Atmospheric Pressure & Circulation – Geography – UGC NET – Solved PYQs

1. Which of the following pairs is correctly matched? (SEPT 2013)

I. Cwa – hot summers, dry winters
II. Cwb – hot dry summers
III. Csb – warm dry summers
IV. Cfb – warm summers

Select the correct answer from the codes given below.

(1) I, II, III and IV
(2) I, III and IV
(3) I and IV
(4) I and II

Correct Answer: (2) I, III and IV

The given climatic symbols belong to the Köppen Climate Classification, one of the most widely used systems for classifying the world’s climates. Developed by Wladimir Köppen, this classification is based on temperature and precipitation patterns. In the notation, the first letter indicates the major climate group, the second letter generally refers to precipitation characteristics, and the third letter represents temperature conditions.

The pair Cwa – hot summers, dry winters is correctly matched. In the Köppen system, C represents a warm temperate or mesothermal climate, w denotes a dry winter season, and a indicates a hot summer with the warmest month having an average temperature above 22°C. This climate is common in parts of northern India, eastern China, and other monsoon-influenced regions.

The pair Cwb – hot dry summers is incorrectly matched. In this classification, w signifies dry winters, not dry summers. The symbol Cwb represents a subtropical highland climate with dry winters and warm summers, not hot dry summers. Such climates are often found in elevated tropical regions, including parts of the Himalayan foothills and East African highlands.

The pair Csb – warm dry summers is correctly matched. Here, s denotes a dry summer, characteristic of Mediterranean climates, while b indicates a warm summer rather than a hot one. This climate is found in regions such as coastal California, central Chile, parts of southern Europe, and southwestern Australia.

The pair Cfb – warm summers is also correctly matched. In this case, f indicates the absence of a dry season, with precipitation distributed throughout the year, and b signifies warm summers. This climate is commonly known as the Marine West Coast Climate and is found in regions such as western Europe, New Zealand, and parts of southern Chile.

Since statements I, III, and IV are correctly matched and statement II is incorrect, the correct answer is (2) I, III and IV.

2. Tornadoes are most likely to occur during (SEPT 2013)

(1) Mid-morning
(2) Mid-afternoon
(3) Noon
(4) Late evening

Correct Answer: (2) Mid-afternoon

A tornado is a violently rotating column of air extending from a cumulonimbus cloud or supercell thunderstorm to the ground. Tornado formation requires a combination of warm, moist air near the surface, colder air aloft, atmospheric instability, and significant wind shear. These conditions are most favorable during the mid-afternoon hours.

During the afternoon, solar heating reaches its maximum effect on the Earth’s surface. As the ground becomes intensely heated, the air above it warms and rises rapidly through the process of convection. This rising warm and moist air increases atmospheric instability and promotes the development of powerful thunderstorms. By mid-afternoon, the temperature difference between the warm surface air and the cooler upper atmosphere is often at its greatest, creating ideal conditions for severe convective activity.

In many tornado-prone regions, especially the Great Plains of the United States, the highest frequency of tornado occurrence is observed between approximately 3:00 PM and 6:00 PM local time. This period coincides with peak surface heating and maximum thunderstorm development. Although tornadoes can occur at any time of the day or night, statistical records show a strong concentration during the afternoon hours.

Mid-morning and noon generally do not provide sufficient atmospheric heating for the most intense convective storms to develop. Late evening tornadoes can occur, particularly when severe storm systems persist after sunset, but they are less common than those forming during the afternoon peak. The strong relationship between solar heating, atmospheric instability, and thunderstorm development makes mid-afternoon the most favorable time for tornado formation.

3. Which US city was struck by Hurricane Katrina? (SEPT 2013)

(1) New York
(2) Houston
(3) New Orleans
(4) Miami (FL)

Correct Answer: (3) New Orleans

Hurricane Katrina was one of the most devastating tropical cyclones in the history of the United States. It struck the Gulf Coast region in late August 2005 and caused catastrophic damage, particularly in the city of New Orleans, located in the state of Louisiana.

