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Pressure belts, winds and jet streams

मराठीत स्पष्टीकरण

Climatology: the atmosphere, winds, weather systems and world climates · Part 2 / 4 · Fact-checked on 8 November 2026 · how we check

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

How atmospheric pressure is measured and mapped with isobars, the pressure belts and the ITCZ, the pressure gradient and Coriolis forces and friction, cyclonic and anticyclonic circulation, the planetary winds and the three cells, monsoons, land, sea, mountain and valley breezes, local winds, and jet streams.

Each idea is explained first in Marathi (मराठी), 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 Marathi and revise it in English.

ऊन सगळीकडे सारखे पडत नाही — विषुववृत्ताजवळ उष्णता जास्त, ध्रुवांजवळ कमी. तापलेली हवा हलकी होऊन वर जाते, तिथे दाब कमी होतो; थंड हवा जड होऊन खाली बसते आणि दाब वाढवते. हवा नेहमी जास्त दाबाकडून कमी दाबाकडे धावते — सायकलच्या ट्यूबचा व्हॉल्व उघडला की हवा फुसकन बाहेर येते तसे. अशी धावताना ती उष्णता आणि ओलावा जगभर वाहून नेते. या भागात दाब, दाबाचे पट्टे, वाऱ्याला वळवणारी बले, विविध वारे आणि वर वाहणारे जेट प्रवाह पाहू. (→ English: wind and pressure · हिन्दी: पवन और दाब)

In exam EnglishPart 1 showed that the Sun heats the Earth unevenly: the tropics gain more energy than they lose, while the poles lose more than they gain. The air answers this imbalance by moving. Warm air expands and rises, leaving lower pressure at the surface; cold air is dense and sinks, building higher pressure. Wind is simply air flowing from higher towards lower pressure. This part follows that chain: how pressure is measured and mapped, the belts of high and low pressure, the forces that steer the wind, the permanent, seasonal and local winds, and the fast currents of air high above called jet streams.

वातावरणीय दाब म्हणजे आपल्या डोक्यावरच्या हवेच्या स्तंभाचे वजन. ते बॅरोमीटरने मोजतात, मिलिबार किंवा हेक्टोपास्कलमध्ये सांगतात — दोन्ही एकच. समुद्रसपाटीला सरासरी 1013 hPa. वर जाईल तसा दाब झपाट्याने घटतो; म्हणून विमानात दाब कृत्रिमरीत्या राखतात. सारख्या दाबाच्या ठिकाणांना जोडणाऱ्या रेषा म्हणजे समदाब रेषा. डोंगराच्या नकाशात उंचीच्या रेषा जवळ असल्या की उतार तीव्र — तसेच समदाब रेषा जवळ असल्या की वारा जोरात, दूर असल्या की मंद. (→ English: isobar · हिन्दी: समदाब रेखा)

In exam EnglishAtmospheric pressure is the weight of the column of air resting on a unit area of the surface. It is measured with a barometer, either the mercury type or the portable aneroid type, and weather services report it in millibars or hectopascals, which are equal units. Average pressure at sea level is about 1013 hPa. Because most of the air's mass lies close to the ground, pressure drops quickly with height, which is why aircraft cabins are pressurised. To compare stations at different heights, readings are reduced to sea level and plotted on a map, and lines are drawn through places of equal pressure; these lines are isobars. Closely packed isobars mean pressure changes sharply over a short distance, a steep pressure gradient and strong winds; widely spaced isobars mean a gentle gradient and light winds.

