Social Science 2 Marks Each

South-West monsoon winds are responsible for the rain in rainy season and the humid and cloudy weather. That is why this is also known as season of ‘South-West Monsoon winds.
Due to the peninsular shape of the South India, the South-West Monsoon winds are divided into two parts:
Arabian Sea Current
Bay of Bengal Current

Indian Meteorological Department of Government of India at Delhi has divided the climate of India into four seasons:

1. Cold weather season: Winter: December to February.
2. Hot weather season: Summer: March to May.
3. Advancing Monsoon: Rainy season: June to September.
4. Retreating Monsoon Season: October to November.

Major portion of annual rainfall in India is due to south-west monsoon winds because the monsoon winds arrive at southern tip of Indian peninsula generally by first week of June. It blows in India, namely the Arabian Sea branch and Bay of Bengal branch. There are rainless intervals in this season.

Except the high mountainous regions, the temperature never decrease below freezing point anywhere in India because Himalayan ranges prevent the chilling cold winds coming from Central Asia and protects India from the severe cold. So except the high mountains, the temperature does not go below pressing point.

There is a large difference in the temperature and rainfall in different parts of the country India because as the Tropic of Cancer passes through almost middle of India, the southern part falls in torrid zone and the northern in temperate zone.

As we go higher from sea-level, air pressure and air temperature both decrease.
Generally air temperature decreases at 1°C for the ascent of 165 metres or by 0.5°C for ascent of every 1000 metres.
Due to the high altitude, the Himalayan peaks remain snow-covered throughout the year, and higher relief gets more rain.
Moist air cools down when it rises and bring rain. With increasing altitude of the mountains in Assam, Meghalaya the rainfall increase.

The axis of the earth is tilted at 23.5° and makes an angle of 66.5° with the orbit. Seasons are caused due to the axial tilt.
Regions receiving more sunlight experience summer while region receiving less sunlight experience winter.
Sun rays fall vertically over Tropic of Capricorn on 22nd December. So, the southern hemisphere experiences summer and the northern hemisphere experiences winter.
The sun rays are vertical over Tropic of Cancer on 21st June. Hence days are longer.
Rotation and Revolution of the earth also play significant role in seasonal change.

India receives rain through monsoon winds. But the onset of these winds is also irregular. The phenomena of ‘Rain break4 is associated with the monsoon winds.
The monsoon rainfalls for many days but there are a few rainless days, and again it is followed by a spell of rain. This phenomenon is called ‘Rain Break’.

In the arid regions of west and north-west India, sandstorms or thunderstorms are common.
In summer especially in May very hot winds blow over North India which are known as ‘Loo’. Direct exposure of these winds may even prove fatal.

The low-pressure pocket over north and north-east India is spread up to Bihar due to which some parts of Odisha and Jharkhand become more hot occasionally.
It is known as Norwester. These winds are locally known as ‘Kaal Baisakhi’ and cause much damage in eastern India.

A large low-pressure area develops over where the trade winds converge. It is called Inter-Tropical Conversion Zone (ITCZ).
The Trade winds rise upwards in the form of air currents.
In July, this conversion zone is stationed over 20° to 25° North latitude. In India, it is stable over Ganga plains.
Due to the low pressure developed over this region, winds over the oceans in southern hemisphere blow towards this area. It causes rain in a few parts of North India.
During colder season, the conversion belt shifts further south, so the winds change their direction to north-east.

Jet stream formed over West Asia blows towards east and affects West Asian countries, North-East India, Pakistan and Afghanistan.
The dust storm accompanying these disturbances leave its effect up to Bangladesh.
This often creates disturbances in the pleasant winter weather of North India.
Very high mountains receive snowfall and to the Ravi crop. This may cause unseasonal rain, locally known as ‘Mavthu’ in Gujarat which may damage crops.

In both hemispheres around 30° latitudes, very powerful winds in a pipe-shaped belt blow with high speed in the atmosphere at an altitude of 8 to 15 km. These winds are known as ‘Jet Streams’.
The average velocity of Jet Streams is about 150 km per hour and in the central part of this wind belt, their velocity is about 400 km.
During winter these winds blow over the southern slope of Himalayas and in summer these are stationed over Peninsular Plateau.
High altitude winds help to bring rain.

• (1) The north-east winds blow over India during winter. These winds blow from land over ? most of the landmass, these are generally dry. Mostly they do not bring any rain.
• (2) As the north-eastern winds blowing along the Coromandel coast come from the Bay of Bengal, they happen to carry much moisture. So they give much rain ? along the Coromandel coast. Thus, Coromandel coast gets its rain during winter.

• (1) The Western Ghats is spread north- south along the western coast of south India, so the west coast plain is narrow.
• (2) As soon as ' the Arabian Sea Current of the monsoon winds enters this plain, it is obstructed by Western Ghats.
• (3) These winds rise as the Western Ghats are very high, and most of the moisture cools down and gives rain in the western plain over the windward slopes of Western Ghats.
• (4) This Sis why the west coast plain in south India gets torrential rain.

• (1) One branch of the south-west monsoon winds blowing from the Arabian Sea brings rain to Gujarat. These winds are weak and also contain less humidity.
• (2) In this part of Gujarat, there are no high mountains or dense forests. So there are least chances for condensation and that is why Gujarat gets less rain.

