climate in india

At One time, Climatology consisted of meteorological parameters like precipitation, temperature, cloudiness, humidity, wind etc. Climatic classification was based on a few of these parameters mostly on precipitation and temperature. Later the interest of meteorologists shifted to the fluctuations around the mean state. Before dealing with climatology we should think in terms of different length scales.
Planetary 5000km
Synoptic 1000km
Meso 100km
Micro 1km or less
Sometimes there will be interaction between different scales. All these scales are earth anchored in position and depend on different systems whose time period varies from few days to one year. The main systems include ITCZ, STR, STJ, PJS, etc.
These are largely responsible for the formation of arid, semiarid, wet
and other climatic zones and also for the seasonal changes of weather in each climatic zone.
Now coming to India, India is in tropical region extending into extra tropical region affected by both tropical and extra tropical systems. Monsoon depressions, and cyclones are major tropical systems affecting coastal areas. Where as western disturbances coming from west affect northern part of the country. Lying between the greatest land mass and the warmest sea, shut in by the loftiest mountains, backed by the highest plateaux of the world, India provides the best conditions for a monsoon. India, especially North West India, thus becomes virtually the terminus for the ocean winds from the south, and only from the south in summer and the center of dispersal of land winds in winter. Within a area of varied relief embracing about 3 million square kilometers and extending through 30 degrees latitude there must naturally occur a great variety of climatic types, ranging from continental to marine and from arid to humid; but its almost complete detachment, by virtue of its natural frontiers, from the rest of Asia makes India, as a climatic unit capable of independent treatment.
Further as we are aware that inclination of the earth and revolution around the Sun causes seasons. According to IMD the year is divided into four seasons.

Winter season (Jan and Feb)
Summer season or premonsoon season (March, April and May)
Southwest Monsoon season (June to Sept)
Post Monsoon or Northeast Monsoon season (Oct to Dec)

So, the climate of different parts of India depends on the above four seasons. Generally southern parts of the country experience warm and humid climate and northern parts experience moderate temperature and dry climates. Further the Climate of a place depends on the Altitude of the place, Orography, Land and sea distribution, Ocean currents etc. A place located at a very high altitude would have a climate quite a different from a place just a few meters above sea level. Mountains play an important role in modifying the climate. When humid air ascends from the mountain it can produce, heavy precipitation on the windward side and less rainfall over the lea side. Over India Himalayan mountains are preventing the polar cold air mass entering to India and further contributing heavy rainfall on the southern and eastern side of the Himalayas. This is the reason for heavy rains in the northeast part of the country.

Seasonal temperature differences between continents and oceans produce temperature variations in pressure, rainfall, wind etc. So marine course gets moderate temperature climate whereas the inner continent gets extreme temperature. In India the northern part is located up by the land and so gets extreme minimum and maximum temperature where as the southern part surrounded by the sea gets moderate temperature.
Ocean currents are produced by the winds over the sea surface and horizontal variations of density of seawater. These currents carry tropical warm waters towards the eastern side of the country in low latitudes and temperate water towards the western side. This causes warming up seawater and instability in the atmosphere in the eastern side.
As already said the climate for a year depends on the four seasons described above.

WINTER SEASON

During winter the land will be much colder than the sea areas . So a high pressure area forms over land in the northern side and low pressure on the sea on the southern side of the country. During this season the sun is in the southern hemisphere. So the equatorial trough lies between the equator and 10 degree south. On sea level chart a trough runs along the west coast and a ridge along the east coast. The winds blow from the land to sea. In the upper atmosphere an anticyclone lies along the center part of the country up to 1.5 Kms. and strong westerlies in the higher levels reaching up to 100 knots over J& K.
Lowest temperatures are recorded over North West India causing cold wave. Western disturbance is the most important weather system during this season. They are the low pressure systems coming from west moving eastwards across northern part of the country causing thunder storms and hailstorms. Western Himalayas experience snowfalls. An average two to three disturbances pass on every month and the WD last for 4 to 5 days. In the rear of the WD radiation fog is observed in the northern part and advection fog in the costal areas. Cold waves are common in this season in the north extending into peninsular India. The minimum temperature fall up to 6to 7 degree causing cold wave and some times 8 to 10 degrees fall causing severe cold wave.


