Climate:
Climate refers to the sum of a total of weather conditions and variation over large areas for a long period of time( more than 30 years.)
Weather:
It refers to a state of the atmospheric conditions over a geographical area at any particular time.
Elements of climate and weather:
- Wind
- Temperature
- Humidity
- Atmospheric pressure
- Precipitation
Climatic control
Six major control of climate of any geographical areas:- Latitude
- Altitude
- Pressure and wind system
- Distance from sea or continentality
- Ocean current
- Relief
Latitude:
Due to the rotation of the earth in the tilted axis and spherical shape of the earth, the amount of solar energy receives varies according to latitude; temperature decrease from the equator to Poles.
Altitude;
The atmosphere becomes less dense and temperature decrease as we go higher altitude. Hills are cooler in summer.
Due to the rotation of the earth in the tilted axis and spherical shape of the earth, the amount of solar energy receives varies according to latitude; temperature decrease from the equator to Poles.
Altitude;
The atmosphere becomes less dense and temperature decrease as we go higher altitude. Hills are cooler in summer.
Pressure and wind system:
It depends on latitude and altitude and it also influences temperature and rainfalls.
It depends on latitude and altitude and it also influences temperature and rainfalls.
As the distance from sea increases moderating influence of sea decreases and people feel extreme weather conditions in interior continents also known as continentality.
- Coastal along with worm ocean current does not freeze in winter and also gets sufficient rainfall.
- Coastal along with cold ocean current are desert-like climate. Because of cold ocean currents, most deserts are located in the western margin of the continent in the subtropics region.
Relief:
High mountains act as a barrier for cold or hot winds and it causes Orographic rainfall if relief is high enough.
High mountains act as a barrier for cold or hot winds and it causes Orographic rainfall if relief is high enough.
Factor affecting India' s climate:
Latitude:- Tropic of Cancer passes the middle of the country from Runn of Kuchchh in the west to Mizoram in the east.
- Half of the country lying south of cancer belongs to tropical areas.
- The rest half of the country lying north of tropics of cancer belong to subtropical areas.
- India's climate is characterized by tropic as well as subtropical climate.
Altitude:
- Himalayan mark the northern boundary of India having an average height of 6000 meters and it prevents cold winds from central Asia from entering India, hence feel mild winter as compare to the same latitude in central Asia.
Pressure and wind system:
The climate and associated weather conditions are governed by the following atmospheric conditions:
The climate and associated weather conditions are governed by the following atmospheric conditions:
- Pressure and surface winds
- Upper air circulation
- Western cyclonic disturbances and tropical cyclone
Western cyclonic disturbances and tropical cyclone:
India lies in the region of the northeastern winds. These winds originated from subtropical high-pressure belts in the northern hemisphere. They blow southward and get deflected right due to Coriolis force. These winds carry little moisture as they originated and blow over lands.
During winter:
High-pressure areas in the north of Himalayan. Cold dry winds blow from this region to this region to low-pressure areas over the ocean to the south.
High-pressure areas in the north of Himalayan. Cold dry winds blow from this region to this region to low-pressure areas over the ocean to the south.
During Summer:
Low-pressure areas developed over interior Asia as well as northwestern India. Because of this, a complete reversal of the direction of winds during summer. Air moves from a high-pressure area over the southern Indian ocean and Cross the equator and turns right ( due to Coriolis force) towards low-pressure areas. This is known as the southwest monsoon. As it blows over the warm ocean and gathers moisture and brings huge rainfall over mainland India.
Low-pressure areas developed over interior Asia as well as northwestern India. Because of this, a complete reversal of the direction of winds during summer. Air moves from a high-pressure area over the southern Indian ocean and Cross the equator and turns right ( due to Coriolis force) towards low-pressure areas. This is known as the southwest monsoon. As it blows over the warm ocean and gathers moisture and brings huge rainfall over mainland India.
Upper air circulation:
It is dominated by the westerly flow. Important components are westerly and easterly Jet streams.Jet streams:
- It is located approximately 27' to 30' north latitude. Therefore also known as subtropical westerly jetstream. It blows south of Himalayan all the year except in Summer.
- Western cyclonic disturbances experienced in north and northwestern part of India are brought it by the western subtropical Jet stream.
