Indian Geography Climate Flashcards
Weather climate
Weather is the momentary state of the atmosphere while climate refers to the average of the weather conditions over a longer period of time. Weather changes quickly, may be within a day or week but climate changes imperceptively and may be noted after 50 years or even more.
Climate of India
Monsoon type with variations- sub-types of monsoon climate.
FACTORS DETERMINING THE CLIMATE OF INDIA
Latitude, distribution of land and water, distance from the sea, altitude, relief including Himalayas
How does Latitude affect the climate of India?
Tropic of Cancer passes through the central part of India in east-west direction. Thus, northern part of the India lies in sub-tropical and temperate zone and the part lying south of the Tropic of Cancer falls in the tropical zone. The tropical zone being nearer to the equator, experiences high temperatures throughout the year with small daily and annual range. Area north of the Tropic of Cancer being away from the equator, experiences extreme climate with high daily and annual range of temperature.
How does The Himalayan Mountains affect the climate of India?
The lofty Himalayas in the north along with its extensions act as an effective climatic divide. The towering mountain chain provides an invincible shield to protect the subcontinent from the cold northern winds. These cold and chilly winds originate near the Arctic circle and blow across central and eastern Asia. The Himalayas also trap the monsoon winds, forcing them to shed their moisture within the subcontinent.
How does Distribution of Land and Water affect the climate of India?
India is flanked by the Indian Ocean on three sides in the south and girdled by a high and continuous mountain-wall in the north. As compared to the landmass, water heats up or cools down slowly. This differential heating of land and sea creates different air pressure zones in different seasons in and around the Indian subcontinent. Difference in air pressure causes reversal in the direction of monsoon winds.
How does Distance from the Sea affect the climate of India?
Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate. That is why, the people of Mumbai and the Konkan coast have hardly any idea of extremes of temperature and the seasonal rhythm of weather. On the other hand, the seasonal contrasts in weather at places in the interior of the country such as Delhi, Kanpur and Amritsar affect the entire sphere of life.
How does Altitude affect the climate of India?
Temperature decreases with height. Due to thin air, places in the mountains are cooler than places on the plains. For example, Agra and Darjiling are located on the same latitude, but temperature of January in Agra is 16°C whereas it is only 4°C in Darjiling.
elements of weather
(temperature, pressure, wind direction and velocity, humidity and precipitation, etc.)
How does Relief affect the climate of India?
the physiography or relief of India also affects the temperature, air pressure, direction and speed of wind and the amount and distribution of rainfall. The windward sides of Western Ghats and Assam receive high rainfall during June-September whereas the southern plateau remains dry due to its leeward situation along the Western Ghats.
Wrt air pressure and winds, mechanism of Weather in the Winter Season
Surface Pressure and Winds : high pressure area near Central and West Asia leads to dry air blowing towards Himalyas which collide with trade winds over Northwestern India, or sometime Ganga plain.
Jet Stream and Upper Air Circulation :3 km above the surface jet streams blow from west to east parallel to the Himalayas. Tibetan highlands bifurcate them–One of its branches blows to the north of the Tibetan highlands, while the southern branch blows in an eastward direction, south of the Himalayas.
Western Cyclonic Disturbance and Tropical Cyclones : The western cyclonic disturbances which enter the Indian subcontinent from the west and the northwest during the winter months, originate over the Mediterranean Sea and are brought into India by the westerly jet stream. Tropical cyclones originate over the Bay of Bengal and the Indian ocean.
Inter Tropical Convergence Zone (ITCZ) wrt India and monsoons
The Inter Tropical Convergence Zone (ITCZ) is a low pressure zone located at the equator where trade winds converge, and so, it is a zone where air tends to ascend. In July, the ITCZ is located around 20°N-25°N latitudes (over the Gangetic plain), sometimes called the monsoon trough. This monsoon trough encourages the development of thermal low over north and northwest India. Due to the shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40° and 60°E longitudes and start blowing from southwest to northeast due to the Coriolis force. It becomes southwest monsoon. In winter, the ITCZ moves southward, and so the reversal of winds from northeast to south and southwest, takes place. They are called northeast monsoons.
Wrt air pressure and winds, mechanism of Weather in the in the Summer Season
Surface Pressure and Winds : ITCZ near equator shifts northwards and the westerly jet streams withdraw in cause-effect relationship. The moist maritime tropical air that rushes towards the subconnent is called he monsoon wind.
Jet streams- Easterly jet stream roughly over southern part of peninsula in June
Easterly Jet Stream and Tropical Cyclones : The easterly jet stream steers the tropical depressions into India. These depressions play a significant role in the distribution of monsoon rainfall over the Indian subcontinent
Onset of the Monsoon
During April and May when the sun shines vertically over the Tropic of Cancer, the large landmass in the north of Indian ocean gets intensely heated. This causes the formation of an intense low pressure in the northwestern part of the subcontinent.
