MPSC 2025 Prelims Paper-I · Question 28 of 100

Correct — option (2), 'due to increase in temperature and decrease in air pressure,' names the actual causal chain behind the storms that form over the Arabian Sea and the Bay of Bengal along the edges of the Indian Peninsula, mainly in the pre-monsoon (April-May) and post-monsoon/retreating-monsoon (October-December) windows. It starts with sea-surface temperature: tropical cyclogenesis generally needs the sea surface warmed to roughly 26-27°C or more. Once the surface is that warm, evaporation off the sea intensifies, pumping large volumes of water vapour and latent heat into the air directly above it. That warm, moisture-laden air is buoyant, so it rises; and as it rises away from the surface, the air pressure at the surface beneath it falls, because there is now less air mass sitting directly overhead. This falling surface pressure is exactly what a meteorologist means by a 'low' — a shallow trough that, given continued convection, deepens into a depression. As the rising moist air cools with height, its water vapour condenses into cloud, releasing further latent heat that reinforces the updraft and deepens the low still more. Provided other conditions are also met — Coriolis force strong enough to organise rotation (which is why cyclones do not form very close to the equator), low vertical wind shear so the storm's vertical structure is not torn apart, and upper-level divergence to keep pulling air out of the top of the system faster than it is fed in at the surface — this deepening low can organise into a depression and then a cyclonic storm. So the two-variable pairing the question asks for is genuinely causal, not coincidental: the temperature rise is the energy source, and the pressure fall is the direct, physical consequence of the warm air rising away from the surface. This basic mechanism is why both seas flanking the Peninsula, despite lying on opposite coasts, produce storms through the same underlying process.

• (1)Due to decrease in temperature and increase in air pressure — This is the description of a cooling, subsiding, stable air mass — essentially an anticyclone — which is the physical opposite of what drives a storm. Falling temperature reduces evaporation and convection rather than fuelling it, and rising pressure means air is sinking and spreading out at the surface, not rising and organising into a low. A storm cannot form under these conditions; they describe fair, settled weather, not cyclogenesis.
• (3)Increase in temperature and air pressure — Half of this option is right and half breaks the physics: temperature genuinely rises (that is the energy source), but pressure does not rise alongside it — it falls. The rising warm, moist air is precisely what lowers the surface pressure beneath it, because that column of air is now lighter and there is less air mass pressing down. A simultaneous rise in both temperature and pressure would actually suppress the convection a storm needs, not enable it; the question is testing whether a candidate notices that these two variables move in opposite directions here, not the same one.
• (4)Decrease in temperature and air pressure — This option gets the pressure half right — the surface pressure genuinely does fall as the storm organises — but gets the temperature half backwards. It is a rise in sea-surface temperature, not a fall, that supplies the evaporative moisture and latent heat which powers the whole convective process in the first place. A cooling sea surface would starve the storm of the energy it needs rather than help it form.

Tropical cyclogenesis over the seas around the Indian Peninsula follows a standard causal chain: a warm sea surface (conventionally at or above roughly 26-27°C) drives intense evaporation and latent-heat transfer into the overlying air; that warm, moist air rises; its rise lowers the surface air pressure beneath it, creating a shallow low/trough; condensation as the air cools with height releases further latent heat, deepening the low into a depression; and, given adequate Coriolis force (so cyclones are rare within about 5° of the equator), low vertical wind shear, and upper-level divergence to keep venting air out of the system's top, the depression can intensify into a cyclonic storm. The temperature-rise-causes-pressure-fall relationship is the crux this question tests.

MPSC's Paper-I climatology section regularly tests cause-and-effect chains like this one rather than detailed storm-structure questions, because they are compact enough to phrase as a single line and still discriminate between candidates who understand the mechanism and those who have only memorised that 'storms form over warm seas.' The Indian Peninsula is flanked by two seas that both generate storms mainly in the pre-monsoon and post-monsoon transition windows, when sea-surface temperatures peak and vertical wind shear is low enough not to disrupt a developing system, which is why the same two-variable (temperature/pressure) logic applies on both coasts even though the Arabian Sea and the Bay of Bengal differ in how many storms they produce.

• Tropical cyclogenesis generally requires sea-surface temperature at or above roughly 26-27°C to sustain the convection a storm needs.
• Warm-sea evaporation supplies the moisture and latent heat that powers the storm; condensation of that moisture as air rises releases further heat, reinforcing the developing low.
• A falling surface air pressure beneath rising warm air is the physical definition of the 'low' or depression from which a storm develops — the two variables move in opposite directions, not together.
• India's coasts see most storms in the pre-monsoon (April-May) and post-monsoon/retreating-monsoon (October-December) windows, when sea-surface temperature is high and wind shear is comparatively low.
• The Bay of Bengal produces roughly four times as many cyclones as the Arabian Sea, mainly because of its warmer, lower-salinity surface waters fed by major rivers.

• Assuming temperature and pressure move together in a developing storm, when the whole mechanism depends on them moving in opposite directions
• Treating any warm sea as sufficient for a storm to form, without factoring in Coriolis force, low wind shear, and a pre-existing disturbance
• Confusing general tropical warmth with the specific sea-surface-temperature threshold that sustains cyclogenesis

MPSC's Paper-I geography section favours short, mechanism-testing questions on cyclone formation over questions about cyclone structure or naming, usually phrased as 'what causes/favours' storm formation along India's coasts. Expect this exact temperature-versus-pressure pairing, or a close variant of it, to recur, since it is compact enough for a one-line stem yet still separates candidates who understand the causal chain from those who have only memorised the fact that storms form over warm seas.

No directly related past PYQ was found.

• practice — not a real PYQ

  A minimum sea-surface temperature of roughly how many degrees Celsius is generally considered necessary for tropical cyclogenesis ?

  • (a)18-20°C
  • (b)22-24°C
  • (c)26-27°C
  • (d)30-32°C

  Answer(c) 26-27°C — sea-surface temperatures at or above this range are conventionally treated as the threshold needed to sustain the evaporation and convection that power a developing tropical storm.

• practice — not a real PYQ

  Which of the following is NOT among the conditions generally required for a tropical depression to intensify into a cyclonic storm ?

  • (a)Low vertical wind shear
  • (b)Adequate Coriolis force away from the equator
  • (c)Upper-level divergence to vent air out of the system
  • (d)Rising surface air pressure beneath the developing system

  Answer(d) Rising surface air pressure beneath the developing system — intensification requires the surface pressure to keep falling as the low deepens, not rise; the other three conditions (low wind shear, sufficient Coriolis force, and upper-level divergence) are all genuine requirements.