JAC Board Class 9th Social Science Notes Geography Chapter 4 Climate.
- The term climate is the sum total of all the weather conditions and variations.
- “Weather” refers to the state of the atmosphere over an area at any point of time.
- Based on the generalised monthly atmospheric conditions, the year is divided into 3 seasons which are winter, summer and rainy season.
- The world is divided into a number of climatic regions.
- The climate of India is described as Monsoon type.
- Monsoon type of climate is also found in South Asia and South-Eastern countries.
→ Climatic Controls
- There are six major controls of the climate at any place. They are: Latitude, Altitude, Pressure, Wind system, Distance rom the sea, Ocean currents, Relief features.
→ Factors Affecting India’s Climate
- Factors Affecting India’s Climate are: Latitude, Altitude, Pressure and surface winds in upper air circulation, Western cyclonic disturbances and tropical cyclones.
→ The Indian Monsoon
- Monsoon winds strongly influence the climate of India.
- The monsoons are experienced in the tropical areas roughly between 20° North and 20° South.
- The word Monsoon is derived from the Arabic word “Mausim” which literally means ‘Season’.
- ‘Monsoon’ refers to the seasonal reversal in the wind direction during a year.
- The differential heating and cooling of land and water creates low pressure on the landmass of India.
- The Inter Tropical Convergence Zone (ITCZ) in summer season shifts its position over the Ganga plain.
- The presence of the high-pressure area east of Madagascar, approximately at 20° South over the Indian Ocean is also responsible for monsoon in India.
- The Tibetan plateau gets intensely heated during summer.
- The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian Peninsula during summer.
- The Inter Tropical Convergence Zone (ITCZ) is a broad trough of low pressure in equatorial latitude. In ITCZ, there is convergence of North-East and South-East trade winds.
- Southern oscillation is the reversal of pressure conditions and vice-versa in Southern Pacific Ocean and Eastern Indian Ocean.
- ENSO is the combination of EL-Nino (a warm ocean current near Peruvian coast) and Southern oscillation. The changes in pressure conditions are connected to EL NINO, hence, the phenomenon is reffered to as ENSO.
→ Advancing Monsoon (The Rainy Season)
- The low pressure area over the Northern plains condenses by mid June and attracts the trade winds.
- These trade winds originate over the warm tropical ocean in the Southern hemisphere. After crossing the equator, these blow in the South-West direction, entering the Indian Peninsula as South-West monsoon.
- They cover the entire sub-continent except extreme North-West in just over one month.
- Maximum rainfall due to these winds occurs in North-Eastern India (mainly Meghalaya and Assam).
- The windward side of the Western Ghats receives very heavy rainfall, more than 250 cm in the early season. While the rain shadow area, the Deccan Plateau and parts of Madhya Pradesh also receive some amount of rainfall.
→ Retreating/Post Monsoon Season (The Transition Season)
- By the beginning of October, the monsoon withdraws from the Northern plains and dry winter conditions prevail by the end of November.
→ Distribution of Rainfall
- Mawsynram located in the Southern ranges of the hills of Meghalaya receives highest rainfall in the world receives.
- Parts of Western Coast and North-Eastern India receive over about 400 cm of rainfall annually.
- However, it is less than 60 cm in Western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab Rainfall is equally low in the interior of the Deccan plateau and East of the Sahyadris.
- A third area of low precipitation is around Leh in Ladakh.
→ Monsoon as a Unifying Bond:
- The monsoon unites the land because it provides a rhythmic cycle of seasons.
- The Indian landscape, its animal and plant life, its entire agricultural calender and the life of the people, including their festivities, revolve around the monsoon phenomenon.
- These monsoon winds bind the whole country by providing water to set the agricultural activities in motion.
→ Climate: It refers to the sum total of all the weather conditions and variations over a large area for a long period of time (more than thirty years).
→ Weather: It refers to the state of the atmosphere over an area at any point of time.
→ Monsoon: It refers to the seasonal reversal in the wind direction during a year.
→ Humidity: Humidity is a measure of dampness of the atmosphere. It varies greatly from place to place and from time to time.
→ Jet streams A narrow belt of high altitude westerly winds in the troposphere.
→ Coriolis force: It is an apparent force caused by the earth’s rotation.
→ Trade winds: These are strong winds that blow towards the equator from the north-east or the south-east.
→ Southern oscillation: The periodic change in pressure condition is called as the southern oscillation.
→ Subtropical high pressure belt It lies between 30°-35° North and South latitudes in both the hemispheres.
→ Equatiorial low pressure zone : It is a thin belt of low pressure found near the Equator between 5° North and South.
→ Leeward side: A rain shadow area of dry land that lies on the downward side of a mountain.
→ Windward side: A rain shadow area of dry land that lies on the windy side of a mountain.
→ Rainfall: It refers to condensed water vapour which falls on the earth from the clouds in the form of water drops.
→ Precipitation: It includes rainfall, sleet, snow and hail.
→ Mango Showers: The pre-monsoon showers which help in the ripening of mangoes in coastal Kerala and Karnataka.
→ Mahawat: Mahawat in geographical terms refers to the winter rainfall that occurs in the Western part of India. This rainfall is non-seasonal, and it occurs as a result of western disturbances the moisture for these rains comes from the Mediterranean Sea and the Atlantic Ocean.
→ Loo: Strong, dusty, hot, dry winds blowing during the day over the north and north¬western India.
→ Low pressure trough: It is an elongated low pressure area.
→ Western disturbances: It is the term used in the Indian subcontinent to describe an extra-tropical storm originating in the Mediterranean that brings sudden winter, rain and snow to the north-western parts of the subcontinent.
→ Inter Tropical Convergence Zone (ITCZ): It is a broad trough of low pressure in equitorial latitudes- this is where the north-east and the south-east trade winds converge. It lies more or less parallel to the Equator, but moves north or south with the apparent movement of the sun.
→ EI Nino: It is a warm ocean current that flows over Peru in an interval of two to five years. ‘El Nino’ is a Spanish word, meaning ‘the child’.
→ ENSO: The phenomenon of El Nino and southern oscillation is jointly known as ENSO (El Nino Southern Oscillation).
→ Kal Baisakhi: In West Bengal, the season for localised thunderstorms is associated with violent winds, torrential downpours, often accompanied by hail; these storms are known as Kal Baisakhi.
→ October Heat: The hot and humid conditions which make the weather oppressive.
→ Altitude: It refers to the height above mean sea level.