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02-03-2015 R. Ezhilraman, PGT-Social Science
1
What is Climate?
Climate is the characteristic condition of the
atmosphere near the earth's surface at a certain
place on earth.
It refers to the sum total of weather conditions and
variation over a large area for a long period of time.
It is the long-term weather of that area which
remains at least 30 years.
02-03-2015 R. Ezhilraman, PGT-Social Science 2
Weather refers to the state of
atmosphere over an area at
any point of time. The
elements of both weather
and climate are same. It is the
combination of temperature,
humidity, precipitation, wind,
cloudiness and other
atmospheric conditions at a
specific time.
What is Weather?
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Monsoon
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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.
The World is divided into a number of Climatic Regions. The
Climate of India is described as the ‘monsoon’ type. This type
of climate is found in South and Southeast Asia. But, there are
perceptible regional variations in climatic conditions within
the country.
Two important elements viz., temperature and precipitation,
often vary from place to place and season to season.
Difference in Temperature
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In summer, the temperature in parts of Rajasthan Desert
is 50°C, and it is around 20°C in Pahalgam in J & K. On
a winter night, temperature at Drass in J & K may less
than -45°C, and at Tiruvananthapuram it may be of
22°C.
In some places temperature between day and
night temperature differs. In the Thar Desert, it rise to
50°C, in day and drop down to near 15°C in night. But
in the Andaman and Nicobar islands or in Kerala, there
is no much difference in day and night temperatures.
Precipitation
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Precipitation varies in its form, types and amount and
seasonal distribution. It is in the form of snowfall in the
upper parts of Himalayas, it rains over the rest of the
country. The annual precipitation varies from 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 Tamil Nadu coast gets rain during
October and November.
Rainfall generally decrease from east to west in the
Northern Plains. These variations have given rise to
variety in lives of people, their food, clothes and houses.
Vegetation
Vegetation can affect both temperature and
the precipitation patterns in an area.
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FACTORS AFFECTING CLIMATE
RELATED TO LOCATION
RELATED TO AIR
PRESSURE & WIND
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Latitude
Latitude is the
equator and
distance a place
lies north or
south of the
is
called lines
measured by an
imaginary line
of
latitude.
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EQUATORIAL REGION
LATITUDE
High range
of Temp
High Temp
Low range
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Latitude
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 As latitude increases, the intensity of solar energy
decreases. Due to curvature of the Earth, the
amount of solar energy varies according to latitude.
 In India, 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.
Tropical, Temperate and Polar Zones
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‱ The tropical zone is between 23.5o north (the tropic of
Cancer) and 23.5o
south (the tropic of Capricorn) of the
Equator. The Sun’s rays are most intense and the
temperatures are always warm.
‱ The temperate zones are between 23.5o and 66.5o
north and between 23.5o and 66.5o south of the
Equator. The Sun’s rays strike Earth at a smaller angle
than near the Equator.
‱ Polar zones are between 66.5o north and south
latitudes and the poles. The sun’s rays strike Earth at a
very small angle in the polar zones.
Highland Climates
In general, highland climates are cooler and wetter than
nearby areas at lower elevations.
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Earth’s Major Climate Zones
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North Frigid Zone
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Temperate Zone
Temperate Zone
South Frigid Zone
Torrid Zone
AGRA
160C in Jan
DARJILING
40C in January
ALTITUDE
HIGH ALTITUDE
LOW ALTITUDE
Temperature decreased from low to high altitude
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Air Temperature decreases with altitude.
As elevation increases, the air gets cooler because of
the energy drawn from the surroundings.
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Factors That Affect Climate
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 Water Bodies
Large bodies of water such as lakes and oceans have an
important effect on the temperature of an area because
the temperature of the water body influences the
temperature of the air above it.
 Atmospheric Circulation
Global winds are another factor that influences climate
because they distribute heat and moisture around Earth.
 Solar Activity
When the Sun is most active, it contains dark blemishes
called sunspots. The formation of sunspots appears to
correspond with warm periods in Europe and North
America.
 Earth Motions
Geographic changes in Earth’s land and water bodies
cause changes in climate. Changes in the shape of
Earth’s orbit and the tilt of Earth on its axis are other
Earth motions that affect global climates.
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Natural Processes That Change Climates
Human Impact on Climate Changes
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 The Greenhouse Effect
The greenhouse effect is a natural warming of both
Earth’s lower atmosphere and Earth’s surface from solar
radiation being absorbed and emitted by the
atmosphere.
 Global Warming
As a result of increased levels of carbon dioxide and
other greenhouse gases, global temperatures have
increased. This increase is called global warming.
The Pressure and Surface Winds
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The pressure and wind system of any area depend on the latitude
and altitude of the place. It influences the temperature and rainfall
pattern.
The climate and weather conditions in India are governed by the
atmospheric conditions like:
‱ Pressure and surface winds;
‱ Upper air circulation; and
‱ Western cyclonic disturbances and tropical cyclones.
India lies in the north easterly winds region. 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 towards equatorial low-pressure area.
NORTH-EAST
TRADE WIND
SOUTH-EAST
TRADE WIND
INTER TROPICAL CONVERGENCE ZONE
SUB TROPICAL HIGH PRESSURE
SUB TROPICAL HIGH PRESSURE
SUB TROPICAL LOW PRESSURE
SUB TROPICAL LOW PRESSURE
POLAR HIGH
POLAR HIGH
SURFACE WIND
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AIR MASSES CIRCULATE GLOBALLY
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‱ At the Equator, temperatures are relatively
high. Land and water masses heat up and as a
result these warm the air over them.