पृथ्वीभोवती दाब कमरपट्ट्यांसारख्या पट्ट्यांत मांडलेला असतो. विषुववृत्ताजवळ खूप तापून हवा वर जाते — कमी दाब; दोन्ही गोलार्धांचे व्यापारी वारे जिथे भेटतात तेच आंतर उष्णकटिबंधीय अभिसरण क्षेत्र. तिथे वारा जवळजवळ हलत नाही, जुन्या खलाशांनी त्याला 'डोलड्रम' म्हटले. 30° जवळ हवा खाली उतरते — जास्त दाब, 'अश्व अक्षांश'. 60° जवळ पुन्हा कमी दाब, ध्रुवांवर जास्त दाब. विषुववृत्त आणि ध्रुवांचे पट्टे तापमानामुळे; 30° आणि 60° चे पट्टे हवेच्या हालचालीमुळे. सूर्य उत्तरेकडे सरकला की पट्टेही उत्तरेकडे सरकतात. (→ English: Inter-Tropical Convergence Zone · हिन्दी: अंतःउष्णकटिबंधीय अभिसरण क्षेत्र)

In exam EnglishOn a uniform Earth, pressure would lie in belts along the parallels. Near the equator lies the equatorial low: strong heating makes the air rise, and the trade winds of the two hemispheres meet in the Inter-Tropical Convergence Zone. Surface winds here are weak and variable, so sailors called the zone the doldrums. Near 30° north and south lie the subtropical highs, where air that rose at the equator sinks; their calm, dry air earned them the name horse latitudes. Near 60° lie the subpolar lows, and over the poles the polar highs. The equatorial low and the polar highs owe their origin mainly to temperature, so they are called thermal; the subtropical highs and subpolar lows are produced mainly by the movement of air, so they are called dynamic. The belts are not fixed: they shift north in the northern summer and south in the northern winter, following the overhead Sun.

The pressure belts of the Earth
Belt	Approximate latitude	Origin	Key features
Equatorial low	About 0–10° N and S	Thermal	Rising air; ITCZ; doldrums
Subtropical high	About 30° N and S	Dynamic	Sinking air; calm, dry horse latitudes
Subpolar low	About 60° N and S	Dynamic	Westerlies meet polar easterlies; stormy
Polar high	Near the poles	Thermal	Cold, dense, sinking air

वाऱ्याची चाल तीन बले ठरवतात. एक दाबातील फरक — हवेला जास्त दाबाकडून कमी दाबाकडे ढकलतो. दोन कोरिओलिस बल — फिरत्या पाळण्यावर उभे राहून चेंडू फेकला तर तो वाकडा जाताना दिसतो ना; तसेच फिरत्या पृथ्वीवर वारा उत्तर गोलार्धात उजवीकडे, दक्षिण गोलार्धात डावीकडे वळतो. ते दिशा बदलते, वेग नाही; विषुववृत्तावर शून्य, ध्रुवांवर सर्वाधिक. तीन घर्षण — जमिनीजवळ वाऱ्याला मंद करते. वर घर्षण नसलेल्या ठिकाणी वारा समदाब रेषांना समांतर वाहतो. (→ English: Coriolis force · हिन्दी: कोरिऑलिस बल)

In exam EnglishThree forces decide how the air actually moves. The pressure gradient force pushes air from high towards low pressure, at right angles to the isobars, and is stronger where they are closer together. The Coriolis force arises from the Earth's rotation: to an observer on the spinning planet, moving air seems to swerve, to the right in the Northern Hemisphere and to the left in the Southern. It alters the wind's direction but not its speed; it is zero at the equator, greatest at the poles, and stronger for faster winds. Friction with the ground slows the wind in roughly the lowest kilometre, so winds over rough land are gentler than over the smooth sea. Higher up, where friction hardly matters, the pressure gradient and Coriolis forces come into balance and the wind blows parallel to the isobars; such a wind is called geostrophic.

ही बले एकत्र आली की वारा दाबकेंद्रांभोवती गोल फिरतो. कमी दाबाच्या केंद्राकडे हवा आत येऊन वर जाते; उत्तर गोलार्धात ती घड्याळाच्या काट्यांच्या उलट, दक्षिण गोलार्धात घड्याळाच्या दिशेने फिरते. जास्त दाबाच्या केंद्रात हवा खाली उतरून बाहेर पसरते — दिशा उलट, हवामान कोरडे आणि शांत. बादलीतले पाणी गोल फिरवले की मध्ये खळगा पडतो, तसे डोळ्यासमोर आणा. उत्तर गोलार्धात वाऱ्याकडे पाठ करून उभे राहिलात तर कमी दाब डावीकडे — हाच बाइज बॅलट नियम. विषुववृत्तावर वळवणारे बल नसल्याने तिथे वादळे क्वचितच. (→ English: cyclone and anticyclone · हिन्दी: चक्रवात और प्रतिचक्रवात)

