Rate of Entry of Electrophonic Bolides

Rate of Entry of Electrophonic Bolides

Meteor fireballs large enough to produce electrophonic sounds are very rare. The majority of people never see one, even if they spend a substantial fraction of their time outdoors at night. Fortunately, sufficient observational evidence exists to relate with the known flux of large meteoroidal bodies onto the Earth and thus calculate the actual chances of witnessing one.In attacking this problem I had the great privilege of working with the Czech astronomer Zdenek Ceplecha, who is widely respected as the leading authority on meteor fireball studies. In central Europe forty years ago he became the first astronomer to photograph a fireball and find the meteorites it dropped, which meant it was the first time anyone knew the pre-entry orbit of the parent body. This was the famous Pribram fireball and Ceplecha's feat has been repeated only three times in the ensuing years. The three were the Lost City and Peekskill fireballs over the United States and the Innisfree fireball over Canada.

The Peekskill fireball in October 1992

Incidentally, Ceplecha's light curve for the Pribram fireball is so good I was able to use it to calibrate my own calculations of the transition altitude at which turbulent flow commences for large fireballs.
Using my criterion in Ceplecha's refined model for the behaviour of meteor fireballs upon entry into the atmosphere, it was determined that the majority of bodies large enough to produce sustained electrophonic sounds by travelling in shallow trajectories are of stony composition, and an estimated 16,000 occur every year over the entire surface of the Earth. These are closely followed in numbers by the more readily fragmenting carbonaceous chondrites at 12,000 per year. Then there are the very fragile bodies of cometary composition at 4,600 per year, and lastly the fluffy very low density bodies also of cometary origin which come in at the rate of 1,300 per year.
Observational evidence, notably through the excellent reports of fireballs in the American State of Oregon by Bob Pugh, and from other sources, is concordant with the above data. With other reasonable assumptions, such as taking the average range of electrophonic sounds to be 100 km from the fireball, one may deduce that at any given location a nighttime electrophonic fireball may be expected about once every two or three years.
However it is found that only between four and eight percent of witnesses of large fireballs actually hear the electrophonic sounds while the others hear nothing apart from the acoustically propagated sonic booms and rumbles arriving minutes later. Taking this into account it is estimated that a person spending every night outdoors may expect to hear an electrophonic fireball once in a lifetime. If daytime fireballs are included the expectancy may be nearly doubled for those in very quiet locations. The average person, who sleeps at night, will be very fortunate to ever hear these strange sounds.
This almost concludes my story of electrophonic meteor fireballs. Answers to questions that arise in your mind from scanning these web pages may be found in the publications listed in my electrophonic bibliographyand some evocative descriptions of the sounds are given in the next page.