Monsoon

About

Monsoon refers to the seasonal reversal in the wind direction during a year.
The word monsoon is derived from the Arabic word ‘mausim’ which literally means season.

Onset of monsoon

- The onset of the monsoon over Kerala marks the beginning of the four-month, June-September southwest monsoon season over India, which brings more than 70% of the country’s annual rainfall.
- The onset of monsoon is announced by the India Meteorological Department (IMD) only after certain defined and measurable parameters, adopted in 2016, are met. Broadly, the IMD checks for the consistency of rainfall over a defined geography, its intensity, and wind speed.

According to the IMD the onset of the monsoon marks a crucial transition in the large-scale atmospheric and ocean circulations in the Indo-Pacific region.

Mechanism

Towards the end of the nineteenth century, it was believed that the differential heating of land and sea during the summer months is the mechanism which sets the stage for the monsoon winds to drift towards the Indian subcontinent.
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 an intense low pressure in the northwestern part of the subcontinent.
Since the pressure in the Indian Ocean in the south of the landmass is high as water gets heated slowly, the low pressure cell attracts the southeast trades across the Equator.
These conditions help in the northward shift in the position of the ITCZ.
The southwest monsoon may thus be seen as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator. These winds cross the Equator between 40°E and 60°E longitudes.
The shift in the position of the ITCZ is also related to the phenomenon of the withdrawal of the westerly jet stream from its position over the north Indian plain, south of the Himalayas. The easterly jet stream sets in along 15°N latitude only after the western jet stream has withdrawn itself from the region. This easterly jet stream is held responsible for the burst of the monsoon in India.

Why in the news?

The India Meteorological Department (IMD) said about the onset of southwest monsoon on the Kerala coast.

Additional Information

India Meteorological Department (IMD)

- It is the National Meteorological Service of the country and the principal government agency in all matters relating to meteorology and allied subjects.
- IMD was established in 1875.

Responsibilities

To take meteorological observations and to provide current and forecast meteorological information for optimum operation of weather-sensitive activities like agriculture, irrigation, shipping, aviation, offshore oil explorations, etc.
To warn against severe weather phenomena like tropical cyclones, norwesters, duststorms, heavy rains and snow, cold and heat waves, etc., which cause destruction of life and property.
To provide meteorological statistics required for agriculture, water resource management, industries, oil exploration and other nation-building activities.
To conduct and promote research in meteorology and allied disciplines.

Sources

Today Current Affairs Upsc Exam Syllabus & Previous Yearpaper.