India has ‘Monsoon’ type of climate. The word monsoon has been derived from the Arabic word ‘mausim’ which means seasonal reversal of the winds during the course of the year.
Ths implies a rhythmic change in the direction of winds and in the distribution of temperature and rainfall with the change of season.
Factors Influencing India’s Weather and Climate
The factors influencing weather and climate of India are given below:
Location and Latitudinal Extent
India lies roughly between 6° to 37° N latitudes. The Tropic of Cancer passes through the middle of the country. The southern parts being closer to the Equator, experience high temperatures throughout the year. The northern parts on the other hand lie in the warm temperate zone. Hence they experience low temperatures particularly in winter. Water bodies surrounding peninsular India make climatic conditions mild along the coastal areas.
Distance from the Sea
Southern or peninsular India is surrounded by the Arabian Sea, the Indian ocean and the Bay of Bengal, hence the climate of coastal regions of India is equable or maritime. Contrary to this, the regions located in the interior of the country are deprived of the moderating influence of the ocean. As a result, they have an extreme or continental type of climate.
Northern Mountain Ranges
The Himalayan and adjoining mountain ranges which extend from Kashmir in the Northwest to Arunachal Pradesh in the Northeast, separate Indian from the rest of Asia. ese ranges protect India from the bitterly cold and dry winds of Central Asia during winter. Further more, they act as an effective physical barrier for the rain bearing southwest monsoon wind to cross the northern frontiers of India. Thus, these ranges act as a climatic divide between Indian Sub-Continent and Central Asia.
The physical features influence the air temperature, atmospheric pressure, direction of winds and the amount of rainfall in different parts of the country. It is due to physiographic setting that Bay of Bengal branch of Southwest monsoon is bifurcated into two parts-one moving along the Ganga Valley to the west and the other along the Brahmaputra Valley to the east. The funnel shaped hills along the steep southern edge of Meghalaya Plateau force the moisture laden monsoon winds from the Bay of Bengal to rise suddenly and make Mawsynram the rainiest place in the world. The Western Ghats present and effective obstacle in the way of south-west monsoons coming from the Arabian sea and cause heavy rainfall in the West Coastal Plain while large parts of Karnataka, Andhra Pradesh and Tamil Nadu in the rain-shadow area receive little rainfall.
Upper Air Circulation
The changes in the upper air circulation over Indian land mass is yet another cause for sudden outbreak of monsoons in India. Jet streams in the upper air system influence the climate of India in the following ways:
Westerly Jet stream and its Impact
During Winter, at about 8 km. above sea level, a westerly jet stream blows at a very high speed over the sub-tropical zone. This jet stream is bifurcated by the Himalayan ranges. The northern branch of this jet stream blows along the northern edge of this barrier. The southern branch blows eastwards, south of the Himalayan ranges, along 25° N latitude. It is believed by meteorologists that this branch of jet stream exercises a significant influence on the winter weather conditions in India. This jet stream is responsible for bringing western disturbances from the Mediterranean region into Indian sub-continent. Winter rain and hail storms in northwestern plains and occasional heavy snowfall in hilly regions are caused by these disturbances. These are generally followed by cold waves in whole of northern plains.
Easterly Jet and its Influence
During summer, due to the apparent shift the sun in northern hemisphere, the reversal in upper air circulation takes place. The westerly stream is replaced by easterly jet stream which owes its origin to the heating of the Tibetan plateau. is leads to the development of an easterly cold jet stream centered around 15° N latitude and blowing over peninsular India. s helps in the sudden onset of Southwest monsoons.
Western Disturbances and Tropical Cyclones
The inflow of western disturbances which move under the influence of Westerly jet streams from the Mediterranean Sea influence winter weather conditions over most of Northern Plains and Western Himalayan region. The tropical cyclones also develop in the Bay of Bengal. The frequency and direction of these cyclones influence weather conditions during southwest monsoons over most parts of India and along the eastern coast during retreating monsoon season i.e. in October and November.