LIGHTENING!
Michael Ellis

The San Francisco Bay area is chock full of natural wonders and I rarely complain about the lack of anything. But there are three things definitely missing here — warm nights, fireflies, and good electrical storms.

I read somewhere that the Bay area only averages three lightening days per year, the Great Plains has 45 and Florida has 90. But if you really want to hear thunder go to Uganda, they have 242 days of thunderstorms! So why are the conditions so poor around here for electrical storms? Well we simply don’t have one of the main ingredients — warm, moist air. We mostly have cool air, in case you haven’t noticed.

When warm, moist air mixes with cold air, gigantic clouds called thunderheads are created. Filled with millions of gallons of water and towering eight miles high these clouds build up tremendous electrical charges. They are positive at the top and negative at the bottom. Lightening is simply the giant spark that arcs between the two charges. And it most often occurs within the cloud.

But occasionally the ground under the cloud becomes highly charged. When this charge becomes so great that it overcomes the natural electrical resistance of the air, a spark called a step leader hurdles down from the cloud. This leader meanders about in many pathways and when it gets about 90 feet above the ground a massive spark leaps up to meet it. This electrical charge moves up through a tree or other tall object. This giant burst of energy traces all the errant paths of the step leader and lights them up all at once, creating the familiar lightening bolt. If you can’t remember anything else remember this – that lightening goes up! This flash is five times hotter than the surface of the sun. The air is immediately superheated and the resulting shock wave we hear as thunder.

COOL!

This is Michael Ellis with a Perspective.

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November 8, 2010