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
Full viewThis 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.
- Directly states tropical cyclones do not occur in the South Atlantic and gives the cause: equatorial convergence zone does not migrate far enough south.
- Links lack of ITCZ migration to insufficient convergence and Coriolis effect needed for cyclogenesis.
- Explains the role of the ITCZ as the convergence zone of trade winds and how temperature contrasts when the ITCZ is farthest from the equator help disturbances intensify.
- Supports the mechanism by which limited ITCZ migration would reduce conditions favourable for tropical cyclone development.
- Defines the typical latitudinal range and seasonal variability of the equatorial low-pressure belt / ITCZ (between about 5° and 20°), implying limits to how far it migrates.
- Provides background that constrained ITCZ movement can limit the convergence zone's presence in certain tropical ocean basins.
- Explicitly states tropical cyclones do not occur in the South Atlantic and gives as cause that the equatorial convergence zone does not migrate far enough south to provide the necessary convergence and Coriolis effect
- Directly links regional absence of cyclones to insufficient Coriolis-related conditions
- States Coriolis force is zero at the equator and absence of Coriolis prevents cyclone formation near the equator
- Supports the idea that low/weak Coriolis at low tropical latitudes inhibits cyclone initiation
- Lists 'presence of the Coriolis force enough to create a cyclonic vortex' as a necessary condition for cyclone formation
- Implicates that where Coriolis is too weak, the necessary vortex cannot form
- Directly lists the primary reasons for the South Atlantic's lack of tropical cyclones: cooler sea surface temperatures, high vertical wind shear, and lack of pre-existing vorticity.
- Attributes lack of cyclones to oceanic and atmospheric conditions rather than to scarcity of land.
- Explains that cold coastal currents (Peru and Benguela) keep sea surface temperatures too cool for hurricane formation off South America and in the South Atlantic.
- Provides a concrete oceanographic mechanism (cold currents) that explains the absence of cyclones independent of land distribution.
- Lists necessary ingredients for cyclone formation: a pre-existing near-surface disturbance and sufficiently warm sea surface temperatures (~27°C).
- Implying that absence of these ingredients (vorticity, warm SST, low shear) explains basin differences rather than land scarcity.
Explicitly notes South Atlantic lacks tropical cyclones because the equatorial convergence zone does not migrate far enough south to provide necessary convergence and Coriolis effect.
A student could check maps of ITCZ seasonal migration and typical genesis latitudes to see if lack of ITCZ/convergence over those ocean areas explains absence rather than land distribution.
States cyclones occur on western margins of oceans between ~8°–25° N/S and are absent near the equator due to weak Coriolis force.
Compare the latitude band of cyclone genesis with the positions of the South Atlantic and SE Pacific and assess Coriolis strength there versus presence/absence of land.
Lists necessary conditions for cyclone formation including large sea surface area with temperature >27°C and presence of Coriolis force.
Use SST charts and ocean basin temperature patterns for the South Atlantic and SE Pacific to test whether thermal conditions (not land) limit genesis.
Explains eastern tropical oceans are cooled by cold currents, lowering surface temperatures and making them unfit for cyclogenesis; cites eastern Pacific exceptions during El Niño.
Check whether cold currents (e.g., Benguela, Humboldt) affect SSTs in the South Atlantic/SE Pacific and whether that explains low cyclone frequency independent of land.
Notes most favorable areas are vast tropical western parts of oceans in the Northern Hemisphere where warm currents prevail — implying ocean thermal structure and margins matter.
Compare western vs eastern tropical ocean thermal patterns and continental margins to evaluate if oceanographic factors (not land absence) better correlate with cyclone occurrence.
- [THE VERDICT]: Trap / Sitter. It is a 'Sitter' if you read the 'Exceptions' paragraph in Majid Hussain; a 'Trap' if you relied solely on the general logic of Cold Currents (Option A).
- [THE CONCEPTUAL TRIGGER]: Global Distribution of Tropical Cyclones > Regional Anomalies (Why South Atlantic/SE Pacific are dead zones).
- [THE HORIZONTAL EXPANSION]: 1. SST Threshold: >27°C up to 60m depth. 2. Coriolis Limit: No formation 0-5° N/S. 3. Cold Currents: Benguela (S. Atlantic) & Humboldt (SE Pacific) suppress convection. 4. ITCZ Asymmetry: In the Atlantic, the Thermal Equator/ITCZ stays mostly in the Northern Hemisphere. 5. Rare Exception: Hurricane Catarina (2004) off Brazil.
