GOES 11 - 12 micron from the Sounder and Imager January 21 Southern U.S. Tornado/Dust Storm Event

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GOES-8 Sounder Band=8 (11.0 UM) from 21:46 UTC 21 January 1999
GOES-8 Imager Band=1 (0.65 UM) from 21:45 UTC 21 January 1999
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GOES-8 Sounder channel differencing of bands 8-7 (11.0-12.0 UM) from 21:46 UTC 21 January 1999.
GOES-8 Imager channel differencing of bands 4-5 (10.7-12.0 UM) from 21:45 UTC 21 January 1999.
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Sounder IR Band 8 image at 21:46 UTC 21 Jan 1999 Sounder Difference of Band 8-7 at 21:46 21 UTC Jan 1999
Java applet animation of IR
Java applet animation of Band 8-7
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Doppler Reflectivity from Little Rock Arkansas
 Imager Difference of Bands 4-5 at 21:45 UTC Jan 21 1999
Java applet animation of Band 4-5

There may be 3 reasons for the negative 11-12 micron differences in the above images:

1)    the dust/sand region (western Texas)
2)    a rapidly growing thunderstorm (eastern Texas, only a few pixels)
3)    instrument mis-registration? (cloud edges in New Mexico)

In general, there may be 3 other reasons that the split window may report a negative difference:

1)    volcanic ash
            http://cimss.ssec.wisc.edu/goes/misc/981204.html
            http://cimss.ssec.wisc.edu/goes/misc/sndvol1.html
            http://cimss.ssec.wisc.edu/goes/misc/VOLC.GIF
2)    near surface inverstions (as reported in Hayden/Wade/Schmit, BAMS, Volume 35,
        No 2, 1996, Derived Product Imagery from GOES-8)
3)    absolute calibration problems or instrument noise

Yet, the fact that different instruments (GOES imager and sounder, MAS and HIS ) all can report a negative difference, this is less likely.

The 11-12 micron difference was described in: Moeller, C., S. A. Ackerman, K. I. Strabala, W. P. Menzel, and W. L. Smith, 1996: Negative 11 micron minus 12 micron brightness temperature differences: A second look. AMS Eighth Conference on Satellite Meteorology and Oceanography, Atlanta, GA, 27 January - 2 February 1996.

For an example of negative 11-12 micron difference from the HIS:

http://cimss.ssec.wisc.edu/success/btdifsuc.htm

Related Links
GOES Gallery 21 January 1999 Arkansas Tornado Outbreak

GOES Gallery 21 January 1999 Blowing Dust Event over N. Mexico and the Southwestern U.S.