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English · हिन्दी · తెలుగు · தமிழ் · മലയാളം · मराठी · ಕನ್ನಡ

How the monsoon works

ಕನ್ನಡದಲ್ಲಿ ವಿವರಣೆ

Climate of India · Part 1 / 3 · Fact-checked on · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

The factors that shape India's climate; the winter and summer patterns of pressure and winds; the ITCZ and monsoon trough, the jet streams and Tibet; the old thermal theory and the modern view; onset, breaks, El Niño and the Indian Ocean Dipole; and withdrawal.

Each idea is explained first in Kannada (ಕನ್ನಡ), ending with the English and Hindi exam terms, followed by the same point in exam English. UPSC Prelims is in English or Hindi, so understand it in Kannada and revise it in English.

ಭಾರತದ ಹವಾಮಾನ ಉಷ್ಣವಲಯದ ಮಾನ್ಸೂನ್ ಮಾದರಿ. 'ಮೌಸಿಮ್' ಎಂದರೆ ಅರಬ್ಬಿಯಲ್ಲಿ ಋತು; ಗಾಳಿ ಕೆಲವು ತಿಂಗಳು ನೆಲದಿಂದ ಸಮುದ್ರದ ಕಡೆಗೆ, ಕೆಲವು ತಿಂಗಳು ಸಮುದ್ರದಿಂದ ನೆಲದ ಕಡೆಗೆ ಬೀಸುತ್ತದೆ — ಮನೆಯ ಕಿಟಕಿಯಿಂದ ಗಾಳಿ ಒಮ್ಮೆ ಒಳಗೆ, ಒಮ್ಮೆ ಹೊರಗೆ ಬೀಸಿದಂತೆ. ವರ್ಷದ ಹೆಚ್ಚಿನ ಮಳೆ ಜೂನ್-ಸೆಪ್ಟೆಂಬರ್ ನಾಲ್ಕು ತಿಂಗಳಲ್ಲೇ; ಹಾಗಾಗಿ ಕೃಷಿ, ನೀರು, ಆರ್ಥಿಕತೆ ಅದನ್ನೇ ಅವಲಂಬಿಸಿವೆ. (→ English: monsoon · हिन्दी: मानसून)

In exam EnglishIndia's climate is described as the tropical monsoon type. The word monsoon comes from the Arabic mausim, meaning season, and it refers to a seasonal reversal of winds: for part of the year they blow from the land towards the sea, and for part from the sea towards the land. In India the change decides almost everything else. Most of the country gets the bulk of its year's rain in about four months, from June to September, and the timing and amount of that rain shape farming, water supply and the economy. This chapter has three parts. This first part explains how the monsoon works; the second follows the four seasons through the year; and the third looks at where the rain falls, how reliable it is, and how it is forecast.

ಹವಾಮಾನವನ್ನು ನಿರ್ಧರಿಸುವ ಅಂಶಗಳು: ಅಕ್ಷಾಂಶ — ಕರ್ಕಾಟಕ ಸಂಕ್ರಾಂತಿ ವೃತ್ತ ದೇಶದ ಮಧ್ಯದಿಂದ ಎಂಟು ರಾಜ್ಯಗಳ ಮೂಲಕ ಹಾದುಹೋಗುತ್ತದೆ; ದಕ್ಷಿಣ ವರ್ಷವಿಡೀ ಬೆಚ್ಚಗೆ, ಉತ್ತರದಲ್ಲಿ ನಿಜವಾದ ಚಳಿಗಾಲ. ಸಮುದ್ರದಿಂದ ದೂರ — ಮುಂಬೈಯಲ್ಲಿ ಬೇಸಿಗೆ-ಚಳಿಗಾಲದ ವ್ಯತ್ಯಾಸ ಕಡಿಮೆ, ದೆಹಲಿಯಲ್ಲಿ ಹೆಚ್ಚು; ಮಡಕೆಯ ನೀರು ನಿಧಾನವಾಗಿ ಕಾದು ನಿಧಾನವಾಗಿ ತಣ್ಣಗಾಗುವಂತೆ ಸಮುದ್ರ. ಎತ್ತರ — ಊಟಿ ಮೇ ತಿಂಗಳಲ್ಲೂ ತಂಪು. ಬೆಟ್ಟಗಳು ಮಳೆ ಎಲ್ಲಿ ಬೀಳಬೇಕೆಂದು ನಿರ್ಧರಿಸುತ್ತವೆ. (→ English: Tropic of Cancer · हिन्दी: कर्क रेखा)

In exam EnglishSeveral factors shape this climate. Latitude comes first: the Tropic of Cancer passes through the middle of India, across eight states from Gujarat to Mizoram, so the south lies in the tropics and the north in the subtropics, and the south stays warm all year while the north has a real winter. Distance from the sea matters next. Coastal places such as Mumbai have a small difference between summer and winter temperatures, because the sea warms and cools slowly, while places deep inland, such as Delhi, have hot summers and cold winters; this is called continentality. Altitude cools the air, which is why hill stations such as Shimla or Ooty stay pleasant in May. Relief decides where rain falls, as the Western Ghats and the hills of the north-east show.

