TX DFW Area 02 Feb 2012 0157 UTC

This one is a big item at the moment, to the point that I really don’t feel the need to describe it. At this time there are three (four?) allsky camera videos of this event, and hundreds of eyewitness reports both on the AMSmeteors.org website and on Dirk Ross’ lunarmeteoritehunters.blogspot.com site. Myself, Rob Matson and others have scoured the weather radar data of this event, and I think we were all expecting to see something like the West, TX fall in there. Unfortunately, we’ve been disappointed to date. There has been a lot of discussion and several “possibles” have been examined and discarded for one reason or another. My own “favorite” radar hit at the moment is this one from the KSHV radar directly over Edgewood, TX.

It appears at the right time and in roughly the right place. Altitude is 12,270′ above the radar. No other returns appear at other elevations, but this may be consistent with a small number of larger masses from this bolide. While I was preparing this post, Dirk Ross came out with an update on his website where he specifies Edgewood, TX as the most likely fall site. It’s not clear what he used to come to that conclusion, but it is certainly interesting.

The TDWR radar sets from the DFW area airports will release their data to the public in about 24 hours. I will examine that data when it becomes available and update this post.

Update: Here’s Dirk Ross’ blog entry where he calls Edgewood, TX as the likely strewn field location. It is worth pointing out that he and I came to this conclusion independently – me from radar data, him from eyewitness reports.

Update: Dirk Ross is estimating ~25 kg of meteorites reached the ground. Estimates of the pre-fireball size from the static radar set in OKC ranged around “bus-sized”. I don’t have an estimate from the NEXRAD radar data, but I can say from the lack of a stream of material that if rocks reached the ground, we’re looking at a small number of large stones rather than an extended strewn field. Everything that passed through the NEXRAD interaction volume came and went quickly, without a lot of fragmentation.

Update: The TDWR airport radar data is up! I have examined the data from both the Love Field (TDAL) and DFW (TDFW, not surprisingly) radars. Unfortunately, the Edgewood area is at the very edge of the range for these radars. One thing shows up – the feature around Allen, TX is definitely some sort of interference and not meteorite-related. Some radar hits occur at relatively high altitude towards the Wills Point/Edgewood area at 0205 UTC in the TDFW data in particular, but the radars can’t quite see Edgewood itself. It is suggestive of supporting evidence, but unfortunately its just a suggestion.

http://lunarmeteoritehunters.blogspot.com/2012/02/texas-meteorite-fall-1feb2012-target.html

UPDATE (09 Feb 2012): A tremendous amount of work has gone into this fireball, with data and analyses provided by Bill Cooke (http://www.billcooke.org/events/20120202_0157.pdf), Mike Hankey (http://www.mikesastrophotos.com/comets/2012-02-01-texas-fireball-trajectory-solutions/), Rob Matson, Jake Schaefer (http://3dradar.wordpress.com/2012/02/09/dfw-tx-222012-0157-utc/), and others that I’m surely forgetting at this hour (my apologies).

Because it is late (or early) I’ll be brief. I used Bill Cooke’s computed meteor track and parameters and calculated a dark flight model product. This is a projected strewn field using Bill’s data, and I’m fairly astounded by the result. The important parameters for this calculation are:
Bolide direction: 75.5 degrees
Altitude: 40 km
Angle below horizontal: 13 degrees (very flat!)
Meteorite velocity on entering dark flight: 9,800 m/s (very fast!)
Meteorites are spheres of L chondrite composition and density, using drag coefficients measured on actual meteorites in a wind tunnel (From Carter R., Jandir P., Kress M. LPSC 2009).