‱ Air heated at the equatorial region rises to
the top of the atmosphere.
‱ More air rising beneath it forces the air mass
to spread north and south toward the poles.
Coriolis Effect
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‱ The rotation of the Earth causes all moving
objects in the Northern Hemisphere,
including air mass, to deflect to the right and
those in the Southern Hemisphere to move to
the left.
‱ This Coriolis effect is absent at the Equator.
‱ Coriolis Force- prevents a direct simple flow
from the Equator to the Poles.
‱ This is also known as ‘Ferrel’s Law’.
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The Pressure and Surface Winds in India
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The pressure and wind conditions in India is unique. During winter,
there is a high-pressure in the 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 and in north-western 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.
ARABIAN
SEA
BAY OF
BENGAL
INDIAN OCEAN
LOW AND HIGH PRESSURE
HIGH PRESSURE
IN WINTER
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CHENNAI
SIMLA
DELHI
KOLKOTA
MUMBAI
DISTANCE FROM SEA
Coastal areas have equable climate where
as Interior parts have extreme climate.
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Relief
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‱ Relief too plays a major role in determining
the climate of a place. High mountains act
as barriers for cold or hot winds; they may
also cause precipitation if they are high
enough and lie in the path of rain-bearing
winds. The leeward side of mountains
remains relatively dry.
Receives high
rainfall
Receives low
rainfall
RELIEF
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RELIEF
The Rain Shadow Effect
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Jet Stream
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‱ The upper air circulation in India is dominated
by a westerly flow, known as the 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.
‱ Many jet streams have been identified. The
most constant are the mid-latitude and the sub
tropical jet stream.
TIBET
JET STREAM IN WINTER
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Jet Stream
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Jet streams are located at 27°-30° north latitude, 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
easterly jet stream, called the
stream blows over peninsular
tropical
India,
approximately over 14°N during the summer.
JET STREAM IN SUMMER
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Western Disturbances
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‱ 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.
‱ Thus very often the coast of Orissa and Andhra Pradesh
are affected by those disasters.
WESTERN DISTURBANCE
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OCEAN CURRENTS
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Solar energy, wind, and Earth’s rotation creates Ocean currents
Current- the systematic patters of water movement.
Gyres- two great circular water motion.
 Northern Hemisphere- the ocean current moves clockwise.
 Southern Hemisphere- the ocean current move anti-clockwise.
 Trade winds push warm surface waters westward at the equator.
 As the waters encounter the continents, they split into north-
and south-flowing currents along the eastern coast, forming
north and south gyres.
Surface Water blown by the winds at point A will weirs to the
right of its initial path and continue eastward. Water at point
B weirs to the right and continues westward.
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Winds driven by uneven solar heating and Earth’s spin, drive the
movement of the ocean’s surface currents. The prime movers are the
powerful westerlies and the persistent trade winds (easterlies)
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 The Köppen climate classification system uses
mean monthly and annual values of temperature and
precipitation to classify climates.
 According to the Köppen classification, the earth can be
divided into several major climatic zones and bands:
The Köppen Climate Classification System
 Tropical climate
 Subtropical climate
 Arid climate
 Equatorial climate
 Semiarid climate
 Mediterranean climate
 Temperate climate
 Oceanic climate
 Continental climate
 Subarctic climate
 Polar climate
 Climate of Antarctica
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Polar Climate
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Polar climates are those in which the mean temperature
of the warmest month is below 10o
C.
The Indian Monsoon
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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’.
Atmospheric Conditions over the Indian Subcontinent
in the Month of January
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Atmospheric Conditions over the Indian Subcontinent
in the Month of June
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Facts of Mechanism of the Monsoons
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In India, the monsoons are experienced in the tropical area
roughly between 20°N and 20°S. The Following facts are the
Mechanism of the Monsoons.
(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. It is also
known as the monsoon-trough during the monsoon season).
Inter Tropical Convergence Zone (ITCZ)
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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.
Facts of Mechanism of the Monsoons
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(c)The presence of the high-pressure area, east of
Madagascar, nearly at 20°S over the Indian Ocean. The
intensity of this high-pressure area affects the Indian
Monsoon.
(d)The Tibetan plateau gets intensely heated during
summer, results in strong vertical air currents and the
formation of low 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.
Southern Oscillation
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The changes in the pressure conditions over the southern
oceans also affect the monsoons. When the tropical eastern south
Pacific Ocean experiences high pressure, the tropical eastern Indian
Ocean experiences low pressure. But sometimes, 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 in Pacific Ocean and Darwin in
northern Australia of Indian Ocean is predicted 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).
Darwin
Tahiti
SOUTHERN OSCILLATION
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Effect of El Niño
El Nino 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.
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Homboldt Cold
Current
EL-NINO EFFECTS
1990
Delay in
Monsoon
Equatorial Warm
Current
El-Nino
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Beginning of the Monsoon
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The duration of the monsoon is between 100-120 days from
early June to mid-September.
During 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 proceeds into two –
(i) the Arabian Sea branch and
(ii) the Bay of Bengal branch.
Beginning of the Monsoon
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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
north-western 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 July
first week, 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.
