Monday, January 6, 2025 6:38 PM
Climate
• Climate refers to the sum total of weather
conditions and variations over a large area for
a long period of time (more than thirty years).
• Weather refers to the state of the atmosphere over an area at any point of time.
• The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind,
humidity and precipitation.
• On the basis of the monthly atmospheric conditions, the year is divided into seasons such as winter,
summer or rainy seasons.
• The climate of India is described as the ‘monsoon’ type. In Asia, this type of climate is found mainly in
the south and the southeast.
• Two important elements are temperature and precipitation
• While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the
rest of the country.
• The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and
western Rajasthan.
• Most parts of the country receive rainfall from June to September. But some parts like the Tamil
Nadu coast gets a large portion of its rain during October and November.
• There is decrease in rainfall generally from east to west in the Northern Plains.
Sub topic -
•
New Section 1 Page 1
Monday, January 6, 2025 6:50 PM
Climatic Controls
• Six climatic controls- latitude, altitude, pressure and wind system, distance from the sea (continentality),
ocean currents and relief features.
• Due to the curvature of the earth, the amount of solar energy received varies according to latitude. As a
result, air temperature generally decreases from the equator towards the poles.
• As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and
temperature decreases. The hills are therefore cooler during summers.
• The pressure and wind system of any area depend on the latitude and altitude of the place. Thus it influences
the temperature and rainfall pattern.
• The sea exerts a moderating influence on climate: As the distance from the sea increases, its moderating
influence decreases and the people experience extreme weather conditions. This condition is known as
continentality (i.e. very hot during summers and very cold during winters).
• Ocean currents along with onshore winds affect the climate of the coastal areas
• Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or
hot winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds.
The leeward side of mountains remains relatively dry
• Latitude
- The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh in the west to
Mizoram in the east. Almost half of the country, lying south of the Tropic of Cancer, belongs to the tropical
area. All the remaining area, north of the Tropic, lies in the sub-tropics. Therefore, India’s climate has
characteristics of tropical as well as subtropical climates.
- Altitude
- India has mountains to the north, which have an average height of about 6,000 metres. India also has a
vast coastal area where the maximum elevation is about 30 metres. The Himalayas prevent the cold winds
from Central Asia from entering the subcontinent. It is because of these mountains that this subcontinent
experiences comparatively milder winters as compared to central Asia.
- Pressure and Winds
- The climate and associated weather conditions in India are governed by the following atmospheric conditions:
- • Pressure and surface winds;
- • Upper air circulation; and
- • Western cyclonic disturbances and tropical cyclones.
New Section 1 Page 2
Monday, January 6, 2025 6:59 PM
Topic
• India is influenced by north-easterly winds that originate from the subtropical high-pressure belt in the
northern hemisphere. These winds blow southward and are deflected to the right due to the Coriolis force,
moving towards the equatorial low-pressure area, but they carry very little moisture since they travel over
land.
• During winter, a high-pressure area forms north of the Himalayas, causing cold, dry winds to flow from this
region to low-pressure areas over the oceans to the south. In summer, a low-pressure zone develops over
the interior of Asia and northwestern India, reversing the wind direction. Winds then blow from the high-
pressure area in the southern Indian Ocean, moving in a south-easterly direction, crossing the equator, and
turning right towards the low-pressure areas over the Indian subcontinent. These winds are known as the
Southwest Monsoon winds, and as they travel over warm oceans, they gather moisture, leading to
widespread rainfall across mainland India.
• Additionally, the upper air circulation in this region is dominated by westerly winds, with an important
component being the jet stream. These jet streams are fast-moving air currents located around 27°-30°
north latitude, known as subtropical westerly jet streams, which significantly influence weather patterns and
can affect the monsoon by steering weather systems.
• Over India, these jet streams blow south of the Himalayas, all through the year except in summer. An
easterly jet stream, called the sub-tropical easterly jet stream blows over peninsular India, approximately
over 14°N during the summer months.
•
•
•
•
Sub topic -
•
New Section 1 Page 3
