10th Social Studies - Relief and Upper Atmospheric Circulation - New Syllabus

Relief: You have learnt that temperature decreases as altitude increases. Hence, hills and mountains will have lower temperature than locations on the plain. Therefore, relief or altitude of a region influences the climate of the area. You would have heard about several hill stations of Himalayan region like Shimla, Gulmarg, Nainital and Darjeeling as places that have a cool climate even during the peak summer months. Similarly Kodaikanal and Udagamandalam (Ooty) on the Western Ghats have colder climate, compared to places near the coast.

* Are Shimla and Delhi located on very different latitudes? Check with your atlas. Is Shimla cooler than Delhi during summer?

* Why does Darjeeling have pleasant weather as compared to Kolkata during summer season?

Upper atmospheric circulation

In the northern hemisphere, subtropical high pressure belts give rise to permanent winds. They blow toward the equatorial low pressure belts by reflecting towards the west and are called Trade winds. The German word ‘Trade’ means ‘Track’ and stands for blowing steadily in the same direction and in a constant course.

India lies in the belt of north-east trade winds without any moisture. This is however only half the story of the Indian climatic phenomenon. Let us see the other half in the study of monsoon in the next section.

The climate of India is also affected by the movement of upper air (air currents) known as ‘jet streams’. These are fast flowing air currents in a narrow zone in the upper atmosphere, above 12,000 m. The speed varies from about 110 km/h in summer to about 184 km/h in winter. An Easterly jet stream develops at about 250 N. A jet stream causes the atmosphere around this to cool. This cooling effect of the easterly jet stream causes rain from clouds already found over this part.

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