Question

why are season change only in India

Answer 1

Because India lies on equater of the earth

Answer 2

In tropical and sub-tropical India, we have four seasons: monsoon, retreat of monsoon, winter and summer. In certain temperate parts of the country (Kashmir valley, for example) the four distinct seasons are Spring, Summer, Autumn and Winter.

In tropical and subtropical India, the seasonal changes may be explained as:

1) Post 21st March Equinox, The apparent position of sun shifts North polewards. Intensified heating results in Indian landmass and over Tibetan Plateau. This is the summer season. During the same period, Southerly branch of Westerly Jet Stream is withdrawn from India and the Inter Tropical Convergence Zone (ITCZ) -an area of intense low pressure- is drawn into mainland India.

2) By June, the ITCZ and Indian Ocean pressure differential is strong enough to draw in South Westerly Marine Trade winds. These are the monsoonal winds. They first appear over the Andamans around 20th May and over Kerala in first week of June. Usually the whole country is covered by July. During the same time, Easterly Jet Streams also come in which help intensify the ITCZ . This is the monsoons.


3) Around September 23rd, the sun shifts apparently South polewards and thus the low pressure ITCZ is no longer sustainable over India. With the shift, the monsoonal winds withdraw too. During this period, the temperature is still moderately high (day temperature in Delhi 30–35 degree celsius). This is also called as “Indian Summer”. Later, in November, some of the withdrawing monsoonal winds pick up moisture over bay of Bengal and cause rain over Tamil Nadu. This is the season of monsoonal retreat.


4) By December 23, the ITCZ has completely shifted out and over to Southern hemisphere. The sun’s position is now apparent over the Southern Hemisphere. Inner parts of mainland India, due to continentality will have a period of intense cold. Northern India will see Western Disturbances (WD) which are Temperate Cyclones from the Central asia/ Mediterranean region. (These are guided by Westerlies into India). Snow and winter rain occur in Northern India due to WD. The southern India will see no drastic changes in temperature because of the moderating influence of sea. This is the Winter Season.

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