Climatology: UPSC Previous Year Questions (Geography)

Explanation

Statement I is correct: Dust particles are more concentrated in subtropical and temperate regions due to the presence of dry winds. These regions often experience arid and semi-arid climates, where the lack of vegetation and strong winds promote the suspension of dust particles in the atmosphere. Deserts such as the Sahara, Thar, and Arabian Desert, all located in subtropical zones, are prime examples of major dust sources. Equatorial regions are humid and vegetated, which suppresses dust through rainfall and plant cover, while polar regions are cold and icy, limiting dust production.

Statement II is incorrect: Dry winds are prevalent in subtropical and temperate regions, and these winds are precisely the reason dust concentration is higher in these areas. In the subtropics, for example, descending air from the subtropical high-pressure belts results in dry and stable conditions, which are associated with low humidity and dusty environments.

Explanation

Statement I is correct: In January, the Northern Hemisphere’s large landmasses cool down rapidly, leading to lower temperatures. Isotherms shift southward (towards the equator) over the continents. In contrast, oceans retain heat longer, so the isotherms bend northward (poleward) when passing over oceans like the North Atlantic, where warm currents like the Gulf Stream increase the surrounding air temperature.

Statement II is correct and explains statement I: Due to the high specific heat capacity of water, oceans cool down more slowly than land. Therefore, in winter (January), the marine areas remain warmer than the adjacent continental interiors. Because of this temperature contrast the isotherms bend equatorward while crossing the landmasses and poleward while crossing the oceans in the month of January in the northern hemisphere.

Explanation

Statement I is correct: You may recall that the earth’s atmosphere is a dynamic mixture of gases that envelops the planet. It plays a great role in making the planet livable for different life forms. It provides us air to breathe, protects us from harmful ultraviolet (UV) radiation coming from the sun, traps the heat and creates a warming effect on the planet making it conducive to live by preventing extremes of temperatures. Without the atmosphere, temperatures would be well below freezing everywhere on earth’s surface.

Statement II is correct: The atmosphere helps regulate the Earth’s temperature by absorbing heat from the Sun during the day and slowing its escape at night. This heat-trapping ability is what keeps the planet’s average surface temperature around 15°C, making it suitable for life. Without this natural insulation, Earth would experience harsh temperature fluctuations between day and night, similar to what occurs on planets and moons with thin or no atmospheres.

Statement III is correct: Certain gases in the Earth’s atmosphere, particularly greenhouse gases like carbon dioxide (CO₂), methane, and water vapor, have the unique ability to absorb and trap radiation. This property makes them especially effective in trapping heat within the atmosphere, contributing significantly to the greenhouse effect.

Explanation

Fig.: Heat budget of the earth Statement-I is incorrect: The atmosphere is primarily heated by terrestrial radiation, which is the longwave radiation emitted by Earth’s surface after it absorbs solar radiation. While the atmosphere does absorb some direct solar radiation, it is the outgoing longwave radiation from the Earth’s surface (which gets trapped by greenhouse gases) that plays a major role in warming the atmosphere. From the diagram above, 65 units out of 100 units of heat are absorbed by the atmosphere in the form of longwave radiation. Thus terrestrial radiation is the major cause behind the heating of the atmosphere. Statement-II is correct: The longwave radiation is absorbed by atmospheric gases, particularly by carbon dioxide and other greenhouse gases. It is mainly because their molecular structure allows them to vibrate and absorb infrared energy emitted by the Earth’s surface.

Explanation

Statement 1 is correct: The troposphere is the low-ermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.

Statement 2 is correct: At the equator, strong convectional currents form due to intense solar heating. These currents carry heat and moisture to great heights, pushing the troposphere upwards and increasing its thickness.

Statement 2 explains Statement 1: The greater thickness of the troposphere at the equator (Statement-I) is due to strong convectional currents (Statement-II). Intense solar heating at the equator causes air to rise, creating powerful convection currents that push the tropopause higher, expanding the troposphere. In contrast, weaker convection at the poles, due to minimal solar heating, results in a thinner troposphere.

