Page 40 - Spring 2015

Concorde booms and the Mysterious east Coast noises
locations for the three signals recorded at Palisades, NY. Acoustic signals were recorded on both the inbound and outbound flights at Durham, NH. Of interest is the sche- matic ray tracing, shown in the upper left inset in Figure 5, that indicates ray paths through the stratosphere (about 40- 50 kilometers) and the thermosphere (100-130 kilometers). The received signals associated with propagation through the stratosphere were much stronger than those propagating through the thermosphere. A typical temperature profile for the atmosphere illustrating the various atmospheric layers is shown in Figure 6.
The Mysterious east Coast booms
The secondary sonic booms went essentially unnoticed in the United States until 1977 when mysterious east coast acoustic disturbances were reported (Shapely, 1978). These mysteri- ous sounds were observed from December 2, 1977 through February 15, 1978, principally in the Charleston, SC, area and on the New Jersey coast. People were saying they heard booms, some low rumblings, and other explosive sounds. A number of suggested causes were put forth that ranged from methane gas bubbles venting from faults in the ocean's floor to lasers being beamed from Russian space platforms. Pre- dictably, the January 24, 1978, issue of the National Enquirer carried a front-page banner headline proclaiming Mystery Blasts Linked To UFOs. One of the things that fueled the in- tense interest and concern about these events was the per- sistent suggestion that they might be a precursor to a major earthquake. This was particularly troubling to residents of Charleston because the city was struck by a huge earthquake in 1886. On December 28, 1977, the Department of Defense tasked the Naval Research Laboratory (NRL) to carry out a 60-day intensive investigation to determine the cause of these startling acoustic events.
According to citizen reports, the disturbances, most fre- quently observed indoors, included window rattles and house vibrations, with the noise consistently identified as coming from the direction of the ocean. Acoustic and seis- mic measurements of these disturbances were being made at the Lamont Observatory and at the Weston Observatory at Boston College (see Figure 5) observatories. Analysis of the Weston data showed that nearly all the signals occurred on workdays. Signals were rarely detected on Saturdays, Sun- days, or national holidays or during nonworking hours. This temporal pattern strongly suggested that the events were due to human activity. The NRL's investigation of possible causes
led them to rule out man-made causes such as military re- search and development activities, military ordnance, civil- ian use of high explosives, missile reentry, and low-altitude satellites. Natural phenomena such as meteorites, winter lightning, biogenic and tectonic methane, and direct seismic generation were thoroughly reviewed and classified as un- likely causes of the events, even without consideration of the their temporal pattern.
The NRL then focused on military operations. They found that there were military aircraft capable of supersonic flight in all of the warning areas adjacent to the New Jersey and South Carolina coastlines. Sonic booms from supersonic operation in these warning areas were not usually a concern to residents because the primary booms do not propagate to the coast under normal atmospheric conditions. Ray tracings based on atmospheric conditions existing on the same day that supersonic flights were made showed that the booms should be observable as far away as 100 kilometers for flights above 5,000 meters.
The NRL examined the Concorde flights in and out of John F. Kennedy International Airport (New York) and Washing- ton Dulles International Airport and found no correlation between their operation and the reported acoustic events in New Jersey and Charleston, SC. In its March 3, 1978, early release of the findings (final report, NRL, 1979), the NRL stated that the most likely source of these events appeared to be high-performance military aircraft operating supersoni- cally and that the degree of disturbance to the citizens was influenced by atmospheric propagation conditions.
There was immediate disagreement with the NRL conclu- sions from Jeremy Stone, president of the Federation of American Scientists (Shapely, 1978; Sullivan, 1978), who suspected that somehow, despite evidence to the contrary, the east coast booms were due to the Concorde. Probably the strongest reason to suspect the Concorde was the timing of the onset of the east coast booms. The NRL report (1978) states that no events were observed at Weston in November “until November 28 when five events appeared as though a switch had been thrown.” Concorde service to New York be- gan on November 22, 1977. Stone enlisted the help of IBM physicist Richard Garwin, a National Medal of Science win- ner, to come up with a plausible way in which a sonic boom could travel faster than the aircraft that generated it. Accord- ing to geometrical acoustics, the upward going sonic booms (both the one that goes directly up and the one that reflects from the water) will turn and return to earth when it reaches
38 | Acoustics Today | Spring 2015