[meteorite-list] PA July 6 Fireball Ground plot update

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Mon, 6 Jul 2009 19:05:31 -0700 (PDT)
Message-ID: <456858.66337.qm_at_web55206.mail.re4.yahoo.com>

I have hand plotted 16 or so AMS reports on a printed map after assigning place marks in Google Earth. One might look at all the reports and wonder if they were looking at the same fireball. Of those, 11 are cleanly plottable, several have glaring holes in them but were partially plotted for backup. Two(2) witnesses report the fireball seen south of Baltimore and DC. e.g I believe they saw the fireball but were totally misoriented on direction, their start and stops are going in the wrong direction. When flipped 180* they fit other observations,but treated skeptically in that we really don't know which way they were looking. (NOTE for fireball chasers: This is where a field investigator goes on a ground interview and has the witness reconstruct the setting and he actually measures the directions with an inclinomenter and compass to improve the quality of the accuracy of the data)

The best preliminary "fit" ,based on AMS filed fireball reports and, NOT including the concentration of ear witness /sonic boom reports vic. York, PA is:

    Thids fireball is inferred to have been moving close to EAST to WEST based on a moderately reliable passage point perpendicular to a NS gridline between Bel Air, MD and Fawn Grove, PA. This is is supported by a medium confidence eastward sighting from West of Hagerstown, MD.

Maximum and probable terminus: a cluster of intersecting witness reports suggest that the fireball was still visible and moving briskly when passing over a gridline generally running NS between Westminster, MD and Hanover , PA. More outlying reports suggest that the fireball was yet visible along a gridline running NS between Mt Airy, MD and Gettysburg, PA. Given the sharp angle in one of the available photos and comparing it to other steep trajectory fireballs, this likely did not make it to Hagerstown and an incandesing fireball probably did not pass the gridline running through Fredrick and Thurmont, MD Depending on upper level winds and dark flight a meteoroid might travel 5 to 30 miles from extinction. Good new for a change on Eastern US fireballs-- This is largely level rural farmland with generous and polite native population that is more genteel. Maryland should by all demeanor have been a southern state.

There were mentioned in some other reports of "extinguishing immediately after fragmenting" which I haven't revisited. Be it remembered this fireball was catching up to Earth at midnight and this would have had the effect of removing 15-17 kps from its approach speed, reducing ablation energies and improving chances that it dropped a meteorite.

The ole disclaimer: This was a shake and bake assembly of an already course measure of bearing--cardinal compass points vs measured degrees of azimuth. Seen as far away as Washington DC is from New York City. Someone with experience and technical judgment could plot sonic boom reports to at least get a maximum distance since they did not necessarily include flash to bang time.

Elton
Received on Mon 06 Jul 2009 10:05:31 PM PDT