This post for the Tnpsc exam in geography from the topic ‘Monsoon, rainfall, weather, and climate’. It is referenced from the Samacheer Kalvi book.
It covers Monsoon winds in India such as Southwest monsoon, north-west monsoon, the direction of retreating monsoon in India, and weather and climate.
Weather and Climate Tnpsc notes
The word Monsoon is derived from the word Mausim, an Arabic word. It is used by Arabic navigators to describe the seasons of the shores of the Indian Ocean.
The winds blow from southwest to northeast during summer. Similarly, the wind blows from northeast to southwest during winter. Different concepts by Meteorologists surrounding this complex phenomenon.
By Dynamic concept, Monsoon wind originates due to seasonal migration of planetary winds and pressure belts following the position of the sun. During summer solstice ‘June 21’, the sun rays fall vertically over the tropic of cancer.
Thereby all the pressure and wind belts of the globe shift northwards. At this time, Inter-Tropical Convergence Zone (ITCZ) also moves northwards and a major part of the Indian landmass comes under the influence of southeast trade winds.
While crossing the equator this wind gets deflected and takes the direction of south-west and becomes south-west monsoon. During winter, the pressure and wind belts shift southward, thereby establishing the northeast monsoon(trade winds) over this region.
This phenomenon of systematic change in the direction of the planetary winds is known as the monsoon.
Types of monsoon in India or Seasons of India
According to the experts, there are four main Monsoon seasons in India namely:
- Winter or Cold weather season (January – February)
- Pre-Monsoon or summer or hot weather season (March-May)
- Southwest Monsoon or rainy season (June – September)
- Northeast monsoon season (October – December)
Winter or cold-weather season or Winter Season in India
During this season, Sun’s vertical rays fall over the tropic of Capricorns which is far away from India. As a result, India receives slanting sun rays that result in low temperatures.
The cold season is characterized by clear skies, fine weather, low humidity, light northerly winds, and large daytime variations of temperature.
High pressure develops in North India and a north-westerly wind blows down the Indus and Ganges valleys.
In South India, the general direction of the wind is from east to west.
The mean temperature increases from North to south, the decrease is sharp as moving towards northwards in the north-western part of the country.
The minimum temperature in the south is 22 degrees Celsius and 10 degrees Celsius in the Northern plains, 6 degrees Celsius in Punjab.
The rain generally falls in the Western Himalayas, Tamil Nadu, and Kerala in this season.
Western disturbances and associated troughs in the west are the main precipitation systems in the northern part of the country.
The jet stream plays a dominant role in bringing these disturbances in India
These disturbances cause rain precipitation in Himachal Pradesh Punjab, Haryana and snowfall in the hills of Jammu and Kashmir. This rainfall is used for the cultivation of Winter Wheat.
Pre Monsoon or hot weather season (March-May) or Summer Season in India
In this season the vertical rays of the sun fall over peninsular India and there is a steady increase in temperature from South to North.
It is almost hot and dry in most of the country in the initial part of the season.
The weather over the land areas of the country is influenced by thunderstorms associated with rain and sometimes with hail mostly in the middle and later part.
During this season, the temperature increases in all parts of the country, and in April the interior part of the southern part of India, the temperature daily mean will be 30 to 35 degrees Celsius.
In the central part of India, the mean temperature would reach up to 40 degrees in most parts.
Some parts of India, such as Gujarat, North Maharashtra, Rajasthan, and North Madhya Pradesh experience high day temperatures and low night temperatures.
Because of the atmospheric pressure, the wind blows from the southwest to the northeast direction in the Arabian Sea and Bay of Bengal.
This brings pre-monsoon showers to the west coast during May month called summer monsoon in India.
There are showers also called ‘Mango Showers’ that helps in the quick ripening of mangoes along the Kerala and Karnataka coast.
Northwesters or Kalbaisakhis are local severe storms associated with strong thunderstorms, winds, and short-duration rains.
Kalbaisakhis occurs over the eastern and northeastern parts of Bihar, West Bengal, and Assam during April and May and approaches from the Northwesterly directions.
Southwest Monsoon Or Rainy Season
South west monsoon in India
The southwest monsoon is the most important feature of the Indian climate. It takes place in the Southern Tip of India Peninsula normally by the first week of June.
South-West monsoon advances along the Konkan coast during starting of June and it covers the whole country by July 15.
