these winds is towards the west due to the Coriolis effect or the rotation of the earth and so in the northern hemisphere these winds move towards the equator from a northeasterly direction and from a southeasterly direction in the southern hemisphere. These winds are known as the trade winds. As the trade winds move from the north and south towards the low pressure area of the equator, they rise, expand and cool. This causes the moisture in the air to condense and accounts for the frequent rainfalls of the tropics.
Poleward of the horse latitudes are the westerlies. Since the identification of a wind is determined by the direction from which it blows, these winds are known as the prevailing westerlies. The direction of the westerlies are greatly influenced by the effects of the migratory cyclonic and anti cyclonic disturbances. Cyclones, which result from the interaction of the air masses, are the typical storms of the northern hemisphere. Most of the changes we see in the weather are the result of the westerlies for they move the air masses. About eight to twelve miles above the surface of the earth, the speed of the westerlies increases rapidly. Here you will find the wind velocity reaching in excess of one hundred miles per hour. The highest recorded speed of this area was three hundred forty miles per hour. This area of concentrated westerlies is known as the jet stream.
In the polar regions of both hemispheres are high pressure areas which deflect towards the west in the direction of the equator.
Seasonal Winds
Temperature is the biggest influence of the seasonal winds. Land, in contrast with the water, absorbs the heat of the sun much quicker during the summer months than do the oceans. This creates a low pressure area over the land with the colder air of the ocean blowing inward towards the land. During the winter, the opposite occurs. The air over the land cools creating a high pressure area. This cool air moves out towards the warmer ocean. Monsoons found in the China Sea and the Indian Ocean are associated with these seasonal winds.
Local Winds
The effects of the temperature on the local winds is diurnal. During the day, the air over the land is warmer than that over the ocean while at night the air over the land is cooler than that of the ocean. The variations in the breezes caused by these temperature changes are associated with other winds such as whirlwinds and those accompanying thunderstorms.