(a) On an outline map of West Africa, mark and name the (i) approximate position of the ITCZ in January; (ii) low pressure belt in January; (iii) high press...

Answer Details

(a) Outline map of West Africa: January conditions

• (i) ITCZ in January: draw the Inter-Tropical Convergence Zone lying to the south, roughly along or just off the Guinea coast (about 5°N over the ocean).
• (ii) Low pressure belt in January: mark it over the equatorial south, close to the ITCZ near the coast, where the sun is nearly overhead.
• (iii) High pressure belt in January: mark it over the Sahara in the north (the sub-tropical high over North Africa).
• (iv) Tropical Continental air mass (cT): show it as the dry, dusty Harmattan blowing from the north-east (Sahara) toward the south-west, with an arrow.
• (v) Guinea current: a warm current flowing eastward along the Guinea coast; (vi) Canary current: a cool current flowing south-westward along the north-west coast (Mauritania/Senegal).

(b) Relationship between pressure belts and rainfall distribution

• The rain-bearing belt follows the low pressure (ITCZ): Rainfall is heaviest where the ITCZ and the low pressure lie, because moist maritime Tropical (mT) south-west monsoon air converges and rises there, cooling to give rain.
• High pressure means dry weather: Under the sub-tropical high, air is subsiding (sinking) and the dry continental Tropical (cT) Harmattan blows out; this area (the north/Sahara) is dry, so rainfall decreases northward.
• The belts migrate with the overhead sun: In July the low pressure and ITCZ move far north, bringing the rainy season to most of West Africa; in January they move south, so only the coast gets some rain while the interior is dry. Hence rainfall is highest and longest near the coast and decreases toward the interior, following the seasonal shift of the pressure belts.