Atmosphere: Composition & Structure – Geography – UGC NET – Solved PYQs

1. Which of the following pairs of countries receive maximum insolation? (SEPT 2013)

(1) Indonesia and Sri Lanka
(2) Indonesia and Libya
(3) Yemen and Somalia
(4) Canada and Australia

Correct Answer: (3) Yemen and Somalia

Explanation:
Insolation refers to the amount of incoming solar radiation received by the Earth’s surface. The distribution of insolation depends on several factors such as latitude, cloud cover, length of day, atmospheric conditions, and the angle at which the Sun’s rays strike the surface. Regions located in the subtropical high-pressure belt generally receive higher amounts of solar radiation because skies remain clear for most of the year and cloud formation is limited.

Yemen and Somalia are situated in the tropical and subtropical regions close to the Tropic of Cancer and the Equator, where solar rays are highly concentrated. Both countries are characterized by extensive arid and semi-arid environments with relatively low cloud cover. The dry atmospheric conditions allow a larger proportion of solar radiation to reach the surface, resulting in very high levels of insolation throughout the year.

Although Indonesia and Sri Lanka are located in low latitudes, they experience significant cloudiness and heavy rainfall due to the influence of the Intertropical Convergence Zone (ITCZ) and monsoonal conditions. Dense cloud cover reflects and absorbs a portion of incoming solar radiation, reducing the actual amount of insolation reaching the ground.

Similarly, Libya receives very high insolation because of the vast Sahara Desert, but when paired with Indonesia, the overall comparison is less suitable since Indonesia’s frequent cloud cover lowers its insolation levels. Canada, despite having long summer days in higher latitudes, receives lower annual insolation because of the low angle of the Sun’s rays and long winters. Australia receives substantial insolation, particularly in its desert interior, but Canada’s inclusion makes that pair unsuitable.

The world’s highest annual insolation values are generally recorded in the desert regions of North Africa, the Arabian Peninsula, and parts of the Horn of Africa, making Yemen and Somalia the pair that best represents countries receiving maximum insolation.

2. Solid material passes directly into vapour state by means of (SEPT 2013)

(1) Condensation
(2) Sublimation
(3) Volatilisation
(4) Convection

Correct Answer: (2) Sublimation

The process by which a solid changes directly into a vapour or gaseous state without passing through the liquid phase is known as sublimation. This phenomenon occurs when the molecules of a solid gain sufficient energy to overcome the intermolecular forces holding them together and escape directly into the atmosphere as gas. Sublimation generally takes place under specific conditions of temperature and pressure where the liquid state is not stable.

Several common substances exhibit sublimation. Dry ice (solid carbon dioxide) is one of the most familiar examples, changing directly from solid carbon dioxide into carbon dioxide gas at normal atmospheric pressure. Other substances such as camphor, naphthalene, iodine, and ammonium chloride also undergo sublimation. In physical geography and environmental studies, sublimation is particularly important in cold regions where snow and ice may convert directly into water vapour without first melting into liquid water. This process contributes to the loss of snow cover in mountainous and polar environments.

Condensation is the reverse process in which a gas changes into a liquid due to cooling. Volatilisation refers more broadly to the conversion of a substance into a gaseous form, usually from a liquid state, and is commonly used in chemistry and environmental science. Convection is a mechanism of heat transfer involving the movement of fluids such as liquids and gases and does not describe a change of state.

The concept of sublimation is represented in phase diagrams, where it occurs along the boundary between the solid and gaseous phases. The water cycle also includes sublimation as an important process, especially in high-altitude and polar regions where frozen water can enter the atmosphere directly as water vapour under suitable atmospheric conditions.

3. Match the List-I with List-II and select the correct answer using the codes given below. (SEPT 2013)

Codes

(1) A-II, B-III, C-IV, D-I
(2) A-III, B-IV, C-I, D-II
(3) A-IV, B-I, C-II, D-III
(4) A-I, B-II, C-III, D-IV

Correct Answer: (2) A-III, B-IV, C-I, D-II

Explanation:

Local winds are winds that develop over a relatively small geographical area due to differences in temperature, pressure, and topographic conditions. They are important in climatology because they significantly influence local weather, agriculture, human activities, and environmental conditions.

The Loo is a hot, dry, and dusty wind that blows during the summer months across the northwestern parts of the Indian subcontinent, particularly in northern India and Pakistan. It originates from intensely heated desert regions and is known for causing heat waves and dehydration. This wind is associated with Pakistan (III) in the given list.

