Mechanism of Weather in the Winter Season

Surface Pressure and Winds

In winter months, the weather conditions over India are generally influenced by the distribution of pressure in Central and Western Asia.

• A high-pressure center in the region lying to the north of the Himalayas develops during winter.
• This center of high pressure gives rise to the flow of air at the low level from the north towards the Indian subcontinent, south of the mountain range.
• The surface winds blowing out of the high-pressure center over Central Asia reach India in the form of a dry continental air mass.
• These continental winds come in contact with trade winds over northwestern India. The position of this contact zone is not, however, stable.
• Occasionally, it may shift its position as far east as the middle Ganga valley with the result that the whole of northwestern and northern India up to the middle Ganga valley comes under the influence of dry northwestern winds.

Jet Streams and Upper Air Circulation

Higher up in the lower troposphere, about three km above the surface of the earth, a different pattern of air circulation is observed.

• The variations in the atmospheric pressure closer to the surface of the earth have no role to play in the making of upper air circulation.
• All of Western and Central Asia remains under the influence of westerly winds along an altitude of 9-13 km from west to east. These winds blow across the Asian continent at latitudes north of the Himalayas roughly parallel to the Tibetan highlands. These are known as jet streams.
• Tibetan highlands act as a barrier in the path of these jet streams. As a result, jet streams get bifurcated.
• One of its branches blows to the north of the Tibetan highlands, while the southern branch blows in an eastward direction, south of the Himalayas.
• It has its mean position at 25°N in February at 200-300 mb level. It is believed that this southern branch of the jet stream exercises an important influence on the winter weather in India.

Western Cyclonic Disturbance and Tropical Cyclones

The western cyclonic disturbances which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream.

• An increase in the prevailing night temperature generally indicates an advance in the arrival of these cyclone disturbances. Tropical cyclones originate over the Bay of Bengal and the Indian Ocean.
• These tropical cyclones have very high wind velocity and heavy rainfall and hit the Tamil Nadu, Andhra Pradesh, and Orissa coasts.
• Most of these cyclones are very destructive due to high wind velocity and torrential rain that accompanies them.

Mechanism of Weather in the Winter and Summer Season: There are variations in weather conditions during different seasons. These changes occur due to weather temperature, pressure, wind direction, velocity, humidity, precipitation, etc.

In this article, we will focus on the weather mechanism during the winter and summer seasons.