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Difficulty: Very hardClimate, Weather Systems, and Monsoon of India

Which of the following statements regarding the atmospheric circulation, extratropical disturbances, and seasonal driving mechanisms of the Indian climate are correct?

  1. The establishment of the Tropical Easterly Jet Stream over peninsular India is directly linked to the northward displacement of the Subtropical Westerly Jet Stream to the north of the Tibetan Plateau.Answer
  2. Western Disturbances originate as extratropical cyclones over the Mediterranean region and are carried towards northwestern India by the Subtropical Westerly Jet Stream during winter.Answer
  3. C
    A positive Indian Ocean Dipole phase features warmer sea surface temperatures in the eastern Indian Ocean relative to the western Indian Ocean, leading to suppressed summer monsoon rainfall over India.
  4. D
    The local pre-monsoon rainfall known as 'Mango Showers' in Kerala and coastal Karnataka is caused by the moisture-laden winds of the winter retreating monsoon.

Answer

The correct statements are the one regarding the relationship between the Tropical Easterly Jet Stream and the northern displacement of the Subtropical Westerly Jet Stream, and the statement describing Western Disturbances as extratropical cyclones originating over the Mediterranean driven by the Subtropical Westerly Jet Stream.
The statement explaining the emergence of the Tropical Easterly Jet Stream is correct because the seasonal shift of the Subtropical Westerly Jet to the north of Tibet is a necessary structural condition for the upper-level Easterly Jet and ITCZ northward movement. The statement regarding Western Disturbances is also correct because these non-monsoonal storms originate over the Mediterranean and move along the upper westerly flow into North India during winter.

Step-by-Step Solution

1
Analyze the upper-atmospheric mechanisms governing the onset of the Indian Southwest Monsoon.
During summer, intense heating of the Tibetan Plateau generates an upper-level warm anticyclone. For the Tropical Easterly Jet Stream to form over southern India, the winter Subtropical Westerly Jet Stream must first retreat to the north of the Himalayas. Hence, the statement linking the establishment of the Tropical Easterly Jet Stream to this northward displacement is accurate.
Upper-air jet stream transitions serve as a primary trigger for atmospheric pressure reversals over South Asia.
2
Evaluate the origin and steering mechanism of Western Disturbances.
Western Disturbances are temperate (extratropical) low-pressure systems originating in the Mediterranean and Atlantic regions. They travel eastward under the influence of the upper-tropospheric Subtropical Westerly Jet Stream, bringing winter precipitation to northwestern India. Thus, the statement describing Western Disturbances is correct.
Extratropical storm tracks in winter are governed by upper-level westerly wind belts.
3
Examine the spatial SST anomaly pattern of the positive Indian Ocean Dipole (IOD).
A positive IOD phase consists of anomalous warming in the western Indian Ocean and cooling in the southeastern tropical Indian Ocean. This thermal gradient strengthens the cross-equatorial flow and boosts monsoon rainfall over India. The statement claiming warmer eastern waters and suppressed rainfall reverses the positive IOD anomaly dynamics and is incorrect.
Ocean-atmosphere coupling parameters like the IOD modify regional atmospheric moisture transport.
4
Assess the seasonal origin of pre-monsoon convective showers in southern India.
Mango Showers occur during the pre-monsoon summer season (April to May) as a result of localized solar insolation and convection cell formation over peninsular India. They are distinct from the retreating northeast monsoon that occurs between October and December. Therefore, attributing them to the retreating monsoon is false.
Pre-monsoon local thunderstorms arise from thermal instability, not winter wind reversal patterns.

Key Concept

Upper Atmospheric Jet Streams, Extratropical Cyclones, and Oceanic Oscillations in Indian Climatology
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Topics

Climate, Weather Systems, and Monsoon of India

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