Just as the 2007 Atlantic Tropical Cyclone season started off a bit early (with Subtropical Storm Andrea in early May), it also is ending a bit late with the formation of Subtropical Storm Olga on 10 December 2007. An animation of GOES-10 IR images (above) sourced from the CIMSS Tropical Cyclones site shows the cluster of cold cloud top temperatures (red to white enhancement) associated with Olga, moving just north of Puerto Rico.

An analysis of the Deep Layer Mean wind field (above) indicated that an upper level low existed just to the south of Olga. The majority of the 00 UTC 11 December 2007 model forecast tracks (below) moved Olga westward toward the Dominican Republic and Jamaica.

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AWIPS images of the GOES-10 10.7 µm IR channel (above) showed a patch of low-level stratus cloud drifting north-northeastward across Iowa, Minnesota, and Wisconsin on 10 December 2007. Note how the tops of the cloud feature appeared warmer (darker gray enhancement) than the adjacent cloud-free (but snow-covered) areas; the term “black stratus” was coined to describe the appearance of these cloud features on grayscale IR imagery. Strong radiational cooling during the night-time hours created a well-defined boundary layer temperature inversion, making the altitude of the stratus cloud tops several degrees C warmer than the surface.

On the comparison of MODIS and GOES-10 “fog/stratus product” images (below), the MODIS image in particular suggested that the leading edge of the stratus cloud feature was notably thicker (orange to red enhancement). This thicker cloud edge may have acted to dramatically slow radiational cooling as the cloud deck moved overhead — in fact, surface temperatures (above) were seen to warm by several degrees F when the cloud feature was overhead.

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On 04 December 2007, GOES-12 (the operational GOES-East satellite at 75º W longitude) experienced an anomaly in spacecraft attitude following a North-South station keeping maneuver; initial efforts to restore GOES-12 to a normal on-orbit mode were unsuccessful. As a result, GOES-10 (at 60º W longitude) was reassigned from South American operations to replace GOES-12 as the operational GOES East satellite on the following day (05 December). •• For the latest information on GOES operations and status, refer to the Satellite Services Division GOES Special Bulletins site.

Due to the age of GOES-10 (which was launched in 1997), increasing satellite inclination (currently more than 2 degrees) was causing more “wobble” to be noted in image animations — as a result, the GOES-10 imager “eXtended GOes High Inclination” (XGOHI) operations were initiated in October 2007. XGOHI re-maps the GOES-10 GVAR data before the satellite imagery is re-broadcast to users, which may have a slight impact on data latency. One important issue with XGOHI is the fact that 3.9 µm “hot spot” detection capability is somewhat diminished using GOES-10.

The image examples shown here demonstrate a few of the subtle differences between GOES-12 and GOES-10, and the early artifacts of the satellite transition.

GOES-12 had the new 4-km resolution, spectrally-wider 6.5 µm “water vapor” channel; the 8-km resolution, spectrally-narrow 6.7 µm “water vapor” channel on GOES-10 is the same as the corresponding water vapor channel on GOES-11. As a result, composites of GOES-11 and GOES-10 water vapor images will exhibit less of a “seam” where the data from the two satellites are merged (see: 16:30 UTC 04 Dec 2007 image | 17:30 UTC 05 Dec 2007 image). Prior to GOES-10 data beginning to appear in AWIPS as of about 17:30 UTC on 05 December, there was only GOES-11 coverage for approximately 24 hours (above).

The 10.7 µm IR “window” channels are identical on GOES-11 and GOES-10 . Prior to GOES-10 data beginning to appear in AWIPS as of about 17:30 UTC on 05 December, there was only GOES-11 IR channel coverage for approximately 24 hours (above).

GOES-12 replaced the 12.0 µm IR channel (the so-called “dirty IR window” channel) with a 13.3 µm “CO2 absorption” IR channel. This new 13.3 µm channel was used to derive cloud height information using the GOES-12 imager, which was also employed for height assignment of GOES-12 water vapor and visible/IR cloud drift winds (atmospheric motion vectors or AMVs). As a result, the GOES-10 (GOES-East) AMV height assignments will not be quite as good without the 13.3 µm channel (instead relying on the less-accurate IR window and water vapor intercept height assignment methods).

The 12.0 µm IR channel on the older GOES (GOES-10 and GOES-11) is useful for detecting volcanic ash or airborne dust/sand using the 11-12 µm IR difference product (above) — so this ash/dust detection capability has returned to GOES East (for the time being). Note, however, that the product in AWIPS is incorrectly labeled as “11µ-13µ” for NWS forecast offices localized to use GOES-East (since GOES-12 had the 13.3 µm channel)

Due to the high satellite viewing angle from GOES-10, GOES sounder coverage will not be available over portions of the central US (affecting sounder-derived products such as Total Precipitable Water). NWS forecast offices who have added CIMSS MODIS products to their local AWIPS (via LDM subscription) can access that particular product suite to help fill in the gap (below).

Note: GOES-12 was returned to service as the operational GOES-East satellite on 17 December 2007. 

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The MODIS true color image (above) centered over northeastern Wisconsin on 03 December 2007 is from the SSEC MODIS Today site. Note the narrow white swath running from southwest to northeast near the center of the image — this feature is the tornado damage path from an EF-3 tornado that went through that area on 07 June 2007, nearly 6 months earlier. Much of northeastern Wisconsin received about 5-9 inches of snow during the 2-3 days prior to this MODIS image, so the fresh snow cover was more evident within the relatively “treeless” tornado damage path (compared to the darker appearance of the heavily-forested surrounding area). The darkest, semi-square area seen on the image (along and south of the tornado damage path) is the more thickly-forested Menominee and Stockbridge Indian Reservation.

The narrow “cloud street” features oriented perpendicular to the tornado damage path were lake-effect cloud bands streaming inland from Lake Superior. In addition, due to recent cold temperatures (+7º F / -14º C at Green Bay WI, and -8º F / -22º C at Athelstane WI on 01 December), you can also see that ice was beginning to form around the edges of Green Bay — and most of the inland lakes across northeastern Wisconsin were also frozen and snow-covered on that day.

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