Katrina originated over the Bahamas and intensified while moving across the warm waters of the Gulf of Mexico. Before making landfall, it reached Category 5 intensity on the Saffir–Simpson Hurricane Wind Scale, making it one of the strongest hurricanes ever recorded in the Atlantic Basin. Although it weakened slightly before landfall, it still caused extensive destruction through powerful winds, storm surges, and heavy rainfall.

The most severe impacts occurred in New Orleans, where the failure of several levees and flood protection structures led to widespread inundation. Large portions of the city, much of which lies below sea level, were submerged under floodwaters. Hundreds of thousands of residents were displaced, critical infrastructure was damaged, and economic losses reached unprecedented levels. The disaster exposed significant challenges in urban planning, disaster preparedness, emergency response, and flood management.

While states such as Mississippi, Alabama, and parts of the Gulf Coast also suffered extensive damage, New Orleans became the symbolic center of the Katrina disaster due to the scale of flooding and human suffering experienced there. The event remains a major case study in hazard management, urban vulnerability, coastal geography, and disaster risk reduction.

For these reasons, the US city most famously struck and devastated by Hurricane Katrina was New Orleans, making Option (3) the correct answer.

4. Considering the Assertion (A) and Reason (R), select the correct answer. (SEPT 2013)

Assertion (A): When the Sun is overhead on a clear sky, one can see blue sky in all directions.

Reason (R): The longer wavelengths of visible light are scattered more effectively than short wavelengths.

Codes

(1) Both (A) and (R) are correct and (R) explains (A)
(2) Both (A) and (R) are correct, but (R) does not explain (A)
(3) (A) is true, but (R) is false
(4) (A) is false, but (R) is true

Correct Answer: (3) (A) is true, but (R) is false

The Assertion (A) is true. When the Sun is overhead and the sky is clear, the sky appears blue in all directions because sunlight interacts with molecules and tiny particles present in the atmosphere. As sunlight enters the atmosphere, it is scattered by gases such as nitrogen and oxygen. This scattering causes the sky to appear blue to an observer on the Earth’s surface.

The phenomenon responsible for the blue colour of the sky is known as Rayleigh scattering, named after the British physicist Lord Rayleigh. According to Rayleigh’s theory, the amount of scattering is inversely proportional to the fourth power of the wavelength. This means that shorter wavelengths of visible light, such as blue and violet, are scattered much more strongly than longer wavelengths such as red and orange. Although violet light is scattered even more than blue light, the human eye is more sensitive to blue light, and part of the violet radiation is absorbed in the upper atmosphere. As a result, the sky appears predominantly blue.

The Reason (R) is false because it states that longer wavelengths are scattered more effectively than short wavelengths. The exact opposite is true. Short wavelengths are scattered far more efficiently than longer wavelengths. This selective scattering of shorter wavelengths is the fundamental reason for the blue appearance of the daytime sky and the reddish colours often observed during sunrise and sunset when sunlight travels through a much greater thickness of the atmosphere.

Since the assertion is correct and the reason is incorrect, the correct answer is (3) (A) is true, but (R) is false.

5. A sudden, violent, gusty wind, which lasts a minute or two and then subsides, usually accompanied by rain or hail, is called (SEPT 2013)

(1) Thunderstorm
(2) Hoar
(3) Blizzard
(4) Squall

Correct Answer: (4) Squall

A squall is a sudden and sharp increase in wind speed that occurs abruptly, lasts for a short duration, and then diminishes quickly. It is characterized by strong, gusty winds that often persist for only a few minutes and are frequently associated with rain, hail, thunderstorms, or cumulonimbus clouds. Meteorologically, a squall is defined as a sudden rise in wind speed of at least several knots that lasts for a brief period before subsiding.

Squalls commonly develop along cold fronts, thunderstorm outflows, and zones of intense atmospheric instability. When powerful downdrafts descend from a thunderstorm cloud and spread outward upon reaching the surface, they generate strong gusty winds that may be accompanied by heavy rainfall, lightning, and hail. These conditions can create hazardous situations for aviation, navigation, and outdoor activities.