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End of the Monsoon
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Withdrawal or the retreat of the monsoon is a more gradual
process. The withdrawal of the monsoon begins in north-western
states of India by early September. By mid-October, it withdraws
completely from the northern half of the peninsula. Then it
quickly withdraw from the southern half of the peninsula. By
early December, the monsoon has totally withdrawn from the
country.
The islands receive the very first monsoon showers, from south to
north, between the last week of April and the first week of May.
Then it withdraw from north to south during the first week of
December to the first week of January. By this time, the other
parts of the country is already influencing the winter monsoon.
02-03-2015 R. Ezhilraman, PGT-Social Science 61
RHYTHM OF SEASONS
COLD WEATHER
RETREATING MONSOON
HOT WEATHER
SOUTH WEST MONSOON
Let us discuss each of them individually
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76
The monsoon type of climate is characterised 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. But, the coastal areas do not
experience much variation in temperature though there is variation
in rainfall pattern.
In India, Four main seasons can be identified:
(i) the cold weather season,
(ii)the hot weather season,
(iii)the advancing monsoon and
(iv) the retreating monsoon with some regional variations.
COLD WEATHER SEASON
â–șIt extends from
December to February.
rays shift
southern
â–șVertical sun
towards
hemisphere.
â–șNorth India experiences
intense cold where as
this season is not well
defined in south India.
â–șLight wind blow makes
this season pleasant in
south India.
â–șOccasional tropical
cyclone visit eastern
coast in this season.
Tropical Cyclone
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78
The cold weather season begins from mid- November in northern India and
stays till February. December and January are the coldest months. 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 winter, the northeast trade winds blow from land to sea. So, most part of
the country faces a dry season. Some amount of rainfall occurs on the Tamil
Nadu coast from these winds as, trade winds 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.
250
C
200
C 200
C
200
C
250
C
150
C
200
C
100
C`
TEMPERATURE- JANUARY
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PRESSURE- JANUARY
101
4
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HIGH
PRESSURE
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In the northern plains, there is the inflow of cyclonic
disturbances from the west and the northwest. These low-
pressure systems, from the Mediterranean Sea and western
Asia and move into India, along with the westerly flow. They
cause the winter rains (locally known as ‘mahawat’) over the
plains and snowfall in the mountains. Although the amount of
rainfall is small, it is more importance for cultivating the ‘rabi’
crops.
But, the peninsular region does not have a well-defined cold
season. There is rare seasonal change in temperature
pattern during winters due to the moderating influence of the
sea.
WIND DIRECTION- WINTER
Bay of Bengal
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WINTER RAINFALL
RAINFALL DUE
TO WESTERN
DISTURBANCES
RAINFALL DUE
TO NORTH EAST
WIND
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⊿ Winter is cold.
⊿Children dress warmly to
play in the snow.
⊿ Animals head to their winter
homes.
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HOT WEATHER SEASON
â–ș It extends from March to
May.
â–ș Vertical sun rays shift
towards Northern
hemisphere.
â–ș Temperature rises
from south to
gradually
north.
â–ș Highest Temperature
experiences in Karnataka
in March, Madhya
Pradesh in April and
Rajasthan in May.
March 300C
April 380C
May 480C
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86
Due to the apparent northward movement of the Sun, the global
heat belt shifts northward. So, from March to May, it is hot weather
season in India. In March, the highest temperature is about 38°C, in
Deccan plateau. In April, temperatures in Gujarat and Madhya
Pradesh are around 42°C. In May, 45°C temperature is common in
the north-western 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. By 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.
R. Ezhilraman, PGT-Social Science
02-03-2015
TEMPERATURE- JULY
250
C
300
C
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PRESSURE- JULY
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LOO
KALBAISAKHI
BARDOLI
CHHEERHA
MANGO
SHOWER
BLOSSOM
SHOWER
STORMS IN HOT WEATHER SEASON
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An important feature of the summer season is the ‘loo’. These are
strong, gusty, hot, dry winds blowing during the day, sometimes till
late evening over the north and North-western India. Direct
exposure to these winds may be harmful. Dust storms are very
common during 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. In West Bengal,
these storms are known as the ‘Kaal Baisakhi’.
By 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’.
⊁ Long, hot days.
⊁ Summer fruit and
vegetables are ready to be
picked.
⊁ You see many bees and
butterflies fly flower to
flower.
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Advancing Monsoon (The Rainy Season)
SOUTH WEST MONSOON SEASON
known as break in
â–ș It extends from June to
September.
â–ș Intense heating in north
west India creates low
pressure region.
â–ș Low pressure attract the
wind from the surrounding
region.
â–ș After having rains for a
few days sometime
monsoon fails to occur for
one or more weeks is
the
monsoon.
H
I
G
L
H
O
W
T
E
P
M
R
P
E
E
S
R
S
A
U
T
R
U
E
R
E
R. Ezhilraman, PGT-Social Science 02-03-2015 80
INTER TROPICA
ELQCUOA
TNOVRERGENCEZONE
MONSOON WIND
Arabian sea
Branch
Bay of Bengal
Branch
R. Ezhilraman, PGT-Social Science 02-03-2015 81
ONSET OF SW MONSOON
R. Ezhilraman, PGT-Social Science 02-03-2015 82
By early June, the low-pressure condition over the northern plains
attracts the trade winds of the southern hemisphere. These south-
east trade winds originate over the warm subtropical areas of the
southern oceans. These winds are strong and blow at an average
velocity of 30 kmph. With the exception of the extreme north-west,
the monsoon winds cover the country in about a month.