ಹಿಮಾಲಯ ಎರಡು ಕೆಲಸ ಮಾಡುತ್ತದೆ — ಮನೆಯ ಸುತ್ತಲಿನ ಎತ್ತರದ ಕಾಂಪೌಂಡ್ ಗೋಡೆಯಂತೆ. ಚಳಿಗಾಲದಲ್ಲಿ ಮಧ್ಯ ಏಷ್ಯಾದ ಹೆಪ್ಪುಗಟ್ಟಿಸುವ ಗಾಳಿಯನ್ನು ತಡೆಯುತ್ತದೆ; ಹಾಗಾಗಿ ಉತ್ತರ ಭಾರತ ಅದೇ ಅಕ್ಷಾಂಶದ ಚೀನಾಕ್ಕಿಂತ ಕಡಿಮೆ ಚಳಿ. ಬೇಸಿಗೆಯಲ್ಲಿ ತೇವದ ಮಾನ್ಸೂನ್ ಗಾಳಿಯನ್ನು ಉತ್ತರಕ್ಕೆ ಹೋಗಲು ಬಿಡದೆ ಮೇಲೆತ್ತಿ ಮಳೆ ಸುರಿಸುತ್ತದೆ. ಹಿಮಾಲಯ ಇಲ್ಲದಿದ್ದರೆ ಉತ್ತರ ಭಾರತ ತಣ್ಣಗೆ, ಒಣದಾಗಿರುತ್ತಿತ್ತು. ಹಾಗಾಗಿ ದಕ್ಷಿಣ ಏಷ್ಯಾ ಒಂದೇ ಹವಾಮಾನ ಘಟಕ. (→ English: monsoon · हिन्दी: मानसून)

In exam EnglishThe Himalaya does two jobs that make India's climate unusual. In winter the great wall of mountains keeps out the bitterly cold air of Central Asia, so north India, although partly outside the tropics, is far milder than places at the same latitude in China or Central Asia. In summer the same wall stops the moist monsoon winds from escaping northwards, forcing them to rise and shed their water over the plains and the mountain slopes. Without the Himalaya much of north India would be both colder and drier. This is why geographers treat the whole of South Asia, cut off from the rest of the continent by the mountains, as a single climatic unit, and why India's climate is called monsoon-type rather than simply tropical or subtropical.

ಚಳಿಗಾಲದಲ್ಲಿ ಮಧ್ಯ ಏಷ್ಯಾ, ವಾಯವ್ಯ ಭಾರತದ ನೆಲ ಚೆನ್ನಾಗಿ ತಣ್ಣಗಾಗಿ ಅಧಿಕ ಒತ್ತಡ; ಗಾಳಿ ನೆಲದಿಂದ ಹೊರಗೆ, ಈಶಾನ್ಯದಿಂದ — ಒಣ ಗಾಳಿ. ಮೇಲೆ ಜೆಟ್ ಪ್ರವಾಹ ಟಿಬೆಟ್‌ನಿಂದ ಎರಡಾಗಿ ಒಡೆದು, ದಕ್ಷಿಣ ಶಾಖೆ ಉತ್ತರ ಭಾರತದ ಮೇಲೆ. ಇದು ಮೆಡಿಟರೇನಿಯನ್ ಕಡೆಯಿಂದ ಕಡಿಮೆ ಒತ್ತಡಗಳನ್ನು ತರುತ್ತದೆ — ನದಿಯ ಹರಿವು ದೋಣಿಗಳನ್ನು ಹೊತ್ತು ತರುವಂತೆ. ಪ್ರತಿ ಪಶ್ಚಿಮ ಪ್ರಕ್ಷುಬ್ಧತೆಯೂ ವಾಯವ್ಯ ಬಯಲಿನಲ್ಲಿ ಸಣ್ಣ ಮಳೆ, ಪಶ್ಚಿಮ ಹಿಮಾಲಯದಲ್ಲಿ ಹಿಮ. (→ English: jet stream; western disturbance · हिन्दी: जेट धारा; पश्चिमी विक्षोभ)

