...The Science of Lightning...
This week is National Lightning Safety Awareness Week. Lightning Kills--play it safe!
All thunderstorms contain thunder and lightning. As lightning passes through the air, it rapidly heats the air to 50,000 degrees Fahrenheit, much hotter than the surface of the sun. During a lightning discharge, the sudden heating of the air causes it to rapidly expand and contract. This in turn causes a shock wave that we hear as thunder.
Lightning can occur completely within the thunderstorm cloud, between clouds, or between the cloud and the ground. Cloud-to-ground lightning can be categorized as negative flashes and positive flashes. Prior to a negative flash, an almost invisible negatively charged channel of air forms near the cloud base and surges downward near the ground. At the same time, streamers of positive charges shoot up from trees, buildings, and other high objects on the ground. When these meet, the connection is complete, and a surge of electrical current moves from the ground to the cloud causing the visible return stroke called lightning.
Positive flashes usually occur between the positively charged upper level of the storm and the negatively charged areas under the storm. The process of a positive flash is similar to that of the negative flash. However, because the distance between the ground and the storm top anvil is much greater, a significantly larger electric potential is needed to initiate a positive flash of lightning. For this reason, positive flashes are infrequent and widely scattered around the storm, but they generally involve the exchange of much greater charge and are much more destructive.
The greatest danger associated with positive charges, however, is that they strike in areas where most people think they are safe from the storm. They can strike well beyond the area where rain is falling and well beyond the area where lightning and thunder are occurring--as much as 10 miles away! Consequently, many victims are caught completely off guard. Do not become a lightning victim--get to a safe place sooner and stay there longer. Remember, if you can hear thunder, you are close enough to get struck! For more on lightning safety, go to www.lightningsafety.noaa.gov.