Howdy, all
It has been a while since I’ve posted to the list, and unfortunately I
have to do so with bad news. You may have noticed that it has been a while
since we’ve found a new meteorite fall in weather radar imagery. We recently
found out why. It turns out that the NEXRAD radar system lost sensitivity in
the last major “upgrade”. The radars were upgraded to allow two polarization
modes instead of one, which improves meteorologists’ ability to discern
different types of precipitation. That upgrade came with a ~3 dBz sensitivity
loss. I’ve gone back to West, TX and found that 3 dBz of sensitivity loss
results in the loss of about 90% of all the meteorite reflectivity signal for
that fall. And it turns out the upgrade was in progress to the point that one
of the nearby radars was upgraded to dual-polarization in time for the Sutter’s
Mill fall. The upgraded radar produced considerably less radar reflectivity
from the Sutter’s Mill fall than another, single-polarization radar that was
about the same distance away. To put it simply, we’ve lost a lot of our
capability to find meteorite falls using the NEXRAD system.
It is not all gloom, however. The next round of NEXRAD upgrades will
install a modern, more sensitive detector to replace the 1980’s-vintage
detectors currently on the NEXRAD sets. Pending availability of funding, that
will commence in 2016 and should get us back to where we were before the
upgrade. Also, now that we know what to look for, I’ll start going back to
recent probable fall events and look for fall signatures. The Columbus OH,
northern Arkansas, and Dec 2013 event outside Tucson are worthy of
re-examination. I’m also looking into alternative sources of radar data.
So at least our extended dry spell has been explained. NOAA couldn’t
care less about meteorite falls and so they don’t communicate this sort of
information widely, and we’re freeloading on their data and don’t have a voice
in whether these “upgrades” are truly useful. If I had my druthers, I would
have asked them to upgrade the detectors first and then install the
dual-polarization capability. In my more official capacities I will try to
arrange a voice for the meteoritics community in radar dealings, but that may
take a while.
Cheers,
Marc Fries
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