In exam EnglishIn winter the pressure pattern favours dry weather. The land of Central Asia and north-west India cools strongly, and high pressure builds over it, while pressure is lower over the warmer Indian Ocean. Surface winds therefore blow outwards from the land, mostly from the north-east over the plains and the Bay of Bengal, and since they come off the land they carry little moisture. High above, the subtropical westerly jet stream flows across Asia; the Tibetan plateau splits it into two branches, and the southern branch runs south of the Himalaya, over north India. This branch steers a series of low-pressure systems eastwards from the Mediterranean region into India. Each western disturbance brings cloud, light rain to the plains of the north-west and snow to the western Himalaya before it moves on.

ಬೇಸಿಗೆ ಬರುವಾಗ ನೆಲ ಸಮುದ್ರಕ್ಕಿಂತ ವೇಗವಾಗಿ ಕಾದು ವಾಯವ್ಯ ಭಾರತದಲ್ಲಿ ಕಡಿಮೆ ಒತ್ತಡ. ಅಂತರ ಉಷ್ಣವಲಯ ಸಂಗಮ ವಲಯ ಸೂರ್ಯನೊಂದಿಗೆ ಉತ್ತರಕ್ಕೆ ಸರಿದು ಜುಲೈ ವೇಳೆಗೆ ಗಂಗಾ ಬಯಲಿನ ಮೇಲೆ — ಅದೇ ಮಾನ್ಸೂನ್ ತಗ್ಗು. ದಕ್ಷಿಣ ಗೋಳಾರ್ಧದ ಆಗ್ನೇಯ ವಾಣಿಜ್ಯ ಮಾರುತಗಳು ಸಮಭಾಜಕ ವೃತ್ತ ದಾಟಿದೊಡನೆ ಕೊರಿಯೊಲಿಸ್ ಬಲ ಅವನ್ನು ಬಲಕ್ಕೆ ತಿರುಗಿಸಿ ನೈಋತ್ಯ ಗಾಳಿಯಾಗಿಸುತ್ತದೆ — ತಿರುಗುವ ಮೇಜಿನ ಮೇಲೆ ಚೆಂಡು ಉರುಳಿದರೆ ದಾರಿ ಬಾಗುವಂತೆ. ಸೊಮಾಲಿ ಜೆಟ್ ತೇವದ ಗಾಳಿಯನ್ನು ಭಾರತದ ಕಡೆಗೆ ತರುತ್ತದೆ. (→ English: ITCZ; monsoon trough; trade winds; Coriolis force · हिन्दी: अंतःउष्णकटिबंधीय अभिसरण क्षेत्र; मानसून द्रोणी; व्यापारिक पवनें; कोरिऑलिस बल)

In exam EnglishBy late spring the pattern reverses. The land heats far faster than the sea, and an intense low-pressure area forms over north-west India and Pakistan. At the same time the Inter-Tropical Convergence Zone, the belt where the trade winds of the two hemispheres meet, moves north with the overhead Sun until, by July, it lies roughly along the Ganga plain; here it is called the monsoon trough. Air flows towards this low from the high-pressure areas of the southern Indian Ocean, including the Mascarene high near Madagascar. The south-east trade winds of the Southern Hemisphere cross the equator, and the Coriolis force, which deflects moving air to the right in the Northern Hemisphere, turns them into south-westerly winds. A fast low-level current off the coast of Somalia, the Somali jet, carries much of this moist air towards India.

