Climates Notes by Vibha Maam
‘Mousim’ is derived from the Arabic word. It means monsoon. This type of climate is found mainly in the south and south-east Asia.
Weather refers to short-run atmospheric conditions of a particular place. Its dominant elements are temperature ,humidity etc.
Climate is the aggregate weather condition of a large area over a long period of time.
The latitude affects the temperature of the place.
the temperature decreases as the distance increases from the equator.
the amount of rainfall also decreases.
As height increases, the density of air decreases.
Pressure and wind
It influences the temperature and rainfall pattern.
Distance from the sea
Land heats up and also cools down faster than water.
places near the sea are cool in summer and warm in winter.
The interiors of the continent are hot in summer and cold in winter.
Ocean currents transfer heat from lower latitudes to the higher latitudes.
Direction of mountain ranges
Mountains act as barriers to the movement of wind and affect both temperature and rainfall.
Factors affecting the climate of India
India lies between 8°N and 37°N latitude. The tropic of Cancer passes through the middle of India, while the southern part lies in the tropical zone and the northern part falls in the subtropical zone. so the temperature remains high during summer and fall in winter.
The Himalayas protect India from the cold wind of the north and obstruct the South westerly monsoon.
Pressure and surface winds
Due to low temperature, there is a high pressure area in the North of the Himalayas. cold dry winds blow from high pressure to low pressure.
In summer due to high temperature, a low- pressure area develops over North-Western India.
Upper air circulation( jet stream)
There are narrow belts of high altitude westerly wind in the troposphere. These Jet streams are located approx. over 27°- 30°N latitude, therefore, they are known as sub-tropical westerly jet streams.
Altitude – about 8 to 15 km
Speed – in summer about 110 km/h
– in winter about 184 km/h
Western cyclonic disturbances
In winter, it is brought in by the westerly flow from the Mediterranean region. They usually influence the weather of the north and the north western region of India.
They occur during the monsoon as well as in Oct -Nov and are part of the Easterly affect on the coastal region of the country.
The Western and Eastern Ghats force the moisture Laden south-west monsoon from the Arabian sea to ascend the slope.
An apparent force caused by the earth’s rotation. this force is responsible for deflecting winds toward the right in the Northern hemisphere and toward the left in the Southern hemisphere. This is also known as Ferrel’s law.
The inter tropical convergence zone( ITCZ)
ITCZ is a broad trough of low pressure in equatorial latitudes.
Southern Oscillation (SO)
Normally when the tropical Eastern South Pacific Ocean experiences high pressure, the tropical Eastern Indian ocean experiences low pressure. the reversal (periodic) change in pressure condition over the Pacific Ocean and the Indian Ocean known as the southern oscillation or SO.
Prediction station of monsoon
Tahiti – Pacific Ocean (18°S /149°W)
Darwin – Indian Ocean (12°30S/ 131°E)
EI Nino is a periodic warm ocean current that flows past the peruvian coast, in place of the cold Perivan current, every two to five years. The changes in pressure condition are connected to the El Nino. Hence, the phenomenon is referred to as ENSO (EI Nino southern oscillation).
Cycle of Seasons
The cold weather season or the winter season
- Clear sky, low temperature and humidity
- Temperature below 21°C
- The coldest month is January, temperature is 10°to 15°C.
- Northeast Trade winds prevail over the country.
- They blow from land to the sea over most parts of the country and do not cause much rainfall.
- Western disturbances cause light rainfall and highly beneficial to the Rabi crops
- Winds blow from land to the sea while crossing the Bay of Bengal cause winter rainfall in Tamilnadu, South Andhra Pradesh, south-east Karnataka, and Kerala.
The hot weather season
- Summer season- March to May
- Rising temperature and falling air pressure
- Average temperature ranges from 42°C to 43°C
- North Western part of the country- temperature 48°C
- The North-East Trade Winds blow from the South-East to the north-west.
The Southwest monsoon season or rainy season
- most parts of the country receive rainfall from June to September
- but some parts like the Tamilnadu coast get most of its rain during October and November.
- North-Western parts have temperature upto 40°C
- By early June, the low pressure conditions are powerful enough to attract the South-East Trade Winds.
- 3/4th of India’s annual rainfall is received during this season.
- The Arabian sea branch monsoon strikes the Western coast of India.
- The Bay of Bengal branch causes widespread rain in North- Eastern India.
When normal rainfall increases suddenly and continuously for several days known as monsoon burst.
The season of retreating monsoon
- Clear skies and rise in temperature
- Oppressive weather in October
- Southwest monsoon gives place to the North East monsoon
- Only Kerala, Tamilnadu, and adjoining Andhra Pradesh receive rainfall.
Monsoon acts as a unifying bond
- Himalayas enable north India to have uniformly higher temperatures.
- The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons.
- The landscape, its animals and plants, and the lives of the people revolve around this phenomenon.
- The 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.
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