climate class 9 notes
Answers
Explanation:
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.
The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation. On the basis of the monthly atmospheric conditions, the year is divided into seasons such as:
Winter
Summer
Rainy Seasons
Climatic Controls
The climate of any place depends on the following factors:
1) Latitude
The amount of solar energy received varies according to latitude due to the curvature of the earth. That’s why air temperature generally decreases from the equator towards the poles.
2) Altitude
The atmosphere becomes less dense and temperature decreases when we go to the higher altitude from the earth surface. This is the reason why hills are cooler during summers.
3) Pressure and wind system
The pressure and wind system of any area depends on the latitude and altitude of the place. It influences the temperature and rainfall pattern.
4) Distance from the sea
The sea exerts a moderating influence on the climate. As the distance from the sea increases, its moderating influence decreases and people experience extreme weather conditions. This condition is known as continentality i.e. very hot during summers and very cold during winters.
5) Ocean currents
Ocean currents along with onshore winds affect the climate of the coastal areas. For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.
6) Relief features
Relief plays a major role in determining the climate of a place. High mountains act as barriers for cold or hot winds. They may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. Precipitation is any form of moisture which falls to the earth. It includes rain, snow, hail and sleet.
Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator and turns right towards the low-pressure areas over the Indian subcontinent. These are known as the Southwest Monsoon winds. These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the territories of India.
Jet streams are fast flowing, narrow, meandering air currents in the atmosphere.
The Indian Monsoon
The climate of India is strongly influenced by monsoon winds. The seasonal reversal of the
wind system is known as “monsoon”. The monsoons are experienced in the tropical area roughly between 20° N and 20° S. Go through the following facts to understand the mechanism of the monsoons in a better way:
The differential heating and cooling of land and water creates low pressure on the landmass of India while the seas around experience comparatively high pressure.
The shift of the position of Inter-Tropical Convergence Zone (ITCZ) in summer, over the Ganga plain, is also known as the monsoon-trough during the monsoon season.
The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean affects the Indian Monsoon.
The Tibetan plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.
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 also impact the Indian Monsoon.
The changes in the pressure conditions over the southern oceans also affect the monsoons. The irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean that affects the climate of the tropics and subtropics is known as Southern Oscillation or SO.
The Onset of the Monsoon and Withdrawal
The duration of the monsoon is between 100-120 days from early June to mid-September. Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days, which is known as the “burst” of the monsoon.
The withdrawal of the monsoon begins in northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. From north to the south, withdrawal of monsoon takes place from the first week of December to the first week of January. By early December, the monsoon has withdrawn from the rest of the country.
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