Loud booms heard in Mitchell Monday, Tuesday and late last month are believed to have been sonic booms.
Monday and Tuesday, The Daily Republic received reports of explosions or thunderous booms in Mitchell. The first was reported around noon Monday; several more came early Tuesday evening.
The Mitchell Department of Public Safety did not receive any official reports of a loud booming noise on Monday, but received numerous reports Tuesday evening. The department also received some reports on Nov. 21.
Tuesday, calls began coming into the Mitchell Regional 911 Communications Center around 6:15 p.m., said Marlene Haines, communications supervisor. Callers from all areas in Mitchell reported hearing the noise.
Chief of Public Safety Lyndon Overweg said that when the department receives such reports, the local fire department is dispatched to the area to see if there is any type of visible damage. When there are no corresponding reports of damage and the reports are widespread, it's determined to be a sonic boom.
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Overweg said some reports even came from Hanson County.
Monday, a reader e-mailed The Daily Republic and reported a "huge shockwave that went by and shook my whole house."
Tuesday, calls came to the newspaper and to its employees at home.
A sonic boom is a thunder-like noise that can be heard on the ground when an aircraft overhead surpasses the speed of sound.
Lt. Col. Reid Christopherson, of the South Dakota Air National Guard, said Mitchell is on the edge of a military operating airspace, approved by the Federal Aviation Association. Supersonic flights are allowed within the airspace for flights higher than 30,000 feet.
Christopherson said that on the days the booms were reported, Air National Guard pilots were flying in the Mitchell area.
"It's very possible that we would have had airplanes operating in that airspace that may have transitioned to that supersonic level," he said. "The density of the (colder) air allows that noise to carry. It's much more noticeable in the winter. If the same event occurred in the summer, you would not even notice."
Temperatures were similar on the days of the reports. On both Nov. 21 and Tuesday, for instance, highs ranged from 28 to 32 degrees and lows from 15 to 23 degrees. Monday, temperatures were a bit colder, yet similar.
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However, Christopherson said he does not know for certain that the booms heard in Mitchell were a direct result of the flight training.
"It's not the flights themselves, but in the course of the training, the airplane may have extended the speed and caused the noise," he said.
The National Weather Service in Sioux Falls has not received any reports of anything out of the ordinary, said Kyle Weisser, a meteorologist. "It's very unlikely that it would be weather-related, especially at this time of the year," said Weisser.
An interesting but unlikely source of such a loud noise is a meteorite strike, Weisser said, but again, the NWS has received no such reports.
