Consider the following Assertion (A) and Reasons(R): (A) Near the equator, the warm rising air that releases latent heat during t…

Question

Consider the following Assertion (A) and Reasons(R): (A) Near the equator, the warm rising air that releases latent heat during the formation of cumulus towers is believed to provide the energy that drives the Hadley cells. As the flow aloft moves poleward, the air begins to subside in a zone between 20° and 35° latitude. (R)(1) As upper-level flow moves away from the stormy equatorial region; radiation cooling becomes the dominant process. As a result, the air cools, becomes denser, and sinks. (R)(2) The Coriolis force becomes stronger with increasing distance from the equator, causing the poleward-moving upper air to be deflected into a nearly west-to-east flow by the time it reaches 30° latitude. This restricts the poleward flow of air. As a result, general subsidence occurs in the zones between 20° and 35° latitude. Choose the correct option among the following with regards to above assertion and reasons:

1. A. Assertion (A) is incorrect and Reason (R)(1) and (R)(2) are correct.
2. B. Assertion (A) is correct but Reason (R)(2) is incorrect explanation of (A).
3. C. Assertion (A) is correct and Reasons (R)(1) and (R)(2) are correct explanations of (A). (Correct answer)
4. D. Assertion (A) is correct but Reason (R)(1) is incorrect explanation of (A).

Correct Answer

Option C — Assertion (A) is correct and Reasons (R)(1) and (R)(2) are correct explanations of (A).

Detailed Solution & Explanation

The correct answer is Assertion (A) is correct and Reasons (R)(1) and (R)(2) are correct explanations of (A).

Key Points

• The Assertion is correct. Near the equator, intense solar heating drives convection. As moist air rises and condenses into cumulus towers, it releases latent heat, and that heat is the energy that drives the Hadley cell. The poleward-moving upper-level flow then subsides between about 20° and 35° latitude.
• Reason (R)(1) is a correct explanation. Away from the equatorial storm belt, radiational cooling dominates the upper-level air. Cooling makes the air denser, and it sinks — the thermodynamic half of the explanation.
• Reason (R)(2) is also a correct explanation. The Coriolis force strengthens with latitude. It deflects the poleward-moving upper air until, by roughly 30°, the flow is almost west-to-east — the subtropical jet. Poleward movement is thereby choked off, air piles up, and general subsidence follows. This is the dynamic half of the explanation.
• Both reasons are valid and complementary, so option C is correct.

Additional Information

• The three-cell model of each hemisphere: the Hadley cell (equator to ~30°), the Ferrel cell (~30° to ~60°), and the Polar cell (~60° to the pole).
• The subsidence belt at 20°–35° produces the subtropical high-pressure zones — the *horse latitudes* — and with them the world's great hot deserts: the Sahara, Arabian, Thar, Kalahari, Atacama and Australian deserts. Sinking air warms adiabatically, its relative humidity falls, and cloud formation is suppressed.
• The Intertropical Convergence Zone (ITCZ) is the ascending limb, marked by the equatorial low (doldrums), and it migrates seasonally with the overhead sun — its northward shift over the Indian subcontinent is central to the south-west monsoon.
• The returning surface flow of the Hadley cell, deflected by the Coriolis force, forms the trade winds — north-easterly in the northern hemisphere and south-easterly in the southern.
• George Hadley proposed the single-cell model in 1735; William Ferrel refined it in the nineteenth century after the Coriolis effect was understood.