The south-west monsoon entirely changes the weather in India. The
Western Ghats receives heavy rainfall, more than 250 cm. The rain
shadow areas like Deccan Plateau and parts of Madhya Pradesh
also receives rain. The north-eastern part of the country receives
the maximum rainfall. 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.
R. Ezhilraman, PGT-Social Science 02-03-2015 83
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. The trough and
its axis keep on moving northward or southward, which determines
the spatial distribution of rainfall. Whenever the axis shifts closer
to the Himalayas, widespread rain occur in the mountainous
catchment areas of the Himalayan rivers, which also cause floods.
The frequency and intensity of tropical depressions determine the
amount and duration of monsoon rains. These depressions form at
the Bay of Bengal and cross over to the mainland. The depressions
follow the axis of the “monsoon trough of low pressure”. It causes
heavy floods in one part, and droughts in the other. Sometimes it
disturbs the farming schedule of millions of farmers all over the
country.
R. Ezhilraman, PGT-Social Science 02-03-2015 84
â–șIt extends from October
to November
â–șVertical sun rays start
shifting towards Northern
hemisphere.
â–șLow pressure region shift
from northern parts of
India towards south.
â–șOwing to the conditions
of high temperature and
the weather
rather
humidity,
becomes
oppressive. This is
commonly known as the
‘October heat’
RETREATING MONSOON SEASON
LOW PRESSURE
R. Ezhilraman, PGT-Social Science 02-03-2015 85
WITHDRAWAL OF MONSOON
R. Ezhilraman, PGT-Social Science 02-03-2015 86
02-03-2015
R. Ezhilraman, PGT-Social Science 99
Parts of western coast and north-eastern India receive over about
400 cm of rainfall annually. But, in western Rajasthan and
adjoining parts of Gujarat, Haryana and Punjab it is less than 60
cm. Rainfall is equally low in the interior of the Deccan plateau,
and east of the Sahyadris. Because of low precipitation found
around Leh in Jammu and Kashmir. The rest of the country
receives moderate rainfall. Snowfall is restricted to the Himalayan
region.
Based on 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. Similarly, the areas of high rainfall are often
affected by floods, areas of low rainfall are drought-prone.
DISTRIBUTION OF RAINFALL
> 200cm
100-200cm
50-100 cm
< 50cm
R. Ezhilraman, PGT-Social Science 02-03-2015 88
⊁ The sun shines more and
the days begin to get
warmer.
⊁ Spring is a time when baby
animals are born.
⊁ Spring is a time when plants
and trees wake up after a
long winters nap.
⊁ Spring showers help to
warm the earth, moisten
the soil, helping new plants
to grow.
R. Ezhilraman, PGT-Social Science 02-03-2015 89
⊁ Leaves change to yellow,
orange, and red.
⊁ Picking fruit and
vegetables.
⊁ Animals get ready for
winter.
R. Ezhilraman, PGT-Social Science 02-03-2015 90
02-03-2015
R. Ezhilraman, PGT-Social Science 103
The 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.
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.
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.
02-03-2015
R. Ezhilraman, PGT-Social Science 104

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CLIMATE...................................

  • 1. 02-03-2015 R. Ezhilraman, PGT-Social Science 1
  • 2. What is Climate? Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It refers to the sum total of weather conditions and variation over a large area for a long period of time. It is the long-term weather of that area which remains at least 30 years. 02-03-2015 R. Ezhilraman, PGT-Social Science 2
  • 3. Weather refers to the state of atmosphere over an area at any point of time. The elements of both weather and climate are same. It is the combination of temperature, humidity, precipitation, wind, cloudiness and other atmospheric conditions at a specific time. What is Weather? 02-03-2015 R. Ezhilraman, PGT-Social Science 3
  • 4. Monsoon 02-03-2015 R. Ezhilraman, PGT-Social Science 4 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. The World is divided into a number of Climatic Regions. The Climate of India is described as the ‘monsoon’ type. This type of climate is found in South and Southeast Asia. But, there are perceptible regional variations in climatic conditions within the country. Two important elements viz., temperature and precipitation, often vary from place to place and season to season.
  • 5. Difference in Temperature 02-03-2015 R. Ezhilraman, PGT-Social Science 5 In summer, the temperature in parts of Rajasthan Desert is 50°C, and it is around 20°C in Pahalgam in J & K. On a winter night, temperature at Drass in J & K may less than -45°C, and at Tiruvananthapuram it may be of 22°C. In some places temperature between day and night temperature differs. In the Thar Desert, it rise to 50°C, in day and drop down to near 15°C in night. But in the Andaman and Nicobar islands or in Kerala, there is no much difference in day and night temperatures.
  • 6. Precipitation 02-03-2015 R. Ezhilraman, PGT-Social Science 6 Precipitation varies in its form, types and amount and seasonal distribution. It is in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country. The annual precipitation varies from 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 Tamil Nadu coast gets rain during October and November. Rainfall generally decrease from east to west in the Northern Plains. These variations have given rise to variety in lives of people, their food, clothes and houses.