The Samun (also spelled Simoom or Samoom) is an extremely hot and dry desert wind that occurs in the arid regions of the Middle East, especially in Iran (IV) and neighboring desert areas. It carries dust and sand and is capable of raising temperatures dramatically over a short period.

The Harmattan is a dry and dusty northeasterly trade wind that blows from the Sahara Desert towards the Gulf of Guinea. It is a characteristic seasonal wind of West Africa (I) and is known for reducing humidity and visibility because of the fine dust particles it transports across the region.

The Bora is a strong, cold, and gusty wind that descends from mountainous interiors toward the Adriatic coast. It is particularly associated with the regions that formed the Former Yugoslavia (II), including present-day Croatia, Slovenia, Montenegro, and surrounding areas. Bora winds develop when cold continental air masses move rapidly toward relatively warmer coastal zones.

The correct matching is A–III, B–IV, C–I, D–II, making option (2) the correct answer. Knowledge of local winds is important in climatology, physical geography, and competitive examinations because these winds illustrate the interaction between relief, temperature contrasts, pressure gradients, and regional climatic conditions across different parts of the world.

4. Ozone hole is located above the (SEPT 2013)

(1) Antarctica
(2) Arctic Ocean
(3) Equatorial zone
(4) Greenland

Correct Answer: (1) Antarctica

The ozone hole refers to a region of severe thinning of the ozone layer in the Earth’s stratosphere. The ozone layer is located approximately 10 to 50 kilometres above the Earth’s surface and plays a vital role in absorbing harmful ultraviolet (UV) radiation emitted by the Sun. By filtering out a large portion of UV-B and UV-C rays, the ozone layer protects living organisms from various harmful effects, including skin cancer, cataracts, immune system suppression, and damage to ecosystems.

The largest and most pronounced ozone hole develops above Antarctica during the Southern Hemisphere spring, particularly between September and November. Scientists first detected this phenomenon in the mid-1980s through observations made by the British Antarctic Survey. The unique climatic conditions over Antarctica contribute significantly to ozone depletion. During the long polar winter, extremely low temperatures lead to the formation of Polar Stratospheric Clouds (PSCs). These clouds provide surfaces for chemical reactions that convert inactive chlorine compounds into highly reactive forms.

When sunlight returns during the Antarctic spring, these reactive chlorine compounds rapidly break down ozone molecules through a series of photochemical reactions. The primary source of chlorine responsible for this depletion has been Chlorofluorocarbons (CFCs) and other ozone-depleting substances released through industrial activities. A single chlorine atom can destroy thousands of ozone molecules before becoming inactive.

Although some ozone depletion also occurs in the Arctic, it is generally less severe because temperatures are not as consistently low as those over Antarctica, and the polar vortex is weaker and less stable. The Equatorial zone and Greenland are not associated with the formation of the major ozone hole observed in global atmospheric studies.

Growing international concern over ozone depletion led to the adoption of the Montreal Protocol (1987), one of the most successful environmental agreements in history. The treaty aimed to phase out the production and consumption of ozone-depleting substances, resulting in gradual recovery of the stratospheric ozone layer in many parts of the world while the seasonal ozone hole continues to be most prominently observed above Antarctica.

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

Assertion (A): The troposphere is the dense lower part of the atmosphere in which all the weather phenomena like condensation and storms occur.

Reason (R): In troposphere the atmospheric temperature decreases with altitude.

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: (2) Both (A) and (R) are true, but (R) is not the correct explanation of (A)

The troposphere is the lowest layer of the Earth’s atmosphere, extending from the surface to an average height of about 8 km at the poles and up to 18 km near the equator. It contains nearly 75% of the total atmospheric mass and almost all of the atmosphere’s water vapour, dust particles, and aerosols. Because of the concentration of moisture and atmospheric gases in this layer, almost all weather phenomena such as cloud formation, condensation, rainfall, thunderstorms, fog, cyclones, and storms take place within the troposphere. The assertion is factually correct.

The reason is also correct because one of the defining characteristics of the troposphere is the normal lapse rate, under which temperature decreases with increasing altitude at an average rate of about 6.5°C per 1000 metres. This decline in temperature occurs because the atmosphere is heated mainly from the Earth’s surface, which absorbs solar energy and transfers heat upward through radiation, conduction, and convection.

