GOES-11, GOES-14, and GOES-12 10.7 µm IR and 6.7/6.5 µm water vapor images

The Galeras volcano in Colombia (located in the Andes Mountains near Colombia’s border with Ecuador) experienced an explosive eruption around 00:43 UTC on 03 January 2010 (Washington VAAC advisory messages). McIDAS images of the GOES-11, GOES-14, and GOES-12 10.7 µm IR (top 3 panels) and 6.7/6.5 µm water vapor channel data (bottom 3 panels) showed the volcanic cloud as it spread outward and drifted to the west for several hours following the eruption.

GOES-11 (GOES-West, positioned at 135º West longitude) only imaged the region once every 3 hours during a full disk scan (in this example, at 00:00, 03:00, and 06:00 UTC). GOES-14 (positioned at 105º West longitude) was emulating GOES-West operations during the final days of its NOAA Science Test, and except for the 3-hourly full disk scans, its imaging area was terminated just to the east of the volcano. GOES-12 (GOES-East, positioned at 75º West longitude) had the best, most consistent view of the South American region.

Note how the signature of the volcanic cloud becomes more difficult to follow on the IR imagery, but is still faintly recognizable for an additional 1-2 hours on the water vapor imagery. The different appearance of the GOES-11 water vapor imagery is due to the fact that the 6.7 µm water vapor channel on GOES-11 is a much “narrower” channel (spectrally) compared to the 6.5 µm water vapor channel on GOES-12 and GOES-14; in addition, the large viewing angle from GOES-11 has shifted the water vapor weighting function to higher (colder) altitudes, making the features appear darker blue to white with this particular water vapor color enhancement.

GOES-11 IR difference product (10.7 µm - 12.0 µm)

A simple method for identifying and tracking volcanic ash clouds is the use of a “reverse absorption” or “split window” IR difference product, subtracting the brightness temperature values of the 12.0 µm IR channel from the 10.7 µm IR channel. The GOES-11 IR difference product at 03:00 and 06:00 UTC (above) showed that the volcanic ash cloud had drifted westward over Ipiales (station identifier SKIP) and Pasto (station identifier SKPS) in Colombia, and was moving just to the north of Quito, Ecuador (station identifier SEQU). Note that on the more recent GOES satellites — GOES-12 and beyond — the 12.0 µm IR channel on the Imager instrument has been replaced with a 13.3 µm IR channel, preventing the application of this type of IR difference volcanic ash identification on the more recently-launched GOES satellites.

A corresponding IR difference product using the MODIS 11.0 µm and 12.0 µm channels at 03:25 and 06:25 UTC is shown below. With finer spatial resolution than GOES (1 km, vs 4 km), the edges of the ash cloud feature appear with greater clarity on the MODIS images.

MODIS IR difference product (11.0 µm - 12.0 µm)

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MODIS true color images (01 December 2009 to 02 January 2010

A sequence of MODIS true color images from the SSEC MODIS Direct Broadcast site (above; also available as a QuickTime animation) showed a few snapshots from the first month of Winter 2009/2010 across southern Wisconsin. You can see the transition from bare ground on 01 December…to a few narrow swaths of snow cover early in the month…to widespread deep snow cover on 10 December in the wake of a major winter storm…and finally to all the lakes freezing in the Madison area (located at the center of the images) on 02 January.

December 2009 was the 5th snowiest December on record in Madison, with 26.8 inches falling (the snowiest December was 40.4 inches, recorded in December 2008). The maximum snow depth on the ground at Madison’s Dane County Regional Airport was 13 inches on 09 December; however, a snow depth of 20 inches was reported on that day at McFarland in southern Dane county.

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MODIS 11.0 µm IR and GOES-12 10.7 µm IR images

AWIPS images of the 1-km resolution MODIS 11.0 µm IR and the 4-km resolution GOES-12 10.7 µm IR channel data (above) showed that large portions of northwestern Minnesota and eastern North Dakota exhibited surface IR brightness temperatures colder than -40º F (-40º C) at 08:45 UTC (2:45 am local time) on 02 January 2010. In northwestern Minnesota, the coldest IR brightness temperature values on the MODIS image were -45º C, compared to -42º C on the GOES-12 image. Note the significantly warmer signature of the Minneapolis/St. Paul urban area, as well as the unfrozen waters of Lake Superior.

A map of the 24-hour minimum temperatures (below; courtesy of MesoWest) showed that 3 sites (Pokegama Lake Dam, Gatzke, and Debs) reported a low of -40º across northern Minnesota on the morning of 02 January.

24-hour minimum temperatures across northern Minnesota (courtesy of MesoWest)

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POES AVHRR 10.8 µm IR images + surface temperatures (F)

McIDAS images of POES AVHRR 10.8 µm IR channel data (above) showed the development of a large terrain-induced “banner cloud” over the eastern part of the Brooks Range in northeastern Alaska on 01 January – 02 January 2010. The IR cloud top brightness temperature values were as cold as -65º C (darker red color enhancement) around 20:26 UTC, which suggested very high cloud tops (GOES-11 10.7 µm IR cloud top brightness temperatures were as cold as -58º C at that time). The terrain of the Brooks Range was acting as an obstacle to the northerly flow aloft (ECMWF 700 hPa winds | 500 hPa winds), which helped to initiate the formation of the banner cloud.

This cloud feature was also apparently thick enough to have a dramatic influence on surface temperatures — note that the temperature at Arctic Village (station identifier PARC) rose from -35º F before the cloud feature developed to +1º F after the cloud feature had been overhead for several hours. A surface meteorogram plot indicated that this temperature rise occurred during a period of light winds, so warm air advection could not account for the warming; instead, the thick cloud deck acted as a blanket to stop radiational cooling over that particular site.

CIMSS has been evaluating and testing a variety of CLAVR-x AVHRR cloud products in AWIPS, which can be used to further characterize this banner cloud that formed over the Brooks Range. The Cloud Type product (below) classified the feature as a combination of Cirrus, Multi-level Cirrus, and Opaque Ice Cloud categories (yellow, orange, and red color enhancements), which is not surprising given the very cold appearance on IR imagery.

AVHRR Cloud Type product

The AVHRR Cloud Top Temperature (CTT) product (below) showed that the tops of the cirrus feature were even colder than what was indicated by the IR imagery, with CTT values as low as -76º C at 20:20 UTC.

AVHRR Cloud Top Temperature product

The AVHRR Cloud Top Height product (below) showed that the tops of the banner cloud feature were generally around 8 km (cyan color enhancement). This height was close to the altitude of the tropopause, as indicated on the Barrow AK rawinsonde data.

AVHRR Cloud Top Height product

As an aside, the eastern Arctic Slope region of Alaska was experiencing blizzard conditions during this period — at Barter Island (station identifier PABA) along the coast, winds gusted as high as 72 mph. The strong westerly winds were in response to a tightening pressure gradient in advance of an approaching cold front (surface pressure and frontal analysis).

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