Monsoons are periodic winds, especially in the Indian Ocean and southern Asia.
The season of the southwest monsoon in India and adjacent areas is characterized by very heavy rainfall.
The monsoon approaches the landmass in two branches: The Arabian Sea branch. The Bay of Bengal branch.
2. Nature of Monsoon
The onset of the monsoon.
Rain-bearing systems (e.g. tropical cyclones) and the relationship between their frequency and distribution of monsoon rainfall.
Break in the monsoon.
2.1 Onset of the Monsoon
Towards the end of 19 the century Arab traders believed that monsoon is differential heating of land and sea
During April and May when the sun shines vertically over the Tropic of Cancer, the large landmass in the north of the Indian ocean gets intensely heated.
This causes the formation of intense low pressure in the northwestern part of the subcontinent and attracts moisture-laden winds
2.2 Entry of Monsoon into India
The southwest monsoon sets in over the Kerala coast by 1st June and moves swiftly to reach Mumbai and Kolkata between 10th and 13th June.
By mid-July, southwest monsoon engulfs the entire subcontinent 2.3 Rain-bearing systems
There seem to be two rain-bearing systems in India.
First originated in the Bay of Bengal causing rainfall over the plains of north India.
Second is the Arabian Sea current of the southwest monsoon which brings rain to the west coast of India.
2.4 Break in the Monsoon
Break in the Monsoon During the southwest monsoon period after having rained for a few days, if rain fails to occur for one or more weeks, it is known as a break in the monsoon.
These dry spells are quite common during the rainy season.
3. Seasons
The cold-weather season
The hot weather season
The southwest monsoon season
The retreating monsoon season.
a) The Cold Weather Season
Usually, the cold weather season sets in by mid-November in northern India.
December and January are the coldest months in the northern plain.
The mean daily temperature remains below 21°C over most parts of northern India.
During the winters, the weather in India is pleasant.
Winter monsoons do not cause rainfall as they move from land to the sea.
It is because firstly, they have little humidity; and secondly, due to anti-cyclonic circulation (High pressure) on land, the possibility of rainfall from them reduces but there are some exceptions.
b) The hot weather season
With the apparent northward movement of the sun towards the Tropic of Cancer in March, temperatures start rising in north India.
In the northwest, the dry and hot winds known as ‘Loo’, blow in the afternoon, and very often, they continue well into midnight.
Dust storms in the evening are very common during May in Punjab, Haryana, Eastern Rajasthan and Uttar Pradesh.
c) The southwest monsoon season
As a result of the rapid increase of temperature in May over the northwestern plains, the low-pressure conditions over there get further intensified.
By early June, they are powerful enough to attract the trade winds of the Southern Hemisphere coming from the Indian Ocean which results in a southwest monsoon.
This sudden onset of the moisture-laden winds associated with violent thunder and lightning, is often termed the “break” or “burst” of the monsoons.
d) Season of Retreating Monsoon
The months of October and November are known for retreating monsoons.
By the end of September, the southwest monsoon becomes weak as the low-pressure trough of the Ganga plain starts moving southward in response to the southward march of the sun.
The retreating southwest monsoon season is marked by clear skies and a temperature rise.
The land is still moist.
Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive which is commonly known as the ‘October heat’. 4. Figure representing arrival and withdrawal of southwest monsoon.
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