I used winds-aloft data collected by a radiosonde balloon released from Fort Worth at 0000Z on 02 Feb 2012, within two hours of the fireball. The balloon ceased transmitting at 31,800 m altitude so I extrapolated the remaining winds up to 40 km using an average of the last ten reported direction/speed values. The combination of a very flat trajectory at high speeds results in a strewn field far from Edgewood or just about anywhere else I had considered…

I found and fixed (hopefully) an error with my dark flight model before running this calculation. The results “look” right given the parameters, but I did not get a chance to test it against the Park Forest fall as I have in the past, so this is not a “flight tested” model at present. I encourage anyone else with this capability to run the numbers and check my result. However, the very high final speed and flat trajectory make this result plausible at first pass.

HERE is the Google Earth .kmz with all the data in the dark flight model as shown above.

I just checked the radar data, and I don’t see anything associated with the calculated strewn field.

UPDATE (10 Feb 2012): Bill Cooke has updated his analysis of this event, which is pretty widely regarded as a likely meteorite fall at this point:

http://www.billcooke.org/events/Darkflight_all.jpg

I would regard his dark flight results as probably more accurate than mine, as he’s working directly from the trajectory he assembled from multiple cameras. There were a couple of items that worried me about the earlier version of the trajectory, most prominently the “ending” velocity of 9.8 +/- 4 km/s. A fireball/meteor/bolide stops being optically bright when it decelerates through ~4 km/s and is no longer generating enough friction to glow. Cooke’s earlier “end” velocity of 9.8 km/s was a loose end when I made the dark flight model above. I was entertaining the notion that, if the bolide had ceased being luminous at 9.8 km/s then it must have ablated away to nothing before slowing to 4 km/s, which doesn’t seem right given the terminal mass estimates of 30-42 kg that are floating around. Now I understand that the 9.8 km/s value was where Bill had ended his trajectory, not where the fireball went dark. Meteor analysis is an evolving thing – we are learning with every passing day as more data is analyzed and shared. This probably drives the folks “on the ground” nuts as us eggheads move the projected strewn field around on them, but with every round of new information (to include new eyewitness reports from “the ground”!), we get closer to reaching a consensus.

Based on Cooke’s dark flight model results, Rob Matson has singled out some radar returns as possible “hits”. I had a look at what he described, and I concur that they look pretty good. I especially like the following, which comes complete with +20.4 kt, single-pixel (unfortunately) velocity signal, and a 5.8 kt spectral width signature as well which make it stand out from the surrounding noise somewhat. This is more consistent with a meteorite signature than with radar noise, but would require hits at additional altitudes, sweeps, and on multiple radars to be bulletproof.

I think the consensus is there that this is more or less a single, large meteorite that survived the fireball and reached the ground. Mass estimates range from 30-42 kg for that meteorite. It’s worth noting that a 30 kg mass of L chondrite density will reach the ground in 2 minutes and 58 seconds from 30,000 m (for the flat trajectory we’re dealing with here), moving at 305 mph (Mach 0.4) when it struck the ground. A 42 kg mass would be moving at 321 mph. That would definitely create an impact pit. Surely someone heard something!

UPDATE: I’ve just gone over my dark flight model results, and there is a bug in there somewhere that seems to be exaggerating the northward drift of the falling body, and so the possibly exists that it is affecting the eastward drift as well. It may have something to do with the fact that the dark flight path overruns the “seam” between two UTM grids – I am using UTM notation to simplify measurement of lateral translation on the ground. Sigh. I will work on fixing the model to test the hypothesis that Cooke’s model is correct, but I have every reason to believe that it is. To those “on the ground”, ignore the dark flight model results I’ve posted and use Bill Cooke’s.

I want to point out the tremendous effort that has gone into researching this bolide on the part of a lot of very skilled people, both on the ground and in the lab. I’m really impressed by the collective effort at work here! This is an example of teamwork and scientific consensus-building at its finest, and I think we’re producing a body of work to be proud of. The ultimate payoff will be to get to see and touch an actual meteorite recovered by this effort, but even if that doesn’t happen I think we are laying the groundwork for a lot of successful collaboration in the future. This is a “stone soup” endeavor, with many different people pitching in their expertise to produce a truly remarkable final product. I look forward to working on more events like this.

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