The global phenomenon El Nino influences the South West Monsoon. In North India, the temperature reaches almost 46-degree Celsius before the southwest monsoon or rainy season.
There occurs a “Burst of Monsoon”, which is termed as Break, which is a sudden approach of monsoon wind over southern India with Thunder Showers. This show reduces the temperature of the country.
South West Monsoon Winds
The monsoon wind that is the southern tip of India’s landmass gets separated into two branches.
One branch starts from the Arabian Sea and Another Branch starts from the Bay of Bengal. The one from the Arabian sea provides heavy showers to the west coast of India and is located on the west ghats windward side.
The other part towards the north hits the Himalayan Mountains and brings heavy rainfall in the North.
Rajasthan and western parts get rain from these winds as the direction of the wind is parallel to the Aravali mountains and there is nothing to hold or intrude the wind.
Direction of South West monsoon in India
The Bay of Bengal wind moves to northeast India, Myanmar and this wind is trapped by mountain groups such as Khasi, Garo, and Jaintia.
This results in the heaviest rainfall in the world, that is Mawsynram located in Meghalaya. Then it moves to the west, which results in a rainfall decrease from east to west.
The southwest monsoon winds in India are responsible for 75% of the Indian rainfall. Tamil Nadu that is located on the leeward side receives less rainfall from this wind.
Post Monsoon or Retreating or Northeast Monsoon in India
The southwest monsoon starts in North India by the end of the second half of September because of the southward shifting of pressure belts.
This wind gets backs from the Indian peninsula and blows towards the Bay of Bengal.
The Coriolis forces deflect this wind and make this wind blow from the Northeast and it is known as North-East Monsoon or Post Monsoon season.
The Northeast Monsoon in India is connected with the formation of the North-Easterly wind system over the Indian subcontinent.
From this season, the states such as Tamil Nadu, Andhra Pradesh, Kerala, and south interior Karnataka get good rainfall that almost 35% of its annual rainfall.
The Retreating monsoon creates a large-scale loss of life during the storms that occur frequently in Tamil Nadu, Andra Pradesh, and some parts of Karnataka.
During these seasons, strong winds and storms hit the coastal regions, and the daytime temperature falls rapidly all over the country. The average temperature over North-west India shows a decreasing trend from 38 and falling to 28-degree celsius in November.
Distribution of Rainfall
About 118 cm is the average rainfall of India. The spatial distribution of the rainfall in the country is uneven.
About 11% area receives over 200 cm,21% area receives 125 to 200 cm, 37 % area receives 75 to 125, 24 % area gets 35 to 75 cm and 7% area gets less than 35 cm of rainfall annually.
Rajasthan, Punjab, Haryana, west and south-west Uttar Pradesh, Western Madhya Pradesh, and the entire Deccan Trap or Plateau region east of Western Ghats except for a narrow strip along Tamil Nadu coast receive less than 100 cm rainfall annually.
The rest of the country receives 100 to 200 cm of rainfall.
Areas of High Rainfall
The west coast has the highest rainfall. The western Ghats, Himalayan areas in the northeast, and hills of Meghalaya. In these areas, the rainfall exceeds 200 cm.
In parts of Khasi and Jaintia Hills, the rainfall exceeds 1000 cm. But in the Brahmaputra valley and its adjoining hills receives less than 200 cm.
Areas of Medium Rainfall
The southern parts of Gujarat, east Tamil Nadu, Northeastern Peninsula covering Odisha, Jharkhand, Bihar, eastern Madhya Pradesh, Northern Ganga Plain along the sub-Himalayas and Cachar valley and Manipur receives rainfall between 100-200 cm.
Area of Low Rainfall
Western Uttar Pradesh, Delhi, Haryana, Punjab, Jammu and Kashmir, eastern Rajasthan, Gujarat, and Deccan Plateau receives rainfall around 50-100 cm.
Areas of Inadequate Rainfall
Some parts of the Peninsula, especially in Andra Pradesh, Karnataka and Maharashtra, Ladakh, and most of western Rajasthan receive less than 50cm of rainfall.
Snowfall occurs only in Himalayan regions.
This article takes about the Monsoon and four primary seasons of the country concerning the precipitation and temperature change as drafted by the India Meteorological Department.
Also provided with data of the distribution of rainfall in the Indian subcontinent.