Thursday, June 18, 2009

C3 Climate of South Asia-Notes

C3




CLIMATE OF SOUTH ASIA

1. a. Explain two factors that influence the climate of South Asia. (2)
Two factors that influence the climate of South Asia are:
* Himalayas Mountains – They are responsible for tropical type of climate in South Asia. It protects
from the cold winds from the north and obstructs the SW monsoon thereby causing heavy rain.
* Jet Stream – These fast moving currents in the upper atmosphere have an impact on the arrival and
departure of the monsoon.
* Distance from the sea. is another factor that influence the climate of South Asia.

b. Mention any three features of climate of south Asia.
* South Asia has tropical Monsoon climate.
* The climate is influenced by the S.W. and N.E. Monsoons.
* The position of the mountain ranges and direction of the rainbearing winds are the two main factors
that determine the climate of India.

c. State the climatic significance of Himalayas to the people of South Asia.
* EFFECT ON CLIMATE: It acts as a climate divide. These act as a guard against the northern cold
winds. the Himalayas act like a natural wall that keeps the fertile Indo-Gangetic plains safe from the
cold, bleak winds from the north.
* The Himalayas cause the monsoon winds to shower life giving rains on the valleys and the plains to
their south.
* FOREST WEALTH: The Himalayas are covered by thick forests which are the source of raw
material.

d. Which winds are responsible for the rainfall experienced over the greater part of the SAARC countries? During which months of the year is this rainfall experienced?
The major portion of the Indian subcontinentgets its rainfall from the South –West Monsoon.
The rainy season in SAARC countries start from May and lasts until September.

e) Why are there great variations in the climate of the Indian Subcontinent? Give three reasons.
* THE HIMALAYAN MOUNTAIN CHAIN: It protects Indian subcontinent from cold winds of the
Central Asia. It creates barriers before the S-W Monsoon.
* THE LARGE COAST LINE: South India is a Peninsula and has a large coast line. Peninsular
situation has helped it to enjoy maritime climate.
* JET STREAMS: The aircurrents blowing in upper layer of the atmosphere are known as jet streams.
These help western disturbances to enter into India.

f. What is a jet stream?
A jet stream is fast wind in a narrow zone in the upper atmosphere.

g. What are trade winds?
Trade winds are strong winds that blow towards the equator from the north-east or south east. They can be defined as Planetary winds blowing constantly from the subtropical high pressure zones towards the equatorial low pressure zones.

h. Give two reasons why the entire Indian sub-continent has the tropical monsoon climate.
The climate of the subcontinent is greatly affected by the presence and influence of the Himalayas. It prevents the cold winds of north Asia from blowing into India.
The monsoon winds which are trapped by the Himalayas give the climate of the continent a tropical touch.

i. What is loo?
It is a local wind which is hot and dry.

j. Give reason why the entire South Asia experiences tropical monsoon climate.
* The Great Himalayas standing to the north of India act as a barrier as it prevents the cold winds of North Asia from entering into South Asia.
* The climate of almost whole of South Asia comes under the influence of monsoon winds that provides it a typical character or feature.

k. Briefly explain how does relief affect the climate of South Asia.
The relief plays an important role in modifying the climate of a particular place. In Case of south Asia relief plays the following roles:
· the Great Himalayas to the North of India prevent us from the cold winds of the North.
· The higher the altitude the cooler the temperature. As we go higher, the temperatures decreases at a very fast rate.
· Mountains coming in the way of monsoon winds help in the rainfall or precipitation.

l. What is windward side?
The upwind side or the side exposed to the direction from which the wind blows. Windward side always receive more rainfall as compared to leeward side. For example, Mahabaleshwar situated on the western side of the Ghats receive 250 cm of rain fall whereas Pune, receives 70 cm as it is on the leeward side.

j. How do Himalayas act as ‘climate divide’?
* It prevents the cold winds of the North Asia from blowing into India.
* It also traps the Monsoon winds in summer and causing them to shed their moisture over huge part of the land located south of it..

k. How is average rainfall calculated?

Total annual rainfall
Average rainfall = ________________________

Number of Months

k. Write two features of tropical climate.
*Tropical climate has relatively high temperature throughout the year.
* Dry winters are another important feature of tropical climate.

l. What is retreating monsoon and name any two months associated with them. Normally by what date does the monsoon advance into Kerala?
During the months of October and November the temperature in the Northern Plains begins to decrease and because of low temperature pressure starts rising and the low pressure is no longer strong enough to attract the monsoon winds. This results in the retreat of the monsoon.
Normally monsoon advances into Kerala on 1st June.

m. State two features of the monsoon climate.
* The monsoon climate comes under the domain of trade wind belt which experiences seasonal shifting.
* Monsoon areas are affected by high and low pressure system due to winter and summer seasons.

n. What is meant by ‘rain shadow’ area or ‘ Leeward Area’? Give two examples of ‘Rain Shadow’ areas in India.
Area which gets a little or no rainfall is called the Rain Shadow area or Leeward area. This side is completely opposite to the windward side of the mountain.
· Eastern side of Eastern Ghats
· North west Deccan trap
· Eastern side of Eastern Ghats during the south-west monsoon.

n. What is meany by ‘monsoon’?
Monsoon is a season in which there is a complete reversal in the direction of wind, i.e. it begins to blow from sea to land contrary to land to sea.

o. What do you understand by ‘Pre-monsoon period’?
The period during which low pressure begins to replace the high pressure due to intense heat in the Northern Plains. This period is said to be ‘Pre-Monsoon period.”


