Cloud Electrification and Lightning Questions and Answers

Answer: A

Correct answer: a tripole with positive above, negative in the middle and a lower positive

The classical picture has a main positive charge in the upper cloud, a main negative centre in the middle at around the minus 10 to minus 20 degree level, and a smaller positive pocket near the cloud base. The lower positive charge is small but important, since it helps initiate the negative cloud-to-ground flash by enhancing the field beneath the negative centre. A simple dipole was the earlier and less complete description.

Answer: B

Both are true and the reason gives its role, and its presence or absence influences the polarity of the flash. Storms lacking it tend to produce fewer negative cloud to ground strokes overall. Its origin is thought to lie in charging below the reversal level.

Answer: C

Correct answer: non-inductive charge transfer during graupel ice collisions

Riming graupel colliding with small ice crystals in the presence of supercooled water exchanges charge, and the sign depends on the temperature and the liquid water content. The mechanism is non-inductive because it requires no pre-existing field, which is what allows electrification to begin from nothing. The updraught and gravity then separate the two - light crystals carried up, heavy graupel falling - which is what builds the field.

Answer: D

The first two are correct and are the necessary conditions. The third describes inductive charging instead, which is generally regarded as secondary to the non-inductive mechanism. Inductive charging amplifies rather than initiates.

Answer: A

Correct answer: the sign of charge transferred to the graupel changes

Above the reversal temperature the riming graupel charges positively and the ice crystals negatively; below it the signs are exchanged. The level at which that changeover occurs therefore separates the region where graupel carries negative charge downward from the region where it carries positive charge, and it is what fixes the height of the main negative centre. Its value is not a constant, depending on the liquid water content present.

Answer: B

Values between about minus ten and minus twenty are reported depending on liquid water content. That this coincides with the region of most active riming is not a coincidence. Charging and riming depend on the same supercooled water.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Falling graupel charges negatively below the reversal temperature and positively above it, so the negative charge accumulates at the level where that changeover occurs - typically minus 10 to minus 20 degrees, or around 6 km in a mid-latitude summer storm. Because the temperature rather than the height governs it, the negative centre sits at a consistent temperature level in storms of very different depth.

Answer: D

The two particle types acquire opposite charge and are then sorted by their differing fall speeds. Without that differential motion the charge would remain mixed and no field would develop. Separation, not charging alone, is what builds the field.

Answer: A

Both are true and the reason gives the requirement, and it also sustains the supercooled liquid charging needs. Storms without vigorous updraughts electrify weakly or not at all. Updraught strength is the best single predictor of flash rate.

Answer: B

The non-inductive mechanism is regarded as dominant, with the others contributing at various stages. Inductive charging can only act once a field already exists. The mechanisms therefore operate in a definite sequence.