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Weather and climate


The general pattern of winds on EarthThe general pattern of winds on Earth Wind is air moving from one area to another. When warm air rises, cooler air flows in to take its place. Winds are the result of the Sun’s uneven heating of the Earth’s surface. In the tropics, the surface is hot. The air rises and cooler air from both to the north and the south blow in to replace it. These are called trade winds. The Earth’s rotation causes the winds in the Northern Hemisphere to the swing to the right, and those in the Southern Hemisphere to the left. Winds carry rain-laden clouds and moist air evaporated from ocean waters around the globe. Winds also cause waves and drive ocean currents.

A cyclone, a region of low pressure, over IcelandA cyclone, a region of low pressure, over Iceland


Cyclones are regions or centres of low pressure around which winds blow. Because of the way the Earth spins around, the winds blow anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, the result of what is called the Coriolis force. In tropical areas where there is intense heating of sea water, winds blowing around a tropical cyclone may increase in speed and tighten into a spiral to become a hurricane (known as a typhoon in the Pacific Ocean).

Trade winds are prevailing winds (ones that normally blow in a single direction) in tropical latitudes. They are so-called because they helped sailing ships travel across the oceans for centuries. They blow from east to west.

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