INDIA

2.a) What type of climate is found in India? Give reason.
Tropical monsoonal climate because the greater part of the country lies within the tropics and it is also
influenced by the W.W. and N.E. Monsoons.

b) It is cooler on the mountain slopes than in the plains during summer. Give reason.
The temperature decreases with increasing altitude. Hence the mountain slopes being higher are cooler than plains.

c) Mumbai is warmer than Kanpur in December. Give reason.
Mumbai is near the coast so it enjoys the equable influence of the sea whereas Kanpur is far away from
the sea, so it does not enjoy the equable climate.

d) Western coastal plains receive more rainfall than the Eastern coastal plains.
Western coastal plains receive more rainfall than the Eastern Coastal plains because winds come from South West direction and are obstructed by Western Ghats.

e) Though Mangalore and Mysore are on the same latitude, Mangalore experiences more rainfall than Mysore. Give reason.
Mangalore is in the windward side of the Western Ghats whereas Mysore is on the leeward side of the
Western Ghats

f. “Western Rajasthan or Thar Desert receives less rainfall.” Or Arabian Sea branch of S-W monsoon does not shed any moisture in western Rajasthan. Or Inspite of Aravalli Hills, many parts of Rajasthan do not receive much rain. Give two reasons.
‘Western Rajasthan receives less rainfall’ because :
* there is no relief or barrier to obstruct the Arabian sea branch of the monsoons. The Aravalli hills
lie parallel to the direction of the monsoon as such they pass without any obstacles. They are also
lower in height.
· Secondly, the summer temperatures in Thar Desert are so high that monsoons that pass over the
desert get dry.

g. Chennai receives less rain than Thiruvanathapuram although it has more rainy days. Give reason.
Chennai receives less rain from northeast monsoons during October-November which is not very strong,
hence gives less rain where as Thiruvanathapuram which is in Kerala receives very heavy rain from South
West Monsoons which are much more powerful.

h. Mangalore and Chennai lie on the same latitude, yet Mangalore receives its rainfall from June to September, Chennai receives most of its rain in November-December. What are the reasons for this difference?
Mangalore receives rain from South West Monsoons, which blow from June-September as it lies on the windward side of the Western Ghats where Arabian sea branch of the South-West Monsoon gives heavy rainfall. By the time, the South-west Monsoon descends on the leeward side, very little mositre is left. Hence, Chennai receives a little or no rain during this period.
Chennai receives its rainfall in November – December from the North-East monsoon winds which blow over the Bay of Bengal and meet with the moist wind of the retreating summer monsoon. These winds, further, cross Bay of Bengal and blow on the Tamil Nadu causing heavy rain in coastal region including Chennai.
Hence, Mangalore and Chennai lie on the same latitude, yet Mangalore receives its rainfall from June to September, Chennai receives most of its rain in November-December.

i. Explain why Nainital is cooler than Agra.
Nainital is a hill station located at a higher altitude. Since temperature decreases with altitude, it is
cooler as compared to Agra which lies in the interior. It experiences continental type of climate.

j. Punjab receives rain in winter. Explain.
Punjab receives rain in winter by westerly depressions which originate in the Mediterranean sea during
January-February.

k. Hill stations in the South never experience snowfall even when temperature fall to 0 degree C. Give reason.
The hill stations in the south are closer towards the Equator, hence the temperatures even if they touch 0
degree C do not experience snowfall.

l. Jaipur has higher annual range of temperature than Mumbai. Give two reasons.
* Jaipur is far away from the moderating influence of the seas. It is an inland town with extreme type of climate but Mumbai has a marine climate.
* It does not get much rain from south west monsoon because the Aravalli range lies parallel to the
direction of winds.
* Jaipur being located in a desert has a high range of temperature. But Mumbai being located on a coastal plain has a low range of temperature.

j. India has varied climatic conditions. Give reason.
India has varied climatic conditions because of its vastness and varied physiographic divisions.

k. South West Monsoons does not give much rainfall to Chennai. Give reason.
Chennai is located on the Eastern Coast. The South-West Monsoon first strikes the Western Ghats and causes a very heavy rainfall. When these winds reach Chennai or the eastern coast they become dry.

l. Patna gets heavier rainfall than Varanasi. Why?
Amount of rainfall decreases as monsoon winds moves westward. These get drier and drier as the distance from sea increases.


m. “Shillong gets less than 200 cm of rainfall in the year while Cherrapunji receives more than 1250 cm of rainfall. Give reason.
Cherrapunji lies on the foothills of Khasi hills in Meghalaya. They are funnel shaped hills. When the moisture laden monsoon winds enter into these hills they are trapped in these hills, causing heavy rainfall. Shillong, on the other hand, lies in the rain shadow area of the Khasi hills and gets less rainfall.

n. Coramandel coast receive most of its rainfall during winter season. Why?
Because its location is on the windward side of the Eastern Ghats.

o. Fishermen are advised not to venture into the Bay of Bengal during months of Oct-Nov. Why?
It is the season of retreating monsoons when tropical cyclones originate over the Bay of Bengal.

p. Amritsar experiences temperatures around 0 degree in December and around 35 degree C + in May. Why?
Amritsar is situated far from the influence of sea, thus experiencing a continental climate with extremes of temperature.

q. The Malabar coast has less rainy months but more rainfall than the Coramandel coast. Why?
* The Malabar Coast in on the windward side of the Western Ghats, while Coromandel Coast is on the
lower side of the Eastern Ghats during summer monsoon.
* The Malabar Coast is first to get rainfall from south-west, while the Coromandel coast gets rainfall
from north-east winds in winter season.

r. The Himalayas act as a perfect climatic divide.
The Himalayas act as a perfect climatic divide as they separate the Indian subcontinent from rest of Asia. On one hand they prevent the chilly cold winds from central Asia from entering the Subcontinent and force the South-West Monsoon winds for rain on the other.

s. The monsoon is unevenly distributed over India. Why?
The amount of rain received by an area depends on its relief, for example, windward side of the mountain receives more rain while leeward side receives less rain. That is why, the monsoon rain is unevenly distributed over India.

t. India is called the ‘Land of Contrast’.
India is called the ‘Land of Contrast’ due to the Himalayas which separate the Indian subcontinent from the rest of Asia and the Tropic of Cancer which divides the country into two halves – North Temperate and South Tropical Zones. These two factors influence the climate of the regions greatly.

u. Most of the rainfall of the Indian subcontinent is received only in 4 months of the year. Why?
Most of the rainfall in the Indian subcontinent occur during mid-June to mid-October due to the South-West monsoon winds as these winds are very strong and laden with plenty of moisture. These moisture laden winds give torrential rain which lasts for 4 months.

