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Difficulty: MediumClimate Types and Characteristics of Africa

During the Northern Hemisphere winter (January), the northern coastal fringe of Africa experiences mild, rainy conditions, whereas the Sudan Savanna belt lying between 10∘N10^\circ\text{N} and 15∘N15^\circ\text{N} experiences an intense dry season. Which atmospheric mechanism primarily accounts for the dry season in the Sudan Savanna belt during this period?

  1. The southward movement of the Inter-Tropical Convergence Zone (ITCZ), allowing the dry Continental Tropical (cT) air mass to dominate the region.Answer
  2. B
    The northward shift of the Inter-Tropical Convergence Zone (ITCZ), bringing moist Maritime Tropical (mT) air masses from the Atlantic Ocean.
  3. C
    The cooling influence of the cold Benguela Current producing atmospheric inversion directly over the continental interior.
  4. D
    The continuous measurement of relative humidity using an anemometer along the Sahara margin.

Answer

The dry season in the Sudan Savanna during January is caused by the southward movement of the Inter-Tropical Convergence Zone (ITCZ), allowing the dry Continental Tropical (cT) air mass (Harmattan) to dominate the region.
In January, during the Northern Hemisphere winter, solar insolation is concentrated in the Southern Hemisphere. Consequently, the Inter-Tropical Convergence Zone (ITCZ) retreats southward. This allows the dry, warm, and dusty Continental Tropical (cT) air mass, commonly known as the Harmattan, to blow from the Sahara Desert southward across the Sudan Savanna, bringing clear skies and dry conditions.

Step-by-Step Solution

1
Identify the seasonal position of the overhead sun in January.
In January (Northern Hemisphere winter), the sun is overhead in the Southern Hemisphere near the Tropic of Capricorn (23.5∘S23.5^\circ\text{S}).
Apparent movement of the sun dictates the thermal equator and low-pressure belt position.
2
Determine the resulting shift of the Inter-Tropical Convergence Zone (ITCZ).
The ITCZ shifts southward toward the Equator and Southern Africa.
The low-pressure zone follows the zone of maximum solar heating.
3
Analyze the prevailing air mass brought by this ITCZ position over West/Central Africa north of the Equator.
The dry Continental Tropical (cTcT) air mass (Harmattan wind blowing from the Sahara Desert) prevails over the Sudan Savanna belt.
With the ITCZ located further south, offshore continental winds blow from high-pressure desert regions toward the low-pressure equatorial belt.

Key Concept

Seasonal movement of the ITCZ and air mass movement in West and Central Africa
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Topics

Climate Types and Characteristics of Africa

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