ಮೇಲಿನ ಗಾಳಿಯ ಬದಲಾವಣೆಗಳೂ ಮುಖ್ಯ. ಬೇಸಿಗೆಯ ಆರಂಭದಲ್ಲಿ ಪಶ್ಚಿಮ ಜೆಟ್ ಪ್ರವಾಹ ಹಿಮಾಲಯದ ಉತ್ತರಕ್ಕೆ ಸರಿಯುತ್ತದೆ; ಅದು ಹಿಂದೆ ಸರಿಯುವುದು ಮಾನ್ಸೂನ್ ಆಗಮನಕ್ಕೆ ಸಂಬಂಧಿಸಿದೆ. ಅದರ ಜಾಗದಲ್ಲಿ ಪರ್ಯಾಯದ್ವೀಪದ ಮೇಲೆ ಸುಮಾರು 15° ಉತ್ತರದಲ್ಲಿ ಉಷ್ಣವಲಯದ ಪೂರ್ವ ಜೆಟ್. ಕಾರಣ ಟಿಬೆಟ್ ಪ್ರಸ್ಥಭೂಮಿ — ಎತ್ತರದ ಕಾವಲಿಯಂತೆ ಚೆನ್ನಾಗಿ ಕಾದು ಮೇಲಿನ ಗಾಳಿಯನ್ನು ಎಬ್ಬಿಸುತ್ತದೆ; ಮೇಲೆ ಅಧಿಕ ಒತ್ತಡ ಉಂಟಾಗಿ ದಕ್ಷಿಣಕ್ಕೆ ಹರಿಯುವ ಗಾಳಿ ಪೂರ್ವ ಜೆಟ್ ಆಗುತ್ತದೆ, ಕೆಳಗೆ ಸಮುದ್ರದ ತೇವದ ಗಾಳಿಯನ್ನು ಸೆಳೆಯುತ್ತದೆ. (→ English: jet stream · हिन्दी: जेट धारा)

In exam EnglishChanges high in the atmosphere matter as much as those at the surface. In early summer the subtropical westerly jet stream that sat south of the Himalaya in winter shifts north of the mountains, and its withdrawal is closely linked with the arrival of the monsoon over India. In its place an upper-level tropical easterly jet develops over the Peninsula at around 15°N during the monsoon months. A key reason is the Tibetan plateau. This huge, high block of land is heated strongly in summer and warms the air above it, which rises and spreads out at great heights, creating an upper-level high pressure area over Tibet. Air flowing outwards from it towards the south becomes the easterly jet, and the rising air over the land strengthens the circulation that draws moist air in from the ocean at the surface.
Winter and summer patterns over India compared
FeatureWinter (December to February)Summer monsoon (June to September)
Surface pressure over north-west IndiaHighLow
Surface windsNorth-easterly, off the land, drySouth-westerly, off the sea, moist
ITCZWell south, over the Indian OceanPulled north into the monsoon trough over the Ganga plain
Westerly jet streamSouth of the Himalaya, over north IndiaNorth of the Himalaya
Tropical easterly jetAbsentOver the Peninsula, around 15°N
Typical weatherCool and mostly dry; western disturbances in the north-westWidespread rain with active spells and breaks

ಹಳೆಯ ವಿವರಣೆ: ಮಾನ್ಸೂನ್ ಒಂದು ದೊಡ್ಡ ಸಮುದ್ರದ ಗಾಳಿ. 1686ರಲ್ಲಿ ಎಡ್ಮಂಡ್ ಹ್ಯಾಲಿ ಹೇಳಿದ — ಹಗಲು ನೆಲ ನೀರಿಗಿಂತ ಬೇಗ ಕಾಯುವಂತೆ, ಬೇಸಿಗೆಯಲ್ಲಿ ಖಂಡ ಸಮುದ್ರಕ್ಕಿಂತ ಬೇಗ ಕಾದು ತೇವದ ಗಾಳಿಯನ್ನು ಸೆಳೆಯುತ್ತದೆ. ಆದರೆ ಮಾನ್ಸೂನ್ ಏಕೆ ಹಠಾತ್ತಾಗಿ ಬರುತ್ತದೆ, ನಡುವೆ ಏಕೆ ನಿಲ್ಲುತ್ತದೆ, ವರ್ಷದಿಂದ ವರ್ಷಕ್ಕೆ ಏಕೆ ಬದಲಾಗುತ್ತದೆ ಎಂಬುದನ್ನು ಇದು ವಿವರಿಸದು. ಆಧುನಿಕ ನೋಟ: ಅಂತರ ಉಷ್ಣವಲಯ ಸಂಗಮ ವಲಯದ ಸರಿಯುವಿಕೆ, ಜೆಟ್ ಪ್ರವಾಹಗಳು, ಟಿಬೆಟ್‌ನ ಶಾಖ, ಸಾಗರಗಳ ಸ್ಥಿತಿ — ಎಲ್ಲವೂ ಸೇರಿ, ಒಂದು ತಂಡದ ಆಟದಂತೆ. (→ English: Inter-Tropical Convergence Zone · हिन्दी: अंतःउष्णकटिबंधीय अभिसरण क्षेत्र)

In exam EnglishThe oldest explanation treats the monsoon as a giant sea breeze. In 1686 the astronomer Edmund Halley suggested that, just as land heats faster than water during the day, a whole continent heats faster than the ocean in summer, pulling in moist sea air, and cools faster in winter, sending dry air back out. This thermal idea explains the basic seasonal reversal, but it cannot explain why the monsoon arrives so suddenly, why it pauses for days or weeks, or why its strength changes from year to year. The modern view therefore treats the monsoon as part of the planet's general circulation: the seasonal shift of the Inter-Tropical Convergence Zone, the movement of the jet streams, the heating of Tibet and conditions over the Pacific and Indian oceans all act together, and land-sea contrast is only one piece.

