Monsoon Systems Questions and Answers

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.

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.

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.

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.

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.

Answer: C

The Konkan subdivision receives the most south-west monsoon rainfall.

The moist south-west monsoon winds from the Arabian Sea strike the Western Ghats, rise and shed heavy orographic rain on the windward coastal strip, the Konkan (with Goa). Its seasonal rainfall is commonly 2,500 to 3,500 mm or more.

Madhya Maharashtra and Marathwada lie in the rain shadow east of the Ghats and receive far less, and Vidarbha, in the east, gets moderate rainfall mainly from monsoon depressions from the Bay of Bengal.

Answer: C

The easterly jet stream over peninsular India is observed during the south-west monsoon season.

The Tropical Easterly Jet develops in the upper troposphere, at about 100 to 150 hPa, over south Asia during June to September. It results from the strong temperature contrast between the heated Tibetan Plateau and the Indian Ocean, and it is closely linked with the strength of the monsoon.

In winter and before the monsoon, the dominant upper-level flow over north India is the subtropical westerly jet. The easterly jet weakens and withdraws with the monsoon in the post-monsoon season.

Answer: B

The North-east monsoon gives rainfall over Tamil Nadu.

From October to December the winds reverse and blow from the north-east. Crossing the Bay of Bengal they pick up moisture and bring rain to the south-east coast, so Tamil Nadu (with coastal Andhra Pradesh and south Kerala) receives about half of its annual rainfall in this season.

North-east India and Maharashtra get most of their rain from the south-west monsoon, and Jammu and Kashmir gets winter precipitation from western disturbances, not from the north-east monsoon.