  • 7. Vegetation Vegetation can affect both temperature and the precipitation patterns in an area. 02-03-2015 R. Ezhilraman, PGT-Social Science 7
  • 8. 02-03-2015 R. Ezhilraman, PGT-Social Science 8
  • 9. FACTORS AFFECTING CLIMATE RELATED TO LOCATION RELATED TO AIR PRESSURE & WIND 02-03-2015 R. Ezhilraman, PGT-Social Science 9
  • 10. Latitude Latitude is the equator and distance a place lies north or south of the is called lines measured by an imaginary line of latitude. 02-03-2015 R. Ezhilraman, PGT-Social Science 10
  • 11. EQUATORIAL REGION LATITUDE High range of Temp High Temp Low range 02-03-2015 R. Ezhilraman, PGT-Social Science 11
  • 12. Latitude 02-03-2015 R. Ezhilraman, PGT-Social Science 12  As latitude increases, the intensity of solar energy decreases. Due to curvature of the Earth, the amount of solar energy varies according to latitude.  In India, 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.
  • 13. Tropical, Temperate and Polar Zones 02-03-2015 R. Ezhilraman, PGT-Social Science 13 ‱ The tropical zone is between 23.5o north (the tropic of Cancer) and 23.5o south (the tropic of Capricorn) of the Equator. The Sun’s rays are most intense and the temperatures are always warm. ‱ The temperate zones are between 23.5o and 66.5o north and between 23.5o and 66.5o south of the Equator. The Sun’s rays strike Earth at a smaller angle than near the Equator. ‱ Polar zones are between 66.5o north and south latitudes and the poles. The sun’s rays strike Earth at a very small angle in the polar zones.
  • 14. Highland Climates In general, highland climates are cooler and wetter than nearby areas at lower elevations. 02-03-2015 R. Ezhilraman, PGT-Social Science 14
  • 15. Earth’s Major Climate Zones 02-03-2015 R. Ezhilraman, PGT-Social Science 15
  • 16. North Frigid Zone 02-03-2015 R. Ezhilraman, PGT-Social Science 16 Temperate Zone Temperate Zone South Frigid Zone Torrid Zone
  • 17. AGRA 160C in Jan DARJILING 40C in January ALTITUDE HIGH ALTITUDE LOW ALTITUDE Temperature decreased from low to high altitude 02-03-2015 R. Ezhilraman, PGT-Social Science 17
  • 18. Air Temperature decreases with altitude. As elevation increases, the air gets cooler because of the energy drawn from the surroundings. 02-03-2015 R. Ezhilraman, PGT-Social Science 18
  • 19. Factors That Affect Climate 02-03-2015 R. Ezhilraman, PGT-Social Science 19  Water Bodies Large bodies of water such as lakes and oceans have an important effect on the temperature of an area because the temperature of the water body influences the temperature of the air above it.  Atmospheric Circulation Global winds are another factor that influences climate because they distribute heat and moisture around Earth.
  • 20.  Solar Activity When the Sun is most active, it contains dark blemishes called sunspots. The formation of sunspots appears to correspond with warm periods in Europe and North America.  Earth Motions Geographic changes in Earth’s land and water bodies cause changes in climate. Changes in the shape of Earth’s orbit and the tilt of Earth on its axis are other Earth motions that affect global climates. 02-03-2015 R. Ezhilraman, PGT-Social Science 20 Natural Processes That Change Climates
  • 21. Human Impact on Climate Changes 02-03-2015 R. Ezhilraman, PGT-Social Science 21  The Greenhouse Effect The greenhouse effect is a natural warming of both Earth’s lower atmosphere and Earth’s surface from solar radiation being absorbed and emitted by the atmosphere.  Global Warming As a result of increased levels of carbon dioxide and other greenhouse gases, global temperatures have increased. This increase is called global warming.
  • 22. The Pressure and Surface Winds 02-03-2015 R. Ezhilraman, PGT-Social Science 22 The pressure and wind system of any area depend on the latitude and altitude of the place. It influences the temperature and rainfall pattern. The climate and weather conditions in India are governed by the atmospheric conditions like: ‱ Pressure and surface winds; ‱ Upper air circulation; and ‱ Western cyclonic disturbances and tropical cyclones. India lies in the north easterly winds region. 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 towards equatorial low-pressure area.
  • 23. NORTH-EAST TRADE WIND SOUTH-EAST TRADE WIND INTER TROPICAL CONVERGENCE ZONE SUB TROPICAL HIGH PRESSURE SUB TROPICAL HIGH PRESSURE SUB TROPICAL LOW PRESSURE SUB TROPICAL LOW PRESSURE POLAR HIGH POLAR HIGH SURFACE WIND 02-03-2015 R. Ezhilraman, PGT-Social Science 23
  • 24. AIR MASSES CIRCULATE GLOBALLY 02-03-2015 R. Ezhilraman, PGT-Social Science 24 ‱ At the Equator, temperatures are relatively high. Land and water masses heat up and as a result these warm the air over them. ‱ Air heated at the equatorial region rises to the top of the atmosphere. ‱ More air rising beneath it forces the air mass to spread north and south toward the poles.
  • 25. Coriolis Effect 02-03-2015 R. Ezhilraman, PGT-Social Science 25 ‱ The rotation of the Earth causes all moving objects in the Northern Hemisphere, including air mass, to deflect to the right and those in the Southern Hemisphere to move to the left. ‱ This Coriolis effect is absent at the Equator. ‱ Coriolis Force- prevents a direct simple flow from the Equator to the Poles. ‱ This is also known as ‘Ferrel’s Law’.