• (1) One branch of the south-west monsoon winds blowing from the Arabian Sea brings rain to Gujarat. These winds are weak and also contain less humidity.
• (2) In this part of Gujarat, there are no high mountains or dense forests. So there are least chances for condensation and that is why Gujarat gets less rain.

• (1) The Bay of Bengal Current of the monsoon winds enters north-east India via Bangladesh with abundant moisture.
• (2) The Garo, Khasi and Jaintia hills of Meghalaya come in their way. So there is torrential rain in Meghalaya.
• (3) Mawsynram and Cherrapunji Situated on the southern slopes of Khasi hills get maximum rainfall of the world. One branch of these winds enters Brahmaputra valley, is obstructed by Himalaya and Purvachal mountains and gives rain in other north-eastern states. So there is heavy rain in the north-eastern (Ishan) India including Meghalaya.

• (1) The Western Ghats is spread north- south along the western coast of south India, so the west coast plain is narrow.
• (2) As soon as ' the Arabian Sea Current of the monsoon winds enters this plain, it is obstructed by Western Ghats.
• (3) These winds rise as the Western Ghats are very high, and most of the moisture cools down and gives rain in the western plain over the windward slopes of Western Ghats.
• (4) This Sis why the west coast plain in south India gets torrential rain.

• (1) The north-east winds blow over India during winter. These winds blow from land over ? most of the landmass, these are generally dry. Mostly they do not bring any rain.
• (2) As the north-eastern winds blowing along the Coromandel coast come from the Bay of Bengal, they happen to carry much moisture. So they give much rain ? along the Coromandel coast. Thus, Coromandel coast gets its rain during winter.

• (1) The windward side of the mountain which obstruct the moisture laden winds gets heavy rain.
• (2) As most of the humidity of these winds drops on the windward side of the mountain, it gives much less rain on the leeward side of the mountain. So the area towards the leeward side is called ‘rain shadow’ area.

• (1) The slope which is on the reverse side of the windward slope is called ‘Leeward slope’.
• (2) With reference to the south-west monsoon winds, the eastern slopes of Western Ghats and the northern slopes of Himalayas are leeward slopes.

• The mountain slope which lies at right angle to the prevailing winds and obstructs them is known as ‘Windward slope.
• The western slopes of the Western Ghats which prevent the south-west monsoon winds and the southern slopes of Himalayas are windward slopes in India.

• Pre-monsoon showers occur in Kerala and Karnataka along Malabar coast during May.
• These showers help the mango crop, so locally these are known as ‘Mango showers’.

• The crop taken during winter is called Rabi crop.
• Cold climate suits this crop. Wheat, gram, mustard, etc. are Rabi crops.

• (1) Turning of the moisture in the atmosphere into snow due to extreme cold and its falling in the form of cotton is called ‘snowfall’.
• (2) In India, snowfall occurs only in Himalayas in winter.

• (1)‘Climate’ of any place means the weather conditions experienced over a place during a period of 35 years or more.
• (2) Atmospheric temperature, pressure, winds, humidity, rain, etc. of a place determine its climate.

• (1) The conditions of air temperature - air pressure, its velocity, humidity, clearness of the sky or the cloud amount, etc. are known as ‘weather’
• (2) Weather conditions are changing. Sometimes the changes are faster or sometimes a uniform condition is experienced for a longer time.

• Mumbai is on the west coast. The Western Ghats obstruct the moisture laden monsoon winds blowing in the monsoon.
• So Mumbai gets more - than 200 cm rain annually. Pune is situated in the leeward side of the Western Ghats. By the : time the south-west monsoon winds cross the Western Ghats and reach Pune, they lose most Of the moisture. So Fune gets only about 75 cm rain annually. Thus, even though the distance between Mumbai and Pune is not much, there is less rain in Pune than in Mumbai.

• (1) South India is a peninsula and none of its places is far away from the sea. So there is a marine influence over its climate which makes heat and cold very moderate.
• (2) The sun rays are vertical in summer, but as its major part is a plateau, it remains moderately hot.
• (3)So due to the maritime climate and height of the -peninsular plateau, the summer in south India is comparatively moderate.

• (1) Snowfall sometimes occurs’ in Himalayas and at that time the wind direction over India is from north to south.
• (2) So the cold and heavy air from Himalaya rushes down . to south. Under its influence, a cold wave prevails – over Rajasthan and Gujarat and the temperature suddenly falls down. Due to frost in some area crop like cotton is damage.

• (1) India is an agrarian country.
• (2) Most of its agriculture is dependent on rain. About 80% of its rainfalls during the monsoon, between June. to September. That is why monsoon is considered - to be the most important season in India.

• (1) The south-west monsoon winds blowing from the Arabian Sea give rain to Gujarat and then enter Rajasthan. These winds have very little moisture.
• (2) The Aravalli range in Rajasthan which lies in the same direction as the winds, does not obstruct them.
• (3) There are less chances for the condensation of the humidity in the monsoon winds. So there is less rain in Rajasthan. In the Tharpakar desert of western Rajasthan there is less than 10 cm of rainfall.