MODIS « CIMSS Satellite Blog

Rain-cooled ground across much of Texas and Oklahoma

January 27th, 2012

1-day observed precipitation for 25 and 26 January 2012

Maps of the 1-day total precipitation for 25 January and 26 January 2012 (above) showed that much of Texas and Oklahoma received several inches of rainfall during that 48 hour period.

AWIPS images of the MODIS 0.65 µm visible channel and the corresponding MODIS Land Surface Temperature (LST) product (below) revealed a large swath of rain-cooled ground across much of that region. LST values where heavy rain fell were in the 60s F (yellow to light orange color enhancement), in contrast to LST values in the 70s and 80s F (darker orange to red color enhancement) to the north and the to the south of the rain-cooled areas.

MODIS 0.65 µm visible chanel image + MODIS Land Surface Temperature product

Posted in General interpretation, Heavy rain / flooding, MODIS | No Comments »

Detection of thin fog/stratus features: MODIS vs VIIRS

January 26th, 2012

Aqua MODIS: 11.0 µm IR images (grayscale, and color-enhanced) + "Fog/stratus product"

A comparison of AWIPS images of 1-km resolution Aqua MODIS 11.0 µm “IR Window” channel data (both grayscale, and color-enhanced) and the corresponding MODIS “Fog/stratus product” (above) showed some areas of fog and/or stratus cloud over the eastern half of Hudson Bay, Canada on 26 January 2012. On the fog/stratus product, low clouds and/or fog appear as the yellow-to-red enhanced features, while cirrus cloud features appear darker black.

The primary feature of interest here is the very thin – almost “translucent” – patch of fog/stratus located in the upper center portion of the image, to the west of Akulivik (station identifier CYKO) and Povungnituq (station identifier CYPX). The exact edges of this feature were difficult to identify in either the grayscale or the color-enhanced IR images — but the conventional “Fog/stratus product” (simply the difference in IR brightness temperature between the 11.0 µm and 3.7 µm channel data) allowed unambiguous identification of the edges.

About 45 minutes earlier, a similar comparison using McIDAS images of of 375-meter resolution Suomi NPP VIIRS 11.450 µm IR data (both grayscale, and color-enhanced) and the corresponding VIIRS “Fog/stratus product” (below) showed much more detail associated with this particular thin fog/stratus feature. The higher spatial resolution allowed many more of the ice leads to be seen — even some of the larger ones that were located below the thin fog/stratus feature.

Suomi NPP VIIRS: 11.450 µm IR (grayscale, and color-enhanced) + "Fog/stratus product"

Posted in Arctic, Fog detection, MODIS, Suomi NPP, VIIRS | No Comments »

Severe weather outbreak across the southeastern US

January 23rd, 2012

GOES-13 10.7 µm IR channel images + severe weather reports (click image to play animation)

A major outbreak of severe thunderstorms along a strong cold frontal boundary swept eastward across much of the southeastern US on 22 January – 23 January 2012, producing widespread damaging winds, large hail, and tornadoes (SPC storm reports). Two tornadoes produced EF-3 damage in Alabama. AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data with overlays of severe weather reports (above; click image to play animation) showed the cold cloud top IR brightness temperatures of -60 to -70 C (red to black color enhancement) associated with some of the strongest storms. For more information, see summaries from the National Weather Service forecast offices at Litttle Rock AR, Jackson MS, and Birmingham AL.

POES AVHRR 12.0 µm and MODIS 11.0 µm IR images

A sequence of 1-km resolution POES AVHRR 12.0 µm IR and MODIS 11.0 µm IR images (above) displayed greater detail in the storm top thermal structures, with a number of -70 to -80 C (black to light gray color enhancement) IR brightness temperature values seen on the higher resolution imagery.

Of particular interest was what appeared to be some sort of “cloud trench” oriented from north to south across Tennessee around 08:00 UTC, which exhibited significantly warmer MODIS 11.0 µm IR brightness temperatures and a warmer/drier signal on the corresponding MODIS 6.7 µm water vapor image (below). This feature was also apparent on a few of the 4-km resolution GOES-13 IR images around that time. The etiology of this satellite signature is unclear at this time.