In exam EnglishPut these forces together and the wind spirals around centres of low and high pressure. A cyclone is a centre of low pressure: air converges towards it and rises. Deflected to the right, the inflowing air in the Northern Hemisphere circles anticlockwise; in the Southern Hemisphere it circles clockwise. An anticyclone is a centre of high pressure with sinking air that spreads outwards, turning clockwise in the Northern Hemisphere and anticlockwise in the Southern, and it usually brings settled, dry weather. A rule of thumb called Buys Ballot's law follows: in the Northern Hemisphere, if you stand with your back to the wind, lower pressure lies to your left. Because the deflecting force vanishes at the equator, cyclones rarely form within about 5° of it, a point taken up in Part 3.

वर्षभर एकाच दिशेने वाहणारे वारे म्हणजे ग्रहीय वारे. 30° च्या जास्त दाबाकडून विषुववृत्ताकडे वाहणारे व्यापारी वारे — पृथ्वीच्या फिरण्यामुळे उत्तरेत ईशान्येकडून, दक्षिणेत आग्नेयेकडून. जुन्या शिडाच्या जहाजांसाठी ते भरवशाच्या एसटी सेवेसारखे. 30° कडून 60° कडे वाहणारे पश्चिमी वारे — उत्तरेत नैर्ऋत्येकडून, दक्षिणेत वायव्येकडून. दक्षिण गोलार्धात 40°–60° दरम्यान अडवायला जमीन नाही, म्हणून ते गर्जत वाहतात: 'रोअरिंग फोर्टीज, फ्यूरियस फिफ्टीज, श्रीकिंग सिक्स्टीज'. ध्रुवांकडून थंड पूर्वी वारे. (→ English: trade winds, westerlies · हिन्दी: व्यापारिक पवनें, पछुआ पवनें)

In exam EnglishWinds that blow between the pressure belts throughout the year are called planetary or permanent winds. From the subtropical highs, air moves towards the equatorial low as the trade winds; turned by the Earth's rotation, they come from the north-east in the Northern Hemisphere and from the south-east in the Southern. Their reliability made them valuable to sailing ships. From the subtropical highs towards the subpolar lows blow the westerlies, from the south-west in the Northern Hemisphere and from the north-west in the Southern. Across the Southern Hemisphere oceans, between about 40° and 60°, almost no land interrupts them, so they become strong and stormy; sailors named them the Roaring Forties, Furious Fifties and Shrieking Sixties after their latitudes. Finally, cold polar easterlies flow out of the polar highs towards the subpolar lows.

प्रत्येक गोलार्धात हवा तीन चक्रांमध्ये फिरते. हॅडली चक्र: विषुववृत्ताजवळ उबदार हवा वर जाऊन, उंचावरून ध्रुवाकडे जाऊन, 30° जवळ खाली उतरून, व्यापारी वाऱ्याच्या रूपात परत येते. ध्रुवीय चक्र: ध्रुवावर थंड हवा खाली उतरून बाहेर वाहते आणि 60° जवळ वर जाते. मध्ये फेरेल चक्र — दोन दातेरी चाकांमधले छोटे चाक शेजारच्या चाकांमुळे फिरते तसे ते स्वतःहून नव्हे तर शेजाऱ्यांमुळे फिरते; त्याचा खालचा भाग म्हणजे पश्चिमी वारे. ही तीन चक्रे आणि सागरी प्रवाह मिळून उष्णकटिबंधातील जादा उष्णता ध्रुवांकडे पोहोचवतात. (→ English: Hadley, Ferrel and polar cells · हिन्दी: हैडली, फ़ेरल और ध्रुवीय कोष्ठ)

In exam EnglishThese surface winds are the lower limbs of three loops of circulation in each hemisphere, known as cells. In the Hadley cell, warm air rises near the equator, flows poleward high up, sinks near 30° and returns to the equator as the trade winds. In the polar cell, cold air sinks over the pole, spreads out as the polar easterlies and rises near 60°. Between the two lies the Ferrel cell, driven by its neighbours rather than directly by heating; its surface branch is the westerlies. The Hadley and polar cells are called thermally direct, because warm air rises and cold air sinks in them, while the Ferrel cell is thermally indirect. Working with the ocean currents, this three-cell circulation carries surplus heat from the tropics towards the poles, completing the heat-budget story of Part 1.