v. Kolkatta receives about 145 cm of rainfall while Lahore gets only 45 cm from the South-West Monsoons.
As the South-West Monsoon winds proceed towards west, moisture content gradually decreases thereby rainfall decreases. That is why Kolkatta receives about 145 cm of rainfall while Lahore gets only 45 cm from the South-West Monsoons.

w. The Indo-Gangetic Plain gets some rainfall in the month of December and January. Give reason.
The Indo-Gangetic Plain gets some rainfallin the months of December and January due to Western Disturbances moving eastward from the Mediterranean Sea. These disturbances cross into the Indian subcontinent through the Khyber, Bolan and Gomal Passes and give rain showers to the Indo-Gangetic Plain.

x. Chennai has more rainy season months but less rain than Mumbai. Why?
Chennai receives most of the rainfall from the North-East monsoon with less moisture thereby causes less rain while Mumbai receives rainfall from the South-West monsoon laden with plenty moisture thereby causes heavy rain.

y. Hot dust-storm are quite common in Thar desert.
Hot and dry weather of the Thar desert creates low pressure over the area which attracts winds from the surrounding areas causing hot dust-storms.

3.a. Which type of climate is experienced in the Northern Plains of India? State one main characteristics of this type of climate.
Tropical monsoon type of climate is experienced in the Northern Plains of India. This type of climate is
marked by very hot summers and very cold winters .

b) Name a state which is influenced by : i) Mango showers ii) Loo
Mango showers – Kerala
Loo – Punjab

C) Name the region in India which receives rainfall from the Western Disturbances. State the importance of this rainfall.
Plains of north-western India i.e. Punjab and Himachal Pradesh.
The rain is highly beneficial to Rabi crop especially wheat.

D) Name and give the direction of winds that cause snow and rainfall in the northern parts of India during the winter season.
‘Western Disturbances’ cause rain in the northern parts during winter season. These Cyclones originate from the Mediterranean Sea. They travel eastwards across Iran and Pakistan and reach India during winter season. On their way, the moisture content gets augmented from the Caspian Sea in the north and the Persian Gulf in the south and give some rain to Punjab and Haryana.

E) Distinguish between windward and leeward side.
WINDWARD SIDE: That side of the mountain which comes across the striking winds and gets heavy rainfall is called windward side. For example, the western side of the Western Ghats gets heavy rainfall 9 like Mangalore 280 cms) because it is in the windward side.
LEEWARD SIDE: It is the other side of the mountain where winds descend after shedding much of the rainfall. This portion receives very less rainfall. For example, Bangalore gets 50 cms rainfall because it is in the leeward side.

g.. What type of climate is found in India? Give reason. (2)
Tropical monsoonal climate because the greater part of the country lies within the tropics and it is also influenced by the South West and North East Monsoons.

h. Name the four seasons of India.
# The Cold weather season – December to February.
# The Hot weathr season – March to May
# Advancing Monsoon Season – June to September
# Retreating Monsoon season – October to November.

i.Name two important features of the Indian Monsoon.
* Most of the country gets rain from the Southwest Monsoon
* the rain is unevenly distributed.
* It is erratic and unpredictable.
* It is seasonal mostly coming in rainy season.
* Monsoon rains have great effect on our economy.

j. Name any two states that receive rain in January – February. What causes this rain?
Punjab, Jammu and Kashmir. Western disturbances originating over the Mediterranean sea causes these
states to receive rainfall.

k. Name the state which experiences the longest monsoon season and another state which has the shortest monsoon season.
Kerala experiences the longest monsoon season. Jammu and Kashmir experiences the shortest monsoon season.

l. Name the two states where “Mango showers’ are common.
Kerala and Karnataka.

m. Much of the Central Maharashtra has only light rainfall. Give reason.
Central Maharashtra has equable climate. So it does not attract South West Monsoon winds.
Secondly, it is not a hilly region which can trap the South West Monsoon.

n. Thar is a desert area. Why?
# The soil contains a high proportion of salts and percentage of organic matter is low.
# Thar does not get much rain because the ‘Aravalli Range’ lies parallel to the direction of winds and so
no condensation occurs. So this region gets less than 25 cm of rainfall per annum.

o. “Loo’ blows over northern and north-western India during the summer season. What is the cause of this ‘Loo’. Give reason.
Because of high temperature in this region low pressure conditions prevail which help the ‘Loo’ to blow.

4.a. How will you differentiate between SW monsoon and NE monsoon?

SOUTH WEST MONSOONS (SUMMER)
NORTH EAST MONSOON (WINTER)
1. They blow during the months of June to September.
They blow during the months of December to February.
2. These cause heavy rainfall almost throughout India.
These cause very less rainfall.
3. These monsoon travel from sea to land.
These monsoon travel from land to sea.
4. These are characterized by oppressive heat and
humidity known as ‘October Heat’.
This is very pleasant season with low temperature,
low humidity and clear skies.

5.a. Name a state which receives rainfall from three different sources and name the three sources of rainfall.
Punjab is the state which receives rainfall from three different sources and the sources are:
a) Northeast Retreating Monsoon
b) Westerly depressions
c) South West Monsoons or cyclonic disturbances originating in the Meditarranean Sea.

b. Mention any two characteristics of winter rainfall in India.
* Winter rainfall is north-western India is due to western disturbances.
* Tamil Nadu receives fair amount of rainfall from N-E monsoons.

c. i) Name the place in India which receives the heaviest rainfall. - MAWSYNRAM

ii) name the state where the place is located. - MEGHALAYA

iii) name the winds which are responsible for this heavy rainfall.- The South West winds coming from the Bay of Bengal branch.

d) What are ‘Western Disturbances’? Name two areas receiving rains from them. What are its importance ?
Western Disturbances are shallow cyclonic depressions originating over Mediterranean sea, disturbing fine
weather conditions in north-western parts of India by little rainfall during winter season.
Punjab and Haryana and Himachal receive rains from the Western Disturbances.
IMPORTANCE: These are highly beneficial to rabi crop especially wheat.

