Your Answer : (Not Answered)

Correct Answer : A

Monsoon depressions form over the NE Bay of Bengal.

During the south-west monsoon, low-pressure systems known as monsoon depressions develop over the northern (head of the) Bay of Bengal, mostly near the north-east of the bay off the Odisha and Bengal coast. They travel west-north-west along the monsoon trough across central India and bring much of the monsoon rain to the plains.

Monsoon depressions rarely form over the Arabian Sea or off the Maharashtra and Gujarat coast. The south-east of the Bay of Bengal is where post-monsoon cyclones often begin, not monsoon depressions.

Your Answer : (Not Answered)

Correct Answer : C

Nor'westers are common in Assam and Bengal.

In the pre-monsoon months of April and May, violent thunderstorms with squalls, hail and heavy rain approach from the north-west over West Bengal, Odisha and Assam. They are called Nor'westers, Kalbaisakhi (the calamity of Baisakh) in Bengal, and Bordoisila in Assam, and their rain helps tea, jute and rice cultivation.

Uttar Pradesh and Rajasthan have hot, dry winds (the loo) and dust storms in this season, and the Konkan and Goa coast gets its main rain from the south-west monsoon later.

Your Answer : (Not Answered)

Correct Answer : B

The correct matching is (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv).

• cP, continental polar: forms over cold land, so it has low temperature and low humidity (iii).
• cT, continental tropical: forms over hot deserts, so it has high temperature and low moisture (i).
• E, equatorial: forms over warm equatorial oceans, so it has high temperature and humidity (ii).
• mT, maritime tropical: forms over warm subtropical oceans, with moderately high temperature and high relative and specific humidity (iv).

The other codes give cP or cT the warm, moist properties of the oceanic air masses, which contradicts their continental source regions.

Your Answer : (Not Answered)

Correct Answer : C

The peaks are in March-May and October-November.

Tropical cyclones over the North Indian Ocean have a bimodal season: a pre-monsoon peak in April-May and a stronger post-monsoon peak in October-November. During the monsoon itself (June-September) strong vertical wind shear stops depressions from deepening into severe cyclones, and in winter the sea is cooler.

January-February and December-January are the quiet winter months, and July-August falls in the monsoon, when monsoon depressions rather than cyclonic storms are the typical systems. Only the March-May and October-November pair spans both peaks.

Your Answer : (Not Answered)

Correct Answer : B

In a tropical cyclone the vertical pressure gradient is larger than the horizontal pressure gradient.

Even in a cyclone the atmosphere stays close to hydrostatic balance. Pressure falls by about 1 hPa for every 8-10 m of height, that is roughly 100 hPa per km vertically, while the steepest horizontal gradient near the eyewall is of the order of a few hPa per km. The vertical gradient is therefore much larger.

So the horizontal gradient is not larger, the two are not nearly equal, and the vertical gradient is never zero, since it balances gravity.

Your Answer : (Not Answered)

Correct Answer : D

A system is a cyclonic storm when the wind speed exceeds 33 knots.

The India Meteorological Department classifies low pressure systems by maximum sustained wind: depression 17-27 knots, deep depression 28-33 knots, and cyclonic storm 34-47 knots, followed by severe cyclonic storm and higher categories. So a cyclonic storm is one whose winds exceed 33 knots.

17 knots marks the start of a depression and 27 knots its upper limit, while 24 knots lies within the depression range. None of them is the cyclonic storm threshold.

Your Answer : (Not Answered)

Correct Answer : B

The shortest-lived system is the thunderstorm.

A single thunderstorm cell lives for about an hour, passing through its cumulus, mature and dissipating stages, and even organised multicell systems last only a few hours.

Tropical cyclones last from several days to two weeks, western disturbances take days to cross north India, and the winter (north-east) monsoon is a seasonal circulation lasting months.

Your Answer : (Not Answered)

Correct Answer : C

The main cause is the difference in the specific heat capacities between the land and the sea.

Water has a specific heat several times that of soil and rock, and the ocean also mixes heat down through a deep layer, while the land surface heats only a thin layer. For the same solar input the land therefore warms much faster by day and in summer, and cools faster by night and in winter. The resulting temperature and pressure contrast drives the sea breeze on a daily scale and the monsoon on a seasonal scale.

Albedo, cloud cover and surface roughness do differ between land and sea and modify the contrast, but they are not its main cause.

Your Answer : (Not Answered)

Correct Answer : A

The spreading leads to the formation of salt fingers.

During the summer monsoon, the Summer Monsoon Current carries warm, high-salinity Arabian Sea water into the south-western Bay of Bengal, where it spreads beneath the fresh, low-salinity surface layer fed by rivers and rain. Warm, salty water above cooler, fresher water is the configuration that favours salt fingering: heat diffuses faster than salt, so parcels of salty water sinking into the cooler layer lose their heat but keep their salt and continue to sink as narrow fingers. The intrusion therefore sets up conditions favourable to this double-diffusive mixing.

Upwelling and downwelling are driven by wind stress and Ekman divergence or convergence, and a western boundary current arises from the basin-scale wind-driven circulation, not from the spreading of a water mass.

Your Answer : (Not Answered)

Correct Answer : B

The feature that is NOT necessary is El Niño.

The Indian summer monsoon is driven by differential heating of land and sea, which sets up a meridional pressure gradient between the heated subcontinent and the Indian Ocean, and it is marked by the seasonal reversal of the winds from north-easterly to south-westerly. It forms every year.

El Niño, the warm phase of ENSO in the Pacific, occurs only every few years and tends to weaken the monsoon rather than create it. It modulates the monsoon's strength but is not needed for it to form.

Your Answer : (Not Answered)

Correct Answer : B

The keyed match is a-iii, b-i, c-iv, d-ii.

Two pairings are firm. The monsoon is driven by the seasonal reversal of the north-south temperature gradient over the tropics, as the land to the north heats in summer and cools in winter relative to the ocean to the south (b-i). The strong southwest monsoon winds cool the surface of the Arabian Sea by evaporation, mixing and upwelling, and deepen its mixed layer (c-iv).

Only one option contains both b-i and c-iv, and it pairs the east-west gradient reversal with the mid-latitudes (a-iii) and the northward movement of the south equatorial current with the Indian Ocean (d-ii). The option a-ii, b-i, c-ii, d-iv uses ii twice and puts the mixed-layer deepening in the whole Indian Ocean rather than the Arabian Sea.

Your Answer : (Not Answered)

Correct Answer : A

The main reason is strong vertical wind shear.

During the summer monsoon, low-level westerlies blow over the Bay of Bengal while the tropical easterly jet blows strongly in the upper troposphere. The large change in wind with height tilts and tears apart developing convective systems and carries away the heat that a warm-core vortex needs to build up. Disturbances therefore usually remain monsoon depressions rather than becoming cyclones. Cyclones over the Bay peak in the pre-monsoon and post-monsoon seasons, when the shear is weak.

The other reasons do not apply in this season: the monsoon trough supplies strong low-level cyclonic vorticity, the mid-troposphere is moist, and the atmosphere is convectively unstable.

Your Answer : (Not Answered)

Correct Answer : C

The main reason is that the Coriolis force is too weak.

A tropical cyclone needs the inflowing air to be deflected into a rotating vortex. The Coriolis parameter \(f = 2\Omega\sin\phi\) is zero at the Equator and very small within about 5° of it, so converging air flows straight in and fills the low instead of spinning up; cyclones therefore rarely form there.

The equatorial sea surface is warm, not too cold. Weak vertical wind shear favours cyclones rather than preventing them, and the beta effect influences cyclone drift, not cloud dissipation.