काही वारे ऋतूनुसार दिशा बदलतात — तेच मान्सून; अरबी शब्द 'मौसिम' म्हणजे ऋतू. उन्हाळ्यात जमीन समुद्रापेक्षा लवकर तापते — तवा पटकन तापतो, हंड्यातले पाणी उशिरा तापते तसे. तेव्हा जमिनीवर कमी दाब, समुद्रावरून ओलसर वारे आत. हिवाळ्यात उलटे, कोरडे वारे जमिनीकडून समुद्राकडे. जून–सप्टेंबरचा नैर्ऋत्य मान्सून भारताचा वर्षभराचा बहुतांश पाऊस देतो; ऑक्टोबर–डिसेंबरचा ईशान्य मान्सून बंगालचा उपसागर ओलांडून तमिळनाडू किनाऱ्याला मुख्य पाऊस देतो. (→ English: monsoon · हिन्दी: मानसून)

In exam EnglishSome winds reverse their direction with the seasons. The best known are the monsoon winds, a name taken from the Arabic word mausim, meaning season. In summer, land heats up faster than the sea, so low pressure forms over the land and moist winds blow in from the ocean; in winter, land cools faster, high pressure builds over it and dry winds blow out towards the sea. This land–sea contrast works together with the seasonal shift of the ITCZ and the pressure belts. Over South Asia the result is the south-west monsoon of June to September, which brings most of India's annual rain, and the north-east monsoon of October to December, which, after crossing the Bay of Bengal, gives the Tamil Nadu coast its main rainy season. How the Indian monsoon sets in, advances and breaks is taught in the chapter on India's climate.

हाच जमीन–समुद्र फरक रोज काम करतो. दिवसा जमीन लवकर तापते आणि समुद्राकडून थंड खारे वारे किनाऱ्याकडे वाहतात; रात्री जमीन लवकर थंड होते आणि मतलई वारे समुद्राकडे वाहतात. म्हणूनच अनेक ठिकाणी कोळी पहाट होण्याआधीच त्या मतलई वाऱ्याच्या मदतीने होड्या समुद्रात नेतात. डोंगरातही असेच: दिवसा उतार तापून दरीचा वारा वर चढतो, दुपारपर्यंत शिखरांवर ढग; रात्री थंड जड हवा डोंगरी वाऱ्याच्या रूपात दरीत घसरते. हीच घसरण पहिल्या भागात सांगितलेल्या दरीतील तापमान व्युत्क्रमाचे कारण. (→ English: land and sea breeze · हिन्दी: स्थलीय और समुद्री समीर)

In exam EnglishThe same land–sea contrast operates every day. By day the land warms faster than the water, air rises over it, and a cool sea breeze blows onshore, usually from late morning; at night the land cools faster and a weaker land breeze blows out to sea. Mountains have a matching daily cycle. During the day the sunlit slopes warm the air beside them, which rises up the valley as a valley breeze, also called an anabatic wind, often building clouds over the peaks by afternoon. At night the slopes cool, and cold, dense air slides downhill into the valley as a mountain breeze, or katabatic wind. That downslope flow is the air drainage that creates the valley inversions described in Part 1.

