what month does a rain band flow across africa to the south of the equator

Precipitation and the Inter Tropical Convergence Zone (ITCZ)

The most of import component of climate is precipitation, because rainfall provides h2o for survival. Equatorial regions have extremely regular annual and inter-annual (brusque-term and long-term) patterns of rainfall. These regions include the rain forest areas of Cote d'Ivoire, Ghana, Togo, Republic of cameroon, the Central African Democracy, and parts of both the Congo and the Democratic republic of the congo. These regions have between 8 and 12 months where rainfall is >50 mm/month and as many as 200 days of precipitation each yr, making the equatorial zone the wettest on the planet. The equatorial region has no real dry season and is constantly hot and humid. This idea should sound familiar to y'all, because the White Nile starts in the equatorial region, and information technology does not take a major alluvion season.

Every bit distance from the equator increases, the duration, amount and reliability of precipitation all subtract. As a result, agricultural enterprises of whatsoever type become a riskier business organization as one moves away from the equator. The extreme, of course, is the Sahara desert in northern Africa.

So what causes the rain to fall at the equator only not in the college latitudes? To answer that question we need to look at the motility of air around the Globe. On a big scale, there are few air masses which shape the rainfall characteristics of tropical Africa. Sub-Saharan Africa (excluding the East African coast) gets its precipitation from tropical moist oceanic air that moves from the Atlantic and Indian Oceans toward an equatorial low pressure zone. This area is the intertropical convergence zone (ITCZ). The ITCZ is besides chosen the "climate equator"—it lies near the geographic equator, and divides the global air apportionment patterns into 2 mirror images to the northward and due south. The ITCZ is an area of low atmospheric pressure that forms where the Northeast Trade Winds meet the Southeast Trade Winds near (actually just north of) the earth'due south equator.

Equally 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 pelting, resulting in a band of heavy atmospheric precipitation around the globe. Air that rises along the ITCZ moves away from the equator and sinks in the subtropics at the Horse Latitudes, rounding out the Hadley Apportionment. This reliable circulation feeds the lush rain forests of primal Africa, and too defines the limits of the Sahara desert. The ITCZ has been called the doldrums by sailors because at that place is essentially no horizontal air motility, that is, no wind (the air but rises). In the US, nosotros are interested in the ITCZ primarily because, nether certain circumstances, tropical depressions moving along the ITCZ intensify to hurricanes.

The position of the ITCZ varies predictably throughout the twelvemonth. Although it remains near the equator, the ITCZ moves farther due north or south over state than over the oceans because it is drawn toward areas of the warmest surface temperatures. The location of the ITCZ can vary as much as xl° to 45° of latitude due north or south of the equator on land. Information technology moves toward the Southern Hemisphere from September through February and reverses management in training for Northern Hemisphere Summer. The ITCZ is less mobile over the sea, although there is 1 exception: during an El Nino outcome the ITCZ is deflected toward the unusually warm sea surface temperatures in the tropical Pacific. Thus the position and migration of the ITCZ are important in defining the Globe'due south climate on a global scale.

So how does information technology work in Africa? The ITCZ migrates latitudinally on a seasonal basis. In July, when the sun is over the Tropic of Cancer, the ITCZ reaches its northernmost position at virtually fifteen°Due north; in January it reaches ~5° S when the sun is over the Tropic of Capricorn. The most important consequence of this shifting is the annual alteration of wet and dry seasons in tropical Africa.

Areas near the equator in western and southern Africa have a single intense rainy season from July to September. In eastern Africa (S. Ethiopia to key Tanzania), however, there are two rainy seasons. The ITCZ moves northward over this region between Feb and May, and southward again betwixt Oct and December. Since the distance covered by the ITCZ is quite large in this part of the continent, the rainy seasons are less intense than those of western Africa. That is, the ITCZ dumps the same amount of rain in the east as it does in the west, but that rain gets distributed over a larger expanse in the east because of the greater movement of the conditions system.

The arid and semi-arid regions of Africa (Sahara and Sahel) lie north of about 10°Due north, near the northern limit of the ITCZ, and receive one rainy flavour with very trivial atmospheric precipitation. Farther to the north, along the Mediterranean Sea coast, the climate is not affected directly by the ITCZ and rain falls in the winter.

Intertropical convergence zone (ITCZ) and rain location. Source: ADDS, the African Information Dissemination Service

Note: Please click on the paradigm to see a larger version.

What do You lot think? ITCZ and hurricanes

Based on what you have only learned well-nigh the ITCZ, how does that tie into the USA's hurricane season? Post your thoughts and opinions to the Lesson 07 Discussion Forum (That discussion forum can exist accessed at any time by clicking on the Communicate tab in ANGEL and and then looking in the Discussion Forums box.)

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Source: https://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03.html