Global Wind Patterns and Atmospheric Circulation

Surface Winds and the Coriolis Effect

Surface winds associated with these areas do not follow straight trajectories but move in spirals. This manner of movement is due to the Coriolis force, which is the force exerted by the rotation of the Earth. The Earth rotates counter-clockwise. Due to the Coriolis force, any fluid displaced horizontally on the surface of the Earth tends to drift to its right in the Northern Hemisphere and to its left in the Southern Hemisphere.

General Atmospheric Circulation

The air in contact with the surface of the Earth in the equatorial region is warmer and lighter; this air rises while being gradually replaced by polar air, which is cold and dense. If the Earth were homogeneous and remained still, the draft would form two convective cells, one for each hemisphere. However, the Earth's rotation provokes a deviation of its path, creating multiple cells. The result of these convective cells is the presence of specific winds in these areas:

• Between 0° and 30°: Winds generated toward the Equator (NE-SE) are known as the trade winds. The convergence of these winds from both hemispheres occurs over an area called the Intertropical Convergence Zone (ITCZ).
• From 30° to 60°: Westerly winds move northwards in the Northern Hemisphere and southwards in the Southern Hemisphere.
• From 60° to 90°: At the North Pole, air descends and is deviated to the right; these are the polar easterlies.

The Polar Front and the Jet Stream

At 60° latitude, there is a special and unique situation. Air converges from the surface of the pole, generating a contact area called the polar front. This is the source of cold and warm air masses and the generator of the storms (borrascas) and anticyclones typical of our latitudes. Parts of the westerly winds that circulate in the troposphere at very high speeds (up to 500 km/h) are called the jet stream.

Consequences for Global Climatic Zones

As a consequence of this circulation, four climatic zones are produced (tropical, warm, polar, and equatorial):

a) Coastal Areas: These regions have a mild climate with small temperature fluctuations between day and night. The Earth warms and cools faster than water. A continent-wide effect is similar; in the case of monsoons, they are produced by the interaction between the oceans and continents.

b) Relief: Altitude implies a drop in temperatures. Mountain ranges act as barriers to air masses; as air ascends, water vapor condenses, and if the cooling is sufficient, precipitation occurs in a watershed.