difference between south west monsoon and the north east monsoon by explaining 4 distinct features of each.
First of all, Southwest monsoon in general is called as Indian monsoon as it covers most parts of the country and Northeast monsoon is called as Retreating monsoon.
South West monsoon
After the spring Equinox on March 21, Sun advances north of the equator and is over the Indian subcontinent. This heats up the Indian landmass rapidly. Heat proceeds staring from the south and reaches Northwest India by March end.
Meanwhile after the equinox, a high pressure area forms over South Indian ocean near Madagascar. This high pressure area blows wind gusts towards African coast. When these winds gusts arrive close to Somalian coast by May it gets deflected due to Coriolis effect towards Indian mainland.
By mid-May heat over Indian subcontinent blisters forming a heat low pressure area over Northwest India. This low pulls in winds from the Indian waters. Once the upper level Easterly jets are replaced by westerly, winds from South Andaman sea blows in a southeast direction and onsets Southwest monsoon on Andaman islands by May 20.
Wind gusts from Somalia pushed by Mascarene high near Madagascar picks up huge amount of moisture from Arabian sea and when it reaches Indian mainland gets an uplift by the terrain of western ghats and precipitates rain marking the onset of Southwest monsoon over Indian mainland in Kerala by June 1.
As the ITCZ starts moving north it pulls the monsoon along with it and both Arabian sea branch and Bay of Bengal branch gets blocked by Himalayas in the Northeast and is diverted towards the heat low pressure area in Northwest India. Thus covering the entire Indian landmass with Southwest monsoon.
Retreating or Northeast monsoon
Indian landmass starts to cooled down by monsoon rains and the heat low weakens by September 1. With less moisture pull by the low pressure, skies started to clear over Northwest India marking the withdrawal of Southwest monsoon by September 1.
After the Autumal equinox on September 22, Sun starts receding south further cooling down the Indian landmass. By October 1, a feeble high pressure area begins to set in over Siberia which pushes air down towards Indian landmass.
As Sun recedes south, ITCZ starts moving south and a high pressure area begins to build over North India. When the wind gusts from Siberian high reaches north Bay of Bengal, it picks up moisture. By October 15, upper level winds turn from westerly to easterly and a low pressure trough forms over Southeast coast of India.
Under the influence of this low pressure trough, winds from North Bay of Bengal is pulled and as it reaches Coastal Tamil nadu precipitates Northeast monsoon by October 20. Southern states of India namely Telangana, Andhra Pradesh, Karnataka, Tamil nadu and Kerala only receives rainfall from Northeast monsoon.
June to September is the season of south-west monsoon rainfall in India. After September 1, the strength of monsoon starts decreasing in North-West part of India/Pakistan region and after certain conditions are met (like cessation of rainfall in this part for at least five days , considerable reduction in the moisture and establishment of high pressure at an altitude of 5,000 feet above ground), monsoon starts withdrawing i.e retreating. Typically this goes on for more than a month and India Meteorological Department (IMD) keeps monitoring this withdrawal. Till 15N latitude, this withdrawing is referred as south-west monsoon withdrawal. After the withdrawal happens till this latitude and some more weather conditions are met (including a norm that at least 10 days have passed in October), IMD declares the onset of Northeast Monsoon. So basically Northeast Monsoon commences if 10 days have passed in October and these conditions are met especially retreat of south-west monsoon till 15N.