Why the summer monsoon winds blow from south- western direction in the northern hemisphere ?

The summer monsoon winds blow from a south-western direction in the Northern Hemisphere primarily due to the Coriolis force. During the summer, intense low-pressure conditions develop over northwest India and interior Asia [c2, c4]. This pressure gradient pulls the southeast trade winds from the Southern Hemisphere across the equator [c2, t3]. According to Ferrel's Law, the Coriolis force—an apparent force caused by the Earth's rotation—deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere [c1, c5]. As these southeast trade winds cross the equator into the Northern Hemisphere, they are deflected to their right, transforming into the south-west monsoon winds [c2, c3, t1]. While the low-pressure core in northwest India acts as the initial attractor for these winds [c4, t4], the specific south-western direction they take is a direct consequence of the Coriolis deflection [c2, t6].

Sources

1. [1] CONTEMPORARY INDIA-I ,Geography, Class IX . NCERT(Revised ed 2025) > Chapter 4: Climate > Pressure and Winds > p. 28
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Monsoons > p. 320
3. [3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 4: Climate of India > The Dynamic Concept by Flohn > p. 3
4. [4] INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 4: Climate > THE SOUTHWEST MONSOON SEASON > p. 35
5. [5] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 23: Pressure Systems and Wind System > Why Tropical Cyclones Do Not Form At The Equator? > p. 310
6. [6] https://cuet.iitk.ac.in/sathee-cuet/student-corner/ncert-books/class-11/geography/india-physical-environment/chapter-04-climate/