The charge structure of a winter thunderstorm often differs from a summer one because
Answer: D
The lower freezing level brings the charging region down towards the surface. Winter storms in coastal Japan are noted for producing unusually energetic positive flashes. The low freezing level brings the charge centres down.
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Assertion (A): Winter thunderstorms can produce unusually powerful positive flashes.
Reason (R): Their charge centres lie low, bringing the upper positive region within reach of the ground.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason explains it. Winter thunderclouds are shallow and their charge centres sit low, so the upper positive region is close enough to the ground for a positive flash to reach it. Positive flashes carry far greater charge and continuing current than negative ones, which is why winter lightning in Japan and Scandinavia is disproportionately damaging to wind turbines and transmission lines.
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Corona discharge from vegetation during a storm
Answer: B
Correct answer: carries a current between the ground and the air
Corona from grass, trees and crops in the strong field beneath a storm passes a small current continuously from the ground into the air, and integrated over the area beneath a storm it forms a significant part of the electrical budget of the global circuit. It occurs before and during the storm rather than after a strike, and it does not prevent lightning - it merely bleeds off a fraction of the charge.
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Three of the following require supercooled liquid water. Which is the odd one out?
Answer: C
Correct answer: the fair weather conduction current
The fair weather conduction current flows in clear air far from any cloud and involves no water at all, supercooled or otherwise; it is carried by ions produced by cosmic rays and natural radioactivity. The other three all require supercooled liquid water: riming builds graupel by freezing droplets onto it, aircraft icing is the same process on an airframe, and non-inductive charging occurs only in its presence.
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Charge in a thundercloud is carried principally by
Answer: D
Ice crystals, graupel and droplets carry the charge and are transported by air motion and gravity. Free ion mobility is far too low to build the charge centres observed. Bulk transport of charged particles does the work.
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Assertion (A): Free ions alone cannot account for thunderstorm charge separation.
Reason (R): Their mobility is far too low to transport charge over kilometres in the time available.
Answer: A
Both are true and the reason gives the objection, and hydrometeors moving bodily do the work instead. This is why the microphysics of the mixed phase region matters so much to electrification. Microphysics and electricity are inseparable here.
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The main negative charge centre in a mid-latitude summer thunderstorm typically lies at a height of about
Answer: B
Correct answer: 6 kilometres
The main negative centre sits near the minus 10 to minus 20 degree level, which in a mid-latitude summer storm is around 6 km. Because it is fixed by temperature rather than by height, it lies lower in winter storms and at higher latitudes and higher in the deep tropics - a shift with real consequences, since a low charge centre is what makes winter positive flashes so powerful.
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A lightning flash rate that suddenly falls to zero in a severe storm may indicate
Answer: C
Correct answer: that the updraught has collapsed and a downburst may follow
Electrification requires an updraught vigorous enough to keep supercooled water and graupel aloft, so when the flash rate stops abruptly the updraught has failed. What was being supported then falls, and the resulting downdraught can reach the surface as a damaging downburst within minutes. Both the sudden rise and the sudden cessation of the flash rate are therefore operationally significant, in opposite ways.
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Consider the following statements about lightning and storm evolution.
1. A lightning jump can precede severe weather at the surface.
2. A sudden cessation may indicate updraught collapse.
3. Flash rate bears no relation to updraught strength.
Answer: D
Correct answer: 1 and 2 only
Statements 1 and 2 are correct and are used operationally: a lightning jump precedes severe weather, and a cessation warns of updraught collapse. Statement 3 contradicts both - the flash rate is closely tied to updraught strength, since it is the updraught that lifts the supercooled water and graupel on which charging depends. That relation is exactly what makes total lightning useful for nowcasting.
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Lightning is more frequent in continental than in maritime convection chiefly because
Answer: A
Higher droplet concentrations and stronger updraughts carry more liquid water above the freezing level. The resulting graupel production is what drives the non-inductive charging. Aerosol and dynamics both contribute to the contrast.
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