Yet, the whole of India remains warm throughout the year. The Himalayas play an important role in lending a sub -tropical touch to the climate of India.
(ii) Himalaya Mountains:
The lofty Himalaya Mountains form a barrier which affects the climate of India. It prevents the cold winds of north Asia from blowing into India, thus protecting it from severely cold winters. It also traps the Monsoon winds, forcing them to shed their moisture within the sub-continent.
Temperature decreases with height. Places in the mountains are cooler than places on the plains. Places on the Deccan Plateau are not very hot in spite of being near the Equator.
(iv) Distance from the Sea:
With a long coastline, large coastal areas have an equable climate. Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate.
(v) Western Disturbances:
The low pressure systems that originate over the eastern Mediterranean region in winter and move eastwards towards India passing over Iran, Afghanistan and Pakistan are responsible for the winter rain in northern India.
(vi) Conditions in the Regions Surrounding India:
Temperature and pressure conditions in East Africa, Iran, Central Asia and Tibet determine the strength of the monsoons and the occasional dry spells. For example, high temperatures in East Africa may draw the monsoon winds from the Indian Ocean into that region thus, causing a dry spell.
(vii) Conditions over the Ocean:
The weather conditions over the Indian Ocean and the China Sea may be responsible for typhoons which often affect the east coast of India.
(viii) Jet Stream:
Air currents in the upper layers of the atmosphere known as jet steams could determine the arrival of the monsoons and departure of the monsoons. The Scientists are studying the jet streams and how it may affect the climate of India but much remains to be learned about this phenomena. The pattern of air circulation is very different at the higher level of the atmosphere.
A westerly air current flows from the Western and Central Asia, north of the Himalayas. The Tibetan Highlands act as a barrier for the westerly Jet stream and it gets bifurcated. The southern branch flows in an eastward direction south of the Himalayas and influences the winter season of India. In summer the westerly jet stream moves northwards and places itself north of the Tien Shan in Central Asia.
An easterly Jet stream takes its place and flows over northern India along 25°N. Low pressure region over land and the easterly Jet stream steer in the tropical depressions into India. These depressions help in distributing the monsoon rainfall over the whole of India.
(ix) Distribution of Atmospheric Pressure and Surface winds:
India lies in the area of northeast trade winds. These winds originate from the subtropical high pressure belts of the northern hemisphere. They flow south towards the equatorial low pressure belt and get deflected to their right i.e. to the west. As such their direction is from north-east to south-west. These are called trade winds.