HOT WEATHER OR SUMMER OR PREMONSOON SEASON.
This season is characterized by extreme high temperature, severe thunderstorm, dust storms/sand storms and cyclones. There will be a pressure difference caused by intense heating between land and sea and as a result winds blow from sea to land. A trough of low pressure lies over central parts of India and two anticyclones in the lower troposphere are seen over Bay and Arabian sea. In the upper troposphere strong westerlies are seen over north India.
The area of highest temperature shifts slowly towards northwards during may and June and northwest India becomes the hottest. The mean maximum temperatures will be more than 40 degrees Celsius in the northern and central parts of the country.
Severe thunderstorms are the major weather systems during this season. NE India experiences a high frequency of thunderstorms during this season and they are called NORWESTERS or KALBAISHAKIS. Where as northwest India experiences dust storms, which are locally known as Andhis. Rajasthan, Punjab, Harayana, Gujarat etc are more vulnerable for dust storms. In the desert areas sand storms cause havoc making the visibility to few meters. There will be thunderstorm activity throughout the country. These thunderstorms are accompanied with squally winds and heavy rain
.
Heat waves are common when the maximum temperature raises by 6to 7 degrees Celsius and in North India severe heat waves occur when the temperature rises by more than 7 degrees. They last for a bout a week
.
Cyclones are also common during this season. They generally form in the Bay of Bengal and affect the east coast of India.

SOUTHWEST MONSOON SEASON.

This is the most important season for India contributing about 70% of annual rainfall. An intense low-pressure area forms over Pakistan and adjoining Rajasthan and a trough from this extends up to head bay. This is called Monsoon trough it extends up to higher levels tilting southwards with height. Even though the Sun is in the northern hemisphere, due to this Monsoon, most parts of the country is covered with clouds and the temperatures starts falling, even the warmer areas in Rajasthan gets cooled by the end of July.
The normal onset of sw monsoon over Kerala is first June; there afterwards it covers entire country by July 15th.The main weather system during this season is formation of monsoon depression. Generally they form in the head bay and move along the monsoon trough giving torrential rains across its track. The life period of a monsoon depression is about 5 days. About 6 to7 depressions form during monsoon season. When the monsoon is active, mid trophospheric circulations form over Gujarat giving heavy rains over Gujarat, Rajasthan and adjoining areas.
There is one period when the monsoon trough shifts to the foot of the Himalayas This shifting leads to significant reduction of rainfall over most parts of India and this situation is called Break Monsoon. During this period Tamilnadu gets rains, which was shadowed by southwest monsoon.
So during sw monsoon all parts of the country get rainfall by some phenomena or other. ` By September 15 SwMonsoon starts withdrawing from NW India and by 30 th September monsoon season ends.

POST MONSOON OR NORTHEAST MONSOON SEASON.

This is the principal rainy season for Tamilnadu , coastal Andhrapradesh and Rayalaseema. When the Sw monsoon with drew from entire country, North east monsoon sets over the southern part of the country. Formation of Depressions and cyclones over Bay of Bengal is the major weather phenomena during this season
Cyclones initially form as low pressure areas over Bay of Bengal or ARABIAN SEA and starts intensifying into depressions, cyclones etc. The cyclones starts moving ina northwesterly direction further intensify into severe cyclonic storms and super cyclones and hit the east coast of India The most affected areas are Tamilnadu, coastal andhrapradesh, orissa and west Bengal. The cyclones in Arabian Sea affect Maharasatra and Gujarat coasts; A cyclone is accompanied with heavy rains gale winds and tidal waves. The tidal waves cause storm surge at the point where they strike the coast. Human loss, structural damage, loss of cattle etc are the main damages caused by a cyclone. Of course by proper warning the loss of life can be reduced.

Reviewing broadly the rainfall of India, it is noticeable that while relief rains give the heaviest falls, it is the monsoon and cyclonic type which, on account of its more even distribution, is of greater economic value as for example, in the Gangetic plain and the deccan plateau during monsoon season, and the Punjab and NWIndia during Cold season. At no time of the year is India entirely without rain. Even though Jan and Feb. are driest months northwest India enjoys rain from westerndistrurbances. March, April and May being thunderstorm season except NW India other party gets rainfall and especially NE India gets about 30% of its annual rainfall. June to October all parts gets monsoon rainfall and Nov and Dec southern parts gets rains due to cyclones and western disturbances activity starts in northern parts.

However the climate is changing at different places due to urbanization, cutting of forests, release of harmful gases etc. Further the Global phenomena, like El Nino, Global warming etc are also affecting the seasonal weather phenomena like Monsoons, winter at different places. This is causing unprecendential rains, floods and droughts in some areas during a year. Let us hope that Nature protects herself and we Indians help in protecting Beautiful Climate of India and make it Heaven in the World.