ಮಾನ್ಸೂನ್ ಸುಮಾರು ಜೂನ್ 1ರಂದು ಕೇರಳ ಕರಾವಳಿ ತಲುಪುತ್ತದೆ (ವರ್ಷದಿಂದ ವರ್ಷಕ್ಕೆ ಒಂದು ವಾರ ಹಿಂದೆ-ಮುಂದೆ). ವಾರಗಳ ಬಿಸಿಲಿನ ನಂತರ ಕೆಲವೇ ದಿನಗಳಲ್ಲಿ ಜೋರು ಗಾಳಿ, ಭಾರಿ ಮಳೆ — ಇದನ್ನು 'ಸ್ಫೋಟ' ಎನ್ನುತ್ತಾರೆ, ಮುಚ್ಚಿದ ಅಣೆಕಟ್ಟಿನ ಗೇಟುಗಳು ಒಮ್ಮೆಲೇ ತೆರೆದಂತೆ. ನಂತರ ಎರಡು ಶಾಖೆಗಳು: ಅರಬ್ಬಿ ಸಮುದ್ರ ಶಾಖೆ ಪಶ್ಚಿಮ ಘಟ್ಟಗಳಿಗೆ ಬಡಿದು ಪಶ್ಚಿಮ ಕರಾವಳಿಯಲ್ಲಿ ಮೇಲಕ್ಕೆ; ಬಂಗಾಳಕೊಲ್ಲಿ ಶಾಖೆ ಈಶಾನ್ಯಕ್ಕೆ ಹೋಗಿ ಗಂಗಾ ಬಯಲಿನಲ್ಲಿ ಪಶ್ಚಿಮಕ್ಕೆ. 2020ರ ಪರಿಷ್ಕರಣೆಯಂತೆ ಜುಲೈ 8ರ ವೇಳೆಗೆ ಇಡೀ ದೇಶ. (→ English: burst of the monsoon · हिन्दी: मानसून का प्रस्फोट)

In exam EnglishThe monsoon reaches the Kerala coast on about 1 June, the normal date used by the India Meteorological Department, give or take about a week in a given year. Its arrival is often sudden: after weeks of heat, strong moist winds and heavy rain set in within a few days, a change popularly called the burst of the monsoon. The winds then advance in two branches. The Arabian Sea branch strikes the Western Ghats and moves up the west coast, while the Bay of Bengal branch moves north towards the north-east and is then turned westward along the Ganga plain by the Himalaya and the monsoon trough. The two branches merge over north-west India. Under the normal dates IMD revised in 2020, the monsoon covers the whole country by about 8 July, a week earlier than the old date of 15 July.

ಮಾನ್ಸೂನ್ ನಿರಂತರ ಸುರಿಯುವುದಿಲ್ಲ: ಕೆಲವು ದಿನ ಜೋರು ಮಳೆ, ಕೆಲವು ದಿನ ಬಿಡುವು. ಮಾನ್ಸೂನ್ ತಗ್ಗು ಮಧ್ಯ ಬಯಲಿನ ಮೇಲಿದ್ದರೆ ಮಳೆ ಎಲ್ಲೆಡೆ; ಹಿಮಾಲಯದ ತಪ್ಪಲಿಗೆ ಸರಿದರೆ ದೇಶವಿಡೀ ಒಣ, ಬೆಟ್ಟಗಳಲ್ಲಿ ಮತ್ತು ಈಶಾನ್ಯದಲ್ಲಿ ಭಾರಿ ಮಳೆ, ಬಿಹಾರ-ಅಸ್ಸಾಂನಲ್ಲಿ ಪ್ರವಾಹ. ಬಿತ್ತಿದ ತಕ್ಷಣ ಬಿಡುವು ಬಂದರೆ ಒಟ್ಟು ಮಳೆ ಸಾಮಾನ್ಯವಿದ್ದರೂ ಬೆಳೆ ಹಾಳು — ಮಗುವಿಗೆ ಸರಿಯಾದ ಸಮಯಕ್ಕೆ ಹಾಲು ಸಿಗದಂತೆ. ಮ್ಯಾಡನ್-ಜೂಲಿಯನ್ ಆಂದೋಲನ 30-60 ದಿನಗಳಿಗೊಮ್ಮೆ ಸುತ್ತುವ ಮೋಡದ ಅಲೆ. (→ English: monsoon trough; break in the monsoon · हिन्दी: मानसून द्रोणी; मानसून में विराम)