- In summer; with the apparent movement of the sun, the subtropical westerly jet stream moves north of Himalayan.
Easterly jet stream:
It is also called subtropical easterly jet stream blow over peninsular India. Approximately over 14 ' N during summer.
It is also called subtropical easterly jet stream blow over peninsular India. Approximately over 14 ' N during summer.
Coriolis force or Ferrel law:
It is caused by earth rotation and responsible for deflecting winds towards the right in the northern hemisphere and left in the southern hemisphere.
Jet stream:
- A narrow belt of high altitude ( 12 km) winds in the troposphere.
- Wind speed: 110 km per hour in summer
- 184 km per hour in winter.
- Types:
- Mid-latitude
- Subtropical jet stream
Indian monsoon
The monsoon is experienced in tropical areas roughly between 20' N and 20 ' S.The following facts are important to understand the mechanism of monsoon:
- The differential heating and cooling of land and water. During summer, low-pressure areas are created in landmass and high-pressure areas in the water.
- The shift of the position of the intertropical convergence zone( ITCZ) over Ganga in summer. Monsoon trough or equatorial trough normally position in 5 ' N of the equator.
- The presence of high-pressure areas east of Madagascar; approximately 20 'S over the Indian ocean.
- The Tibetan plateau gets intensely heated during summer. At the result, strong vertical air current and formation of low-pressure areas at 9 km above the sea level.
- During summer, movement of the westerly jet stream in North of Himalayan and presence of tropical Easterly jet stream over the Indian peninsula.
- SO or southern Oscillation.
ITCZ:
- Generally, ITCZ lies parallel to the equator but moves north and south with the apparent movement of the Sun.
- It has a broad trough of low pressure in an equatorial latitude where northeast and southeast trade winds converge.
Southern Oscillation:
Normally, tropical eastern south pacific experience high pressure and tropical eastern Indian ocean experience low pressure. But in certain years, there is a reversal in pressure condition, the coastal area of Peruvian has low pressure as compared to the eastern Indian ocean. This phenomenon is known as Southern oscillation or SO.
If the pressure in Peruvian coast - pressure in northern Australian coast then
Below average of late monsoon.
Normally, tropical eastern south pacific experience high pressure and tropical eastern Indian ocean experience low pressure. But in certain years, there is a reversal in pressure condition, the coastal area of Peruvian has low pressure as compared to the eastern Indian ocean. This phenomenon is known as Southern oscillation or SO.
If the pressure in Peruvian coast - pressure in northern Australian coast then
Below average of late monsoon.
El Nino condition:
if cold Peruvian current replaced by the warm ocean current.
if cold Peruvian current replaced by the warm ocean current.
The onset of the monsoon:
Monsoon is not steady winds as trade winds.A burst of monsoons:
Normal rainfall increases suddenly and continues constantly for several days called a burst of monsoon.
Two Branches of monsoon:
- Southwest branches from the Arabian sea.
- the southeast branch from the Bay of Bengal.
Withdrawal of monsoon:
The retreat of monsoon is a gradual process. It begins in the northwestern state of India by Early September. By the end of December or early January, India is under the influence of winter monsoon.
The retreat of monsoon is a gradual process. It begins in the northwestern state of India by Early September. By the end of December or early January, India is under the influence of winter monsoon.
Four seasons in India:
- Winter season
- Summer season
- Rainy season or advance monsoon
- Retreating or post-monsoon season
Distribution of rainfall:
Annual rainfall is highly variable from year to year. Variability is high in the region of low rainfall such as Rajasthan and leeward side of western Ghats.
Over 400 cm of rainfall annually received on the western coast and northeastern India.
Moderate rainfall areas:
Northern plains and Deccan plateau
Low rainfall areas:
Northern plains and Deccan plateau
Low rainfall areas:
- Less than 60 cm rainfall annually in western Rajasthan and parts of Gujarat.
- Low rainfall in the interior of the Deccan plateau.
- Very low rainfall in Leh areas of Ladakh region.
Monsoon as a unifying bond:
- As the Himalayan protect subcontinent from extremely cold winds from central Asia and peninsular plateau under the influence from the sea from three sides enable the moderate temperature.
- Despite such moderate influence, there is a great variation in temperature. Monsoon other hand is unifying features that bind the whole country by providing water to set agricultural activities.
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