e) Why is it that India gets abundant rainfall and still is a thirsty land?
* All the rain is concentrated during a few months (June – Sep.) of the year.
* Distribution of rainfall is uneven.
* No proper facilities are available to store the rain water.

f. Why is the diurnal range of temperature during summer, greater at Bikaner (Rajasthan) than at
Panjim (Goa)
Bikaner at Rajasthan has very high temperature (45 degree C) due to being located further inland experiences a continental climate or it being an arid region, absence of clouds, the day is hot and night temperatures too low resulting in a great diffence or range.. Whereas Panjim (Goa) is in coastal region, and due to moderating influence of the sea, has lower temperature. (27 degree – 32 degree C)

g. Name any two local winds which blow in India and write briefly about each.
i) Loo – It is the hot and dry wind which blows in the northern plains.
ii) Land breeze – The wind blows in the coastal regions. These blow from land to sea.

h. Write two features of mango showers.
* These are the result of contact between dry and moist air masses.
* These are common towards the close of summer and basically found in Kerala and the coastal areas of
Karnataka.

i. State two differences between tropical cyclones and temperate cyclones.

TEMPERATE CYCLONES
TROPICAL CYCLONES
1
The origin and influence of these cyclones is in the temperate zone due to which they are known as temperate cyclones.
These cyclones originate and travel in the tropical zone and are known as tropical cyclones.
2.
The wind velocity is very low.
The wind velocity is very high.
3.
They are more active in winter season.
They are more active in summer season.
4.
Temperate cyclones are bigger in size.
Tropical cyclones are small in size.
5
Temperate cyclones cause less rain useful for wheat crop.
Tropical cyclones cause heavy rains with more destruction.

j. Name the factors which influence the climate of India or South Asia. Or Why are there great variations in the climate of the Indian subcontinent?
* THE HIMALAYAN MOUNTAIN CHAIN: It protects Indian subcontinent from cold winds of the
Central Asia. It creates barriers before the S-W Monsoon.
* THE LARGE COAST LINE: South India is a Peninsula and has a large coast line. Peninsular
situation has helped it to enjoy maritime climate.
* JET STREAMS: The air currents blowing in upper layer of the atmosphere are known as jet
streams. These help western disturbances to enter into India.
* LOCATION AND VAST EXTENT OF THE COUNTRY: India is a vast country. It is located
between 8 degree 4’ N and 37 degree 6’ latitude and 68 degree 7 ‘ to 97 degree 25’E longitude . India
is divided in almost two equal parts by the Tropic of Cancer.


k. Mention two weather conditions which are associates with the ‘break’ or ‘burst monsoon’. Name two states which are affected by ‘Kal Baisakhi’.
Violent thunder and lightening re associated with ‘break’ or ‘burst’ of monsoons.
Assam and West Bengal are affected by ‘Kal Baisakhi’.

l. What is meant by ‘rain shadow area’? Give two examples of ‘rain shadow’ areas in India.
‘Rain Shadow area’ is an area sheltered by the hills from the prevailing winds and having a lighter rainfall than the windward side of the hills.
i) Bangalore ii) Shillong

m. Name one part of India that receives rainfall both in the winter and summer.
Punjab – In winter, Punjab gets rainfall from western disturbances and in summer from South West monsoons.

n. What is the general direction of prevailing winds over the Indian Sub continent in April – May and in July?
IN April – May – N-E Trade Winds , IN July – South West Monsoon

o. Name the place in India which receives the heaviest rainfall. Name the state and the winds which are
responsible for this heavy rainfall.
Mawsynram receives the heaviest rainfall. It is in Meghalaya. They Bay of Bengal branch of South West monsoon winds are responsible for this heavy rainfall.

p. How are the sources of rainfall in the north-west part of India different from the rainfall experienced on the coastal area of eastern India in winter?
In the North-West part of India winter rainfall is brought by ‘Western Disturbances’ which originate in the Mediterranean sea.
The coastal area of Eastern India gets rainfall from North – East trade winds which picks moisture from the Bay of Bengal.

q. Name the season during which the North East Trade Winds dominate the Indian subcontinent? In which season do the above mentioned winds get completely reversed? Name the four months covered by this season.
The North East trade winds dominate the India subcontinent during cold weather season. (Dec to Feb)
The North East trade winds get completely reversed during summer season. Four months covered by this season are June, July, August and September.

r. Name the region in India which receives rainfall from the Western Disturbances. State the importance of this rainfall.
During the winter season because of low temperature, pressure is sufficiently high in the North-Western part of India. On the Southern India, there is low pressure. Light winds with a low velocity (5 km) begin toblow from North – West to Southern part. The system of pressure and winds is disturbed as a result of the inflow of shallow cyclonic depressions from the West and the North-West which originate from the Mediterranean Sea. These low pressure depressions are called Western Disturbances. Due to Western disturbances, the moisture content of the wind gets augmented from Caspian and Persian Gulf. These cause rainfall in Punjab and Himachal Pradesh.
The rain is highly beneficial to Rabi crop especially wheat.

s. What is meant by ‘the season of retreating monsoon’? Name the months of retreating monsoons. Explain how these winds are different from the north-east Trades?
The withdrawal of south-west monsoons in the months of October to November is called the season of retreating monsoon.
These are the same winds of summer which come back due to the migration of the sun. North-east trade winds return between the months of December to February when north-western part becomes cold and winds give rainfall on Tamilnadu coast after collecting moisture from Bay of Bengal.

