Contemporary India I Chapter 4 Climate

B.

Mawsynram

C.

Loo

C.

Western disturbances

C.

Early June

B.

Warm days and cold nights

Because India is strongly influenced by monsoon winds.

The Thar desert experiences the highest diurnal range of temperature.
The difference between the daily maximum and daily minimum temperature is large. The sandy soils become heated during day and cool down during night.

The Southwest Monsoon winds.

Jet stream:
(i)These are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere.

(ii)Their speed varies from about 110 km/h in summer to about 184 km/h in winter.
A number of separate jet streams have been identified. The most constant are the mid-latitude and the sub tropical jet stream.
These jet streams are located approximately over 27°-30° north latitude, therefore, they are known as subtropical westerly jet streams. Over India, these jet streams blow south of the Himalayas, all through the year except in summer. The western cyclonic disturbances experienced in the north and north-western parts of the country are brought in by this westerly flow.

Bay of Bengal branch of Monsoons move from East to West. These move up the Ganga Valley along the Himalayas. As these winds move westward, these become drier and give less rainfall.
The maximum rainfall of the season is received in the north-eastern part of the country. Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.
Rainfall in the Ganga valley decreases from the east to the west. Rajasthan and parts of Gujarat get scanty rainfall.

The bulk of rainfall in India is received during the four months of the rainy season i.e. June, July, August and September.
This is the period of South-West monsoons blowing from sea to land. These sea to land winds are the rain bearer, as these moisture-laden winds are on-shore winds. 

The low-pressure conditions, over northwestern India, get transferred to the Bay of Bengal by early November. This shift is associated with the occurrence of cyclonic depressions, which originate over the Andaman Sea. 

Despite an overall unity in the general pattern, there are perceptible regional variations in climatic conditions within the country.

(i) Temperature - Barmer (Rajasthan) has recorded day temperatures of 50°C in summer, during day time (15°C at night), while hilly regions like Gulmarg (Kashmir) have a day temperature of 20°C in June. The winter temperatures at Dras and Kargil (Leh) fall as low as –45°C, on the other hand Chennai may record only 20°C in December. The annual range of temperature is about 12°C at Cochin while it is about 40°C in Punjab. Coastal regions have almost uniform temperatures throughout the year.

(ii) Monsoons - The dates of onset and withdrawal of monsoons differ in various parts. The west coast gets monsoons in the first week of June, while the interior parts like Punjab have monsoons by the first week of July.  Striking differences are found in rainfall pattern. Mawsynram (Meghalaya) with an annual rainfall of 1140 cms. is the rainiest place in the world, while Jaisalmer (Rajasthan) rarely gets more than 12 cms. of annual rainfall and Leh gets only 10 cm. of rainfall. The East coastal plain gets rain-storms while Coromandel coast remains dry. When Brahmaputra valley is submerged with floods, it drought in Bihar.

(iii) Seasons - The southern parts of the country have uniformly high temperatures throughout the year. There is no winter season in the south. On the other hand seasonal extremes are found in the north. ‘Loo’ produces a heat wave in summer while cold wave is felt in winter.

The mechanism of monsoons are discussed below:
(i)The differential heating and cooling of land and water creates low pressure on the landmass of India while the seas around experience comparatively high pressure.
(ii)The shift of the position of Inter Tropical Convergence Zone (ITCZ) in summer, over the Ganga plain (this is the equatorial trough normally positioned about 5°N of the equator – also known as the monsoontrough during the monsoon season).
(iii)The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean. The intensity and position of this high-pressure area affects the Indian Monsoon.
(iv)The Tibetan plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of high pressure over the plateau at about 9 km above sea level.
(v)The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.

The characteristics of monsoon rainfall are following:

C.

Dras

C.

Barmer

A.

South-West

B.

West Bengal

A.

Peru

C.

Cyclonic

C.

Wheat

D.

Mango Showers

C.

Leh

C.

Punjab

A.

Deccan Plateau

C.

In October

C.

120 days

C.

20°C

D.

–45°C

A.

June to September

A.

East to West

C.

6000 metres

A.

N.W. India

C.

27°–30°N

C.

Sailors

D.

10th June

C.

25°C

A.

Cyclonic rainfall

C.

Karnataka

They are:
(i)Temperature
(ii)Atmospheric Pressure
(iii)Winds 

Tropical monsoon climate.

From Arabic word ‘Mausim.’

Tropic of Cancer 

They are: Tropical and sub-tropical.

Barmer (50°C) in Rajasthan.

Thar desert.

Mawsynram (Meghalaya).

Tamil Nadu.

South-west monsoons.

Loo are strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.

Sudden approach of South Western monsoons.

Deccan Plateau.

Kerala.

Punjab.

South-West.

North-East.

Kerala.

The areas are: Western coastal plain and N.E. hilly area.

West Bengal 

Mango-showers.

Tamil Nadu

Climate refers to the sum total of weather conditions and variations over a large area for a long period of time, more than thirty years.

The states are: Tamilnadu, Andhra Pradesh, West Bengal and Orissa.

The branches are : Bay of Bengal Branch and Arabian Sea.

The leeward dry slope of a mountain.

Extreme weather conditions.

To avoid intense heat.

To drain out water quickly, as this regions receive heavy rainfall.

In order to protect it from floods.

Due to cold currents on their coast.

An apparent force caused by earth's Rotation.

Over 27°-30° North latitude.

Kal Baisakhi are localised thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail.

