All of the following are recognised lightning safety measures EXCEPT
Answer: C
A tall isolated tree is among the most likely strike points and side flash is a serious risk. The other three each reduce the chance of being on the discharge path. Substantial buildings and vehicles are the safest places.
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A side flash occurs when
Answer: D
Correct answer: current jumps from a struck object to a nearby person
A side flash occurs when current flowing down a struck object - a tree, a mast, a wall - meets enough resistance to raise its potential above that of a nearby person, and the difference breaks down the intervening air. It is one of the main lightning injury mechanisms, and it is why sheltering under a tree is more dangerous than standing in the open.
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Match each lightning injury mechanism with its description.
List I
A. Direct strike
B. Side flash
C. Ground current
D. Contact injury
List II
1. current spreads through the earth from the strike
2. the current passes through the person
3. the person touches an object carrying current
4. current arcs from a struck object nearby
Answer: A
Ground current accounts for the largest share of casualties, although direct strikes are the most often imagined. Understanding the mechanisms informs the standard safety advice. Most casualties arise from mechanisms other than a direct hit.
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Assertion (A): Ground current causes more lightning casualties than direct strikes do.
Reason (R): Current spreading through the earth affects a far larger area than the strike point itself.
Answer: B
Both are true and the reason gives the reason for the disparity, and livestock losses illustrate it clearly. Keeping the feet close together reduces the potential difference across the body. The advice matters most for people caught in the open.
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The charge moment change of a flash is
Answer: C
Correct answer: the charge transferred multiplied by the height it moved
Charge moment change, measured in coulomb-kilometres, is the quantity that determines the electric field the flash imposes on the atmosphere far above it, so it is what governs whether a sprite is produced. A flash of 100 C over 10 km gives 1000 C km, well above the threshold. It is more informative than the peak current for effects at a distance, since it captures both the charge and the geometry.
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Consider the following statements about thunderstorm charge structure.
1. The main negative centre lies in the mixed phase region.
2. A broad positive region sits above it near the anvil.
3. The charge structure is identical in every thunderstorm.
Answer: D
The first two are correct and describe the classical tripole. The third is not so, and inverted structures with the polarity reversed are observed in some severe storms on the plains. Such storms produce anomalously many positive flashes.
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Assertion (A): Some severe storms exhibit an inverted charge structure.
Reason (R): High liquid water content shifts the sign of the non-inductive charge transfer.
Answer: A
Both are true and the reason gives the microphysical cause, and such storms produce anomalously many positive cloud to ground flashes. The link between microphysics and flash polarity is direct here. Liquid water content is the controlling variable.
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Lightning activity in a storm is often observed to peak
Answer: B
Charging is most vigorous during the growth of the updraught and the graupel it supports. The lightning jump is used operationally as a short term indicator of storm intensification. The signal often leads severe weather by tens of minutes.
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State whether the following is true or false.
A rapid increase in total lightning rate can precede severe weather at the surface.
Answer: C
Correct answer: True
A sharp increase in total flash rate - the lightning jump - reflects an intensifying updraught carrying more ice aloft, and it frequently precedes hail, damaging wind or a tornado at the surface by five to twenty minutes. Because total lightning includes intracloud flashes, which respond earlier than cloud-to-ground ones, it is used operationally as a nowcasting signal.
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Total lightning refers to
Answer: D
Networks measuring both give a fuller picture of storm electrification than cloud to ground alone. The intracloud rate responds to updraught changes earlier than the cloud to ground rate does. Charging begins aloft before the lower centre forms.
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