Consider the following statements on 'Fog' : 1. Fog is simply a cloud that forms close to the ground. 2. Radiation fog is associated with radiation cooling of the land at night. 3. Advection fog forms when moisture is blown over a cold surface and is chilled by contact. Which of the statements given above are correct ?
- A.1 and 2 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
Correct answer
Explanation
The correct answer is D, 1, 2 and 3. All three statements are correct descriptions of fog and its two main types.
Fog forms when air near the ground cools to its dew point and its water vapour condenses on tiny dust and smoke particles, so it is in effect a cloud at or near ground level. Radiation fog forms on clear, calm nights when the land loses heat quickly by radiation and chills the air just above it; it is common in winter in the Indo-Gangetic plains and usually lifts after sunrise. Advection fog forms when warm, moist air moves horizontally over a cold land or sea surface and is cooled by contact, as off the coast of Newfoundland where the warm Gulf Stream meets the cold Labrador Current.
Option A is wrong because statement 3 is also correct. Option B is wrong because statement 1 is also correct. Option C is wrong because statement 2 is also correct.
Exam tip: radiation fog, night cooling of land; advection fog, warm moist air over a cold surface; fog = cloud at ground level.
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