Mechanism of Weather in the Winter and Summer Season

Last Updated : 16 Apr, 2024

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.

Difference Between Weather and Climate

Before understanding the weather mechanism, we need to know the difference between weather and climate.

Weather	Climate
Weather is the momentary state of the atmosphere	Climate refers to the average of the weather conditions over a longer period.
Weather changes quickly, maybe within a day or week	Climate change imperceptibly may be noted after 50 years or even more.
Weather forecasting is observed by the Metrological Department.	Climatology is the scientific study of the climate.
Weather is affected by temperature, pressure, humidity, and cloudiness.	Atmospheric conditions at any location like humidity, temperature, sunshine, wind, etc are affected by the climate.

To understand the differences in local climates, we need to understand the mechanism of the following three factors:

Distribution of air pressure and winds on the surface of the earth.
Upper air circulation is caused by factors controlling global weather and the inflow of different air masses and jet streams.
The inflow of western cyclones generally known as disturbances during the winter season and tropical depressions during the southwest monsoon period in India, create weather conditions favorable to rainfall.

Factors determining the climate of India

Factors	Characteristics
Latitude	The Tropic of Cancer passes through the central part of India in the east-west direction. Thus, the northern part of India lies in the sub – tropical and temperate zone, and the part lying south of the Tropic of Cancer falls in the tropical zone. The tropical zone being nearer to the equator experiences high temperatures throughout the year with a small daily and annual range. Areas north of the Tropic of Cancer, being away from the Equator experience extreme climate.
The Himalayan Mountain	The lofty Himalayas in the north along with its extensions act as an effective climatic divide. The towering mountain chain provides an invincible shield to protect the subcontinent from the cold northern winds. These cold and chilly winds originate near the Arctic Circle and blow across central and eastern Asia. The Himalayas also trap the monsoon winds, forcing them to shed their moisture within the subcontinent
Distance from the Sea	With a long coastline, large coastal areas have an equable climate. Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate. On the other hand, the seasonal contrasts in weather at places in the interior of the country such as Delhi, Kanpur, and Amritsar affect the entire sphere of life.
Altitude	Temperature decreases with height. Due to thin air, places in the mountains are cooler than places on the plains.
Relief	The physiography or relief of India also affects the temperature, air pressure, direction and speed of wind, and the amount and distribution of rainfall. The windward sides of Western Ghats and Assam receive high rainfall during June-September whereas the southern plateau remains dry due to its leeward situation along the Western Ghats.

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 Summer Season

Surface Pressure and Winds

As the summer sets in and the sun shifts northwards, the wind circulation over the subcontinent undergoes a complete reversal at both, the lower as well as the upper levels.
By the middle of July, the low-pressure belt nearer the surface [termed as Inter Tropical Convergence Zone (ITCZ)] shifts northwards, roughly parallel to the Himalayas between 20° N and 25° N.
By this time, the westerly jet stream withdraws from the Indian region.

Jet Streams and Upper Air Circulation

Easterly Jet Streams flows over the southern part of the Peninsula in June and has a maximum speed of 90 km per hour. In August, it is confined to 15 degrees north latitude, and in September up to 22 degrees north Latitude.

The easterlies normally do not extend to the north of 30 North degrees latitude in the upper atmosphere.

Easterly Jet Streams and Tropical Cyclones

The easterly jet stream steers the tropical depressions into India. These depressions play a significant role in the distribution of monsoon rainfall over the Indian subcontinent.

The tracks of these depressions are the areas of highest rainfall in India.
The frequency at which these depressions visit India, their direction, and intensity, all go a long way in determining the rainfall pattern during the southwest monsoon period.

Conclusion

Weather is caused mainly by the changes in air pressure, temperature, and moisture from one location to another.
The significant temperature difference between polar and tropical air causes large-scale atmospheric circulation cells and the jet streams.
In India, during the winter, the northern region near the Himalayas experiences high pressure. As a result, winds from this area move south, where the pressure is lower.
The northern section of the country has lower pressure in the summer.

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