Option (1), thunderstorm, refers to an entire weather phenomenon involving thunder, lightning, heavy rain, strong winds, and sometimes hail. A squall may occur within or ahead of a thunderstorm, but it is not synonymous with a thunderstorm itself. Option (2), hoar, refers to a type of frost formed by the direct deposition of water vapour onto cold surfaces under freezing conditions. Option (3), blizzard, is a severe snowstorm characterized by strong winds, blowing snow, and reduced visibility, usually lasting for several hours rather than a minute or two.

The defining features of a squall are its sudden onset, short duration, violent gustiness, and frequent association with rain or hail, making Option (4) the correct answer.

6. Considering the Assertion (A) and Reason (R), select the correct answer. (SEPT 2013)

Assertion (A): The thunderstorms of Bengal and the adjoining Bihar, Odisha and Assam are known as North-westers.

Reason (R): The squalls come predominantly from the North-East.

Codes

(1) Both (A) and (R) are correct and (R) explains (A)
(2) Both (A) and (R) are correct, but (R) does not explain (A)
(3) (A) is true, but (R) is false
(4) (A) is false, but (R) is true

Correct Answer: (3) (A) is true, but (R) is false

The Assertion (A) is true. The severe pre-monsoon thunderstorms that occur during the months of March, April, and May in West Bengal, Bihar, Odisha, Assam, and parts of Bangladesh are popularly known as Nor’westers or Kalbaisakhi. These storms are characterized by violent winds, thunder, lightning, heavy rainfall, and sometimes hail. They play an important role in providing relief from intense summer heat and are particularly beneficial for crops such as jute, tea, and paddy.

The name Nor’wester originated because these thunderstorms generally approach from the north-western direction. They develop due to strong convective activity created by intense surface heating and the interaction of warm, moist air from the Bay of Bengal with relatively cooler and drier air masses from the north-west. The resulting instability leads to the formation of powerful cumulonimbus clouds and severe thunderstorms.

The Reason (R) is false because it states that the squalls come predominantly from the North-East. In reality, these storms are called Nor’westers precisely because the associated squalls and storm systems usually move from the north-west towards the east and south-east. The direction of movement is a defining characteristic of these storms and forms the basis of their name.

Nor’westers are among the most significant local weather phenomena of eastern India. They are often accompanied by strong gusts exceeding 80–100 km per hour, intense lightning activity, and short-duration but heavy rainfall. Their occurrence is closely linked to seasonal atmospheric instability during the pre-monsoon period and represents a classic example of convective thunderstorms in tropical and subtropical climates.

Since the assertion is correct and the reason is incorrect, the correct answer is (3) (A) is true, but (R) is false.

7. The following question consists of two statements, one labelled as Assertion (A) and the other as Reason (R). (SEPT 2013)

Assertion (A): Jet streams play an important role in intensifying weather phenomena such as cyclones, hurricanes and typhoons.

Reason (R): There are severe storms when jet streams interfere with surface wind systems.

Codes

(1) Both (A) and (R) are true and (R) is the correct explanation of (A)
(2) Both (A) and (R) are true, but (R) is not the correct explanation of (A)
(3) (A) is true, but (R) is false
(4) (A) is false, but (R) is true

Correct Answer: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

The Assertion (A) is true. Jet streams are narrow bands of very strong winds that flow in the upper troposphere, generally at altitudes between 8 and 16 kilometres. These high-speed air currents exert a significant influence on global weather patterns and play an important role in the development, movement, and intensification of atmospheric disturbances such as cyclones, hurricanes, and typhoons. By affecting upper-air circulation and pressure distribution, jet streams can enhance the growth of storm systems and increase their intensity.

The Reason (R) is also true and correctly explains the assertion. When jet streams interact with or influence surface wind systems, they create conditions favorable for strong vertical air movements and atmospheric instability. The divergence of air in the upper atmosphere associated with jet streams promotes the upward movement of surface air. As air rises, surface pressure decreases, encouraging the inflow of more air toward low-pressure centres. This process strengthens cyclonic circulation and can lead to the development of severe storms.

In the case of extratropical cyclones, the position and strength of the polar front jet stream are critical in determining storm intensity and movement. For tropical cyclones, favorable upper-level winds linked to jet-stream patterns can enhance outflow at higher altitudes, allowing storms to strengthen further. Conversely, unfavorable jet-stream conditions can create excessive wind shear, which may weaken developing tropical systems.

