RAS question
The South-East Trade Winds cross the Equator and turn into South-West Monsoon winds due to which force?
Correct answer: (A) Coriolis Force.
South-East Trade Winds become the South-West Monsoon after crossing the Equator because the Coriolis Force, produced by Earth's rotation, deflects them to the right in the Northern Hemisphere.
Explanation
South-East Trade Winds do not change direction because of a pull or surface drag; their turn is a rotation effect. This rotation effect is the Coriolis Force, produced by Earth's rotation, which deflects winds to the right in the Northern Hemisphere. The PIB monsoon explainer describes the same mechanism in Indian monsoon terms: as the ITCZ shifts northward, it draws trade winds from the southern hemisphere; after crossing the Equator, these winds bend due to Earth's rotation and reach India from the southwest. That is why the same wind stream is recognised as the South-West Monsoon, the rain-bearing monsoon flow for India.
Why the other options are wrong
- (B) Gravitational Force explains attraction due to mass, not the rightward deflection of winds after they enter the Northern Hemisphere.
- (C) Centrifugal Force is not the mechanism for the bending of cross-equatorial trade winds in the PIB account.
- (D) Frictional Force can affect wind near surfaces, but the stated change into South-West Monsoon winds is explained by Earth's rotation through the Coriolis Force.
Concept
This tests the physical mechanism behind the Indian monsoon, especially cross-equatorial trade winds and Coriolis deflection. It recurs in RAS because monsoon formation links basic climatology with India's rainfall pattern.