Context-2019 was a year of bountiful rain. The year’s Northeast monsoon ended on a high, with the season’s total rainfall recorded remaining 30 per cent surplus

• India Meteorological Department Department (IMD) recognizes October to December as the period for Northeast monsoon.
• As the Southwest monsoon adamantly lingered on from its withdrawal, there was a delay for the onset of the winter monsoon. Despite which, all sub-divisions in the southern peninsula received normal or above normal rainfall during the three months.
• The year that just went by witnessed the rare meteorological coincidence of the northeast (winter) monsoon making its onset on the same day as the southwest monsoon withdrew officially.
• The two events rarely happen simultaneously, although the three-month winter monsoon season is supposed to begin almost immediately after the end of the June-September summer monsoon season.
• In 2019, the retreat of the southwest (summer) monsoon was delayed by a record margin, while the northeast (winter) monsoon set in on time
• Recording significantly large amounts of rain, it was an extremely wet season for Lakshdweep (172 per cent) and Karnataka (70 per cent) in particular while 27 per cent excess rainfall was recorded over Kerala and Mahe, till December end

what is the northeast (winter) monsoon?

• In common parlance, a reference to the “monsoon” usually means the southwest summer monsoon. It is the main monsoon season, which brings widespread rain across the country.
• For many parts of India, this is the only time they receive rain. These four months bring about 75 per cent of India’s annual rainfall.
• However, for some regions of South India, it is the winter monsoon that is much more important. Though much less heard of, especially in the north of the country, the northeast monsoon is as permanent a feature of the Indian subcontinent’s climate system as the summer monsoon.
• The India Meteorological Department (IMD) recognises October to December as the time for the northeast monsoon.
• During this period, rainfall is experienced over Tamil Nadu, Kerala, and Andhra Pradesh, along with some parts of Telangana and Karnataka.

why are these two monsoons named thus?

• The northeast monsoon does not have anything to do with India’s Northeast, even though a part of the system does originate from the area above it.
• Rather, it derives its name from the direction in which it travels — from the northeast to the southwest. (In fact, all winds are named for the direction from which they blow. Thus the westerlies blow from the west, and the easterlies from the east.)
• Similarly, the summer monsoon (at least the Arabian Sea branch of it; there is also a branch that swerves in an anticlockwise direction in the Bay of Bengal before entering the Indian landmass and bringing rain to the eastern, northeastern and northern parts of the country) moves in exactly the opposite direction — from the southwest to the northeast. That is why it is called the southwest monsoon.

When does the northeast monsoon set in?

• Although October, November, and December are supposed to comprise the northeast monsoon season, the rains normally set in only around October 20.
• The southern peninsular region receives rain in the first half of October as well, but that is attributable to the retreating summer monsoon. The summer monsoon season ends on September 30 but the withdrawal does not happen overnight.
• The southward withdrawal takes place over a period of three to four weeks. It usually starts around the second week of September and continues till about the second week of October, bringing rain as it retreats. 2019 was unusual in that the withdrawal was completed in just eight days, beginning on October 9.

Where does it rain during the northeast monsoon season?

• The northeast monsoon brings rain to just five of the 36 meteorological divisions in the country — Tamil Nadu (which includes Puducherry), Kerala, Coastal Andhra Pradesh, Rayalaseema and South Interior Karnataka.
• As such, this season contributes only 11 per cent to India’s annual rainfall of 1,187 mm, compared to about 75 per cent in the summer monsoon season (the remaining rain comes in other non-monsoon months).
• Many other parts of the country, like the Gangetic plains and northern states, also receive some rain in November and December but this is not due to the northeast monsoon.
• It is caused mainly by the Western Disturbances, an eastward-moving rain-bearing wind system that originates beyond Afghanistan and Iran, picking up moisture from as far as the Mediterranean Sea, even the Atlantic Ocean. In the higher reaches of Jammu and Kashmir, Himachal Pradesh, and Uttarakhand, the precipitation is often in the form of snow.
• The northeast monsoon is particularly important for Tamil Nadu, which receives almost half its annual rainfall (438 mm of the annual 914.4 mm) during this season.
• The southwest monsoon contributes just 35 per cent to Tamil Nadu’s annual rainfall (the rest comes in other non-monsoon months). Within the state, some districts get up to 60 per cent of their annual rainfall during this time.
• Similarly, Rayalaseema region and Coastal Andhra Pradesh both about 30 per cent, and South Interior Karnataka receives about 20 per cent of its annual rainfall during the northeast monsoon season.

Meteorology in India

can be traced to ancient times.

Early philosophical writings of the 3000 B.C. era, such as the Upanishadas, contain serious discussion about the processes of cloud formation and rain

Varahamihira's classical work, the Brihatsamhita, written around 500 A.D., provides a clear evidence that a deep knowledge of atmospheric processes existed even in those times

Kautilya's Arthashastra contains records of scientific measurements of rainfall and its application to the country's revenue and relief work. Kalidasa in his epic, 'Meghdoot', written around the seventh century, even mentions the date of onset of the monsoon over central India and traces the path of the monsoon clouds

India Meteorological Department

• In the year 1875, the Government of India established the India Meteorological Department,
• At present IMD is under the Ministry of Earth Sciences (MoES)
• The Director General of Meteorology is the Head of the India Meteorological Department

Mandate

• 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 detect and locate earthquakes and to evaluate seismicity in different parts of the country for development projects.