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Solar flare produces radio shock wave
(Nov 6, 2006 [REVISED Nov 7, 2006 17:14 ET])
-- A solar flare from an emerging sunspot Monday, November 6, between 1740 and 1748 UTC, produced a fast-moving radio shock wave. "It sounded like a freight train," says Thomas Ashcraft, who recorded the burst at his radio observatory in New Mexico and maintains a Web site on audible solar phenomena. Ashcraft says the C8.8 solar X-ray flare caused a moderate-to-strong -- and especially fast -- Type II radio burst event, traveling from the sun at 2230 km per second! His stereo recording of the November 6 event provides solar radio noise on 18.7 MHz in one channel and on 22.2 MHz in the other. SpaceWeather.com reports the sunspot, hidden just behind the sun's eastern limb, has been erupting and hurling clouds of magnetized gas high above the solar surface for the past thee days. Given its position on the solar sphere, the flare did not significantly raise the K index, a measure of solar storm activity based on perturbations of Earth's magnetic field. The K Index has remained at or below 1 since November 5. That could change once the sun's rotation turns the sunspot earthward to provide a direct view of the active region. The resulting stormy space weather could adversely affect HF radio propagation. 
