May 6, 2015 by Sci-News.com
Scientists at the Southwest Research Institute say they have visually captured the sound waves created by lightning.
Acoustic signature of thunder. Image credit: University of Florida / Florida Institute of Technology / Southwest Research Institute.
Lightning strikes Earth an estimated 100 times per second – or more than eight million times a day. The United States alone receives as many as 20 million strikes per year from perhaps 100,000 thunderstorms.
Lightning is a spark that can reach more than 5 miles in length, attain a temperature of 50,000 degrees Fahrenheit (27,000 degrees Celsius) and contain more than 100 million electrical volts.
“The physics behind this violent process remains poorly understood. While we understand the general mechanics of thunder generation, it’s not particularly clear which physical processes of the lightning discharge contribute to the thunder we hear,” said Dr Maher Al-Dayeh of the Southwest Research Institute’s Science and Engineering Division.
To capture the acoustic signature of thunder, Dr Al-Dayeh and his colleague, Dr Neal Evans, used a 15-m long, one-dimensional microphone array consisting of 16 receivers situated 95 meters from the lightning channel.
The measurements were taken at the International Center for Lightning Research and Testing in Camp Blanding, FL during the summer of 2014.
“The linear array was oriented in an end-fire position so that the peak acoustic reception pattern can be steered vertically along the channel with a frequency-dependent spatial resolution, enabling us to sample the acoustic signatures from different portions along the lightning channel,” the scientists explained.
“Results show a significant high frequency component measured in the near-field of the channel that enables acoustic imaging along the vertical profile of the channel and for individual return strokes, thus inferring the radiated acoustic energy as a function of altitude.”
The results were presented May 6 at a joint meeting of American and Canadian geophysical societies in Montreal, Canada.
Future experiments could allow scientists to study the probable acoustic signatures of current pulses, step leader branches, and discharge channel zigzags independently.
Maher Al-Dayeh & Neal Evans. Acoustic imaging of thunder from rocket-triggered lightning. 2015 Joint Assembly of American and Canadian Geophysical Societies. Abstract # AS31A-07
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