  • 26. 02-03-2015 R. Ezhilraman, PGT-Social Science 26
  • 27. The Pressure and Surface Winds in India 02-03-2015 R. Ezhilraman, PGT-Social Science 27 The pressure and wind conditions in India is unique. During winter, there is a high-pressure in the 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 and in north-western 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.
  • 28. ARABIAN SEA BAY OF BENGAL INDIAN OCEAN LOW AND HIGH PRESSURE HIGH PRESSURE IN WINTER 02-03-2015 R. Ezhilraman, PGT-Social Science 28
  • 29. CHENNAI SIMLA DELHI KOLKOTA MUMBAI DISTANCE FROM SEA Coastal areas have equable climate where as Interior parts have extreme climate. 02-03-2015 R. Ezhilraman, PGT-Social Science 29
  • 30. Relief 02-03-2015 R. Ezhilraman, PGT-Social Science 30 ‱ Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or hot winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of mountains remains relatively dry.
  • 32. RELIEF The Rain Shadow Effect 02-03-2015 R. Ezhilraman, PGT-Social Science 32
  • 33. 02-03-2015 R. Ezhilraman, PGT-Social Science 33
  • 34. Jet Stream 02-03-2015 R. Ezhilraman, PGT-Social Science 34 ‱ The upper air circulation in India is dominated by a westerly flow, known as the 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. ‱ Many jet streams have been identified. The most constant are the mid-latitude and the sub tropical jet stream.
  • 35. TIBET JET STREAM IN WINTER 02-03-2015 R. Ezhilraman, PGT-Social Science 35
  • 36. Jet Stream 02-03-2015 R. Ezhilraman, PGT-Social Science 36 Jet streams are located at 27°-30° north latitude, 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 easterly jet stream, called the stream blows over peninsular tropical India, approximately over 14°N during the summer.
  • 37. JET STREAM IN SUMMER 02-03-2015 R. Ezhilraman, PGT-Social Science 37
  • 38. Western Disturbances 02-03-2015 R. Ezhilraman, PGT-Social Science 38 ‱ 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. ‱ Thus very often the coast of Orissa and Andhra Pradesh are affected by those disasters.
  • 39. WESTERN DISTURBANCE 02-03-2015 R. Ezhilraman, PGT-Social Science 39
  • 40. OCEAN CURRENTS 02-03-2015 R. Ezhilraman, PGT-Social Science 40 Solar energy, wind, and Earth’s rotation creates Ocean currents Current- the systematic patters of water movement. Gyres- two great circular water motion.  Northern Hemisphere- the ocean current moves clockwise.  Southern Hemisphere- the ocean current move anti-clockwise.  Trade winds push warm surface waters westward at the equator.  As the waters encounter the continents, they split into north- and south-flowing currents along the eastern coast, forming north and south gyres.
  • 41. Surface Water blown by the winds at point A will weirs to the right of its initial path and continue eastward. Water at point B weirs to the right and continues westward. 02-03-2015 R. Ezhilraman, PGT-Social Science 41
  • 42. 02-03-2015 R. Ezhilraman, PGT-Social Science 42
  • 43. 02-03-2015 R. Ezhilraman, PGT-Social Science 43
  • 44. Winds driven by uneven solar heating and Earth’s spin, drive the movement of the ocean’s surface currents. The prime movers are the powerful westerlies and the persistent trade winds (easterlies) 02-03-2015 R. Ezhilraman, PGT-Social Science 44
  • 45.  The Köppen climate classification system uses mean monthly and annual values of temperature and precipitation to classify climates.  According to the Köppen classification, the earth can be divided into several major climatic zones and bands: The Köppen Climate Classification System  Tropical climate  Subtropical climate  Arid climate  Equatorial climate  Semiarid climate  Mediterranean climate  Temperate climate  Oceanic climate  Continental climate  Subarctic climate  Polar climate  Climate of Antarctica 02-03-2015 R. Ezhilraman, PGT-Social Science 45
  • 46. Polar Climate 02-03-2015 R. Ezhilraman, PGT-Social Science 46 Polar climates are those in which the mean temperature of the warmest month is below 10o C.
  • 47. The Indian Monsoon 02-03-2015 R. Ezhilraman, PGT-Social Science 47 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’.
  • 48. Atmospheric Conditions over the Indian Subcontinent in the Month of January 02-03-2015 R. Ezhilraman, PGT-Social Science 48
  • 49. Atmospheric Conditions over the Indian Subcontinent in the Month of June 02-03-2015 R. Ezhilraman, PGT-Social Science 49
  • 50. Facts of Mechanism of the Monsoons 02-03-2015 R. Ezhilraman, PGT-Social Science 50 In India, the monsoons are experienced in the tropical area roughly between 20°N and 20°S. The Following facts are the Mechanism of the Monsoons. (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. It is also known as the monsoon-trough during the monsoon season).
  • 51. Inter Tropical Convergence Zone (ITCZ) 02-03-2015 R. Ezhilraman, PGT-Social Science 51 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.