Even though both statements are true, the decrease of temperature with altitude is not the primary reason why weather phenomena occur in the troposphere. Weather activities are concentrated in this layer mainly because it contains most of the atmosphere’s water vapour, atmospheric mass, and suspended particles, which are essential for cloud formation and precipitation. The temperature decrease with height contributes to vertical air movements, atmospheric instability, and condensation processes, but it does not fully explain why the troposphere is the principal zone of weather activity. The presence of abundant moisture and dense air near the Earth’s surface is the more direct factor responsible for the concentration of weather phenomena in the troposphere.

6. Increase in temperature with increase in height is known as (DEC 2013)

(1) Lapse rate
(2) Adiabatic lapse rate
(3) Inversion of temperature
(4) Normal rate

Correct Answer: (3) Inversion of temperature

Explanation:

Under normal atmospheric conditions, air temperature decreases with increasing altitude in the troposphere. This decrease is known as the normal lapse rate, which averages about 6.5°C per 1000 metres. Occasionally, the atmosphere exhibits a reverse condition in which temperature increases rather than decreases with height. This phenomenon is called temperature inversion or inversion of temperature.

During a temperature inversion, a layer of warm air overlies a layer of cooler air near the Earth’s surface. This arrangement is opposite to the normal atmospheric structure and creates a highly stable atmospheric condition. Since warm air is lighter and remains above the colder, denser air, vertical air movement becomes restricted. As a result, pollutants, smoke, dust, and fog can become trapped near the ground, leading to reduced visibility and poor air quality.

Temperature inversions commonly occur during clear winter nights when the Earth’s surface loses heat rapidly through terrestrial radiation. The air in contact with the ground becomes cooler than the air above it. Inversions are also frequently observed in valleys, where cold air drains downslope and accumulates at lower elevations, creating colder conditions at the valley floor than on surrounding slopes. This type of inversion is known as valley inversion.

The term lapse rate refers to the normal decrease in temperature with altitude. Adiabatic lapse rate describes the rate at which the temperature of a rising or descending air parcel changes due to expansion or compression without exchanging heat with its surroundings. The expression normal rate generally refers to the normal lapse rate and does not indicate an increase in temperature with height.

Temperature inversion has significant effects on weather, agriculture, transportation, and environmental conditions. It influences frost occurrence, fog formation, air pollution concentration, and atmospheric stability, making it an important concept in climatology, meteorology, and physical geography.

7. Identify the correct sequence of the given processes regarding rainfall. (DEC 2013)

(1) Unsaturated air → condensation → dew point → precipitation
(2) Dew point → condensation → unsaturated air → precipitation
(3) Unsaturated air → dew point → condensation → precipitation
(4) Dew point → precipitation → condensation → unsaturated air

Correct Answer: (3) Unsaturated air → dew point → condensation → precipitation

Explanation:

Rainfall is the result of a series of atmospheric processes involving the cooling of air and the transformation of water vapour into liquid water. The correct sequence begins with unsaturated air, which contains water vapour but has not yet reached its maximum moisture-holding capacity. As this air rises or cools, its temperature gradually decreases. Cooler air can hold less water vapour than warmer air, causing the relative humidity to increase.

When the air cools sufficiently, it reaches the dew point, which is the temperature at which the air becomes saturated and can no longer retain all of its water vapour. At this stage, the relative humidity reaches 100 percent. Any further cooling causes excess water vapour to change into tiny water droplets or ice crystals.

This change of water vapour into liquid water is known as condensation. Condensation generally occurs around microscopic particles called condensation nuclei, such as dust, smoke, salt particles, or pollen present in the atmosphere. The accumulation of countless condensed droplets leads to the formation of clouds.

As condensation continues, cloud droplets grow larger through processes such as coalescence and the Bergeron process. When these droplets or ice particles become heavy enough that atmospheric currents can no longer support them, they fall to the Earth’s surface as precipitation. Depending on atmospheric temperature conditions, precipitation may occur in the form of rain, snow, sleet, or hail.

The sequence Unsaturated air → Dew point → Condensation → Precipitation accurately represents the natural progression of atmospheric events leading to rainfall and forms the basis of cloud formation and precipitation processes studied in meteorology, climatology, and physical geography.

8. Read out the following conditions. Which of the above conditions promote inversion of temperature? (DEC 2013)

I. Cloudy sky
II. Cold dry air
III. Strong winds
IV. Long winter nights

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

Correct Answer: (4) II and IV

Explanation:

Temperature inversion is a meteorological condition in which air temperature increases with altitude instead of decreasing. This phenomenon commonly develops near the Earth’s surface when the ground cools rapidly and chills the air directly above it, while the air at higher levels remains relatively warmer. Certain atmospheric conditions favor the formation and persistence of inversion layers.

