CLIMATE:
Climate, conditions of the atmosphere at a particular location over a long period of time; it is the long-term summation of the atmospheric elements that, over short time periods, constitute weather.
Climate is therefore time-dependent, and climatic values or indexes should not be quoted without specifying what years they refer to.
India’s climate is predominantly of the monsoon type, climate associated with seasonal reversal of winds.
1.FACTORS DETERMINING INDIA’S CLIMATE:
The factors determining India’s climate are classified into two categories:
- factors related to location and relief.
■ latitude:
latitude is a geographic coordinate that specifies the north–south position of a point on the Earth’s surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator.
India is located partially in the tropical region and partially in the temperate region ,as a Tropic of Cancer passes through the central part of India .the southern parts, begin closer to the equator, experience high temperature throughout the year. the nothern parts are distant from the equator and experience comparatively lower temperature, particularly in winters. this the monthly average temperature of the warmest and the coldest month in North India are 32 degree Celsius and 21 degree Celsius ,the monthly average temperature of the warmest and the coldest month in South India 33 degree Celsius and 26 degree Celsius.
Www.vinayiasacademy.com - ■ Himalayas:
The Himalayas is the highest mountain range in the world, and has 9 out of 10 of the world’s highest peaks, including Mount Everest. These mountains, referred to as the Third Pole, are the source of some of Asia’s major rivers and also help to regulate our planet’s climate. They act as a barrier for bitterly cold and dry winds coming from Central Asia and the Siberian region they. They also limit the northward journey of the rain bearing Southwest monsoon winds, forcing them to shed their moisture in the Indian subcontinent. the Himalaya act as a climate division between the Indian subcontinent and Central Asia.
■ Distribution of land and water:
distribution of land and water on Earth’s surface is markedly different in the Northern and Southern hemispheres. The Southern Hemisphere may be called the water hemisphere, while the Northern Hemisphere is the land hemisphere.
As compared to land mass ,water heats up or cools down slowly .this cause differential heating of land and sea.
the differential heating causes seasonal reversal of wind .India experiences Southwest monsoon during summer and Northeast monsoon during winter.
■ Distance from sea:
The sea affects the climate of a place. Coastal areas are cooler and wetter than inland areas. Clouds form when warm air from inland areas meets cool air from the sea. The centre of continents are subject to a large range of temperatures.
Southern or peninsular India is surrounded by the Arabian sea, the Indian Ocean,and the bay of bengal.the climate of coastal regions of India is equable or maritime.the region located in the interior of the country are cut of from the oceanic influence .they have an extreme or Continental type of climate .the areas in South India ,in comparison to the areas in North India, experience lower annual range and daily range of temperature.
■ Altitude :
altitude is a distance measurement, usually in the vertical or “up” direction, between a reference datum and a point or object. The reference datum also often varies according to the context. Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.
We have read earlier that the temperature decreases with increase in altitude. temperature of air increases when it comes into contact with warm land mass.
■ Relief:
relief is the difference between its highest and lowest elevations.A two-dimensional relief map displays the topography of a given area.Physical relief maps actually have raised areas that represent different elevations. However, if you’re going for a hike, they’re not very practical to carry in your pocket. - Factors related to air pressure and wind;
The wind blows because of differences in air pressure from one location to another. Wind blows from areas of high pressure toward areas of low pressure. If the high pressure area is very close to the low pressure area, or if the pressure difference is very great, the wind can blow very fast.
■ Lower air pressure or monsoon.
The circulation of wind in the atmosphere is driven by the rotation of the earth and the incoming energy from the sun. Wind circulates in each hemisphere in three distinct cells which help transport energy and heat from the equator to the poles. The winds are driven by the energy from the sun at the surface as warm air rises and colder air sinks. The complete reversal in the direction of wind over India brings about a change in season. These winds that change their direction with the change in season are called monsoon wind. the word monsoon is derived from the Arabic word “Mousim” which means ” season”. this wind have such a far-reaching influence on India Climate that India climate is termed”. “monsoon type of climate”.
2.INDIAN MONSOON: MECHANISM AND ONSET.
The period June to September is referred to as the ‘Southwest Monsoon’ period. Southwest Monsoon period is the principal rainy season for the Indian subcontinent. This is the summer monsoon period where the southwest monsoon holds away over the country. The whole country receives nearly 75% of its rainfall during this period. during summer in the Northern hemisphere, the inter-tropical convergence zone shifts northwards from the equator to Indian land mass .the southeast trade wind in the southern hemisphere ,are under the impact of intense low pressure, cross over the equator and enter the northern hemisphere.Southwest monsoon sets in over the extreme southwestern tip of the peninsula by the end of May. The onset of Monsoon is characterized by a sudden spurt of rainfall activity. It progresses inland in stages and covers the entire country by the middle of July.
Remember that wind blow from high pressure to low pressure area .winds deflects towards their right in the Northern hemisphere and towards the left in the southern hemisphere. the low pressure belt shift northwards over the the North Indian Plains ,during summer .on the other hand, the water body adjoining the Indian peninsula has comparatively high pressure. this leads to wind movement from the Sea to the land the Southwest wind together moisture over the sea and bring rainfall in the Indian subcontinent. These wind touch the coast of Kerala on 1st June and cover entire Indian land mass by 15 July.
These winds bifurcated into two branches:
1 .Arabian sea branch :
The Arabian Sea branch of the southwest monsoons is divided into three distinct streams on arriving in the mainland of India. The first stream strikes the west coast of India and gives extremely heavy rainfall of over 250 cm.
It blows over Arabian Sea and enters Indian land mass. it is further the divided into the following:
▪︎ First branch: it is obstructed by the Western Ghats .after crossing the Western Ghats, this branch descends downwards and get heated up ,causing little rainfall in the rain Shadow area .the windward side of the Western Ghats receives heavy rainfall.
▪︎ second branch: it strikes the coast of Maharashtra and moves along the river valley of Narmada and Tapi .this winds cause rainfall in Central India.
▪︎third branch: it enters from the cost of Gujarat and leads to rainfall in entire Gujarat. this branch also cause scanty rainfall in western Rajasthan and while moving along the Aravalli.
- Bay of Bengal branch:
It Gathers moisture from the Bay of Bengal and strikes Myanmar and Southeast Bangladesh. this branch, in North East India and West Bengal from the south and south east direction Instead of the south west direction .arakan yoma Hills deflect this branch towards Indian subcontinent.
This branch, after coming into contact with the Himalayas, further splits into the following:
■ the first branch: moves westwards along the Ganga Plains, covering the whole of North India.
■ the second branch: moves up from the Brahmaputra valley in northeast India, causing widespread rains .its sub branch strikes the Garo and Khasi hills in Meghalaya. that trapped clouds pour heavy rainfall, making Mawsynram and Cherrapunji the wettest places in the world.
■ also the Western Ghats block the extension of the Arabian Sea branch .during summer, Tamil Nadu coast remains in the rain Shadow region.
■ the rain bearing Bay of Bengal branch moves parallel to the Tamil Nadu coast. as a result ,Tamilnadu does not receive rainfall from the Bay of Bengal branch during summer.
