Lightning Flashcards
What are the two types of lightning?
Sheet lightning - 80%
Cloud to ground lightning - 20%
What is sheet lightning vs cloud to ground
Voltage gradient within or among clouds: An electrical discharge is obscured by the clouds, so it lights up the sky uniformly (like a sheet)
Voltage gradient between the cloud and surface: electrical discharge travels between the base of the cloud and the surface
In electricity, opposites ____, and insulators ____? How does a voltage gradient come to be?
Opposites attract, and insuators inhibit
- the separation of +ve and -ve charges results in a voltage gradient
When does lightning occur?
When the force of the lightning gradient overcomes the inhibiting and insulating properties of the air in between the charges.
- When the charge threshold is reached, the strength of the voltage gradient overpowers the airs insulating properties and lightning results
How much charge has to be built up for lightning to occur?
A tremendous amount because air is a very good insulator
Which specific clouds do lightning only occur in?
- clouds that extend above freezing level
- clouds that are precipitating
In the clouds, where do positive charges accumulate vs negative charges?
Positive charges accumulate in the upper portions of the cloud
Negative charges in the lower
Why did a recent study indicate that ice crystals, hail, and graupel are essential to lightning development?
Because storms that fail to produce large quantities of ice usually fail to produce lightning
Describe the pathway for hail showers
- Updraft: Each hailstone starts with a small nucleus that attracts supercooled water droplets to grow in size. The updraft lifts these drops into the below-freezing ice nucleus.
- As the updraft carries the nucleus, higher supercooled droplets collide and freeze onto it. The updraft repeatedly carries the nucleus up and down across freezing, growing it in size by collecting more supercooled water.
- Eventually, the hailstone becomes too heavy and falls to the ground with the help of the downdraft within the thunderstorm
Define a stepped leader
A rapid and staggered advance of a shaft of negative electrical air that precedes the lightning event
A stepped leader steps at about ___m at a time
50m at a time
Describe how the leader connects with the ground to strike
A spark surges upward from the ground toward the leader; when they connect, they create a pathway for the flow of electrons that initiates a sequence of STROKES.
How much heat does a lightning strike output compared to the sun
A lightning current heats the air temperature 5x more than the sun (30,000K)
When is most of the charge neutralized in a lightning strike
The initial stroke
How does a dart leader form?
It forms if there is still charge separation in the cloud
How often can the sequence of dart leaders and strokes repeat?
4-5 times
Because the individual strokes occur in rapid succession, they appear to be a single stroke that flickers and dances about from a cloud
What is a lightning flash?
the combination of strokes from the transfer of electrons from the cloud to the ground
Lightning discharges in ___ voltage, ___ amperage?
Low voltage
High amperage (15-25 KA)
Ball Lightning
Appears as a round, glowing mass of electrified air up to the size of a basketball that seems to roll across the surface for 15 seconds before dissipating or exploding
St-Elmos Fire
When positive electrical charges accumulate on the surface, they emit energy before the lightning strike, causing the surfaces to glow
- can cause lightning to skip off buildings or ships
Sprites
What do they rise from?
“Spurts” - Very large but short-lived electrical bursts that rise from cloud tops as lighting occurs below’
- Look like a giant red jellyfish
Blue jets
What do they eject upward from?
Upward moving electrical ejections from the tops of the most active regions of thunderstorms
How is upward lightning triggered?
By a nearby cloud to ground lightning strike
- forms upward leaders
- caused by positive electrical charge built up around the tops of buildings, which leaps up and connects with above cloud
Why is thunder produced? How many seconds do between thunder sounds = 1km away?
The tremendous increase in temperature during a lightning stroke causes the air to expand explosively and produce sound from the stroke path
- 2 seconds between = 1km away
