Why do trade winds occur

By late afternoon, a strong breeze can be blowing dozens of miles inland. A similar effect can occur near big lakes, where the wind is referred to as a lake breeze.

Land breezes come at night, when inland temperatures drop enough that the ocean is now warmer than the land, reversing the effect. Similar forces produce global wind patterns that affect climate. The tropics, for example, are always hot. Air rises here and spreads north and south, high above the land. Lower down, air is pulled in from the north and south. The coriolis effect , an offshoot of the Earth's rotation, makes moving air masses curve, so that the winds converging on the Equator come from the northeast in the Northern Hemisphere and the southeast in the Southern Hemisphere.

These winds are called the trade winds. Farther from the Equator, the surface winds try to blow toward the Poles, but the coriolis effect bends them the opposite direction, creating westerlies. This is why so many weather events in the United States come from the west. Within the mid-latitudes, weather effects create high- and low-pressure zones, called highs and lows , respectively.

Air moves from areas of high pressure to low pressure. As it moves, however, it spirals due to the coriolis effect, producing the shifting winds we experience from day to day, as highs and lows drift under the influence of the prevailing westerlies. Winds reaching the center of a low-pressure area have nowhere to go but up. Thus causing no Coriolis effect. The equation of motion for an object in an inertial reference is as follows:.

The above equation can be turned into a non-inertial reference frame is:. It is because of such a high temperature the air of that region heats up and the hot air rises causing a low-pressure area under it, also known as the monsoonal trough.

On the contrary, the temperature over the Indian Ocean is relatively low therefore a relatively high-pressure region is created over the sea. The air from the high-pressure region moves towards the low-pressure region because of the pressure difference between the Indian Ocean and North Central Indian Plains. This signifies that the movement of air is from the equatorial region of the Indian Ocean to the Indian subcontinent in the South-West to North-East direction in June which is exactly opposite to that of the trade winds North-East to South-West in India prevailing during winter.

The Sun shines very directly at the equator, creating very intense heat. The heat warms the air and causes some ocean water to evaporate, meaning air in the doldrums becomes warm and moist. This warm, moist air rises in the atmosphere and cools, becoming clouds — and eventually rain and storms — in tropical regions.

In the Atlantic Ocean, some of these storms become hurricanes, and the trade winds can steer hurricanes west toward the United States. In this view, the ocean water is black, the low clouds are blue and lavender, and the higher clouds are yellow. You can also see this circulation on the wind maps. On the world map you well recognise how the trade winds of the tropics blow in the direction of the equator. This effect appears mainly above the oceans, and moves seasonally to the north or south, according to the highest angle of the Sun.

Thus, the North and South Trade winds meet approximately km to the north of the equator during the months July and August; from January to February, they meet about km to the south of the equator. The Trade winds are diverted or interrupted by bigger land masses or obstacles.

Hence, little or no Trade wind circulation takes place above the continents Africa, South America , because it is interrupted by the local convection rise of air above the land masses. Over the Indonesian islands, the Trade wind circulation is reduced by many small islands, which interrupt these winds.

In the northern part of the Indian ocean, the Trade wind circulation can be diverted by the high pressure differences between Africa, the Arabian peninsula and the Indian subcontinent: The strong warming of the Arabian peninsula and the Indian subcontinent during the drying times leads to a constant flow of colder air from the ocean towards the continent, and this creates a northern air flow from the northern Indian ocean towards the Indian continent for several months per year.

Because of these temperature stratifications of the very warm air from the equator region on the relatively less warm air of the higher latitudes, the steady "trade inversion" is formed. This trade inversion prevents the vertical air exchange between the high streaming towards the polar region and the near-ground streaming towards the equator.

Therefore this circulation is very stable. Above the continents Africa, South America there is nearly no trade circulation because it is interrupted or redirected because of the local convections the airdraft over the landmasses.