Lightning causes more static on the low end of the AM dial than on the high end. Why does this happen?

Weather Blog

Dear Tom,
Lightning causes more static on the low end of the AM dial than on the high end. Why does this happen?
Fred Mercan, 
Chicago

Dear Fred,
A lightning strike is like a radio transmitter, producing radio waves knows as sferics that cause the familiar static we hear on AM radio. Lightning generates a broad spectrum of radio frequencies, peaking at about 10 KHz. The power emitted by a radio wave decreases rapidly as the frequency increases, so the power received from a lightning strike at the low end of the AM dial is about ten times stronger than that received at the high end of the dial. For this reason, the static is considerably more noticeable at the low end of the AM band. Higher frequencies like FM are affected even less.

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