Explanation

Option (a) is incorrect: Though it is accurate that the equator receives greater direct sunlight in comparison to the poles, the disparity in insolation is not as substantial as tenfold. The variance in insolation between the equator and poles predominantly arises from the curvature of the Earth and the inclination of its axis, causing sunlight to strike different latitudes at varying angles. Instead of a tenfold difference, the actual variation is estimated to be around 2.5 times.

Option (b) is incorrect: Insolation denotes the entirety of solar radiation reaching the Earth’s surface, encompassing a wide range of electromagnetic radiation. Although infrared radiation constitutes a substantial portion (about 49 %) of solar radiation, it does not represent two-thirds of the insolation. Insolation comprises visible light, ultraviolet (UV) radiation, and various other wavelengths along-side infrared radiation.

Option (c) is correct: The atmosphere warms up by absorbing longwave radiation emitted from the Earth’s surface, mainly in the form of infrared radiation. Water vapor is a strong absorber of infrared radiation. In the lower atmosphere, where its concentration is higher, it absorbs a significant portion of the Earth’s emitted infrared radiation.

Option (d) is incorrect: Infrared radiation is not part of the visible range, infrared radiation has wavelengths longer than those of visible light and is not perceptible to the human eye.

Explanation

Statement-I is incorrect: The tropical rainforest occurs near the equator and close to the tropics. Thus it receives heavy rainfall throughout the year. The heavy rain causes intense leaching of the soil which increases the acidity of the soil. Due to increased acidity, there is an issue of less nutrient absorption from the soil. Thus the claim that tropical rain forests are rich in nutrients is inappropriate.

Statement II is correct: As the tropical rainforest lies in a region of heavy rainfall and near to tropics, thus the climate here is hot and humid. This causes the rapid decomposition of the dead organic material present in the soil. Hence, Statement-I is incorrect, but Statement-II is correct.

Explanation

Statement-I is incorrect: The temperature contrast between continents and oceans is greater during winter than in summer. The reason for this is:

In summer, the land heats up faster than water due to its lower specific heat capacity. However, both the land and oceans are warm, so the temperature difference is relatively smaller. In winter, land cools down more rapidly than water because water has a higher specific heat capacity. This leads to a larger temperature contrast between the cooler land and relatively warmer oceans. Statement-II is correct: Specific heat is the amount of heat energy it takes to raise or lower the temperature of 1 gram of a substance by 1°Celsius. The specific heat of water is greater than that of dry soil, thus, water absorbs and releases heat more slowly than land.

Explanation

Statement 1 is incorrect: Low, thick clouds, not the high clouds primarily reflect solar radiation and cool the surface of the Earth.

Statement 2 is incorrect: High, thin clouds, not the low clouds primarily transmit incoming solar radiation. At the same time, they trap some of the outgoing infrared radiation emitted by the Earth and radiate it back downward, thereby warming the surface of the Earth.

Explanation

Statement 1 is correct: In the tropical zone, trade winds blow from the east towards the west. These winds push warm surface water towards the western parts of the oceans (e.g., the western Pacific Ocean and the western Atlantic Ocean). As a result, the water in the western parts of tropical oceans is warmer than in the eastern parts. The eastern sections of the oceans tend to have upwelling, where colder, nutrient-rich waters from deeper layers rise to the surface.

Statement 2 is correct: In the temperate zone, the westerlies (winds blowing from the west towards the east) push the surface water eastward, causing the western parts of oceans (like the western coast of continents) to be colder. The water in the eastern sections of oceans tends to be warmer due to the Ekman transport, which moves warm water towards the eastern coasts. For example, in the North Atlantic Ocean, the Gulf Stream carries warm water from the tropics to the eastern coasts of North America and Europe, keeping the eastern sections warmer than the western parts.