Lightning

During a thunderstorm, some amazing things occur, the least of which can be incredible downpourings of rain in a very short time. In addition, thunder and lightning provides extraordinary air shows, but also present some dangers. Although the actual cause of lightning is rather complex, here is a slightly simplified view.

Cumulonimbus clouds possess a strong electrical charge which varies as you move upwards through the cloud. Nearer the base, it is strongly negative, becoming strongly positive in the upper reaches. The Earth also normally has a negative charge, but during a thunderstorm this charge becomes positive. The simplest explanation for this can be found in a comparison to magnets. Since the lower portion of the cloud and the planet are both negatively charged, they repel each other, much like two magnets placed with their north poles together. As the clouds charge becomes more and more negative, so does the charge on the surface become more positive. These positive ions will then begin to move to the top of tall trees (and tall hikers on ridges) as they are attracted to the negative charge in the cloud. Because air is a very poor conductor, these ions cannot easily travel to one another. Lightning is the result of this electrical field building up to such an extent to overcome the poor conductivity of the air. Suddenly, the insulating capacity of the air breaks down and lightning occurs. Quite simply when there are enough charged particles, a sudden violent movement of negatively charged particles from the cloud to the Earth will occur lightning. This will continue for up to about a second; until the difference in charge is reduced sufficiently. The process of build up will then begin again.

Thunder is the result of an instantaneous expansion and contraction of the air producing pulses of pressure that we hear as loud crashing sounds.

Yes, it's true! You can estimate the distance to a storm by counting the number of seconds between the flash and the crash however this number must be divided by five. If the sound and the bold occur almost simultaneously, it's definitely close by

Dangers of lightning, Safety tips

When you're out hiking and a sudden storm blows in take cover. Mountain hiking can be exhilarating but it does have its hazards. During a storm, avoid mountain summits, open stands of trees and shallow caves. The best places are at least a hundred metres below the summit, inside shallow crevasses, deep caves, the base of a cliff, or even better, warm and cozy in your car. If you feel your hair standing on end make for cover at warp speed.

All Material Ward Cameron 2005