In exam EnglishOnce established, the monsoon does not rain steadily. It alternates between active spells, with widespread heavy rain, and breaks, when rain stops over large parts of the country for days or even a couple of weeks. The position of the monsoon trough explains much of this. When its axis lies over the central plains, rain is widespread. When it shifts north to the foothills of the Himalaya, most of India dries out while heavy rain falls in the mountains and the north-east, often bringing floods to the rivers of Bihar and Assam. Breaks that come at the wrong moment, such as just after sowing, can damage crops even in a year whose total rain is normal. One cause of these swings is the Madden-Julian Oscillation, a pulse of cloud and rain that travels eastward around the tropics every 30 to 60 days.

ದೂರದ ಸಾಗರಗಳೂ ಮಾನ್ಸೂನ್ ಬಲವನ್ನು ಬದಲಿಸುತ್ತವೆ. ಎಲ್ ನಿನೊ ವರ್ಷ ಪೆಸಿಫಿಕ್‌ನಲ್ಲಿ ವಾಣಿಜ್ಯ ಮಾರುತಗಳು ದುರ್ಬಲವಾಗಿ ಬೆಚ್ಚನೆಯ ನೀರು ಪೂರ್ವಕ್ಕೆ; ನಮ್ಮ ಮಳೆ ಕಡಿಮೆಯಾಗುವ ಸಾಧ್ಯತೆ. ಲಾ ನಿನಾ ವರ್ಷ ಸಾಮಾನ್ಯವಾಗಿ ಒಳ್ಳೆಯ ಮಳೆ. ದಕ್ಷಿಣ ಆಂದೋಲನವನ್ನು ಗಿಲ್ಬರ್ಟ್ ವಾಕರ್ ವಿವರಿಸಿದರು. ಹಿಂದೂ ಮಹಾಸಾಗರ ದ್ವಿಧ್ರುವ: ಪಶ್ಚಿಮ ಭಾಗ ಬೆಚ್ಚಗಿದ್ದರೆ (ಧನಾತ್ಮಕ) ಮಳೆಗೆ ಸಹಾಯ, ಎಲ್ ನಿನೊ ಪರಿಣಾಮವನ್ನು ಕಡಿಮೆ ಮಾಡಬಹುದು — 1997ರಂತೆ. ಒಂದು ಏಟಿಗೆ ಪಕ್ಕದಿಂದ ಇನ್ನೊಂದು ಕೈ ಆಸರೆ ಕೊಟ್ಟಂತೆ. (→ English: El Niño; La Niña; Indian Ocean Dipole · हिन्दी: एल नीनो; ला नीना; हिंद महासागर द्विध्रुव)

In exam EnglishConditions far away in the oceans also affect how strong a monsoon is. In an El Niño year the trade winds over the Pacific weaken and unusually warm water spreads east; this shifts rising air away from the Indian region, and Indian monsoons in El Niño years have tended to be weak. In a La Niña year the reverse happens and the monsoon is usually normal or good. The see-saw of air pressure across the tropical Pacific linked to these events, the Southern Oscillation, was first described by Gilbert Walker while he headed the Indian meteorological service. Closer to home, the Indian Ocean Dipole compares the temperature of the western and eastern Indian Ocean. A positive dipole, with a warmer west, tends to help the monsoon and can offset an El Niño, as in 1997, when a strong El Niño was accompanied by normal Indian rainfall.

