The Anatomy Of A Sonic Boom: What Caused N.J. To Shake?

Reports of rattling homes and loud rumbles that were felt from South Jersey all the way to Long Island Thursday were the result of a sonic boom caused by a U.S. Navy fighter plane off the coast of Maryland, the Navy says.

But how does a sonic boom actually work and why could it be felt so far away from where it originated?

According to NASA, sonic booms are “the thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound.”

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NASA further explains the phenomenon of a sonic boom as follows:

“As objects travel through the air, the air molecules are pushed aside with great force and this forms a shock wave much like a boat creates a bow wave. The bigger and heavier the aircraft, the more air it displaces.

The resulting shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions and extend to the ground. As the cone spreads across the landscape along the flight path, they create a continuous sonic boom along the full width of the cone’s base. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.”

How large a sonic boom is and how far it can travel depends on the size of the aircraft and how close to the ground the aircraft is, NASA says:

“There are several factors that can influence sonic booms -- weight, size, and shape of the aircraft or vehicle, plus its altitude, attitude and flight path, and weather or atmospheric conditions.

“A larger and heavier aircraft must displace more air and create more lift to sustain flight, compared with small, light aircraft. Therefore, they will create sonic booms stronger and louder than those of smaller, lighter aircraft. The larger and heavier the aircraft, the stronger the shock waves will be.”

In April 2014, an F/A-18 Super Hornet caused a sonic boom so intense that residents in Los Angeles and Orange County insisted it was an earthquake, according to the Los Angeles Times.

The F/A-18 jet was flying in the Pacific Ocean about 35 miles southwest of San Diego when it flew faster than the speed of sound, the U.S. Navy told the L.A. Times.

Because the jet was headed in a northern and northwest direction, the sonic boom produced by the fighter jet headed toward the coast of Los Angeles and Orange counties — more than 100 miles away.

The sound moves in the same direction as the aircraft, Navy officials said at the time.

The USGS told the Patch Thursday that sonic booms can be felt hundreds of miles away, so it’s possible that planes flying from as far away as Maryland could have caused the rumbling felt in New Jersey and Long Island.

While some may equate sonic booms to sounding like sharp cracks, the farther away you are from the jet, the more likely you might hear a rumbling sound that can shake buildings, similar to what happens when lightning strikes during a thunderstorm, NASA told the L.A. Times.

“Altitude determines the distance shock waves travel before reaching the ground, and this has the most significant effect on intensity. As the shock cone gets wider, and it moves outward and downward, its strength is reduced. Generally, the higher the aircraft, the greater the distance the shock wave must travel, reducing the intensity of the sonic boom.”

”The width of the boom ’carpet’ beneath the aircraft is about one mile for each 1,000 feet of altitude. An aircraft, for example, flying supersonic at 50,000 feet can produce a sonic boom cone about 50 miles wide.

“Maximum intensity is directly beneath the aircraft, and decreases as the lateral distance from the flight path increases until it ceases to exist because the shock waves refract away from the ground. The lateral spreading of the sonic boom depends only upon altitude, speed and the atmosphere - and is independent of the vehicle’s shape, size, and weight.”

“The direction of travel and strength of shock waves are influenced by wind, speed, and direction, and by air temperature and pressure.”

There have been multiple instances where the sound and rumbling from military maneuvers at Joint Base McGuire-Dix-Lakehurst have been felt a good distance from the base, including last spring when the rumblings were felt in Monmouth County during one weekend’s training -- a much smaller force of sound than a sonic boom.

Sound waves travel slower in cold air than through warm air, because the molecules move more slowly, according to the site Physics Stack Exchange. But the layer of snow on the ground may have contributed to the distance the boom traveled, because the snow “helps confine and preserve sound because it looks to smooth the long wavelengths of sound.” That causes the sound to travel farther, the site says.

And though the cold air slows it down, it doesn’t decrease the intensity, the site says.

NASA says sonic booms are measured in pounds per square foot of overpressure. This is the amount of the increase over the normal atmospheric pressure which surrounds us (2,116 psf/14.7 psi). At one pound overpressure, no damage to structures would be expected. Overpressures of 1 to 2 pounds are produced by supersonic aircraft flying at normal operating altitudes. Some public reaction could be expected between 1.5 and 2 pounds. Rare minor damage may occur with 2 to 5 pounds overpressure.

As overpressure increases, the likelihood of structural damage and stronger public reaction also increases. Tests, however, have shown that structures in good condition have been undamaged by overpressures of up to 11 pounds. Sonic booms produced by aircraft flying supersonic at altitudes of less than 100 feet, creating between 20 and 144 pounds overpressure, have been experienced by humans without injury.

(Photo Credit: Ensign John Gay, USS Constellation, US Navy)