Question map
In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?
Explanation
The correct answer is option B. Tropical cyclones do not occur in the South Atlantic Ocean because the equatorial convergence zone does not migrate far enough south to provide the necessary convergence and Coriolis effect[1]. The Inter-Tropical Convergence Zone (ITCZ) is crucial for tropical cyclone formation as the convergence of air masses of different temperatures along the inter-tropical front results in instability causing low-level disturbances, which are a prerequisite for the origin and growth of violent tropical storms[2].
While sea surface temperatures in the South Atlantic tend to run cooler than ideal for tropical cyclone formation[4], this is a contributing factor rather than the primary reason. The Coriolis force argument (option C) is misleading because these regions are still in tropical latitudes where sufficient Coriolis effect exists—the issue is that the ITCZ doesn't migrate there to provide the necessary convergence. Option D is incorrect as the absence of land does not prevent cyclone formation over ocean waters; in fact, cyclones form over open oceans.
Sources- [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Te following conditions are required for the origin and development of a tropical cyclone: > p. 49
- [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > Temperature Contrast Between Air Masses > p. 359
PROVENANCE & STUDY PATTERN
Guest previewThis is a classic 'Source-Specific' question. While general logic suggests 'Low SST' (Option A) due to cold currents, the standard text (Majid Hussain, p.49) explicitly attributes the absence to the ITCZ not migrating far enough south (Option B). This proves that for 'Exceptions' in Geography (e.g., where things *don't* happen), you must rely on the specific reasoning given in standard texts rather than just applying general principles.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: Are average sea surface temperatures in the tropical South Atlantic and southeastern Pacific during cyclone season below the ~26.5°C threshold required for tropical cyclone formation?
- Statement 2: Does the Intertropical Convergence Zone (ITCZ) occur infrequently or is effectively absent in the tropical South Atlantic and southeastern Pacific, reducing conditions for tropical cyclogenesis?
- Statement 3: Is the Coriolis force at the tropical latitudes of the South Atlantic and southeastern Pacific too weak to allow initiation of tropical cyclones?
- Statement 4: Does the absence (or scarcity) of land in the tropical South Atlantic and southeastern Pacific explain the lack of tropical cyclone formation in those regions?
Gives a specific numeric threshold (~26.5°C) as a criterion for tropical cyclone formation and notes regions that meet or exceed such thresholds.
A student could compare the 26.5°C threshold cited here with observed SST charts for the South Atlantic and SE Pacific during cyclone season to judge whether those regions meet it.
Lists 'Sea surface temperatures are low' as a proposed reason why cyclones do not originate in the South Atlantic and south-eastern Pacific.
A student could take this stated cause and check seasonal SST values (maps/records) for those basins to see if they are indeed below the threshold.
Explains that cold currents lower surface temperatures on eastern parts of tropical oceans, making them unfit for cyclogenesis; gives an oceanographic mechanism relevant to the SE Pacific.
A student could identify known cold eastern boundary currents (e.g., Peru/Humboldt) on a world map and compare local SSTs during cyclone season to the 26.5°C threshold.
States a commonly used SST criterion for cyclones ('higher than 27°C') as a favourable condition for formation.
A student can use this alternate threshold (≈27°C) alongside the 26.5°C figure to evaluate whether observed SSTs in those regions are too cool for cyclogenesis.
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This statement analysis shows book citations, web sources and indirect clues. The first statement (S1) is open for preview.
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