Quick Revision Notes: Climate

Class 9 | Social Science (Geography) - MP Board

Climate (जलवायु): The sum total of weather conditions and variations over a large area for a long period of time (more than 30 years).
Weather (मौसम): The state of the atmosphere over an area at any point in time.
Monsoon (मानसून): Refers to the seasonal reversal in the wind direction during a year.
Precipitation (वर्षा): Rain, snow, sleet, or hail falling to the ground.
Atmospheric Pressure (वायुमंडलीय दबाव): The pressure exerted by the weight of air in the atmosphere.
Coriolis Force (कोरियोलिस बल): An apparent force caused by the earth's rotation that deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Jet Stream (जेट स्ट्रीम): A narrow belt of high-altitude winds in the troposphere (above 12,000 meters) with high speeds.

The climate of any place is governed by six major controls:

Latitude (अक्षांश): Due to the curvature of the earth, the amount of solar energy received varies according to latitude.
Altitude (ऊंचाई): As we go up from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases.
Pressure and Wind System (दाब और पवन तंत्र): Depends on the latitude and altitude of the place; influences temperature and rainfall.
Distance from the Sea (समुद्र से दूरी - Continentality): The sea exerts a moderating influence on climate. As distance from the sea increases, its moderating influence decreases.
Ocean Currents (महासागरीय धाराएँ): Along with onshore winds, affect the climate of the coastal areas.
Relief Features (उच्चावच लक्षण): High mountains act as barriers for cold or hot winds; also affect rainfall if they lie in the path of rain-bearing winds.

India's climate is controlled by three main factors:

Latitude: The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh to Mizoram, dividing India into tropical and subtropical zones.
Altitude: India has mountains to the north (Himalayas) with an average height of about 6,000 meters, which prevent freezing winds from Central Asia from entering India.
Pressure and Surface Winds:
- Surface winds and pressure
- Upper air circulation (Jet streams)
- Western cyclonic disturbances and tropical cyclones

To understand the onset of the monsoon, the following facts are important:

Differential heating and cooling of land and water: Creates low pressure on the landmass of India while the seas around experience high pressure.
Shift of Inter Tropical Convergence Zone (ITCZ): In summer, the ITCZ shifts northward over the Ganga plain (this is known as the monsoon trough).
High-pressure area over Madagascar: The presence of a high-pressure area east of Madagascar (Indian Ocean) intensely affects the Indian Monsoon.
Tibetan Plateau: Gets intensely heated during summer, resulting in strong vertical air currents and the formation of low pressure over the plateau.
Movement of Jet Streams: The westerly jet stream moves north of the Himalayas, and the tropical easterly jet stream flows over the Indian Peninsula during summer.

India has four main seasons:

Period: Mid-November to February (December and January are the coldest months).
Characteristics: Days are warm and nights are cold. Frost is common in the north.
Rainfall: Winter rainfall locally known as 'Mahawat' is caused by western disturbances. It is small in amount but extremely important for the cultivation of Rabi crops.

Period: March to May.
Characteristics: High temperatures and falling air pressure.
Loo: Strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.
Kaal Baisakhi: Localized thunderstorms associated with violent winds and torrential downpours in West Bengal ("Calamity of the month of Baisakh").
Mango Showers: Pre-monsoon showers in Kerala and Karnataka that help in the early ripening of mangoes.

Period: Early June to September.
Characteristics: South-West monsoon winds blow over the warm oceans, gather moisture, and bring widespread rainfall.
Monsoon Burst: The sudden arrival of the monsoon-bearing winds, accompanied by violent thunder and lightning.
Two Branches of South-West Monsoon:
1. Arabian Sea Branch
2. Bay of Bengal Branch
Monsoon Trough: The trough of low pressure low-pressure zone that keeps shifting north and south, determining the spatial distribution of rainfall.

Period: October and November.
Characteristics: Clear skies and rise in temperature. The land is still moist.
October Heat: Conditions of high temperature and humidity, making the weather oppressive.
Tropical Cyclones: The low-pressure conditions get transferred over the Bay of Bengal, resulting in destructive cyclones that hit the eastern coasts (deltas of Godavari, Krishna, and Kaveri).

High Rainfall Areas (Over 200 cm): Western slopes of the Western Ghats and the North-Eastern parts of India.
Low Rainfall Areas (Below 60 cm): Western Rajasthan, parts of Gujarat, Haryana, Punjab, and the rain-shadow area of the Deccan Plateau (interior of the Deccan plateau).
Snowfall: Restricted to the Himalayan region.

The seasonal alteration of wind systems and the associated weather conditions provide a rhythmic cycle of seasons.
The entire landscape of India, its animal and plant life, its agricultural calendar, and the people—including their festivities—are heavily revolve around the monsoon phenomenon.
Farmers across India eagerly await the arrival of the monsoon, which binds the country together in a single agricultural organism.

Climate