“Black stratus” over the Upper Midwest

December 10th, 2007 |

GOES-10 10.7 µm IR images (Animated GIF)

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.

GOES-10 + MODIS fog/stratus product

GOES-10 replaces GOES-12

December 5th, 2007 |

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.

AWIPS GOES water vapor channel images (Anmated GIF)

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).

AWIPS GOES IR images (Animated GIF)

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-10 11-12 µm IR difference

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).

Total Precipitable Water (GOES Sounder + MODIS)

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

Plane crash in Sao Paulo, Brazil

July 17th, 2007 |

GOES-10 10.7µm IR image

The worst airline disaster in Brazil’s history occurred on the evening of 17 July 2007 as a TAM Airlines Airbus A320 was attempting to land at the Congonhas airport in Sao Paulo, Brazil. Early media reports (CNN) indicated that the plane was landing during a “driving rainstorm”, which led us to take a look at GOES-10 satellite imagery to examine the meteorological conditions leading up to the crash. However, GOES-10 10.7µm InfraRed (IR) imagery (above; Java animation) suggests that only light (to possibly moderate) rain might have been falling from the comparatively warm cloud top brightness temperatures (-30 to -40º C, dark blue to green enhancement) seen in the vicinity of Sao Paulo (station identifier SBSP) — the closest area of significantly cold cloud top temperatures (-60 to -70º C, red to black enhancement) indicative of heavy to severe convective rainfall was still far to the west of SBSP over interior southern Brazil at that time.

Indeed, a time series of surface observations or “meteorogram” from SBSP (below) showed only light rain which was reducing surface visibility to 4-7 miles during the hours leading up to the crash at 21:50 UTC (18:50 local time). The rainfall was likely a factor in contributing to this particular tragedy, but it is important to note that the relatively short runway that was used (which had just been resurfaced in June 2007) had not yet been grooved to facilitate water run-off and prevent hydroplaning — other media reports (BBC) also stated that two additional smaller planes had skidded off that same runway only a day before the 17 July accident.

Sao Paulo surface reports

The extensive cloud cover across much of southern Brazil prevented GOES-10 sounder retrievals necessary for the generation of Total Precipitable Water (TPW) Derived Product Imagery (below), which may have offered an additional clue as to the precipitation potential of any convective activity in the Sao Paulo region that day.

GOES-10 sounder total precipitable water

Changes to GOES-10 Sounder scanning strategy

February 19th, 2007 |

GOES-10 sounder coverage

On 18 February 2007 NOAA/NESDIS/OSO implemented a new schedule for GOES-10 sounder scans during house-keeping periods. The previous sounder schedule had spatial gaps between the hourly scan sectors (above), while the new sounder schedule allows for continuous north-to-south coverage of the entire South American continent (below), while making narrower scans. The GOES-10 satellite has been postioned at 60º W longitude to support the Earth Observation Partnership of the Americas (EOPA) project. The latest GOES-10 sounder and imager products are available on the CIMSS GOES Realtime Derived Products site.
GOES-10 sounder coverage