In order to understand thunder, one needs to know about lightning. Well! Lightning is electricity discharged during a thunderstorm. It is caused due to the build-up and discharge of electrical energy in the thunderstorm clouds, which are about 15,000 to 25,000 feet above sea level. Lightning usually occurs within clouds, between the cloud and air or between the ground and cloud. Based on the nature of lightning, there are various types such as in-cloud lightning, cloud-to-ground lightning, cloud-to-cloud lightning, sheet lightning, bead lightning, ribbon lightning, ball lightning and bolt from the blue.
What Causes Thunder
The cause of thunder has been a subject of discussion for a long time. In the third century BC, it was believed that thunder is caused due to collision of clouds. However, the most accepted theory was developed in the 20th century. According to this theory, the bolts of lightning are very hot, much hotter than the surface of the sun. It is estimated that the bolt has a temperature of 30,000 to 50,000 degrees F (28,000 degrees C). When this high temperature bolt hits the surrounding air, there is an instant expansion of the air, sending out a shock wave or vibration, which we hear as a sound of explosion. Thus, in short, thunder is caused due to rapid heating and cooling of the air, near the stroke of lightning.
The sound intensity of thunder varies, depending upon the nature of lightning and the distance of the hearer from the origin of the sound. You can estimate the distance (miles) from the strike; first count the interval between the flash of lightning and the sound of thunder in seconds and then divide the interval by five. In case, you are near to the flash of lightning, you will hear thunder as a sharp crack; whereas, if you are far from the lightning stroke, then the sound will seem a low rumble. The rumbling sound is because of the echo, occurring due to the reflection of sound waves from the buildings, trees and hillsides.
Thunder can be dangerous, depending on how close we are from the stroke of lightning. If the sound is very loud, it can hurt our ears. However, it is to be noted that it is lightning, which is more dangerous. On an average, about one hundred people die every year in the United States and several people suffer from lifelong disability due to lightning. Most of the lightning casualties occur, when people are caught outdoors during rainy weather. In case, you are outside during a thunderstorm, it is advisable to avoid open fields, beaches and lakes and also stay away from tall trees. The safest way is to get inside your home or stay in the car. In the latter situation, you should not touch metal, as it is a good conductor of electricity.