काही प्रदेशांचे स्वतःचे वारे असतात. उत्तर भारताच्या मैदानात मे–जूनच्या दुपारी वाहणारा उष्ण कोरडा पश्चिमी वारा 'लू' — उष्माघात आणतो. ओलसर हवा डोंगर चढताना एका बाजूला पाऊस पाडते आणि दुसऱ्या बाजूने उतरताना दाबली जाऊन तापते — पंपाने टायरमध्ये हवा भरताना पंप तापतो तसे. आल्प्समध्ये त्याला 'फॉन', रॉकीजच्या पूर्वेला 'चिनूक' (बर्फ खाणारा) म्हणतात. थंड वारे: फ्रान्समध्ये 'मिस्ट्रल', अॅड्रियाटिक किनाऱ्यावर 'बोरा'. सहारातून धुळीचा उष्ण वारा 'सिरोको'; पश्चिम आफ्रिकेत कोरडा 'हरमट्टन' दमटपणा कमी करतो म्हणून 'डॉक्टर'. (→ English: local winds · हिन्दी: स्थानीय पवनें)

In exam EnglishMany regions have winds of their own. Over the plains of north India, the Loo is a hot, dry westerly that blows on May and June afternoons and can cause heatstroke. When moist air is forced across a mountain range, it drops its moisture on the windward side and then descends the leeward slope, warming as it is compressed; such warm, dry downslope winds are called the Foehn in the Alps and the Chinook on the eastern side of the Rockies, where they can melt snow so fast that they are nicknamed snow-eaters. Some local winds are cold: the Mistral rushes down the Rhône valley to the Mediterranean coast of France, and the Bora sweeps down to the Adriatic coast. The Sirocco carries hot, dusty air from the Sahara northwards across the Mediterranean, while the Harmattan, a dry north-easterly from the Sahara, brings dust to West Africa together with relief from sticky heat, earning it the nickname 'the doctor'.

Local winds often asked about
Wind	Region	Nature
Loo	Plains of north India	Hot, dry westerly (May–June)
Foehn	Alps	Warm, dry downslope wind
Chinook	Eastern side of the Rockies	Warm, dry downslope wind; 'snow-eater'
Sirocco	Sahara to the Mediterranean and southern Europe	Hot, dusty
Mistral	Rhône valley, southern France	Cold, dry, northerly
Bora	Adriatic coast	Cold, dry
Harmattan	West Africa	Dry, dusty north-easterly; 'the doctor'

खूप उंचावर, ट्रोपोपॉजजवळ, अरुंद पट्ट्यांमध्ये अतिवेगाने वाहणारे वारे म्हणजे जेट प्रवाह. ते मुख्यतः पश्चिमेकडून पूर्वेकडे, ताशी 100 किमीपेक्षा वेगाने — आकाशातला द्रुतगती महामार्गच. उष्ण आणि थंड हवा भेटते त्या सीमांवर ते तयार होतात. ते सरळ न जाता सापासारखे वळणे घेत जातात (रॉस्बी तरंग), खालच्या हवामानाला दिशा देतात. हिवाळ्यात उपोष्ण पश्चिमी जेट हिमालयाच्या दक्षिणेला राहून वायव्य भारताला हिवाळी पाऊस आणि बर्फ आणणाऱ्या पश्चिमी विक्षोभांना दिशा देतो. उन्हाळ्याच्या सुरुवातीला तो तिबेटच्या उत्तरेला सरकतो आणि द्वीपकल्पावर पूर्वी जेट तयार होतो — नैर्ऋत्य मान्सूनच्या आगमनाशी जोडलेला बदल. (→ English: jet stream · हिन्दी: जेट धारा)

In exam EnglishHigh in the atmosphere, close to the tropopause, flow narrow bands of very fast wind called jet streams. They blow mainly from west to east, often faster than 100 km/h and at times much faster, and they form where air masses of sharply different temperature meet. The polar front jet lies over the middle latitudes, above the boundary between polar and tropical air; the subtropical jet lies at the poleward edge of the Hadley cell, near 30°. Jet streams do not run straight but meander in huge waves called Rossby waves, and these bends steer the highs and lows at the surface. Over India, the subtropical westerly jet sits south of the Himalaya in winter and helps steer the western disturbances that bring winter rain and snow to the north-west. In early summer it moves north of the Tibetan Plateau and a tropical easterly jet sets up over the peninsula, a switch closely tied to the onset of the south-west monsoon.