6. a. What is meant by ‘Kal Baisakhi’?
Kal Baisakhi are local thunderstorm experienced in the month of Baisakh (april) in West Bengal.

b. Name two states which receive rain in January and February.
Tamilnadu and Andhra Pradesh, Jammu and Kashmir receive rain in Jan and Feb.

c. What causes the winter rain? How does the winter rain benefit agriculture in the area?
North-Eastern winds while passing over the Bay of Bengal pick up moisture and cause rain on the south-eastern coast of India.
The winter rain is beneficial for rice and millet crops in Tamilnadu and for Rabi crops in Punjab.

d. What is the cause or reason for the winter rain in northern India.
* Northern India receives rainfall due to western disturbances, originated over the Mediterranean Sea.
* In Tamil Nadu the northeast monsoon winds pick up moisture from the Bay of Bengal and bring rain.

e. Under what rainfall conditions are the Tropical Rain forests found?
They are found in those regions having rainfall more than 200 cm.

f. India is considered a subcontintent. Give two reasons.
India is considered a Subcontinent because :
· India is a part of Asia from which it is separated by the Great Himalayas.
· It is a large, relatively self contained land mass forming a part of Asia.
· It has varied vegetation and climate of its own. It has tropical monsoon climate.

g. Which wind is responsible for the rainfall experienced over the greater part of the Subcontinent? During which part of the year is this rainfall experienced? Why does Coromandel coast receive most of its rain during winter?
Wind responsible for the rainfall experienced over the greater part of the subcontinent is South West Arabian Sea branch of the monsoon.
They experience the above rainfall during June-September.
The northeast monsoon winds blow over the Bay of Bengal. Before reaching the Coromandel Coast they become moisture laden and give rain to this area during winter season. (Dec-Jan)

h. What is the general direction of prevailing winds over the Indian subcontinent?
i) in April-May - the direction is north east
ii) In July - the direction is southwest to northeast.

i) Why does the most of central Maharashtra have only light rainfall?
Most of central Maharasthtra has only light rainfall because it lies in the rain shadow area of the Western Ghats.

j. What are there great variations in climate of the Indian subcontinent?
There are great variations in the climate due to:
· the vast latitudinal expanse
· the varied topographical features
· size of the land
· distance from the sea.

k. A cricket match at Chennai from Oct 24 to 28 had to be abandoned because of bad weather. As a student of geography provide an explanation for this happening. Ensure that your explanation provides the technical name of this seasonin India, the atmospheric pressure conditions over the Bay of Bengal during this part of the year and the typical rainfall regime experienced in Chennai city.
The technical name of the season is ‘the season of retreating monsoon’/’northeast monsoon’.
The atmospheric condition over Bay of Bengal during this season is very unstable causing severe cyclones or it can be a low pressure area too.
The months of October and November are the rainiest months.

l. Name the seasons during which the northeast trade winds dominate the Indian subcontinent. In which season do the above mentioned winds get completely reversed? Name the four months of this season.
The season during which these winds dominate are winter/summer.
During the Southwest Monsoon season, the winds get reversed. The four months are June, July, August and September.
m. Name the state which receives rainfall from three different sources and name the three sources of rainfall.
Punjab is the state that receives rainfall from three different sources and the sources are:
· Northeast Retreating Monsoons
· Westerly depressions
· Southwest Monsoons or cyclonic disturbances originating in the Mediterranean Sea.

n. Give two reasons why India is considered a Subcontinent?
The two reasons for India being considered a Subcontinent are:-
India is a part of Asia from which it is separated by the great Himalayas
It is a large, relatively self-contained landmass forming a part of Asia.
It has a varied vegetation and climate of its own.
NEPAL

7.a. Parts of Nepal experience the Arctic type of climate.
Most parts of Nepal is located at height altitude, the height more than 6000 metres above the sea level.

b) “The latitude of Nepal usually denotes a tropical climate but there are notable regional differences.’ Give two reasons.
* The regional differences are due to difference in altitude.
* Precipitation decreases from east to west.
* Direction of wind is also responsible because the southern slopes are more humid, since the Shiwalik
and Mahabharat ranges act as a barrier.

c) The southern slopes of Nepal are more humid. Give reason.
The southern slopes are more humkid since the Shiwalik and the Mahabharat ranges act as barrier, preventing the humid winds from reaching the Great Himalayas and Trans-Himalayas.

d. Briefly explain about the climate of Nepal?
The climate of Nepal varie with regions respectively. The greater Himalayan region having very harsh climte with chilly and long winters and short summers.
In the middle Himalayan region, the climate is cold and moderately dry in winter. It is cool during summer with heavy rainfall.
The Outer Himalayas have warm and humid climate. It experiences the monsoon which causes considerable rain in summer.


BANGLADESH

8A.. Mention two features of the climate of Bangladesh. (2)
* Bangladesh has tropical monsoon type of climate. It is generally warm and humid throughout
the year.
· It receives heavy rainfall of over 200 cm annually from South-West monsoons.

b. Mention any two characteristics of the climate of Bangladesh. * Bangladesh has tropical monsoon climate with hot and humid weather almost throughout the year.
* 75% of the rain is brought by the South West monsoons, often causing floods.

c. When are cyclonic storms experienced in Bangladesh?
Cyclonic storms in Bangladesh are experienced during April-June and October-November.




PAKISTAN
9. a. State two characteristics of the monsoon climate. Why is Pakistan not greatly influenced by this type of
climate?
* The Monsoon are periodic seasonal winds.
* Most of the rainfall is received between 100 – 120 days.
Pakistan is not much influenced by the monsoon winds because:
# Plains do not get much rain as there are no mountain barrier against the direction of the moisture
laden winds.
# The monsoon winds get exhausted by the time they reach Pakistan and thus the western part of
Pakistan remains dry.

b) Which South Asian country is the last to receive the South-West monsoon? Why the country receives scanty rainfall? or “Arid conditions prevail inmost of Pakistan.” Give two reasons for this.
Pakistan
*Pakistan receives scanty rainfall because it is located in the western limits of the monsoon regions, monsoons progressively lose moisture and are dry when they arrive at the Satluj valley of the Indus.
* The rainfall occurs predominantly in late summer and the moisture quickly evaporates due to high temperature.


c) Compare the climatic conditions of Bangladesh with Pakistan.