Since the pressure in the Indian Ocean in the south of the landmass is high as water gets heated slowly, the low pressure cell attracts the southeast trades across the Equator. These conditions help in the northward shift in the position of the ITCZ. The southwest monsoon may thus, be seen as a continuation of the southeast trades deflected towards the Indian subcontinent after crossing the Equator. These winds cross the Equator between 40°E and 60°E longitudes. The shift in the position of the ITCZ is also related to the phenomenon of the withdrawal of the westerly jet stream from its position over the north Indian plain, south of the Himalayas. The easterly jet stream sets in along 15°N latitude only after the western jet stream has withdrawn itself from the region. This easterly jet stream is held responsible for the burst of the monsoon in India.
Entry of Monsoon into India
The southwest monsoon sets in over the Kerala coast by 1st June and moves swiftly to reach Mumbai and Kolkata between 10th and 13th June. By mid- July, southwest monsoon engulfs the entire subcontinent
Rain-bearing Systems and Rainfall Distribution
- First originate in the Bay of Bengal causing rainfall over the plains of north India. Second is the Arabian Sea current of the south- west monsoon which brings rain to the west coast of India. Much of the rainfall along the Western Ghats is orographic as the moist air is obstructed and forced to rise along the Ghats. The intensity of rainfall over the west coast of India is, however, related to two factors: (i) offshore meteorological conditions. (ii) The position of the equatorial jet stream along the eastern coast of Africa.
The frequency of the tropical depressions originating from the Bay of Bengal varies from
year to year. Their paths over India are mainly determined by the position of ITCZ which is generally termed as the monsoon trough.
Break in the Monsoon
During the south-west monsoon period after having rains for a few days, if rain fails to occur for one or more weeks, it is known as break in the monsoon. These dry spells are quite common during the rainy season. These breaks in the different regions are due to different reasons:
(i) In northern India rains are likely to fail if the rain-bearing storms are not very frequent along the monsoon trough or the ITCZ over this region.
(ii) Over the west coast the dry spells are associated with days when winds blow parallel to the coast.
THE RHYTHM OF SEASONS
(i) the cold weather season (ii) the hot weather season
(iii) the southwest monsoon season (iv) the retreating monsoon season.
The Cold Weather Season Temperature
Temperature : Usually, the cold weather season sets in by mid-November in northern India. December and January are the coldest months in the northern plain. The mean daily temperature remains below 21°C over most parts of northern India. The night temperature can go below 0. Reasons for excesive cold-1. Faraway from moderating sea influence 2. Snowfall in Himalayas 3. Cold winds from Caspian Sea and Turkmenistan. The Peninsular and coastal regions of India, however, does not have any well-defined cold weather season
The Cold Weather Season pressure and winds
3 points as discussed + feeble high and low presure gradients north and south india respectively cause wind to blow from N to S.
The Cold Weather Season Rainfall
Mostly no rainfall since wind moving from land to sea has little moisture and due to anti cyclonic circulation onland, the possibility of rainfall from them reduces. However, there are some exceptions to it:
1. In northwestern India, some weak temperate cyclones from the Mediterranean sea cause rainfall in Punjab, Haryana, Delhi and western Uttar Pradesh. Although the amount is meagre, it is highly beneficial for rabi crops. The precipitation is in the form of snowfall in the lower Himalayas.
2. Central parts of India and northern parts of southern Peninsula also get winter rainfall occasionally.
3. Arunachal Pradesh and Assam in the northeastern parts of India also have rains between 25 mm and 50 mm during these winter months.
4. During October and November, northeast monsoon while crossing over the Bay of Bengal, picks up moisture and causes torrential rainfall over the Tamil Nadu coast, southern Andhra Pradesh, southeast Karnataka and southeast Kera
The Hot Weather Season Temperature:
Temperature: With the apparent northward movement of the sun towards the Tropic of Cancer in March, temperatures start rising in north India. April, May and June are the months of summer in north India. In most parts of India, temperatures recorded are between 30°-32°C. In March, the highest day temperature of about 38°C occurs in the Deccan Plateau while in April, temperature ranging between 38°C and 43°C are found in Gujarat and Madhya Pradesh. In May, the heat belt moves further north, and in the north-western part of India, temperatures around 48°C are not uncommon .
The hot weather season in south India is mild and not so intense as found in north India. The Peninsular situation of south India with moderating effect of the oceans keeps the temperatures lower than that prevailing in north India.
Some Famous Local Storms of Hot Weather Season
(i) Mango Shower : Towards the end of summer, there are pre-monsoon showers which are a common phenomena in Kerala and coastal areas of Karnataka. Locally, they are known as mango showers since they help in the early ripening of mangoes.
(ii) Blossom Shower : With this shower, coffee flowers blossom in Kerala and nearby areas.
(iii) Nor Westers : These are dreaded evening thunderstorms in Bengal and Assam. Their notorious nature can be understood from the local nomenclature of ‘Kalbaisakhi’, a calamity of the month of Baisakh. These showers are useful for tea, jute and rice cultivation. In Assam, these storms are known as “Bardoli Chheerha”.
(iv) Loo : Hot, dry and oppressing winds blowing in the Northern plains from Punjab to Bihar with higher intensity between Delhi and Patna.
Burst/ break of the monsoon
This sudden onset of the moisture-laden winds associated with violent thunder and lightening, is often termed as the “break” or “burst”.
