The Indian monsoon complex phenomenon influenced by various climatic factors. Critically examine the role of oceanic and atmospheric factors in determining the intensity and distribution of monsoon rainfall in India.

It is a complex phenomenon due to involvement of multiple variable factors of ocean and atmosphere.

Role of oceanic factors:

1. Mascrenes high → Presence of high pressure over Madagascar region of Indian ocean → pushes SW monsoon.

2. Indian ocean dipole(IOD) → Positive IOD (warmer West Indian ocean) helps in more rainfall over India and opposite in negative IOD.

3. ENSO - or El-Nino Southern Oscillation over south equatorial pacific ocean impact monsoon.

[E.g] El-Nino → higher oceanic temp over Peru coast → Low monsoon rainfall.

La-Nina → high temperature over Australia → High monsoon rainfall.

4. Other oceanic factors like:

(i) Pacific decadal oscillation

(ii) Eurasian snow cover

Also impact monsoon in complex way.

Role of atmospheric factors:

1. Somali Jet stream, Eastern Tropical Jet stream as well as Sub-tropical polar jetstream influence or intensity of monsoon.

2. Malan-Julian oscillation → eastward moving moisture-laden wind on Indian ocean → Presence over North Indian ocean in monsoon → Higher rainfall

2. Western disturbances → Impacts rainfall intensity over north India.

[E.g] Recent Yamuna flood due to mix convergence of WD and SW monsoon.

4. Similarly, formation of cyclones, also impact onset and movement of monsoon.

[E.g] Cyclone Nisarga - delayed monsoon

However, apart from ocean & atmosphere, the topography also decides the intensity of monsoon by shaping the direction of the wind and with lee-ward / wind-ward effect in orography rainfall.

— Prajnanandan Giri · AIR 24