ಮಾನ್ಸೂನ್ ಬಂದಷ್ಟು ವೇಗವಾಗಿ ಹೋಗುವುದಿಲ್ಲ. ಸೂರ್ಯ ದಕ್ಷಿಣಕ್ಕೆ ಸರಿದಂತೆ ನೆಲ ತಣ್ಣಗಾಗಿ ಮಾನ್ಸೂನ್ ತಗ್ಗು ದಕ್ಷಿಣಕ್ಕೆ ಜಾರುತ್ತದೆ. 2020ರ ಪರಿಷ್ಕರಣೆಯಂತೆ ಸುಮಾರು ಸೆಪ್ಟೆಂಬರ್ 17ರಂದು ಪಶ್ಚಿಮ ರಾಜಸ್ಥಾನದಿಂದ ಹಿಂದೆ ಸರಿಯುವಿಕೆ ಆರಂಭವಾಗಿ ಸುಮಾರು ಅಕ್ಟೋಬರ್ 15ರ ವೇಳೆಗೆ ಇಡೀ ದೇಶದಿಂದ. ಆದರೆ ಬಂಗಾಳಕೊಲ್ಲಿಯ ಮೇಲೆ ಈಶಾನ್ಯ ಗಾಳಿ ತೇವ ಹೀರಿ ಅಕ್ಟೋಬರ್-ನವೆಂಬರ್‌ನಲ್ಲಿ ತಮಿಳುನಾಡು ಕರಾವಳಿಗೆ ಮುಖ್ಯ ಮಳೆ ತರುತ್ತದೆ — ನಮ್ಮಲ್ಲಿ ಹಿಂಗಾರು ಮಳೆ ಎನ್ನುವುದು ಇದೇ ಕಾಲ. (→ English: withdrawal of the monsoon; monsoon trough · हिन्दी: मानसून की वापसी; मानसून द्रोणी)

In exam EnglishThe monsoon leaves more gradually than it comes. As the Sun moves south after the summer solstice, the land cools, the low over north-west India weakens and the monsoon trough slides back south. Under IMD's revised normal dates, withdrawal begins from western Rajasthan around 17 September, and the monsoon has left the whole country by around 15 October. Skies clear in the north, days stay hot while nights cool, and winds slowly turn back to blowing from the land. The withdrawing monsoon does not end the rain everywhere: as the winds turn north-easterly over the Bay of Bengal, they pick up moisture and bring the main rainy season to the Tamil Nadu coast in October and November, and the Bay often breeds cyclones in these months. Those events belong to the seasons described in Part 2.

ಒಟ್ಟಾರೆ ಮಾನ್ಸೂನ್ ದಕ್ಷಿಣ ಏಷ್ಯಾದ ಮೇಲಿನ ಇಡೀ ವಾಯುಮಂಡಲ ವ್ಯವಸ್ಥೆ ಋತುವಿಗೆ ತಕ್ಕಂತೆ ತೂಗುವ ಉಯ್ಯಾಲೆ, ಕೇವಲ ದೊಡ್ಡ ಸಮುದ್ರದ ಗಾಳಿಯಲ್ಲ. ಚಳಿಗಾಲ: ನೆಲದ ಮೇಲೆ ಅಧಿಕ ಒತ್ತಡ, ಪಶ್ಚಿಮ ಜೆಟ್, ಪಶ್ಚಿಮ ಪ್ರಕ್ಷುಬ್ಧತೆಗಳು — ತಂಪು, ಒಣ. ಬೇಸಿಗೆ: ವಾಯವ್ಯದಲ್ಲಿ ಕಡಿಮೆ ಒತ್ತಡ, ಉತ್ತರಕ್ಕೆ ಸರಿದ ಅಂತರ ಉಷ್ಣವಲಯ ಸಂಗಮ ವಲಯ, ನೈಋತ್ಯ ಗಾಳಿ, ಪೂರ್ವ ಜೆಟ್, ಕಾದ ಟಿಬೆಟ್ — ತೇವದ ಗಾಳಿ ದೇಶವಿಡೀ. ಬಲ ಎಲ್ ನಿನೊ, ದ್ವಿಧ್ರುವವನ್ನು ಅವಲಂಬಿಸಿದೆ. (→ English: Inter-Tropical Convergence Zone · हिन्दी: अंतःउष्णकटिबंधीय अभिसरण क्षेत्र)

In exam EnglishPut together, the monsoon is a seasonal swing of the whole atmospheric system over South Asia, not just a sea breeze on a large scale. In winter, high pressure over the land, the westerly jet south of the Himalaya and western disturbances give north India cool, mostly dry weather. In summer, the low over the north-west, the Inter-Tropical Convergence Zone pulled north into the monsoon trough, cross-equatorial winds turned south-west by the Coriolis force, the easterly jet and a heated Tibet combine to draw moist ocean air across the country. The monsoon's timing and strength then depend on the trough's movements, on oscillations such as the MJO, and on El Niño and the Indian Ocean Dipole. Part 2 shows how this mechanism plays out season by season across India.

Exam traps

Recap

Practice questions

Q1. Western disturbances, which bring winter rain to north-west India, originate over which region?

