SYNOPSIS (TERM II)

GRADE: IX SUBJECT: Geography LESSON: Climate

Key words/Glossary:

1. Continentality – Lying away from the influence of the sea; characterised by extremes of temperatures. 2. Trade Winds – Winds which blow from the sub-tropical belts of high pressure towards the equatorial region of low pressure, from the north-east in the northern hemisphere and south-east in the southern hemisphere. Name derived from the nautical expression 'to blow trade' which means to 'blow along a regular track' because of the regularity with they blow in some areas, especially over oceans, throughout the year. 3. ITCZ - The inter tropical low pressure zone where the the trade winds converge; the ITCZ ; usually lying between 5 degree north and 5 degrees south , its position varies due to differences in land temperatures; called doldrums by sailors because of lack of horizontal air movement (the hot air rises with convection in this belt) 4. Jet Stream – A narrow belt of high-speed wind in the upper troposphere. 5. Cyclonic Depression - A low pressure weather system, around which winds circulate in an anti- clockwise direction in the northern hemisphere and in a clock-wise direction in the southern hemisphere. 6. Western Disturbances - It refers to the depressions originating over the Mediterranean Sea and Western Asia, travelling in a north westerly direction and bringing rain and snow to northern and north western . 7. Pre- Showers - Light showers accompanied by thunderstorms preceding the called mango showers in nad because it helps in the ripening of mangoes. 8. Loo - Hot and dry winds blowing over north west India during the summer season.

Did you know? The Aravallis are an important reason why Gujarat and north western India receive low rainfall. They lie parallel to the direction of the monsoons and hence do not offer an aerographic barrier for the winds to strike against.

Think about this If the Indian plate had not broken away from Gondwanaland and the Indian and Eurasian plates had not collided, we would not have had the Himalayas; and Mumbai and Goa would have been freezing cold and far away from the sea. The region beyond the Himalayas, despite having ranges parallel to the Himalayas, receives very little rain during the rainy season because it lies in the rain shadow area of the Himalayas. It receives most of its precipitation in the winter from the north western disturbances.

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Points to remember:  Temperature, humidity, atmospheric pressure and wind are the elements of both weather and climate. But while weather is a local short term phenomenon liable to change any time, climate refers to the pattern of weather over a larger area established over a longer period of time.  Several factors affect the climate of India – latitude, altitude, wind and pressure systems including cyclones and jet streams , distance from the sea, and relief.  While the North East trades are the wind system by default account of India’s location, the development of the monsoon trough and associated conditions result in the reversal of these winds with the establishment of the SW monsoons from June to September.  India has four seasons: • Winter season, dominated by the North East Trades and the north western disturbances • Summer season, characterised by high temperatures, especially inland in the north west; moderating influence of the sea in the peninsular region • Rainy season, characterised by the monsoon low pressure trough over north west India and the Ganga plain resulting in the South West monsoons • Transition season, characterised by oppressive heat and withdrawal of the monsoons  India receives most of its rainfall from the SW monsoons. However, some parts get more rain from other sources – from the North East Trades, trans-Himalayan region from the north western disturbances and the eastern coastal region from the Bay of cyclones.

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