Which one of the following is NOT a favourable condition for occurrence of a thunderstorm?
- A.Conditional and convective instability
- B.Adequate supply of moisture in the lower atmosphere
- C.Advection of cold dry air in the lower troposphere and warm moist air in the upper troposphere
- D.A synoptic situation of low level convergence and upper level divergence
Correct answer
Explanation
The correct answer is C. Cold dry air below and warm moist air above makes the atmosphere stable, which suppresses rising air; a thunderstorm needs the reverse, warm moist air near the ground and colder, drier air aloft.
A thunderstorm grows in a tall cumulonimbus cloud. It needs three things: moisture in the lower layers, an unstable atmosphere in which a rising parcel stays warmer than its surroundings, and a trigger such as surface heating, a front or hills that lifts the air. As moist air rises and condenses, it releases latent heat, which drives the updraft higher. India's pre-monsoon storms, such as the Kalbaisakhi of Bengal, form when warm moist air from the bay is overrun by dry air from the north-west.
Why the others are wrong: A, conditional and convective instability lets rising air keep accelerating upward, which is essential. B, ample low-level moisture supplies the water vapour and latent heat that feed the cloud. D, convergence near the ground with divergence aloft forces air to rise steadily and favours deep convection.
Exam tip: thunderstorm needs moisture, instability and lift; warm air over cold air (an inversion) blocks it.
Practice Questions
View allConsider the following statements : 1. Areas where rainfall exceeds 250 cm 2. Annual temperature 25°C - 27°C 3. Average humidity exceeds 75% 4. Trees do not shed the leaves To which one of the following types of vegetation does the above represent ?
- A.Tropical wet evergreen
- B.Tropical semi evergreen
- C.Tropical moist deciduous
- D.Tropical dry evergreen
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- A.A pesticide
- B.A manure that supplies nutrients to the soil
- C.A weedicide that kills the forest roots
- D.A means of levelling the slope
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Read the full explanation →Mediterranean agriculture is particularly famous for which activity?
- A.Viticulture
- B.Dairy farming
- C.Shifting cultivation
- D.Commercial grain farming
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- A.Cooperative farming
- B.Collective farming
- C.Plantation agriculture
- D.Market gardening
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Read the full explanation →Intensive subsistence agriculture, marked by very small holdings, heavy use of manure and a high yield per hectare, is characteristic of
- A.The prairies of North America
- B.The monsoon lands of Asia
- C.The steppes of Eurasia
- D.The pampas of South America
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