  1. The Bay of Bengal
  2. The Mediterranean region
  3. The South China Sea
  4. The Tibetan plateau
Show answer

Answer: B. The Mediterranean region

Western disturbances are low-pressure systems from the Mediterranean region, steered east by the westerly jet. The Bay of Bengal and the South China Sea lie to the east and send systems westward, not these winter lows; the Tibetan plateau splits the jet but is not their source.

Q2. Consider the following statements:
1. In winter the subtropical westerly jet stream flows south of the Himalaya.
2. The tropical easterly jet develops over the Indian Peninsula in winter.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: A. 1 only

Statement 1 is correct. Statement 2 is wrong: the tropical easterly jet develops in the summer monsoon months, not in winter. So '2 only' and 'Both' are wrong, and 'Neither' rejects the true first statement.

Q3. The south-west monsoon winds over India are best explained as:

  1. North-east trades blowing out from Central Asia
  2. South-east trades that cross the equator and are deflected to the right by the Coriolis force
  3. Westerlies brought in by western disturbances
  4. Polar easterlies diverted by the Himalaya
Show answer

Answer: B. South-east trades that cross the equator and are deflected to the right by the Coriolis force

The south-east trades of the Southern Hemisphere cross the equator towards the low over north-west India and are turned to the right, becoming south-westerly. North-east winds blow off the land in winter; western disturbances are winter systems; polar easterlies do not reach India.

Q4. A 'break' in the south-west monsoon is usually associated with:

  1. The monsoon trough shifting to the foothills of the Himalaya
  2. The monsoon trough moving south of the equator
  3. The westerly jet returning south of the Himalaya in July
  4. A La Niña developing in the Pacific
Show answer

Answer: A. The monsoon trough shifting to the foothills of the Himalaya

During a break the trough's axis moves north to the Himalayan foothills, so the plains dry out while the hills and the north-east get heavy rain. The trough does not cross the equator in the season; the westerly jet stays north of the Himalaya in July; La Niña tends to help the monsoon.

Q5. According to the normal dates revised by the India Meteorological Department in 2020, by about which date does the south-west monsoon cover the whole of India?

  1. 1 June
  2. 8 July
  3. 15 July
  4. 17 September
Show answer

Answer: B. 8 July

The revised normal date is about 8 July. 1 June is the normal onset over Kerala; 15 July was the old date before the revision; 17 September is when withdrawal normally begins from western Rajasthan.

Q6. Consider the following statements:
1. A positive Indian Ocean Dipole, with a warmer western Indian Ocean, tends to help the Indian monsoon.
2. In every El Niño year, India's monsoon rainfall has been deficient.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: A. 1 only

Statement 1 is correct. Statement 2 is wrong: El Niño only tends to weaken the monsoon; in 1997 a strong El Niño came with normal rainfall. So '2 only' and 'Both' are wrong, and 'Neither' rejects the true first statement.

Q7. Match List I (feature) with List II (description):
A. Monsoon trough
B. Somali jet
C. Mascarene high
D. Madden-Julian Oscillation
1. High-pressure area near Madagascar
2. The ITCZ pulled north over the Ganga plain
3. Eastward-moving pulse of tropical cloud and rain
4. Fast low-level wind current off the East African coast
Select the correct answer using the code given below.

  1. A-2, B-4, C-1, D-3
  2. A-2, B-1, C-4, D-3
  3. A-3, B-4, C-1, D-2
  4. A-4, B-2, C-3, D-1
Show answer

Answer: A. A-2, B-4, C-1, D-3

The monsoon trough is the ITCZ over the Ganga plain, the Somali jet a low-level current off East Africa, the Mascarene high lies near Madagascar, and the MJO is an eastward-moving pulse of cloud and rain. The second code swaps the Somali jet and the Mascarene high; the third swaps the trough and the MJO; the fourth mismatches all four.

Q8. Consider the following statements:
1. Counted state by state, the Tropic of Cancer crosses eight Indian states.
2. Coastal places such as Mumbai have a larger annual range of temperature than inland places such as Delhi.
3. The heating of the Tibetan plateau in summer helps strengthen the monsoon circulation.
Which of the statements given above are correct?

  1. 1 and 2 only
  2. 1 and 3 only
  3. 2 and 3 only
  4. 1, 2 and 3
Show answer

Answer: B. 1 and 3 only

Statements 1 and 3 are correct. Statement 2 is wrong: the sea moderates coastal temperatures, so Mumbai's annual range is smaller than Delhi's; this is continentality. So every option containing statement 2 is wrong.

All partsNext: Part 2 →

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