More blowing dust in Texas

March 1st, 2007 |

GOES-11 IR difference image / GOES-12 visible image

Another case of blowing dust was noted across the southern Texas panhandle region on 01 March 2007. Unlike the stronger blowing dust event in that same area 5 days earlier (on 24 February), there was no distinct dust cloud feature evident on the GOES-12  visible channel imagery (above, right) — however, an IR difference product using the 10.7 µm and 12.0 µm channels available on GOES-11  did reveal a subtle “dark blowing dust signature” (above, left; Java animation). No surface stations in the area reported blowing dust during the time period shown; visibilities did drop to 2-4 miles at Big Spring TX (station identifier KBPG), but remained at 9-10 miles at San Angelo TX (station identifier KSJT).

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A color-enhanced version of the GOES-11 IR difference product or “split window difference” (below) shows that this “dust signature” occurs when the difference between the 10.7 µm and 12.0 µm brightness temperatures is in the -1º K to -2º K range (yellow enhancement). Note that there is also a “false dust signal” farther to the west over regions of higher albedo soil — but the “dust signature” would propagate in the direction of the boundary layer wind flow (in this case, toward the southeast) on an image animation, while the “false signal” would remain stationary. The 12.0 µm IR channel is not available on GOES-12, having been replaced by a 13.3 µm IR channel that is used for better cloud top height assignment; however, the 12.0 µm IR channel is available on the polar-orbiting MODIS and AVHRR instruments, which is useful for the detection of airborne dust and volcanic ash.
GOES-11 IR difference image