हा पूर्ण भाग एक साखळी: असमान उष्णता → दाबातील फरक (समदाब रेषा, पट्टे) → हवेची हालचाल → पृथ्वीच्या फिरण्याने वळण, जमिनीच्या घर्षणाने मंदावणे → व्यापारी, पश्चिमी, ध्रुवीय वारे, तीन चक्रे उष्णता ध्रुवांकडे नेतात. त्यावर ऋतूंचे वारे, रोजचे वारे, स्थानिक वारे; वरून जेट प्रवाह हवामानाला दिशा देतात. हे वारे वाहून नेत असलेला ओलावा थंड होऊन, वेगवेगळ्या हवेचे साठे एकमेकांना भिडले की ढग, पाऊस, वादळे — तोच तिसरा भाग. (→ English: planetary winds · हिन्दी: ग्रहीय पवनें)

In exam EnglishThe logic of this part runs in one line. Uneven heating creates differences in pressure, which are mapped with isobars and arranged in belts that shift with the Sun. Pressure differences set the air moving; the Coriolis force turns it and friction slows it, producing the trade winds, westerlies and polar easterlies and the three cells that carry heat poleward. On top of this pattern sit the seasonal monsoons, daily breezes and local winds, while jet streams steer weather systems from above. When the moisture these winds carry condenses and unlike air masses meet, the result is cloud, rain, fronts and cyclones, the subject of Part 3.

Exam traps

The equatorial low and polar highs are thermal in origin; the subtropical highs and subpolar lows are dynamic, not the other way round.
The Coriolis force is zero at the equator and greatest at the poles; it changes the wind's direction, not its speed.
Northern Hemisphere: deflection to the right, cyclones anticlockwise, anticyclones clockwise. The Southern Hemisphere is the reverse.
Winds are named after the direction they come from: north-east trades in the Northern Hemisphere, south-east trades in the Southern.
The westerlies blow from the south-west in the Northern Hemisphere; the Roaring Forties, Furious Fifties and Shrieking Sixties are Southern Hemisphere westerlies.
The Ferrel cell is thermally indirect; the Hadley and polar cells are thermally direct.
Sea breeze and valley breeze (anabatic) blow by day; land breeze and mountain breeze (katabatic) blow by night.
Foehn and Chinook are warm, dry winds; Mistral and Bora are cold. The Loo is a hot wind of north India, not a cold one.

Recap

Pressure is the weight of the air column; about 1013 hPa at sea level; falls quickly with height.
Isobars join places of equal pressure; close isobars mean a steep gradient and strong winds.
Belts: equatorial low (ITCZ, doldrums), subtropical highs (horse latitudes), subpolar lows, polar highs; they shift with the Sun.
Forces: pressure gradient starts the wind, Coriolis turns it (right in NH, left in SH, zero at equator), friction slows it; aloft the wind is geostrophic.
NH cyclones turn anticlockwise and anticyclones clockwise; Buys Ballot's law: back to the wind, low pressure on the left (NH).
Planetary winds: NE and SE trades, westerlies (Roaring Forties in the south), polar easterlies; Hadley, Ferrel and polar cells.
Monsoons are seasonal reversals; land and sea breezes and mountain and valley breezes are daily ones.
Local winds: Loo, Foehn, Chinook (warm); Mistral, Bora (cold); Sirocco, Harmattan (dusty, from the Sahara).
Jet streams: fast westerlies near the tropopause; the subtropical westerly jet guides western disturbances in winter; the tropical easterly jet comes with the monsoon.

Practice questions

Q1. The Coriolis force is zero at:

The poles
The Tropic of Cancer
The equator
60° latitude

Show answer

Answer: C. The equator

The deflecting force depends on latitude: it is zero at the equator and greatest at the poles. It is therefore at its maximum, not zero, at the poles; at the Tropic of Cancer and at 60° it has intermediate values that grow towards the poles.

Q2. Consider the following statements:
1. The subtropical high-pressure belts are mainly thermal in origin.
2. The doldrums lie in the equatorial low-pressure belt.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: B. 2 only

Statement 1 is wrong: the subtropical highs form mainly because air that rose at the equator sinks there, so they are dynamic. Statement 2 is right: the calm, variable winds of the equatorial low are the doldrums. So '1 only', 'both' and 'neither' are incorrect.

