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Difficulty: HardClimate and Climatic Regions of Nigeria

Southern Nigeria's coastal regions experience a double rainfall maximum with a noticeable drop in precipitation during July and August known as the 'August Break' (Little Dry Season). Which atmospheric mechanism accounts for this temporary dry spell while the Inter-Tropical Convergence Zone (ITCZ) is located at its northernmost position over West Africa?

  1. A
    The deflection of rain-bearing South-West Monsoon winds away from the Atlantic coast toward the Jos Plateau due to orographic suction.
  2. The inland migration of the ITCZ deep into northern Nigeria, placing coastal areas under stable marine air with lower sea surface temperatures and atmospheric divergence.Answer
  3. C
    The temporary southward surge of the dry North-East Trade Winds bringing Continental Tropical (cT) air across southern Nigeria.
  4. D
    The complete weakening and collapse of the Tropical Maritime (mT) air mass over the Gulf of Guinea during the summer solstice.

Answer

The inland migration of the ITCZ deep into northern Nigeria, placing coastal areas under stable marine air with lower sea surface temperatures and atmospheric divergence.
The correct option identifies that as the ITCZ advances to its northernmost position over West Africa during July and August, southern Nigeria is positioned well behind the main convective rain belt. Localized oceanic upwelling along the Gulf of Guinea brings cooler water to the coast, creating atmospheric stability, subsidence, and divergence that temporarily suppresses rain-producing convective clouds in the south.

Step-by-Step Solution

1
Analyze ITCZ position during the northern summer (July–August).
The ITCZ reaches its northernmost latitude (around 20°N–22°N) near the southern border of the Sahara Desert.
Solar heating at the Tropic of Cancer draws moisture-laden Tropical Maritime (mT) winds far into northern Nigeria.
2
Examine coastal oceanographic and atmospheric conditions in southern Nigeria during this period.
The coastal marine atmosphere undergoes cooling due to localized upwelling along the Gulf of Guinea, generating a temperature inversion and stable air stratification.
Atmospheric stability prevents strong convective updrafts, inhibiting deep cumulonimbus cloud formation along the coast.
3
Synthesize the mechanism causing the 'August Break' (Little Dry Season).
The deep inland position of the moisture front leaves coastal southern Nigeria under a zone of surface wind divergence and atmospheric stability.
This structural change causes a temporary cessation of heavy convection, creating the double rainfall maximum characteristic of the Sub-Equatorial climate belt.

Key Concept

Atmospheric mechanisms underlying the double rainfall maximum and August Break in Southern Nigeria
Estimated Time:2m 0s
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Topics

Climate and Climatic Regions of Nigeria

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