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. 

View only this post Read Less

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.

View only this post Read Less

A patch of dense cirrus clouds developed to the lee (downwind) of the mountains of the Colorado “Front Range” on 02 December 2007 — this cloud feature marked the crest of a standing wave that had formed as stable air flowed from west to east across the Rocky Mountains. GOES-11 visible images (above) showed that these cirrus clouds quickly increased in areal coverage during the afternoon hours. A closer view using 250-m resolution MODIS true imagery from the SSEC MODIS Today site (below) revealed the shadow cast on the ground by the dense cloud patch that was located near Denver; deep snow cover in the higher elevations of the Rocky Mountains to the west of Denver was also clearly evident.

One isolated pilot report of moderate turbulence was noted by an aircraft in the area of the dense cirrus patch near Denver (KDNR), as seen on a AWIPS 4-panel of MODIS images (below); while the turbulence report was plotted on AWIPS at the default altitude of 26,000 feet (“260”), the actual pilot report indicated “FLUNKN” (Flight Level Unknown). As expected, the lee cloud features exhibited a bright appearance on the MODIS “cirrus detection channel” (lower left panel), with fairly cold pixels on the MODIS 11.0 µm IR channel image (-67º C, upper right panel) and the MODIS Cloud Top Temperature product (-63º C, lower right panel).

The coldest MODIS 11.0 µm IR brightness temperature (below) of -67ºC corresponded to an altitude of about 53,000 feet above ground level according to the most recent Denver (KDNR) rawinsonde data.

In contrast, the coldest GOES-12 10.7 µm IR brightness temperature (below) from around that same time was -59º C, which corresponded to a lower altitude of about 38,200 feet above ground level.

View only this post Read Less

(Image source: The CIMSS/SSEC MODIS Today Page)

Lake effect clouds and snows are a common wintertime occurrence downwind of the warm waters of the Great Lakes, and such weather events have been discussed frequently on this blog (See here, here, and here, for example) and elsewhere. When cold air moves over a warm water surface, the air is warmed via convection and moistened via evaporation, and that input heat and moisture can be sufficient to generate cumuliform clouds downwind of the moisture source. If Lake waters are about 13 C warmer than the temperature at 850 mb, then clouds and snow occur downwind of the Great Lakes.

Lake Oahe is a large artificial impoundment of water on the Missouri River in central South Dakota. It is sufficiently large that, given the right wind trajectory, clouds can form downwind of the lake. Even in late November, it retains some warmth, as noted in the MODIS-derived “Sea” surface temperature product here. Note the pixels that suggest water temperatures in the 40s in the region where the clouds formed today.

A loop of the GOES-12 (GOES-EAST) imagery from today clearly shows the region where the Lake Effect clouds formed. Note how the cloud streets align themselves with the wind direction as reported at PIR (the station in central South Dakota); the other stations are Chamberlain to the southeast and Mobridge to the northeast. As the temperatures warm during the day, the thermal differences that support the cloud development weaken and the cumuliform clouds dissipate as mid-level clouds move in from the west.

Another intriguing feature in the MODIS true-color imagery above is the smear of white near Fort Thompson, just north of the southeast corner of the image. For a chilly west-northwest airflow, this region is just downwind of the prominent oxbow on the Missouri River near Fort Thompson and Lower Brule, to the north of Chamberlain and to the east of Pierre. Is this a signature of Lake/River effect snow in that area?

View only this post Read Less