In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?

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Accepted Answer

Inter-Tropical Convergence Zone seldom occurs Quick Verdict: The Inter-Tropical Convergence Zone (ITCZ) seldom shifts into these regions. Without the ITCZ to provide a pre-existing low-pressure disturbance, tropical cyclones cannot initiate. (Note: While low sea surface temperatures are the underlying cause of the ITCZ's absence, the absence of the ITCZ itself is the direct climatological reason cyclones do not form). Thematic Discussion: The Missing Cyclones Tropical cyclogenesis (the birth of a cyclone) is highly conditional. According to NCERT fundamentals, a cyclone requires six strict prerequisites: Sea surface temperature (SST) > 27°C Sufficient Coriolis force High mid-troposphere moisture Low vertical wind shear Upper-air divergence A pre-existing low-pressure disturbance. Here is the causal chain of why the South Atlantic and South-Eastern Pacific fail to meet these conditions: The Cold Current Effect: These two specific oceanic basins are dominated by powerful cold currents—the Benguela Current (South Atlantic) and the Humboldt/Peru Current (South Pacific). The ITCZ Anchor: Because these cold currents depress the surface temperatures of the tropical waters, the "thermal equator" remains pinned to the Northern Hemisphere. Consequently, the ITCZ (which follows maximum heat) rarely shifts more than 1 to 2 degrees south of the geographic equator in these zones. The Missing Trigger: The ITCZ is the primary generator of pre-existing atmospheric disturbances. Because the ITCZ seldom occurs in the South Atlantic and South-Eastern Pacific, the initial low-pressure trigger is missing. Furthermore, these regions experience high vertical wind shear (i.e., change in wind speed or wind direction with increasing altitude), which would decapitate any storm system that attempted to form. 💡 The Examiner’s Mindset: The Catarina Exception In geography, absolutes are rare. While the South Atlantic is historically devoid of hurricanes, Hurricane Catarina (March 2004) is the famous exception. A highly unusual combination of a stalled frontal boundary and momentarily warmer-than-average waters off the coast of Brazil allowed a rare Category 2 hurricane to strike the states of Santa Catarina and Rio Grande do Sul. However, climatologically, Catarina remains an extreme anomaly, not the rule.   Mains Concept Builder: The Desert Connection The exact same mechanism preventing cyclones also creates some of the driest places on Earth. The cold Benguela and Humboldt currents chill the air above them, inhibiting evaporation and preventing the formation of rain-bearing clouds. When this stable, dry air blows inland, it creates extreme coastal deserts right next to the ocean—specifically the Namib Desert (Africa) and the Atacama Desert (South America). 📝 Mains Practice Question (GS Paper 1 - Physical Geography): Explain the role of ocean currents in preventing the formation of tropical cyclones in the South Atlantic Ocean. How do these same currents influence the climate of the adjacent western continental margins? (150 words, 10 marks)