Indian Monsoon - Free MCQ Practice Test with solutions, SSC CGL

• The primary cause is the northward shift of the Inter-Tropical Convergence Zone (ITCZ) during the summer; this shift brings the zone of maximum convection and rainfall closer to the Indian subcontinent.
• Rapid heating of the land produces a strong low pressure over the Indian region, which helps draw in moist south-westerly winds from the Indian Ocean toward the land.
• The northward shift of the ITCZ and the resultant pressure gradient together cause the prevailing south-westerly moisture-laden winds to move onto the Indian landmass and produce the monsoon rains.
• The westerly jet stream shifts northwards and its change in position affects the monsoon's progress, but it is not the primary cause.
• Final decision: The shift of the ITCZ, aided by land-sea thermal contrast and the resulting low pressure over the heated land, is the principal reason for the onset of the south-west monsoon.

• The Thar Desert lies to the northwest of the Aravalli Hills.
• The Aravalli range runs parallel to the southwest monsoon winds coming from the Arabian Sea.
• Because of this alignment, the Aravallis do not force the winds to rise, which is necessary for orographic rainfall.
• As a result, very little moisture is left for the regions lying to the northwest, making the Thar Desert a dry region.
• This phenomenon is called the rain shadow effect.

Other options:

b) Incorrect: The Bay of Bengal branch mainly affects eastern and northeastern India, not the Thar region.
c) Incorrect: The Thar is influenced by monsoon winds, but it receives little rainfall due to topography.
d) Incorrect: While high pressure can inhibit rainfall, it is not the main reason in this context.

So, option (a) is the most accurate answer.