CLIMATE OF BANGALADESH
CLIMATE OF PAKISTAN
1
It has tropical monsoonal climate.
It has arid and semi arid type of climate.
2.
Most parts receive very heavy rainfall.
Most parts receives very low rainfall.
3.
Some parts of the country receives rainfall from Western disturbances.
It does not receive rainfall from Western disturbances.


d. Pakistan does not receive much rainfall from the South West Monsoon, Give reason.
Pakistan does not receive much rainfall from the South West Monsoon because it is located at the western limits of the monsoon region and the monsoon progressively lose moisture and are dry when they arrive at the Satluj Valley of the Indus.
Plains do not get much rain as there are no mountain barrier against the direction of the moisture laden winds.

e. Pakistan has scanty vegetation. Give reasons.
* In most parts of Pakistan the climate is predominantly dry with extreme temperatures.
* Most parts of Pakistan receive very less rainfall as Pakistan is located at the western limits of the
monsoon region.
* The rainfalls predominantly in late summer and quickly evaporates due to high temperature.

f. Precipation is rare in Sind or Most of the Pakistan is predominantly dry. Give reason.
* Most parts of Pakistan receive rainfall from South-West monsoon but it is located at the western limits
of the monsoon regions; monsoon progressively lose moisture and are dry when they arrive at the
valley of the Indus.
* The plains also do not get much rain. There is no mountain barrier against the direction of wind.
* Baluchistan is arid barren plateau with high temperature, so it receives very less rainfall.

g. Mention two differences between the cyclonic rain in Bangladesh and the cyclonic rain in Pakistan.

CYCLONIC RAIN IN BANGLADESH
CYCLONIC RAIN IN PAKISTAN
1
Cyclonic rain occur in summer.
Cyclonic rain occur in winter.
2.
The rainfall of Bangladesh occur because of tropical cyclone which originate Bay of Bengal and Arabian Sea.
The rainfall of Pakistan occur due to western disturbances which originate from the Mediterranean sea.


MALDIVES

10.a. Which SAARC country is the first to receive the South West Monsoons? Give a reason.
Maldives. Because it is close to equator. The South-East trade winds are of oceanic origin. Coming from the Indian Ocean, they cross the Equator and enter Maldives.

b. Write any two characterictics of Maldives’ climate.
* Maldives have a tropical climate with two seasons and a consistent temperature ranging from 25
degree C to 30 degree C.
* Maldives receives abundant precipitation during rainy season from the south-west summer monsoon.


SRI LANKA

11A. Most of Sri Lanka has the Equatorial type of climate. Give reason.
Most of Sri Lanka has the equatorial type of climate because it is near the equator and surrounded by
sea from all sides..

b. Why does Sri Lanka experience a hot and humid climate throughout the year?
* Sri Lanka is situated near the Equator and receives direct sun rays throughout the year.
* It receives rainfall throughout the year with high temperature. It receives rainfall both from North-
West and South-East trade winds.


c. What type of climate prevails in Sri Lanka?
Sri Lanka has equatorial or tropical type of climate.

d. Which region of Sri Lanka receives more rainfall. Give reason.
South Western parts receive more rainfall. The region receives heavy rainfall from the South-West monsoon for nearly for four months.

e. Why northern region of Sri Lanka receives less rainfall?
Northern region of Sri Lanka receives less rainfall because it lies in the dry zone. The region receives most of the rainfall from north-east monsoon which is a land wind and causes less rainfall. This monsoon, being a land wind, has lost most of its rain content by the time it arrives in Sri Lanka.

f. Sri Lanka receives rainfall throughout the year. Why?
Sri Lanka receives rainfall from ‘Great Monsoon as well as from ‘Small Monsoon’. ‘Great Monsoon’ (South West Monsoon) rains from May to late August where as ‘Small Monsoon’ (North-East Monsoon) rains from November to December.


Climate

Climate: 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).

Weather: Weather refers to the state of the atmosphere over an area at any point of time.

The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation. The weather conditions fluctuate very often even within a day. But there is some common pattern over a few weeks or months, i.e. days are cool or hot, windy or calm, cloudy or bright, and wet or dry. On the basis of the generalized monthly atmospheric conditions, the year is divided into seasons such as winter, summer or rainy seasons.

Monsoon

The climate of India is described as the ‘monsoon’ type. The word monsoon is derived from the Arabic word ‘mausim’ which literally means season. ‘Monsoon’ refers to the seasonal reversal in the wind direction during a year.

This type of climate is found mainly in the south and the Southeast Asia. Despite an overall unity in the general pattern, there are perceptible regional variations in climatic conditions within the country. In summer, the mercury occasionally touches 50°C in some parts of the Rajasthan desert, whereas it may be around 20°C in Pahalgam in Jammu and Kashmir. On a winter night, temperature at Drass in Jammu and Kashmir may be as low as minus 45°C. Tiruvananthapuram, on the other hand, may have a temperature of 20°C. In certain places.

There are variations not only in the form and types of precipitation but also in its amount and the seasonal distribution. While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country. The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan. Most parts of the country receive rainfall from June to September. But some parts like the Tamil Nadu coast get most of its rain during October and November. In general, coastal areas experience less contrasts in temperature conditions. Seasonal contrasts are more in the interior of the country. There is decrease in rainfall generally from east to west in the Northern Plains. These variations have given rise to variety in lives of people – in terms of the food they eat, the clothes they wear and also the kind of houses they live in.

CLIMATIC CONTROLS

There are six major controls of the climate of any place. They are:

1. Latitude

2. Altitude

3. Pressure and wind system

4. Distance from the sea

5. Ocean currents and

6. Relief features

FACTORS AFFECTING INDIA’S CLIMATE

Latitude: The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh in the west to Mizoram in the east. Almost half of the country, lying south of the Tropic of Cancer, belongs to the tropical area. All the remaining area, north of the Tropic, lies in the sub-tropics. Therefore, India’s climate has characteristics of tropical as well as subtropical climates.

Altitude: India has mountains to the north, which have an average height of about 6,000 metres. India also has a vast coastal area where the maximum elevation is about 30 metres. The Himalayas prevent the cold winds from Central Asia from entering the subcontinent. It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to central Asia.

Pressure and Winds: The climate and associated weather conditions in India are governed by the following atmospheric conditions:

Pressure and surface winds;

Upper air circulation; and

Western cyclonic disturbances and tropical cyclones.

