CIMSS Satellite Blog

GOES-12 10.7 µm IR images

AWIPS images of the GOES-12 10.7 µm “IR window” channel (above) showed extensive cloudiness associated with a shortwave trough that was moving eastward across the Upper Midwest region during the morning hours on 17 October 2008. IR cloud top brightness temperatures of -20º to -40º C (blue to green colors) corresponded to areas of light precipitation (radar mosaic). Also shown on the IR imagery were  aircraft Icing AIRMET advisories (outlined in red) that were issued at 09:00 UTC and 14:00 UTC –  the 14:00 UTC AIRMET was forecasting moderate icing between the freezing level (which was between 5,000 and 10,000 feet) and 20,000 feet. In fact, there were a number of aircraft pilot reports of icing (plotted in yellow) within the boundaries of these Icing AIRMETs.

A closer view using AWIPS images of the MODIS visible channel, 11.0 µm “IR window” channel, Cloud Top Temperature (CTT) product, and Cloud Phase product at 17:29 UTC (below) indicated that much of the cloud shield along the trailing (western) edge of the shortwave over Minnesota and Iowa exhibited cloud top temperatures that were below freezing (generally in the -5 to -12º C range), but the MODIS Cloud Phase product designated those trailing edge clouds as “Water droplet” clouds (blue enhancement). Within this area of supercooled water droplet clouds were several pilot reports of icing at the 8000-foot altitude  across southern Minnesota and western/central Iowa.

MODIS visible + IR window + Cloud Top Temperature + Cloud Phase

A comparison of AWIPS images of the MODIS Cloud Phase product and the GOES-12 sounder Cloud Top Height product (below) showed that these pilot reports of icing at the 8000 foot level were well below the tops of the clouds, which were generally in the 13,000-15,000 foot range (green colors on the Cloud Top Height product).

MODIS Cloud Phase product + GOES-12 sounder Cloud Top Height product

GOES-12 6.5 µm water vapor images

GOES-12 6.5 micrometer “water vapor channel” imagery (above) revealed a pronounced warming/drying signature (darker orange colors) as Hurricane Kyle was beginning the transition to an extratropical system on 28 September 2008. GOES-12 water vapor brightness temperatures were as warm as 268º K (-5.15º C) at 16:45 and 17:02 UTC — and the rapid trend of warming/drying suggested that strong subsidence was occurring in that region.

A comparison of the 4-km resolution GOES-12 and the 1-km resolution MODIS water vapor channel data (below) yielded similar brightness temperature values within the core of the warm/dry region (-5.1º C on MODIS, -7.5º C on GOES-12).

GOES-12 6.5 µm and MODIS 6.7 µm water vapor images

Curiously, the GOES-12 sounder total column ozone product (animation) did not exhibit a high ozone feature co-located with the warm/dry pocket seen on the water vapor imagery (below) — if this dry air were due to a stratospheric intrusion or a tropopause fold, ozone values would normally increase to the 350-400 Dobson Unit range (green to red colors).

AWIPS images of GOES-12 water vapor and total column ozone