The Wonder of Thunder

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

In similar fashion, the speed of sound is also partly responsible for the rumbling we hear, due to refraction - the bending of sound waves. Although its change in speed is not great, sound travels faster in warm air than in cold, increasing in speed by about one foot per second with each degree Fahrenheit rise in temperature. These small changes are important because air temperature varies significantly across the atmosphere, and especially during storms.

Atmospheric temperature change can also be abrupt, as when incoming warm air slides over existing cold air. When this happens and a sound wave in cold air approaches the warm air at an angle, those portions of wave front that enter the warm air first will speed up, thereby rotating the entire front a few degrees and changing the wave's travel direction. Conversely, sound waves entering cold air from warm air at an angle will slow the wave and bend it in opposite manner. Bear in mind, even a gradual change in temperature can cause sound waves to bend. In some cases, rising sound waves can keep bending and, depending on rise-angle and other conditions, head back to Earth.

When sound waves radiate from a lightning bolt, vertical changes in air temperature cause extensive bending. Horizontal temperature changes, due mainly to air pockets and columns of rising or falling air, also bend sound waves. A11 this simultaneous refraction results in myriad crisscrossing sound waves.

Sound waves are also influenced by destructive interference. When similar waves are superimposed, their vibrations oppose or support each other, which results in a haphazard mixture of cancelled and reinforced sounds. Therefore, when lightning is a few miles away, we hear throbbing variations of sound - the rumble of thunder.

-Walter S. Andariese

RSS | Comments | E-mail | Print