India lies in the region of north easterly winds. These winds originate from the subtropical high-pressure belt of the northern hemisphere. They blow south, get deflected to the right due to the Coriolis force, and move on towards the equatorial low-pressure area. Generally, these winds carry very little moisture as they originate and blow over land. Therefore, they bring little or no rain. Hence, India should have been an arid land, but, it is not so.

The pressure and wind conditions over India are unique. During winter, there is a high-pressure area north of the Himalayas. Cold dry winds blow from this region to the low-pressure areas over the oceans to the south. In summer, a low-pressure area develops over interior Asia as well as over northwestern India. This causes a complete reversal of the direction of winds during summer. Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator, and turns right towards the low-pressure areas over the Indian subcontinent. These are known as the Southwest Monsoon winds. These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the mainland of India. The upper air circulation in this region is dominated by a westerly flow. An important component of this flow is the 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. In summer, the subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun. An easterly jet stream, called the tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer months.

THE INDIAN MONSOON

The climate of India is strongly influenced by monsoon winds. The sailors who came to India in historic times were one of the first to have noticed the phenomenon of the monsoon. They benefited from the reversal of the wind system as they came by sailing ships at the mercy of winds. The Arabs, who had also come to India as traders named this seasonal reversal of the wind system ‘monsoon’. The monsoons are experienced in the tropical area roughly between 20° N and 20° S. To understand the mechanism of the monsoons, the following facts are important.

(a) 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.

(b) 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 monsoon trough during the monsoon season).

(c) 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.

(d) 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.

(e) 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.

Apart from this, it has also been noticed that changes in the pressure conditions over the southern oceans also affect the monsoons. Normally when the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. But in certain years, there is a reversal in the pressure conditions and the eastern Pacific has lower pressure in comparison to the eastern Indian Ocean. This periodic change in pressure conditions is known as the Southern Oscillation or SO. The difference in pressure over Tahiti (Pacific Ocean, 18°S/149°W) and Darwin in northern Australia (Indian Ocean, 12°30’S/131°E) is computed to predict the intensity of the monsoons. If the pressure differences were negative, it would mean below average and late monsoons. A feature connected with the SO is the El Nino, a warm ocean current that flows past the Peruvian Coast, in place of the cold Peruvian current, every 2 to 5 years. The changes in pressure conditions are connected to the El Nino. Hence, the phenomenon is referred to as ENSO (El Nino Southern Oscillations).

THE ONSET OF THE MONSOON AND WITHDRAWAL

Onset: The Monsoon, unlike the trades, are not steady winds but are pulsating in nature, affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas. The duration of the monsoon is between 100- 120 days from early June to mid-September. Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days. This is known as the ‘burst’ of the monsoon, and can be distinguished from the pre-monsoon showers. The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. Subsequently, it divides into two – the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10th of June. This is a fairly rapid advance. The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June. The lofty mountains causes the monsoon winds to deflect towards the west over the Ganga plains. By mid-June the Arabian Sea branch of the monsoon arrives over Saurashtra-Kuchchh and the central part of the country. The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains. Delhi generally receives the monsoon showers from the Bay of Bengal branch by the end of June (tentative date is 29th of June). By the first week of July, western Uttar Pradesh, Punjab, Haryana and eastern Rajasthan experience the monsoon. By mid-July, the monsoon reaches Himachal Pradesh and the rest of the country.

Withdrawal: Withdrawal or the retreat of the monsoon is a more gradual process . The withdrawal of the monsoon begins in northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. The withdrawal from the southern half of the peninsula is fairly rapid. By early December, the monsoon has withdrawn from the rest of the country. The islands receive the very first monsoon showers, progressively from south to north, from the first week of April to the first week of May. The withdrawal, takes place progressively from north to south from the first week of December to the first week of January. By this time the rest of the country is already under the influence of the winter monsoon.

THE SEASONS

The monsoon type of climate is characterized by a distinct seasonal pattern. The weather conditions greatly change from one season to the other. These changes are particularly noticeable in the interior parts of the country. The coastal areas do not experience much variation in temperature though there is variation in rainfall pattern. Four main seasons can be identified in India – the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon with some regional variations.

The Cold Weather Season (Winter)

The cold weather season begins from mid- November in northern India and stays till February. December and January are the coldest months in the northern part of India. The temperature decreases from south to the north. The average temperature of Chennai, on the eastern coast, is between 24° - 25° Celsius, while in the northern plains, it ranges between 10° - 15° Celsius. Days are warm and nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall. During this season, the northeast trade winds prevail over the country. They blow from land to sea and hence, for most part of the country, it is a dry season. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as, here they blow from sea to land. In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area. Influenced by the relief, these winds blow through the Ganga valley from the west and the northwest. The weather is normally marked by clear sky, low temperatures and low humidity and feeble, variable winds. A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances from the west and the northwest. These low-pressure systems, originate over the Mediterranean Sea and western Asia and move into India, along with the westerly flow. They cause the much-needed winter rains over the plains and snowfall in the mountains. Although the total amount of winter rainfall locally known as ‘mahawat’ is small, they are of immense importance for the cultivation of ‘rabi’ crops. The peninsular region does not have a welldefined cold season. There is hardly any noticeable seasonal change in temperature pattern during winters due to the moderating influence of the sea.

The Hot Weather Season (Summer)

Due to the apparent northward movement of the sun, the global heat belt shifts northward. As such, from March to May, it is hot weather season in India. The influence of the shifting of the heat belt can be seen clearly from temperature recordings taken during March-May at different latitudes. In March, the highest temperature is about 38° Celsius, recorded on the Deccan plateau. In April, temperatures in Gujarat and Madhya Pradesh are around 42° Celsius. In May, temperature of 45° Celsius is common in the northwestern parts of the country. In peninsular India, temperatures remain lower due to the moderating influence of the oceans. The summer months experience rising temperature and falling air pressure in the northern part of the country. Towards the end of May, an elongated low-pressure area develops in the region extending from the Thar Desert in the northwest to Patna and Chotanagpur plateau in the east and southeast. Circulation of air begins to set in around this trough. A striking feature of the hot weather season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day over the north and northwestern India. Sometimes they even continue until late in the evening. Direct exposure to these winds may even prove to be fatal. Dust storms are very common during the month of May in northern India. These storms bring temporary relief as they lower the temperature and may bring light rain and cool breeze. This is also the season for localised thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail. In West Bengal, these storms are known as the ‘Kaal Baisakhi’ calamity for the month of Baisakh. Towards the close of the summer season, pre-monsoon showers are common especially, in Kerala and Karnataka. They help in the early ripening of mangoes, and are often referred to as ‘mango showers’.

