climate chapter notes class 9 ncret
Answers
Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than thirty years).
• Weather refers to the state of the atmosphere over an area at any point of time.
• Elements of Weather and Climate:
→ Temperature
→ Atmospheric pressure
→ Wind
→ Humidity
→ Precipitation
Climatic Controls
• There are six major controls of the climate of any place. They are:
→ Latitude
→ Altitude
→ Pressure and wind system
→ Distance from the sea (continentality)
→ Ocean currents
→ Relief features
Factors affecting India's Climate
→ Latitude
→ Altitude
→ Pressure and Winds
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
• Atmospheric conditions that govern climate and associated weather conditions in India are:
→ Pressure and surface winds
→ Upper air circulation
→ Western cyclonic disturbances and tropical cyclones.
Upper Air Circulation
• The higher level of the atmosphere is dominated by a westerly flow. An important component of this flow is the jet stream.
• Jet Streams are a narrow belt of high altitude westerly winds in the troposphere (transition between troposphere and stratosphere.
Western cyclonic disturbances and tropical cyclones
• The western disturbances, which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream.
• Tropical cyclones originate over the Bay of Bengal and the Indian ocean.
• Tropical cyclones occur during the monsoon as well as in October-November, and are part of the easterly flow.
The Indian Monsoon
• Monsoon are seasonal winds which reverse their direction of flow with the change of season.
• The climate of India is strongly influenced by monsoon winds.
Factors that affect the mechanism of Indian Monsoon
• Differential heating and cooling of land and water create low pressure on land while the sea experiences high pressure.
• Shifting of Inter Tropical Convergence Zone (ITCZ) over the Ganga plain during summers.
• The intensity and position of high-pressure area towards the east of Madagascar approximately at 20°S over the Indian Ocean affects the Indian Monsoon. affects the Indian Monsoon.
• The heating up of the Tibetan plateau in summers creates low pressure above the plateau.
• 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.
• Southern Oscillation.