NOAA-15 visible and 10.8 µm IR images

A large severe thunderstorm that was developing in southern Kansas during the afternoon hours on 15 June 2009 had a very nice satellite presentation on NOAA-15 visible and 10.8 µm IR imagery (above). A “warm trench” signature appeared to be surrounding the cluster of coldest pixels associated with the strongest overshooting top located to the northeast of Dodge City, Kansas (station identifier KDDC). Around the time of these images, SPC storm reports included a tornado, hail of 1.75 inch in diameter, and wind gusts to 60 mph just to the east of Dodge City.

A comparison of the 1-km resolution NOAA-15 10.8 µm IR and the 4-km resolution GOES-12 10.7 µm IR data (below) showed that the coldest cloud top IR brightness temperature was -86º C on the NOAA-15 image (versus -73º C on the corresponding GOES-12 image). In addition, a significant parallax shift was seen on the GOES-12 image, due to the large viewing angle of the geostationary satellite — image features were located several miles to the north-northwest on the GOES-12 image.

NOAA-15 10.8 µm and GOES-12 10.7 µm IR images

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GOES-11 visible images

Well, not really — but a very interesting cloud plume formed yesterday and streamed off the 20,318-ft (6194-m) summit of Denali (“Mt. McKinley”) in southern Alaska on 10 June 2009, which almost had the  appearance of a volcanic eruption plume. GOES-11 visible images (above) showed this thin cloud plume spreading out as it curved to the southeast and then to the south, eventually moving over Anchorage and then the Kenai Peninsula.

A 1-km resolution NOAA-18 AVHRR 10.8 µm IR image (below) indicated that IR brightness temperatures were quite warm for such a high-altitude cirrus plume, barely reaching the -15 to -20º C range. Due to the thin nature of this cloud plume, a significant amount of radiation from the warmer ground surfaces below was bleeding upward through the thin cloud layer and reaching the satellite detectors.

NOAA-18 AVHRR 10.8 µm IR image

A false-color NOAA-18 Red/Green/Blue (RGB) image (below) showed the “transparent” nature of the cloud plume, with snow cover features on the ground clearly recognizable beneath the cloud.

NOAA-18 AVHRR false color RGB image

Tracking the location of the leading edge of the thin cloud plume feature was difficult using single-channel satellite imagery, which underscores the importance of using multi-spectral satellite products such as the 10.8 – 12.0 µm IR difference  (below) to correctly analyze the cloud location. Areas where the IR difference product reached +7 to +10 K (cyan colors) corresponded to the thicker portions of the cloud plume.

NOAA-18 IR difference product (10.8 - 12.0 µm, channel 04 - 05)

The cloud plume was curving to the southeast and then to the south due to the presence of a ridge of high pressure aloft over southern Alaska, as seen on an AWIPS image of the GOES-11 IR channel with an overlay of the GFS model 500 hPa winds (below).

GOES-11 10.7 µm IR image + GSF 500 hPa winds

A tip of the hat to Emily Niebuhr, UW-Madison / AOS graduate student, who is currently up in Alaska and brought this to our attention!

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GOES-12 6.5 µm water vapor images

AWIPS images of the GOES-12 6.5 µm “water vapor channel” (above) showed the development of widespread severe convection across parts of Kansas on 09 June 2009. Of particular interest was the appearance of an arc of significantly warmer/drier air (signified by the darker blue colors) along the upwind (western) edge of the thunderstorm cloud as the convection continued to intensify. This water vapor image signature likely indicates areas of well-defined compensating subsidence along with the possible “detrainment” of dry stratospheric air around the cloud edge. Note that the upstream cirrus cloud features also appeared to erode and disappear as they arrived at this region of subsidence along the western cloud edge.

There was one pilot report of moderate turbulence at an altitude of 38,000 feet around 16:00 UTC (below), which was near the water vapor signature of compensating subsidence.

GOES-12 water vapor image + pilot reports of turbulence

A comparison of the 1-km resolution MODIS 6.7 µm water vapor channel and the 4-km resolution GOES-12  6.5 µm water vapor channel data (below) shows that MODIS water vapor brightness temperature values were as warm as -26.5º C (yellow color enhancement) just to the west of the thunderstorm edge — the warmest GOES-12 water vapor brightness temperature value was -29º C.

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

A similar comparison of MODIS and GOES-12 water vapor images about 10 hours later (below) displayed a very pronounced signature of a gravity wave train along the western edge of the ongoing thunderstorm complex. There were no pilot reports of turbulence in that particular region at that time.

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

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MODIS true color and false color images

It’s a sure sign that Summer can’t be far off when Hudson Bay in Canada finally begins to lose its ice coverage — and a comparison of MODIS true color (channels 01/04/03) and false color (channels 01/07/07) Red/Green/Blue (RGB) images from the SSEC MODIS Direct Broadcast site (above) showed that large portions of the bay were indeed ice-free on 09 June 2009. Much of Hudson Bay appeared bright white on the true color image, but the false color image revealed that the bright white appearance was due not only to thick ice, but also a thin layer of supercooled water droplet cloud that had  formed as warmer air moved over the cold ice surface. The ice in the bay (along with deeper areas of snow cover on the ground, and thick high clouds composed of ice crystals) appeared as darker red features on the false color image.

A comparison of the 17:11 UTC Terra and the 18:56 UTC Aqua MODIS false color images (below) indicated that the thin supercooled water droplet cloud layer above the ice was moving during that short time period, as evident by the changes in the location of the cloud edges.

MODIS false color images

While this type of RGB imagery is currently not available on today’s 8-bit AWIPS system, changes to the AWIPS II architecture will allow  24-bit RGB images to be created and displayed; a simulated AWIPS RGB false color image is shown below.

Simulated AWIPS MODIS false color RGB image

You may have noticed the appearance of several very thin linear features on the true and false color images above; these were contrail segments from aircraft flying over the region, which were more easily seen on an AWIPS image of the MODIS near-IR “cirrus detection” channel (below). In addition to ice crystal clouds, the “cirrus detection” imagery is also useful for detecting the presence of airborne particles that are good scatterers of light (such as smoke, dust, volcanic ash) — and the large patches of brighter gray shades seen over Hudson Bay could be areas of smoke aloft from recent fire activity in Alaska and northern Canada.

MODIS "cirrus detection" image

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