It is trough of low pressure.

Inter Tropical Convergence Zone.

El Nino Southern Oscillations.

Tahiti is located in Pacific Ocean. (18°S-149°W).

 Darwin is located in Northern Australia (12°30£S-131°E).

December.

It extends from Thar to Patna.

Due to Ferral’s Law, these turn to the right.

Above 12000 metres.

110 km per hour in summer while 184 km per hour in winter.

Due to influence of the sea from three sides.

‘Monsoon’ refers to the seasonal reversal in the wind direction during a year.

The four seasons are:

(i)The Cold weather season — December to February

(ii)The Hot weather season — March to May

(iii)The Rainy season — June to September

(iv)The season of Retreating Monsoons — October to November.

Mawsynram is the wettest place of the world with an average annual rainfall of 1140 cms.
It is located on the southern slopes of Khasi Hills (Meghalaya) at a height of 1500 metres above sea level. This place is enclosed by hills on three sides. The relief features give this place a funnel shaped location. The Bay of Bengal of monsoons is trapped in these hills. These winds try to get out of it. These are forced to rise again and again resulting heavy rainfall.

Relief rainfall:
(i)Orographic features play an important role in the distribution of rainfall in India. The amount of rainfall in an area is determined by the location of the mountains. 
(ii)In mountainous areas of Khasi Jaintia hills annual rainfallexceeds 1000 cms. In Ganges valley, the amount of rainfall goes on decreasing up the Ganges Valley.
(iii)The on-shore winds give heavy rainfall on windward slopes ; but rain shadow areas remain dry. Garo Khasi hills get more than 1000 cms of annual rainfall, but the amount drops to 200 cms over Shillong plateau and Brahmaputra Valley lying in the rain shadow.
(iv)Malabar Coast and Western Ghats get more than 300 cms of rainfall, but Deccan plateau lies in the rain shadow of Western Ghats and remains dry (60 cms rainfall).
(v)In Rajasthan, the Aravalli system lies parallel to the direction of the S.W. monsoons and is unable to force these winds to rise. So Rajasthan remains practically dry.

Distribution of Rainfall in India:

Mango-showers: Mango-showers are actually pre-Monsoon showers. These are common in Kerala and coastal areas of Karnataka in the months of March and April.
These are locally known as Mango-Showers because these help in the early ripening of mangoes. These are local storms which develop due to high temperatures.

Kal Baisakhi: Kal-baisakhis are local thunder storms experienced in the month of Baisakh (April) in West Bengal. It is associated with violent winds, torrential downpours and accompanied by hail.

In the month of June, South-West monsoons advance from Indian Ocean, whereby increases the rainfall suddenly and is called ‘Burst of monsoons’.
The Arabian Sea branch reaches Thiruvananthapuram by 1st of June. Western ghats, on windward slope, give heavy rainfall. But in July, break in monsoon reduces the rainfall.
Similarly, Bay of Bengal branch reaches by 1st of June at Shillong. This is a rapid advance. So, Shillong gets heavy rainfall in June whereas in July the rainfall is reduced.

Both Mumbai and Thiruvananthapuram receive rainfall from South West Monsoons in Summer.
South West Monsoons reach Thiruvananthapuram by 1st of June. But in July, there is a break in monsoons thereby reducing rainfall. In Mumbai, South West Monsoons reach by 10th June causing continuous rainfall for a month.  Hence, July is rainier in Mumbai.

The Arabian Sea branch of South West Monsoons strike west ghats, first. After crossing, west ghats, these winds descend down the leeward slope of west ghats where they do not give much rain.
The Karnataka and Tamil Nadu remain in rain shadow. Low eastern ghats also do not check these winds. So, these winds give less rainfall in Chennai. S.W. monsoons give 35 cms of rainfall in June — September period, but N.E. monsoons give 85 cms of rainfall in Winter.

Shillong receive an annual rainfall of 225 cms whereas Kolkata gets an annual rainfall of 162 cms. Shillong has a long rainy season lasting 9 months. Cyclones also add to this rainfall. But in Kolkata, rainy season lasts for 6 months.

Jodhpur is located in Thar Desert region, where Aravallis are unable to check monsoons because it lies parallel to the direction of Monsoons. But Delhi gets more rainfall due to advancing monsoons and nearness to axis of monsoon trough of low pressure. Jodhpur is also located at further distance from Himalayas.

Thiruvananthapuram is located in Kerala along Malabar coast. The climate is equable due to moderating influence of ocean.

The duration of monsoons in India is about 120 days. The monsoons withdraw from India by December completely. The retreating monsoons get the direction of N.E. Monsoons. The winds pick up moisture while crossing Bay of Bengal. The winds give winter rainfall in Tamil Nadu on S.E. Coastal plain. So, Chennai gets more rains in winter.

Jodhpur is an inland town in North Western  part of India, located away from the Sea. It is a sandy desert where hot-dry winds and sandy thunder storms blow. Aravallis are unable to check monsoons and give no rainfall. 

Leh is located to the north of Great Himalayas. It gets rainfall as well as snowfall throughout the year due to height and northern cold winds. Winter cyclones also causes snowfall. 

South Western monsoons rapidly advance towards Thiruvananthapuram and Shillong and reach by 1st of June. These areas get cyclonic rainfall too.
Monsoons withdraw from this region by December. So, rainy season is long. But Delhi and Jodhpur has short rainy season due to late arrival of Monsoons.