Jet streams act as steering mechanisms for many weather systems and contribute to the transfer of energy and momentum within the atmosphere. Their interaction with lower atmospheric circulation helps generate intense weather events, making them a key factor in the dynamics of powerful storms across different climatic regions of the world.

Since both the assertion and reason are true, and the reason correctly explains the assertion, the correct answer is (1) Both (A) and (R) are true and (R) is the correct explanation of (A).

9. Mediterranean climate is characterized by (DEC 2013)

(1) Dry summer and humid winter
(2) Humid summer and dry winter
(3) Dry summer and dry winter
(4) Humid summer with no winter

Correct Answer: (1) Dry summer and humid winter

The Mediterranean climate is one of the most distinctive climatic types in the world and is characterized by hot, dry summers and mild, humid (wet) winters. In the Köppen Climate Classification, it is represented by the symbols Csa and Csb, where the letter s indicates a dry summer season.

This climate develops mainly between 30° and 45° latitudes on the western margins of continents. During summer, these regions come under the influence of the subtropical high-pressure belt, which causes descending air, stable atmospheric conditions, and a marked absence of rainfall. The descending air suppresses cloud formation, resulting in clear skies, abundant sunshine, and prolonged dry conditions.

In winter, the subtropical high-pressure belt shifts equatorward, allowing the region to come under the influence of the westerlies and associated temperate cyclones. These cyclonic disturbances bring rainfall, making winters relatively wet and mild. The seasonal migration of global pressure belts and wind systems is the fundamental reason for the unique precipitation pattern of the Mediterranean climate.

This climate is found around the Mediterranean Sea, from which it derives its name, and also occurs in other parts of the world such as California in the United States, Central Chile, the Cape Province of South Africa, and South-Western Australia. The region supports characteristic vegetation known as sclerophyllous vegetation, including olive trees, cork oak, grapevines, and various drought-resistant shrubs.

The combination of dry summers and wet winters makes the Mediterranean climate highly suitable for specialized agriculture, particularly the cultivation of olives, grapes, citrus fruits, and figs. The seasonal contrast between summer drought and winter rainfall is its most defining climatic feature, making Option (1) Dry summer and humid winter the correct answer.

10. As per Köppen’s scheme, the BWhw type of climate is found in (DEC 2013)

(1) Jammu and Kashmir
(2) Rajasthan
(3) Gujarat
(4) Odisha

Correct Answer: (2) Rajasthan

The Köppen Climate Classification system, developed by Wladimir Köppen, classifies climates based on temperature and precipitation patterns. In this system, the symbol BWhw represents a hot desert climate with a dry winter season. Each letter in the notation has a specific meaning. The letter B denotes a dry climate, W indicates a desert region, h signifies high temperatures with an annual mean temperature above 18°C, and w refers to a marked dry winter season.

In India, the BWhw climate is predominantly associated with the Thar Desert region of Rajasthan. This area experiences extremely low annual rainfall, often less than 250 mm in many locations. High temperatures prevail throughout much of the year, especially during summer when temperatures frequently exceed 45°C. The region also exhibits high rates of evaporation, resulting in a significant moisture deficit.

The aridity of Rajasthan is influenced by several geographical and atmospheric factors. The Aravalli Range runs parallel to the direction of the south-west monsoon winds and therefore does not effectively obstruct them to produce substantial rainfall. The region’s inland location, distance from major moisture sources, and dominance of subsiding dry air during much of the year further contribute to desert conditions.

Jammu and Kashmir contains diverse climatic zones, including alpine, tundra, and cold desert climates, but it is not characterized by the hot desert climate denoted by BWhw. Gujarat includes semi-arid and tropical climates, although parts of Kachchh approach arid conditions; the classic BWhw climatic region in India is centered in Rajasthan. Odisha experiences a humid tropical monsoon climate with abundant summer rainfall and does not fall under the desert category.

The BWhw climate is marked by scanty rainfall, extreme summer heat, sparse vegetation, sandy soils, and a large diurnal temperature range, all of which are characteristic features of the Thar Desert of Rajasthan, making Option (2) Rajasthan the correct answer.