Cold dry air promotes inversion because dry air contains less water vapour, allowing the Earth’s surface to lose heat more efficiently through terrestrial radiation. As the ground cools, the air in contact with it also becomes colder, creating conditions suitable for the development of an inversion layer. Dry atmospheric conditions are particularly effective in facilitating rapid nocturnal cooling.

Long winter nights also encourage inversion formation. During winter, nights are longer, giving the Earth’s surface more time to radiate heat into space. Continuous cooling throughout the night causes the lower air layers to become much colder than the air above them. This type of inversion is often called radiation inversion and is common during winter in valleys and plains.

A cloudy sky generally inhibits inversion formation rather than promoting it. Clouds act like a blanket by absorbing and re-radiating outgoing terrestrial radiation back toward the surface. This reduces nighttime cooling and prevents the strong temperature contrasts necessary for inversion development.

Similarly, strong winds tend to destroy or weaken inversion layers. Winds create atmospheric mixing and turbulence, allowing colder air near the ground to mix with warmer air aloft. Such vertical mixing reduces temperature differences between layers and prevents the stable conditions required for inversion.

The combination of cold dry air and long winter nights provides the most favorable conditions for the formation of temperature inversion, particularly in regions experiencing calm weather, clear skies, and intense nighttime radiational cooling. Temperature inversions play an important role in weather forecasting, air pollution studies, fog formation, and agricultural climatology, especially in areas where pollutants become trapped close to the Earth’s surface under stable atmospheric conditions.

9. When the wind is deflected due to the rotation of the Earth it is known as (DEC 2013)

(1) Planetary wind
(2) Geostrophic wind
(3) Accidental wind
(4) Forced wind

Correct Answer: (2) Geostrophic wind

Explanation:

Wind is primarily generated by differences in atmospheric pressure, causing air to move from areas of high pressure to areas of low pressure. If the Earth did not rotate, winds would blow directly along the pressure gradient. However, because the Earth rotates on its axis, moving air is deflected by the Coriolis force, a phenomenon first explained by the French scientist Gaspard-Gustave de Coriolis. In the Northern Hemisphere, this deflection is toward the right of the direction of motion, while in the Southern Hemisphere it is toward the left.

A geostrophic wind develops when the pressure gradient force and the Coriolis force become balanced. Under such conditions, the wind no longer moves directly from high pressure to low pressure but flows parallel to the isobars. Geostrophic winds generally occur in the upper atmosphere where frictional effects from the Earth’s surface are negligible. Since the question specifically refers to wind deflected due to the Earth’s rotation, the most appropriate answer among the given options is geostrophic wind.

Planetary winds are permanent global wind systems such as the trade winds, westerlies, and polar easterlies, but the term itself does not specifically describe wind deflection caused by Earth’s rotation. Accidental wind is not a standard climatological term, and forced wind usually refers to winds influenced by local topographic or external factors rather than by planetary rotation.

The deflection of winds by the Earth’s rotation plays a crucial role in shaping global atmospheric circulation patterns, ocean currents, cyclones, anticyclones, and weather systems. The interaction between the pressure gradient force, Coriolis force, and frictional force forms the basis of modern meteorology and climatology, helping explain the movement of air masses across different latitudes and the organization of global wind belts.

10. A counter-clockwise atmospheric circulation in the Northern Hemisphere is known as (DEC 2013)

(1) Pressure gradient
(2) Cyclone
(3) Anticyclone
(4) Tornado

Correct Answer: (2) Cyclone

Explanation:

A cyclone is a large-scale atmospheric system characterized by a low-pressure center around which winds converge and circulate. In the Northern Hemisphere, cyclonic winds move in a counter-clockwise direction due to the influence of the Coriolis force, which deflects moving air to the right of its path. As air flows toward the low-pressure center, it spirals inward and rises, often leading to cloud formation, precipitation, and unsettled weather conditions.

The development of cyclones is closely associated with differences in atmospheric pressure and temperature. Rising air within a cyclone cools as it ascends, causing water vapour to condense into clouds. This process frequently produces rainfall, thunderstorms, and strong winds. Cyclones may vary greatly in size and intensity, ranging from temperate cyclones affecting mid-latitudes to powerful tropical cyclones over warm ocean waters.

An anticyclone is the opposite of a cyclone. It is a high-pressure system where air descends and moves outward from the center. In the Northern Hemisphere, anticyclonic circulation occurs in a clockwise direction. Anticyclones are generally associated with clear skies, stable weather, and lower chances of precipitation because descending air suppresses cloud formation.

