Cloud Electrification and Lightning Questions and Answers

Answer: A

The channel is still partly ionised from the previous stroke, so no stepping is needed. Dart leaders therefore travel considerably faster than the original stepped leader. No stepping is needed through partly ionised air.

Answer: B

The sequence of these components determines both the appearance of the flash and its capacity to start fires. Continuing current is the component most associated with ignition on the ground. Duration matters more than peak current for setting fires.

Answer: C

Both are true and the reason gives the difference, and sustained heating matters more for ignition than peak current does. Flashes carrying long continuing currents are described as hot lightning. The distinction is operationally useful for fire forecasting.

Answer: D

They typically originate in the upper positive charge region, often in the stratiform area of a system. Their long continuing currents make them disproportionately effective at starting fires. Wildfire ignition is strongly weighted towards positive flashes.

Answer: A

The first two are correct. The third reverses the comparison, since positive flashes commonly transfer considerably more charge and carry longer continuing currents. Their rarity is offset by their greater individual effect.

Answer: B

It is the most common form of lightning, outnumbering cloud to ground flashes several times over. It is also harder to detect from the ground, which historically led to it being undercounted. Total lightning networks have corrected much of that bias.

Answer: C

Intracloud discharges outnumber cloud to ground flashes by a factor of about three. The ratio varies with latitude and with the depth of the storms involved. Deeper storms produce proportionally more intracloud flashes.

Answer: D

Both are true and the reason gives the bias, and modern total lightning networks detect both. Satellite optical sensors have also improved the picture considerably. Global flash rates are now reasonably well constrained.

Answer: A

Channel temperatures reach tens of thousands of degrees in microseconds, driving a shock wave. The shock decays into an acoustic wave within a few metres of the channel. What is heard is the decayed remnant of a shock.

Answer: B

Correct answer: 3 seconds

Sound travels at about 340 metres a second, so a kilometre takes very nearly three seconds - and about five seconds to the mile. Light arrives effectively instantly, so counting the seconds between the flash and the thunder and dividing by three gives the distance in kilometres. It is the basis of the standard advice to take shelter when that interval falls below thirty seconds.