Geography Quiz: Weather, Climate and Seasons of India | 30 June, 2021

The Ganga delta and the coastal plains of Orissa are hit by strong rain-bearing storms almost every third or fifth day in July and August while the Coromandal coast, a thousand km to the south, goes generally dry during these months.

Most parts of the country get rainfall during June-September, but on the coastal areas of Tamil Nadu, it rains in the beginning of the winter season.

Source: NCERT – India Physical Environment

Known to sailors around the world as the doldrums, the Inter-Tropical Convergence Zone, (ITCZ pronounced and sometimes referred to as the “itch”), is a belt around the Earth extending approximately five degrees north and south of the equator.

· Here, the prevailing trade winds of the northern hemisphere blow to the southwest and collide with the southern hemisphere’s driving northeast trade winds.

· Due to intense solar heating near the equator, the warm, moist air is forced up into the atmosphere like a hot air balloon. As the air rises, it cools, causing persistent bands of showers and storms around the Earth’s midsection.

The rising air mass finally subsides in what is known as the horse latitudes, where the air moves downward toward Earth’s surface.

· Because the air circulates in an upward direction, there is often little surface wind in the ITCZ.

· That is why sailors well know that the area can be calm sailing ships for weeks. And that’s why they call it the doldrums.

Source: NOAA

The Inter Tropical Convergence Zone (ITCZ) is a low-pressure zone located at the equator where trade winds converge, and so, it is a zone where air tends to ascend.

· In July, the ITCZ is located around 20°N-25°N latitudes (over the Gangetic plain), sometimes called the monsoon trough.

· This monsoon trough encourages the development of thermal low over north and northwest India.

· Due to the shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40° and 60°E longitudes and start blowing from southwest to northeast due to the Coriolis force.

· It becomes southwest monsoon. In winter, the ITCZ moves southward, and so the reversal of winds from northeast to south and southwest, takes place. They are called northeast monsoons.

Source: NCERT – India Physical Environment

The atmosphere consists of different layers with varying density and temperature. Density is highest near the surface of the earth and decreases with increasing altitude.

· The column of atmosphere is divided into five different layers depending upon the temperature condition. They are: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

· The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.

· The stratosphere is found above the tropopause and extends up to a height of 50 km.

· One important feature of the stratosphere is that it contains the ozone layer. This layer absorbs ultra-violet radiation and shields life on the earth from intense, harmful form of energy.

· The mesosphere lies above the stratosphere, which extends up to a height of 80 km.

· In this layer, once again, temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.

· The upper limit of mesosphere is known as the mesopause.

· The ionosphere is located between 80 and 400 km above the mesopause. It contains electrically charged particles known as ions, and hence, it is known as ionosphere.

· Radio waves transmitted from the earth are reflected back to the earth by this layer. Temperature here starts increasing with height.

· The uppermost layer of the atmosphere above the thermosphere is known as the exosphere. This is the highest layer but very little is known about it.

Source: ICSE – Total Geography

The retreating southwest monsoon season is marked by clear skies and rise in temperature. The land is still moist.

· Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive. This is commonly known as the ‘October heat’.

· In the second half of October, the mercury begins to fall rapidly, particularly in northern India.

· The weather in the retreating monsoon is dry in north India but it is associated with rain in the eastern part of the Peninsula. Here, October and November are the rainiest months of the year.

Source: NCERT – India Physical Environment

The peninsular shape of India divides these Southwest monsoons into two branches – Arabian Sea branch and Bay of Bengal branch.

· Arabian Sea branch of Southwest monsoons strikes the western coast of India and causes heavy rains on the western slopes of the Western Ghats.

· After crossing the Western Ghats, these winds cause less rainfall on the eastern slopes as they gain temperature while descending. This area is, therefore, known as rain shadow zone.

· The Bay of Bengal branch is divided into two sub branches after striking eastern Himalayas. One branch moves towards the east-northeast direction and causes heavy rains in Brahmaputra valley and northeast hills of India.

· The other branch moves towards northwest along the Ganga valley and the Himalayan ranges causing heavy and widespread rains over vast areas.

· In this region, the amount of rainfall decreases from east to west owing to the progressive decrease in humidity of these winds.

Source: NCERT – India Physical Environment

In low latitudes, an intense depression with a low-pressure centre is known as a Tropical cyclone in the Indian Ocean area, as hurricanes in the Caribbean, typhoons in China and Willy-willies in Australia.

Source: ICSE – Total Geography

Local Winds are produced due to local variability in temperature and pressure conditions. Thus, they are more localized in their extent and cover limited horizontal and vertical dimensions and confined to the lower levels of the troposphere.

Source: ICSE – Total Geography and NOAA

The Himalayas act as a climatic divide between India and Central Asia.

· During winter, Himalayas protect India from cold and dry air masses of Central Asia.

· During monsoon months these mountain ranges act as an effective physical barrier for rain bearing south-west monsoon winds.

· Himalayas divide the Bay of Bengal branch of monsoon winds into two branches – one branch flowing along the plain regions towards north-west India and the other towards South-East Asia.

· If the Himalayas were not present, the monsoon winds would simply move into China and most of the north India would have been a desert.

Source: NCERT – India Physical Environment

India’s climate closely resembles the climate that of a tropical country although it’s northern part (north of tropic of cancer) is situated in the temperate belt.

· Indian subcontinent is separated from the rest of Asia by the lofty Himalayan ranges which block the cold air masses moving southwards from Central Asia.

· As a result, during winters, the northern half of India is warmer by 3°C to 8°C than other areas located on same latitudes.

· During summer, due to over the head position of the sun, the climate in the southern parts resemble equatorial dry climate.

· The north Indian plains are under the influence of hot dry wind called ‘loo’ blowing from the Thar, Baloch and Iranian Deserts, increasing the temperatures to a level comparable to that of the southern parts of the country.

· The climate in most of the regions is characterized by distinct wet and dry seasons.

· Some places like Thar desert, Ladakh have no wet season. Mean annual rainfall varies substantially from region to region.

· Mawsynram and Cherrapunji in Meghalaya receive around 1,000 cm of annual rainfall while at Jaisalmer the annual rainfall rarely exceeds 12 cm.

Source: NCERT – India Physical Environment