A pressure gradient refers to the rate of change of atmospheric pressure over a given distance and is the force responsible for initiating wind movement. It is not a circulation system. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. Although tornadoes involve rotational motion, they are much smaller in scale than cyclones and are not defined by the general counter-clockwise atmospheric circulation described in the question.

The direction of cyclonic and anticyclonic circulation reverses in the Southern Hemisphere because the Coriolis force acts toward the left there. Understanding cyclonic circulation is fundamental to the study of meteorology, climatology, and weather forecasting, as cyclones play a major role in the distribution of rainfall, storms, and atmospheric energy across the Earth.

11. Insolation reaches the Earth’s surface in the form of (DEC 2013)

(1) Short waves
(2) Long waves
(3) Microwaves
(4) Lorenz curve

Correct Answer: (1) Short waves

Explanation:

Insolation is the abbreviation of incoming solar radiation, which represents the energy received by the Earth from the Sun. This solar energy is the primary source of heat and light for the Earth’s atmosphere, oceans, and land surfaces. Insolation reaches the Earth mainly in the form of short-wave radiation, consisting of visible light, ultraviolet rays, and a portion of near-infrared radiation.

The Sun, having a very high surface temperature of approximately 5,500°C to 6,000°C, emits energy predominantly at shorter wavelengths. These short waves can pass relatively easily through the Earth’s atmosphere. Some of the incoming solar radiation is reflected back into space by clouds, atmospheric particles, and the Earth’s surface, while the remaining portion is absorbed by land, water bodies, and the atmosphere.

After absorbing solar energy, the Earth’s surface becomes heated and re-emits energy in the form of long-wave terrestrial radiation or infrared radiation. Since the Earth has a much lower temperature than the Sun, the radiation emitted by the Earth consists of longer wavelengths. This distinction between incoming short-wave solar radiation and outgoing long-wave terrestrial radiation forms the basis of the Earth’s heat budget and energy balance.

Microwaves are a part of the electromagnetic spectrum but do not constitute the primary form in which solar energy reaches the Earth’s surface. The Lorenz curve is an economic concept used to represent income or wealth distribution and has no relation to atmospheric radiation or climatology.

The interaction between incoming short-wave radiation and outgoing long-wave radiation controls atmospheric temperatures, weather patterns, climate systems, ocean circulation, and the functioning of the greenhouse effect. Variations in the amount of insolation received at different latitudes and seasons are responsible for the distribution of climatic zones and the occurrence of seasonal changes across the globe.

12. The atmosphere gets heated by which one of the following? (DEC 2013)

(1) Direct rays of the Sun
(2) Volcanic activity
(3) Burning of organic material
(4) Radiation from the Earth

Correct Answer: (4) Radiation from the Earth

Explanation:

The Earth’s atmosphere is heated primarily by radiation from the Earth rather than directly by the Sun’s rays. Solar energy reaches the Earth in the form of short-wave radiation, much of which passes through the atmosphere with relatively little absorption. The land and water surfaces absorb this incoming solar energy and become heated.

Once heated, the Earth’s surface emits energy back into the atmosphere in the form of long-wave terrestrial radiation or infrared radiation. Atmospheric gases such as water vapour, carbon dioxide, methane, and other greenhouse gases absorb a significant portion of this outgoing long-wave radiation. This absorbed energy warms the atmosphere, making the Earth’s surface the principal source of atmospheric heating.

This process is often described as the atmosphere being heated from below. The lower layers of the atmosphere, particularly the troposphere, receive heat through terrestrial radiation, as well as through conduction and convection. The warm Earth’s surface transfers heat to the air in direct contact with it, and convection currents then distribute this heat upward through the atmosphere.

The direct rays of the Sun are not the main source of atmospheric heating because most atmospheric gases are largely transparent to incoming short-wave solar radiation. Although certain layers, such as the stratosphere, absorb ultraviolet radiation through the ozone layer, the general warming of the lower atmosphere depends mainly on terrestrial radiation. Volcanic activity and burning of organic material may release heat locally and temporarily, but they do not constitute the primary mechanism responsible for heating the atmosphere on a global scale.

This principle is fundamental to understanding the Earth’s heat budget, energy balance, and the greenhouse effect. The continuous absorption and re-radiation of terrestrial heat by atmospheric gases regulate global temperatures and influence weather systems, climate patterns, and the distribution of heat across the planet.