Why is rainfall associated with itcz

The sun crosses the equator twice a year in March and September, and consequently makes for two wet seasons each year. In December and July, when the sun is at its greatest extent north or south of the equator makes for two dry seasons. Further away from the equator, the two wet seasons merge into one, and the climate becomes more monsoonal, with one wet season and one dry season.

Because of its location just north of the equator, Nigeria's climate is characterized by the hot and wet conditions associated with the movement of the Inter-Tropical Convergence Zone ITCZ north and south of the equator. This is easily seen in the normal monthly rainfall for two cities, Kano and Lagos, separated by miles km. When the ITCZ is to the south of the equator, the north-east winds prevail over Nigeria, producing the dry-season conditions. When the ITCZ moves into the Northern Hemisphere, the south westerly wind prevails as far inland to bring rain fall during the wet season.

The implication is that there is a prolonged rainy season in the far south of Nigeria, while the far north undergoes long dry periods annually. Nigeria, therefore, has two major seasons, the dry season and the wet season, the lengths of which vary from north to south. In southern Nigeria, Lagos averages The four observed seasons are:.

As these winds converge, moist air is forced upward, forming one portion of the Hadley cell. The air cools and rises see image below , causing water vapor to be "squeezed" out as rain, resulting in a band of heavy precipitation around the globe. This reliable circulation feeds the lush rain forests of central Africa, and also defines the limits of the Sahara desert. The ITCZ has been called the doldrums by sailors because there is essentially no horizontal air movement, that is, no wind the air simply rises.

Hadley Circulation. The position of the ITCZ varies predictably throughout the year. Although it remains near the equator, the ITCZ moves farther north or south over land than over the oceans because it is drawn toward areas of the warmest surface temperatures.

It moves toward the Southern Hemisphere from September through February and reverses direction in preparation for Northern Hemisphere Summer.

Thus the position and migration of the ITCZ are important in defining the Earth's climate on a global scale. So how does it work in Africa? The ITCZ migrates latitudinally on a seasonal basis. The most important consequence of this shifting is the annual alteration of wet and dry seasons in tropical Africa. Brooks , C. Braby , : The clash of the trades in the Pacific. Crowe , P.

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