  • 52. Facts of Mechanism of the Monsoons 02-03-2015 R. Ezhilraman, PGT-Social Science 52 (c)The presence of the high-pressure area, east of Madagascar, nearly at 20°S over the Indian Ocean. The intensity of this high-pressure area affects the Indian Monsoon. (d)The Tibetan plateau gets intensely heated during summer, results in strong vertical air currents and the formation of low 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.
  • 53. Southern Oscillation 02-03-2015 R. Ezhilraman, PGT-Social Science 53 The changes in the pressure conditions over the southern oceans also affect the monsoons. When the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. But sometimes, 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 in Pacific Ocean and Darwin in northern Australia of Indian Ocean is predicted 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).
  • 54. Darwin Tahiti SOUTHERN OSCILLATION 02-03-2015 R. Ezhilraman, PGT-Social Science 54
  • 55. Effect of El Niño El Nino 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. 02-03-2015 R. Ezhilraman, PGT-Social Science 55
  • 56. Homboldt Cold Current EL-NINO EFFECTS 1990 Delay in Monsoon Equatorial Warm Current El-Nino 02-03-2015 R. Ezhilraman, PGT-Social Science 56
  • 57. Beginning of the Monsoon 02-03-2015 R. Ezhilraman, PGT-Social Science 57 The duration of the monsoon is between 100-120 days from early June to mid-September. During 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 proceeds into two – (i) the Arabian Sea branch and (ii) the Bay of Bengal branch.
  • 58. Beginning of the Monsoon 02-03-2015 R. Ezhilraman, PGT-Social Science 58 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 north-western 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 July first week, 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.
  • 59. 02-03-2015 R. Ezhilraman, PGT-Social Science 59
  • 60. End of the Monsoon 02-03-2015 R. Ezhilraman, PGT-Social Science 60 Withdrawal or the retreat of the monsoon is a more gradual process. The withdrawal of the monsoon begins in north-western states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. Then it quickly withdraw from the southern half of the peninsula. By early December, the monsoon has totally withdrawn from the country. The islands receive the very first monsoon showers, from south to north, between the last week of April and the first week of May. Then it withdraw from north to south during the first week of December to the first week of January. By this time, the other parts of the country is already influencing the winter monsoon.
  • 61. 02-03-2015 R. Ezhilraman, PGT-Social Science 61
  • 62.
  • 63. RHYTHM OF SEASONS COLD WEATHER RETREATING MONSOON HOT WEATHER SOUTH WEST MONSOON Let us discuss each of them individually 02-03-2015 R. Ezhilraman, PGT-Social Science 75
  • 64. 02-03-2015 R. Ezhilraman, PGT-Social Science 76 The monsoon type of climate is characterised 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. But, the coastal areas do not experience much variation in temperature though there is variation in rainfall pattern. In India, Four main seasons can be identified: (i) the cold weather season, (ii)the hot weather season, (iii)the advancing monsoon and (iv) the retreating monsoon with some regional variations.
  • 65. COLD WEATHER SEASON â–șIt extends from December to February. rays shift southern â–șVertical sun towards hemisphere. â–șNorth India experiences intense cold where as this season is not well defined in south India. â–șLight wind blow makes this season pleasant in south India. â–șOccasional tropical cyclone visit eastern coast in this season. Tropical Cyclone 02-03-2015 R. Ezhilraman, PGT-Social Science 77
  • 66. 02-03-2015 R. Ezhilraman, PGT-Social Science 78 The cold weather season begins from mid- November in northern India and stays till February. December and January are the coldest months. 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 winter, the northeast trade winds blow from land to sea. So, most part of the country faces a dry season. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as, trade winds 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.
  • 67. 250 C 200 C 200 C 200 C 250 C 150 C 200 C 100 C` TEMPERATURE- JANUARY R. Ezhilraman, PGT-Social Science 02-03-2015 67
  • 68. PRESSURE- JANUARY 101 4 R. Ezhilraman, PGT-Social Science 02-03-2015 68 HIGH PRESSURE
  • 69. 02-03-2015 R. Ezhilraman, PGT-Social Science 81 In the northern plains, there is the inflow of cyclonic disturbances from the west and the northwest. These low- pressure systems, from the Mediterranean Sea and western Asia and move into India, along with the westerly flow. They cause the winter rains (locally known as ‘mahawat’) over the plains and snowfall in the mountains. Although the amount of rainfall is small, it is more importance for cultivating the ‘rabi’ crops. But, the peninsular region does not have a well-defined cold season. There is rare seasonal change in temperature pattern during winters due to the moderating influence of the sea.
