Climate Class 9 Notes Geography - Chapter 4
What are Climate ?
- Climate refers to the total sum of weather conditions and variations over a large area for along period of time (more than thirty years).
- Weather refers to the day to day state of the atmosphere over an area at any point of time.
Elements Of Weather
Factors Affecting India’s Climate
- Latitude: The tropic of cancer passes through the middle of the country. Half of the country lying south of the Tropic of Cancer, belongs to the tropical area.
- Altitude: The Himalayas prevent the cold winds from Central Asia from entering the subcontinent making winter milder as compared to Central Asia.
- Pressure and winds: The wind move from high pressure area to low pressure area.
(a) High pressure area developed over North India.
(b) During winter, cold and dry wind blows from the Himalyas towards the low pressure area over the oceans in south.
(c) During summer low pressure area developed over Northwest India therefore wind direction reversed.
The Indian Monsoon
• The climate of India is strongly influenced by monsoon winds.
• Factors that affect the mechanism of Indian monsoon:
(a) The differential heating and cooling of land and water.
(b) The shift of the position of Inter Tropical Convergence Zone (ITCZ).
(c) The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean. The intensity and position of this high-pressure area affects the Indian Monsoon.
(d) The Tibetan plateau gets intensely heated during summer which creates low pressure of the plateau.
(e) 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.
(f) Southern Oscillation.
Four main seasons identified in India are:
- The Cold Weather Season (Winter): The cold weather season begins from mid- November and stays till February.
- The Hot Weather Season (Summer): Due to the apparent northward movement of the sun, the global heat belt shifts northwards. As such, from March to May, it is hot weather season in India.
- Advancing Monsoon (The Rainy Season): By early June, the low-pressure condition over the northern plains intensifies. It attracts, the trade winds of the southern hemisphere.
- Retreating/Post Monsoons (The Transition Season): During October-November, with the apparent movement of the sun towards the south, the monsoon trough or the low-pressure trough over the northern plains becomes weaker.
Monsoon As Unifying Bond
The monsoon winds bind the whole country by providing water to set the agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.