- [THE STRATEGIC METACOGNITION]: When studying a global phenomenon (like Cyclones, Volcanoes, Deserts), explicitly map the 'Negative Zones' (Where do they NOT occur?). The exam loves testing the *reason* for the absence (e.g., No volcanoes in Himalayas due to C-C collision vs No cyclones in S. Atlantic due to ITCZ).
Several references state a minimum warm SST is required for tropical cyclogenesis (values ~26.5–27°C are cited), which is the numerical threshold in the question.
High-yield physical geography fact often tested: knowing the SST threshold helps explain global cyclone distribution and why some ocean basins are more active. It links to questions on cyclone formation conditions and impacts of ocean warming. Memorise the threshold range and practice applying it to basin-wise comparisons.
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 9: Atmospheric Circulation and Weather Systems > Tropical Cyclones > p. 83
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > All Because of Global Warming > p. 378
One reference explains that cold currents lower surface temperatures of eastern parts of tropical oceans, making them unfavourable for cyclone formation — directly relevant to the southeastern Pacific.
Useful for basin-specific reasoning: explains why eastern ocean margins (e.g., SE Pacific) often lack cyclones despite tropical latitudes. Connects physical oceanography (currents) with meteorology (cyclogenesis). Prepare by linking major currents (e.g., Humboldt/Peru current) to regional cyclone frequency.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > Why Are Tropical Cyclones Very Rare on The Eastern Margins Of The Oceans (Western Margins of The Continents)? > p. 355
A provided reference states tropical cyclones do not occur in the South Atlantic and attributes this to limited ITCZ southward migration and weak Coriolis force — alternative explanations to low SST.
Important to avoid over-simplified answers: multiple factors (dynamics, convergence, Coriolis) control cyclone genesis beyond SST. UPSC questions often require multi-factor explanations; practise contrasting thermal vs. dynamical controls on cyclone distribution.
- 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
References link the north–south movement of the ITCZ to the availability of low-level convergence and temperature contrasts required for cyclone formation.
High-yield for UPSC geography: explains why some ocean basins (e.g., South Atlantic) are cyclone-poor. Connects atmospheric circulation, monsoon dynamics and cyclone genesis; useful for questions on tropical weather systems and regional climatology. Master by comparing ITCZ seasonal positions and their effects across ocean basins using textbook references.
- 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
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > Temperature Contrast Between Air Masses > p. 359
The equatorial low/ITCZ varies seasonally within limited latitudes (roughly 5°–20°), constraining where convergence occurs.
Fundamental for questions on heat belt migration, doldrums, and why convergence zones may be absent in some regions. Links to solar declination, thermal equator and regional monsoon behaviour. Learn by memorising typical latitudinal ranges and implications for regional weather.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Equatorial Low-Pressure Belt or 'Doldrums' > p. 311
Evidence explicitly attributes South Atlantic cyclone scarcity to inadequate ITCZ migration and related lack of convergence/Coriolis effect.
Directly relevant to many UPSC MCQs and mains answers about distribution of tropical cyclones; ties atmospheric dynamics to regional exceptions. Prepare by noting stated regional exceptions and the physical causes (ITCZ behaviour, Coriolis, SST).
- 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
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > Temperature Contrast Between Air Masses > p. 359
Multiple references state that an adequate Coriolis force is required to produce and sustain the cyclonic vortex; its absence or weakness prevents cyclone formation.
High-yield for UPSC geography questions on tropical cyclones and atmospheric dynamics; links to topics on wind circulation, pressure systems and hurricane/typhoon genesis. Master by memorising the role of Coriolis in vortex spin and practicing map-based questions about latitudinal limits of cyclone formation.
- Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 26: Tropical Cyclones > 26.1. Conditions Necessary for The Formation of A Tropical Cyclone > p. 355
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 9: Atmospheric Circulation and Weather Systems > Coriolis Force > p. 79
The 'Fujiwhara Effect'. Since they asked about cyclone formation failure, the next logical step is cyclone interaction. When two cyclones get close, they orbit each other (Fujiwhara effect). Also, look for 'Annular Cyclones' (stronger, more stable eyes) as a future term.
The 'Structural vs. Variable' Hack. Option D (No land) is irrelevant (cyclones need water). Option C (Coriolis) is weak (latitudes are correct). The fight is A vs B. SST (A) is a variable that changes seasonally; ITCZ Asymmetry (B) is a permanent structural feature of the Atlantic climate system. For a permanent 'Does Not Originate' phenomenon, choose the permanent structural cause over the seasonal variable.
GS-3 Disaster Management & Climate Change: Link this to 'Expanding Cyclone Basins'. As Global Warming alters the ITCZ position and raises SSTs, will the South Atlantic remain a safe haven? (Reference Hurricane Catarina as a warning signal for changing baselines).