A dramatic concoction of electrical discharges and loud thunders along with torrential downpour, hail and sometimes snow is a thunderstorm. Everyday about 40000 thunderstorms occur in the world, most commonly in the equatorial region and in the United States, specifically in the Midwest and the South of the nation.
Moisture, instable climate and air lift are the three primary causes of thunderstorms. Thunderstorms are examined to go through 3 distinct stages: the cumulus (or the developing) stage, the stage of maturity and that of dissipation.
The first stage takes place when warm and moist air flows upward replacing the cold air. The air rises for convectional movement or frontal clashes or even orographic lift. The moisture content in the mass of air cools down and forms cumulus clouds. Condensation of the moisture also causes convection.
The mature stage of the storm begins with the rising air meeting the tropopause. Then the clouds spread on top and gives the cloud its characteristic anvil shape. In case of sever storms the updrafts are so strong that they even punch up to the stratosphere from the tropopause.
Within the clouds the water droplets turn into raindrops and even ice particles at times. Theses particles become rain again as they fall. Sometimes the updraft is so strong that it forms larger ice particles which do not melt and come down to the earth as hail.
Lightning and Thunder
When electrical charge builds up in a thunderstorm then the lightning is formed. These electrically charged particles emits bright light and the electrical current heats up the air into a plasma mass which produces the acoustic shocks which we can hear as the roaring of the thunder.
It is not fully known exactly how the electrical discharge creates thunder. The widely accepted idea says that it is the polarization of the precipitation within the cumulus cloud that produces it. As the ice crystals and water droplets move along the earth's electric field they take up positive and negative charges. The positively charged particles tend to go up while the negatively charged particles accumulate in the bottom of the cloud.
The oppositely charged particles attract each other but are insulated by the mass of air. When the charge builds quite strength, there might occur an electrical discharge within the cloud or between the clouds and even turn from the clouds to the ground. But one out of four thunders reaches the earth. Bolts of lightning moves at about 60000 miles an hour.
About 95% of the lightning is negative. This is because it is the negative charged particles that get discharged from the cloud. However 5% of the thunders are positive which travels down to the negatively charged ground. It was discovered only in the 1970s that the positive lightning is 6 to 10 times more powerful than the negative ones. It has the potential to become a threat to all mankind and technology.
Thunder forms when the lightning bolt heats its surroundings to a great extent and this makes it to expand and then contract fast. Sound travels slower than the light. This makes it possible for us to calculate how far the lightning is by counting the time between the light and the sound of the thunder. Sound travels at around one mile in 5 seconds. The thunders that occur about 20 miles away are usually not heard.