Advancing Monsoon (The Rainy Season)

By early June, the low-pressure condition over the northern plains intensifies. It attracts, the trade winds of the southern hemisphere. These south-east trade winds originate over the warm subtropical areas of the southern oceans. They cross the equator and blow in a southwesterly southwesterly direction entering the Indian peninsula as the south-west monsoon. As these winds blow over warm oceans, they bring abundant moisture to the subcontinent. These winds are strong and blow at an average velocity of 30 km per hour. With the exception of the extreme north-west, the monsoon winds cover the country in about a month. The inflow of the south-west monsoon into India brings about a total change in the weather. Early in the season, the windward side of the Western Ghats receives very heavy rainfall, more than 250 cm. The Deccan Plateau and parts of Madhya Pradesh also receive some amount of rain in spite of lying in the rain shadow area. The maximum rainfall of this 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. Another phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall. Thus, it has wet and dry spells. In other words, the monsoon rains take place only for a few days at a time. They are interspersed with rainless intervals. These breaks in monsoon are related to the movement of the monsoon trough. For various reasons, the trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall. When the axis of the monsoon trough lies over the plains, rainfall is good in these parts. On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains, and widespread rain occur in the mountainous catchment areas of the Himalayan rivers. These heavy rain bring in their wake, devastating floods causing damage to life and property in the plains. The frequency and intensity of tropical depressions too, determine the amount and duration of monsoon rains. These depressions form at the head of the Bay of Bengal and cross over to the mainland. The depressions follow the axis of the “monsoon trough of low pressure”. The monsoon is known for its uncertainties. The alternation of dry and wet spells vary in intensity, frequency and duration. While it causes heavy floods one part, it may be responsible for droughts in the other. It is often irregular in its arrival and its retreat. Hence, it sometimes disturbs the farming schedule of millions of farmers all over the country.

Retreating Monsoon (The Transition Season)

During October-November, with the apparent movement of the sun towards the south, the monsoon trough or the low-pressure trough over the northern plains becomes weaker. This is gradually replaced by a high-pressure system. The south-west monsoon winds weaken and start withdrawing gradually. By the beginning of October, the monsoon withdraws from the Northern Plains. The months of October-November form a period of transition from hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and rise in temperature. While day temperatures are high, nights are cool and pleasant. The land is still moist. Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day. This is commonly known as ‘October heat’. In the second half of October, the mercury begins to fall rapidly in northern India. 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. These cyclones generally cross the eastern coasts of India cause heavy and widespread rain. These tropical cyclones are often very destructive. The thickly populated deltas of the Godavari, the Krishna and the Kaveri are frequently struck by cyclones, which cause great damage to life and property. Sometimes, these cyclones arrive at the coasts of Orissa, West Bengal and Bangladesh. The bulk of the rainfall of the Coromandel Coast is derived from depressions and cyclones.

DISTRIBUTION OF RAINFALL

The western coast and northeastern India receive over about 400 cm of rainfall annualy. However, it is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Rainfall is equally low in the interior of the Deccan plateau, and east of the Sahyadris. Why do these regions receive low rainfall? A third area of low precipitation is around Leh in Jammu and Kashmir. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region. Owing to the nature of monsoons, the annual rainfall is highly variable from year to year. Variability is high in the regions of low rainfall such as parts of Rajasthan, Gujarat and the leeward side of the Western Ghats. As such, while areas of high rainfall are liable to be affected by floods, areas of low rainfall are drought-prone.

MONSOON AS A UNIFYING BOND

Himalayas protect the subcontinent from extremely cold winds from central Asia. This enables northern India to have uniformly higher temperatures when compared to other areas on the same latitudes. Similarly, the peninsular plateau, under the influence of the sea from three sides, has moderate temperatures. Despite such moderating influences, there are great variations in the temperature conditions. Nevertheless, the unifying influence of the monsoon on the Indian subcontinent is quite perceptible. The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons. Even the uncertainties of rain and uneven distribution are very much typical of the monsoons. The Indian landscape, its animal and plant life, its entire agricultural calendar and the life of the people, including their festivities, revolve around this phenomenon. Year after year, people of India from north to south and from east to west, eagerly await the arrival of the monsoon. These monsoon winds bind the whole country by providing water to set the agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.

Key Terminologies

Coriolis force: An apparent force caused by the earth’s rotation. The Coriolis force is responsible for deflecting winds towards the right in the northern hemisphere and towards the left in the southern hemisphere. This is also known as ‘Ferrel’s Law’.

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

Western Cyclonic Disturbances: The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region. They usually influence the weather of the north and north-western regions of India. Tropical cyclones occur during the monsoon as well as in October - November, and are part of the easterly flow. These disturbances affect the coastal regions of the country.

Inter Tropical Convergence Zone: The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes. This is where the northeast and the southeast trade winds converge. This convergence zone lies more or less parallel to the equator but moves north or south with the apparent movement of the sun.

El Nino: This is a name given to the periodic development of a warm ocean current along the coast of Peru as a temporary replacement of the cold Peruvian current. ‘El Nino’ is a Spanish word meaning ‘the child’, and refers to the baby Christ, as this current starts flowing during Christmas. The presence of the El Nino leads to an increase in sea-surface temperatures and weakening of the trade winds in the region.


13 comments:

Joydeep said...

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anuj said...
This comment has been removed by the author.
hiten said...

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