  • 70. WIND DIRECTION- WINTER Bay of Bengal R. Ezhilraman, PGT-Social Science 02-03-2015 70
  • 71. WINTER RAINFALL RAINFALL DUE TO WESTERN DISTURBANCES RAINFALL DUE TO NORTH EAST WIND R. Ezhilraman, PGT-Social Science 02-03-2015 71
  • 72. ⊿ Winter is cold. ⊿Children dress warmly to play in the snow. ⊿ Animals head to their winter homes. R. Ezhilraman, PGT-Social Science 02-03-2015 72
  • 73. HOT WEATHER SEASON â–ș It extends from March to May. â–ș Vertical sun rays shift towards Northern hemisphere. â–ș Temperature rises from south to gradually north. â–ș Highest Temperature experiences in Karnataka in March, Madhya Pradesh in April and Rajasthan in May. March 300C April 380C May 480C R. Ezhilraman, PGT-Social Science 02-03-2015 73
  • 74. 86 Due to the apparent northward movement of the Sun, the global heat belt shifts northward. So, from March to May, it is hot weather season in India. In March, the highest temperature is about 38°C, in Deccan plateau. In April, temperatures in Gujarat and Madhya Pradesh are around 42°C. In May, 45°C temperature is common in the north-western 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. By 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. R. Ezhilraman, PGT-Social Science 02-03-2015
  • 75. TEMPERATURE- JULY 250 C 300 C R. Ezhilraman, PGT-Social Science 02-03-2015 75
  • 76. PRESSURE- JULY R. Ezhilraman, PGT-Social Science 02-03-2015 76
  • 77. LOO KALBAISAKHI BARDOLI CHHEERHA MANGO SHOWER BLOSSOM SHOWER STORMS IN HOT WEATHER SEASON R. Ezhilraman, PGT-Social Science 02-03-2015 77
  • 78. 02-03-2015 R. Ezhilraman, PGT-Social Science 90 An important feature of the summer season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day, sometimes till late evening over the north and North-western India. Direct exposure to these winds may be harmful. Dust storms are very common during 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. In West Bengal, these storms are known as the ‘Kaal Baisakhi’. By 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’.
  • 79. ⊁ Long, hot days. ⊁ Summer fruit and vegetables are ready to be picked. ⊁ You see many bees and butterflies fly flower to flower. R. Ezhilraman, PGT-Social Science 02-03-2015 79
  • 80. Advancing Monsoon (The Rainy Season) SOUTH WEST MONSOON SEASON known as break in â–ș It extends from June to September. â–ș Intense heating in north west India creates low pressure region. â–ș Low pressure attract the wind from the surrounding region. â–ș After having rains for a few days sometime monsoon fails to occur for one or more weeks is the monsoon. H I G L H O W T E P M R P E E S R S A U T R U E R E R. Ezhilraman, PGT-Social Science 02-03-2015 80
  • 81. INTER TROPICA ELQCUOA TNOVRERGENCEZONE MONSOON WIND Arabian sea Branch Bay of Bengal Branch R. Ezhilraman, PGT-Social Science 02-03-2015 81
  • 82. ONSET OF SW MONSOON R. Ezhilraman, PGT-Social Science 02-03-2015 82
  • 83. By early June, the low-pressure condition over the northern plains attracts the trade winds of the southern hemisphere. These south- east trade winds originate over the warm subtropical areas of the southern oceans. These winds are strong and blow at an average velocity of 30 kmph. With the exception of the extreme north-west, the monsoon winds cover the country in about a month. The south-west monsoon entirely changes the weather in India. The Western Ghats receives heavy rainfall, more than 250 cm. The rain shadow areas like Deccan Plateau and parts of Madhya Pradesh also receives rain. The north-eastern part of the country receives the maximum rainfall. 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. R. Ezhilraman, PGT-Social Science 02-03-2015 83
  • 84. 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. The trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall. Whenever the axis shifts closer to the Himalayas, widespread rain occur in the mountainous catchment areas of the Himalayan rivers, which also cause floods. The frequency and intensity of tropical depressions determine the amount and duration of monsoon rains. These depressions form at the Bay of Bengal and cross over to the mainland. The depressions follow the axis of the “monsoon trough of low pressure”. It causes heavy floods in one part, and droughts in the other. Sometimes it disturbs the farming schedule of millions of farmers all over the country. R. Ezhilraman, PGT-Social Science 02-03-2015 84
  • 85. â–șIt extends from October to November â–șVertical sun rays start shifting towards Northern hemisphere. â–șLow pressure region shift from northern parts of India towards south. â–șOwing to the conditions of high temperature and the weather rather humidity, becomes oppressive. This is commonly known as the ‘October heat’ RETREATING MONSOON SEASON LOW PRESSURE R. Ezhilraman, PGT-Social Science 02-03-2015 85
  • 86. WITHDRAWAL OF MONSOON R. Ezhilraman, PGT-Social Science 02-03-2015 86
  • 87. 02-03-2015 R. Ezhilraman, PGT-Social Science 99 Parts of western coast and north-eastern India receive over about 400 cm of rainfall annually. But, in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab it is less than 60 cm. Rainfall is equally low in the interior of the Deccan plateau, and east of the Sahyadris. Because of low precipitation found around Leh in Jammu and Kashmir. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region. Based on 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. Similarly, the areas of high rainfall are often affected by floods, areas of low rainfall are drought-prone.
  • 88. DISTRIBUTION OF RAINFALL > 200cm 100-200cm 50-100 cm < 50cm R. Ezhilraman, PGT-Social Science 02-03-2015 88
  • 89. ⊁ The sun shines more and the days begin to get warmer. ⊁ Spring is a time when baby animals are born. ⊁ Spring is a time when plants and trees wake up after a long winters nap. ⊁ Spring showers help to warm the earth, moisten the soil, helping new plants to grow. R. Ezhilraman, PGT-Social Science 02-03-2015 89
  • 90. ⊁ Leaves change to yellow, orange, and red. ⊁ Picking fruit and vegetables. ⊁ Animals get ready for winter. R. Ezhilraman, PGT-Social Science 02-03-2015 90
  • 91. 02-03-2015 R. Ezhilraman, PGT-Social Science 103 The 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. 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. 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.