What is lightning?
A giant spark of electricity in the atmosphere that occurs between clouds, the air, or the ground.
What percentage of lightning occurs as cloud-to-cloud lightning?
Approximately 80%.
Cloud-to-cloud lightning occurs when a _____ gradient overcomes the electrical resistance of the air.
voltage
What is sheet lightning?
Cloud-to-cloud lightning where the flash is obscured by the cloud.
What percentage of lightning is cloud-to-ground lightning?
Approximately 20%.
What fundamental process is required for all lightning to form?
The separation of positive and negative charges into different regions of the cloud.
What is the charging mechanism of a thunderstorm?
Collisions between ice crystals and pellets or graupel.
In a typical thunderstorm cloud, where do positive and negative charges accumulate?
Positive charges accumulate at the top, and negative charges accumulate in the lower part.
What is a stepped leader in the formation of lightning?
The rapid and staggered advance of a shaft of negatively charged air from the cloud.
How are return strokes formed during a lightning event?
When the stepped leader and a spark from the ground connect, a flow of electrons illuminates the cloud.
What is a lightning flash?
The combination of all strokes involved in the entire process of transferring electrons from the cloud to the ground.
The channel of air through which lightning passes can be heated to what temperature?
Up to 50,000°F, which is hotter than the surface of the sun.
What is the direct cause of thunder?
The explosive expansion of air heated by a lightning stroke.
Why is there a time lag between seeing a lightning strike and hearing the thunder?
Light travels through the air approximately a million times faster than sound does.
What is ‘heat lightning’?
Lightning from a distant storm that seems to occur without audible thunder.
What causes thunder to sound like it is rumbling?
The echoing of sound waves off of objects like buildings and hills when the storm is farther away.
What are the three essential ingredients needed for every thunderstorm to form?
Moisture, unstable air, and a lifting mechanism.
What are the characteristics of an air mass thunderstorm?
They are relatively small, localized, short-lived, and the least destructive type of thunderstorm.
What are the three stages of an air mass thunderstorm, in order?
The cumulus stage, the mature stage, and the dissipating stage.
What happens during the cumulus stage of an air mass thunderstorm?
Uplift begins, a towering cumulus cloud forms, there is little to no rain, and it lasts about 10 minutes.
During which stage of an air mass thunderstorm is hail, heavy rain, and frequent lightning most likely?
The mature stage.
What is the dominant air flow during the dissipating stage of an air mass thunderstorm?
Downdrafts, which are downward flowing air currents.
What are multicell thunderstorms?
Thunderstorms that develop into organized clusters.
Organized groups of thunderstorms are referred to as _____.
mesoscale convective systems (MCSs)
