Class 11 Geography Indian Monsoon Notes: The Indian Monsoon is an important topic in CBSE Class 11 Geography. These notes about the Indian monsoon are useful for class 11 students. It explains important details about the monsoon, like how it starts, how it affects the weather, and its impact on people’s lives.
Understanding the monsoon is important for geography students because it helps them understand how weather patterns affect different regions. These notes are written in a way that makes it easy for students to learn about the Indian monsoon and its significance.
Indian Monsoon| Class 11 Geography Notes
Indian Monsoon
During the Indian monsoon, the winds blow from the northeast in the winter and from the southwest in the summer. This change in wind direction brings heavy rainfall to the region between June and July. By February, the surface easterlies only reach latitudes near 20° N, and then they retreat northward quickly.
This transition period between one monsoon and the next marks the onset of atmospheric instability, convection clouds, and rain as the high-sun season progresses northward from the Equator. Northern India remains influenced by the westerly subtropical jet stream and experiences northeast to north-easterly surface winds.
Understanding Indian Monsoon
The Indian Peninsula receives rainfall due to the convergence of winds and equatorial westerlies moving northward. The northeast monsoon, or winter monsoon, dominates peninsular India from May to February. Most of India experiences rainfall from June to September, with the southwest monsoon contributing to about 75% of the annual rainfall.
The northeast monsoon brings rain to Tamil Nadu, Andhra Pradesh, Karnataka, and Kerala. October sees clear skies as temperatures rise, followed by a faster decrease in temperature than in South India. Traveling to the northwest of India takes about a month. The different types of monsoons in India are:
- Winter Monsoon
- Summer Monsoon (Pre-Monsoon Season)
- South-West Monsoon Season
- North-East Monsoon or Post-Monsoon Season/Winter Season (January – February)
Reason for Different Types of Indian Monsoon
Peninsular India experiences a relatively cooler climate compared to northern India. Heatwaves are prevalent in northern and central India during this time. Northwestern India remains dry and hot. Thunderstorms or thunder showers occur in the evening in regions like Rajasthan, Punjab, Haryana, and Uttar Pradesh, with similar weather patterns observed in at least three other states.
These intense thunderstorms are known as “Andhi” or “North-western Storms.” Apart from the Deccan plateau, the Indian Peninsula receives rainfall as tropical convergence and equatorial westerlies move northward. Kerala and the west coast experience rainy weather during early June, marking the onset of the monsoon season along the Kerala coast.
Summer Monsoon / Pre-monsoon Season (March-May)
During this period, a low-pressure area gradually replaces the high-pressure system. Seasonal cyclonic winds gain strength. By May and June, northwestern India and Pakistan experience high solar radiation, leading to a thermal high and warm air rising, resulting in a low-pressure region known as the thermally produced low-pressure zone.
Northwestern India records the highest temperatures, with midday temperatures in Rajasthan ranging from 40°C to 50°C. Peninsular India experiences significantly cooler temperatures compared to northern India. Heatwaves are widespread in the northern and central regions, while northwestern India remains hot and dry.
Despite the arid climate, intense convection can trigger thunderstorms in states like Rajasthan, Punjab, Haryana, and Uttar Pradesh. Evening thunderstorms are common in Assam, West Bengal, and Bihar. These severe thunderstorms, known as “andhis,” appear to originate from the northwest.
The Indian Peninsula receives rainfall due to the convergence of inter-tropical and equatorial westerlies heading northward. Pre-monsoon showers hit Kerala and the western coast, marking the beginning of the Indian monsoon season, usually in late May or early June along the Kerala coast.
Winter Monsoon (January to February)
During the cold weather season, anticyclonic winds prevail, characterized by the winter monsoon, which lingers until February. Northwestern India experiences cold, dry, and persistent winds. Clear skies are common during this period. Temperatures gradually decrease from south to north across India.
Northern India experiences cold air masses, leading to chilly waves and frosty nights due to cold advection from the north. The subtropical westerly jet stream moves over Northern India at an altitude of 12 km, with a central core reaching speeds of up to 400 km/h. Westerlies dominate north of 20°N, while northeast winds dominate south of this latitude.
Rainfall from western disturbances passing across northern India falls on northwest India, benefiting rabi crops. These western disturbances also influence the climate, favoring crop growth. The northeast monsoon, or winter monsoon, dominates peninsular India, bringing rain to the southeastern coast of India.
Other Monsoons
South-west Monsoon (June – September):
During the South-west monsoon season, a seasonal low-pressure system develops across north-west India and Pakistan due to the intense warmth. Across northern India, westerly winds are replaced by southeasterly winds. A monsoon trough extends from the seasonal low-pressure area to the head Bay of Rajasthan, Uttar Pradesh, Bihar, and West Bengal.
There is a south-to-north pressure gradient in the Indian Ocean, with temperatures decreasing from north to south. Winds blow southeasterly north of the trough, while west to south-west winds prevail south of the monsoon trough, and south-east winds dominate southern India. The subtropical westerly jet stream shifts 12 km north of the Himalayas.
A tropospheric anticyclone known as the Tibetan High forms above Tibet, aiding in the persistence of the monsoon across India. The monsoon is crucial for agriculture, with farming success depending on its duration and intensity. The rainy season in India occurs from June to September, with the monsoon crossing the Kerala coast in early June.
Travelling to north-west India during this time takes about a month. Storms and squalls are common during the Indian monsoon. After the monsoon, the weather becomes calmer and less stormy. Most of India’s annual rainfall is attributed to the South-west monsoon, while north-west and northern India receive rain from western disturbances. Southern India experiences rains from the north-east monsoon or pre-monsoon thundershowers.
North-east Monsoon/ Post Monsoon (October – December):
As the South-west monsoon retreats from several parts of India, the West Indian low-pressure area is replaced by an anticyclonic high-pressure area. Dry northwestern or western winds replace most southeasterly winds over central India.
In the Southern Hemisphere’s tropical regions, high temperatures weaken the high-pressure area over the Indian Ocean. When the ridgeline crosses central India, anticyclonic circulation strengthens. North-eastern north-easterly winds replace westerly winds over south India, initially dry over land but becoming moist as they cross the Bay of Bengal.
The northeast monsoon brings rain to Tamil Nadu, Andhra Pradesh, Karnataka, and Kerala. October brings clear skies, causing temperatures in north India to rise by mid-October and decline faster than in south India. Despite dry weather in north and northwest India, western disturbances may create rainfall shortages.
Conclusion
Indian monsoon blows from the north-east in the winter and from the south-west in the summer. Northern India experiences dominance by the westerly subtropical jet stream, along with north-eastern north-easterly surface winds.
While most of the Deccan plateau remains dry, the Indian Peninsula receives rain due to inter-tropical convergence and equatorial westerlies flowing northward. During the cold weather season, anticyclonic winds characterize the cold air mass across northern India, with north-west India experiencing the highest temperatures during this period.
Related Links
Indian Monsoon- FAQs
What is the Indian monsoon?
Indian monsoon refers to the seasonal wind pattern that brings heavy rains to the Indian subcontinent during the summer months.
When does the Indian monsoon occur?
The Indian monsoon occurs from June to September each year.
How does the Indian monsoon affect India?
Indian monsoon is important for agriculture and replenishing water resources. It also impacts the climate and weather patterns across the country.
What are the different types of monsoons in India?
The major types of monsoons in India include the southwest monsoon, northeast monsoon, winter monsoon, and pre-monsoon season.
How does the southwest monsoon affect India?
The southwest monsoon, occurring from June to September, brings around 75% of India’s annual rainfall and is vital for agriculture. It affects different regions of India with varying intensity and timing.
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