Those "mysterious" and "baffling" booming noises that have been startling coastal residents from South Carolina to Connecticut since December have a simple explanation tied to extremely cold weathter, according to two government scientists.
The explosions are simply "to side" sonic booms, bounced back to earth by warmer, high altitude air above the frigid air masses that have covered much of the nation, according to Harvey H. Hubbard and Domenic J. Maglieri of the National Aeronautics and Space Administration's Langley Research Center.
A supersonic aircraft produces a "normal" sonic boom that travels downward in a path 15 to 30 miles wide, said Hubbard, assistant chief of the acoustics and noise reduction division at the Hampton, Va., facility.
The top of the aircraft also sends a boom upward, which in normal weather dissipates in the upper atmosphere, he said.
But with prevailing weather conditions, warmer air above the 20,000 to 35,000 foot altitudes at which military aircraft practice combat tactics over the Atlantic Ocean can produce a pecular effect, Hubbard said.
The temperature causes the to side booms to bend back toward the earth, striking 100 to 200 miles away from their source, said Hubbard, who has studied sonic booms for 20 years.
Hubbard and Maglieri, who announced their findings yesterday, have pressented their report to the Naval Research Laboratory, one of the government agencies directed by the White House to solve the mystery.
The noises, sometimes a rumble and sometimes a sharp crack, had been blamed on evreything from spaceships and oil rig tests to secret weapons experiments and Russian submarines.
"We believe we have an explanation for almost all of those sounds," Hubbard said. He said there was "a very nice correlation" between the noise reports and high performance military training flights off the coast of Virginia and North Carolina.
"Pilots in aircraft a couple hundred miles away aren't aware that they may have been the cause of one of those mysterious explosions," Hubbard said.
"In the case of observations involving low rumbling noises of fairly long duration or building vibrations, or both, the booms will bave traveled extremely long distances," 100 miles or more, before hitting earth, he said.
"On the other hand, those observations involving sharp, short-duration noises will probably have traveled relatively short distances," Hubbard said.
These particular booms don't sound like the sonic booms we normally hear," said Maglieri, Langley's noise control chief.