Q3. On a weather map, isobars drawn very close together over a region indicate:

Calm conditions and light winds
A steep pressure gradient and strong winds
Uniform pressure over the area
A temperature inversion

Show answer

Answer: B. A steep pressure gradient and strong winds

Closely spaced isobars mean pressure changes sharply over a short distance, so the pressure gradient force and the wind are strong. Calm conditions go with widely spaced isobars; uniform pressure would show no isobars crossing the area; and isobars show pressure, not the vertical temperature profile that defines an inversion.

Q4. Match List I (local wind) with List II (region):
List I: A. Chinook B. Mistral C. Harmattan D. Loo
List II: 1. West Africa 2. Plains of north India 3. Eastern slopes of the Rockies 4. Rhône valley of France
Select the correct answer using the code below:

A-3, B-4, C-1, D-2
A-4, B-3, C-2, D-1
A-3, B-1, C-4, D-2
A-1, B-4, C-3, D-2

Show answer

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

The Chinook descends the eastern side of the Rockies, the Mistral funnels down the Rhône valley, the Harmattan blows over West Africa and the Loo over the plains of north India. The second code swaps the Chinook and Mistral and misplaces the other two; the third puts the Mistral in West Africa and the Harmattan in France; the fourth puts the Chinook in West Africa and the Harmattan in the Rockies.

Q5. In the Northern Hemisphere, the surface winds around a low-pressure centre:

Blow outwards in a clockwise direction
Blow inwards in a clockwise direction
Blow inwards in an anticlockwise direction
Blow outwards in an anticlockwise direction

Show answer

Answer: C. Blow inwards in an anticlockwise direction

Air converges into a low and, deflected to the right in the Northern Hemisphere, circles anticlockwise. Outward clockwise flow describes a Northern Hemisphere anticyclone; inward clockwise flow is a Southern Hemisphere cyclone; outward anticlockwise flow is a Southern Hemisphere anticyclone.

Q6. The 'Roaring Forties' are:

Trade winds of the Northern Hemisphere
Westerlies of the Southern Hemisphere
Polar easterlies near Antarctica
Monsoon winds of the Arabian Sea

Show answer

Answer: B. Westerlies of the Southern Hemisphere

Between about 40° and 60° S there is little land, so the westerlies blow strongly; sailors called them the Roaring Forties, Furious Fifties and Shrieking Sixties. Trade winds blow towards the equator in the tropics, polar easterlies blow from the polar highs, and monsoon winds are seasonal, not named after latitudes.

Q7. Consider the following statements about jet streams:
1. They blow mainly from west to east near the tropopause.
2. In winter the subtropical westerly jet lies south of the Himalaya.
3. The tropical easterly jet forms over peninsular India in winter.
Which of the statements given above are correct?

1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3

Show answer

Answer: A. 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is wrong: the tropical easterly jet sets up over the peninsula in summer, with the south-west monsoon, not in winter. Every option containing statement 3 is therefore incorrect.

Q8. Which one of the following circulation cells is described as thermally indirect?

Hadley cell
Ferrel cell
Polar cell
All three cells

Show answer

Answer: B. Ferrel cell

The Ferrel cell of the middle latitudes is driven by the cells on either side rather than by direct heating, so it is thermally indirect. In the Hadley and polar cells warm air rises and cold air sinks, so they are thermally direct, which also rules out 'all three'.

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Sources

NOAA National Weather Service, JetStream online school: air pressure, the global circulation, wind and the Coriolis force, local winds and jet streams (US government) — https://www.noaa.gov/jetstream/global
India Meteorological Department, Ministry of Earth Sciences: meteorological glossary and public material on pressure, winds, heat waves, western disturbances and the monsoon — https://mausam.imd.gov.in
NASA Earth Observatory: Climate and Earth's Energy Budget; the transport of heat from the tropics towards the poles (US government) — https://earthobservatory.nasa.gov/features/EnergyBalance