Tropical Storm Olga

December 11th, 2007 |

GOES-10 IR image + QuikSCAT winds

GOES-10 IR imagery with QuikSCAT winds (above) sourced from the CIMSS Tropical Cyclones site showed that the maximum surface winds associated with Subtropical Storm Olga were located well to the north of the center of the circulation early in the day on 11 December 2007. However, ASCAT wind data later in the day (below) indicated that the radius of the maximum surface winds had decreased somewhat, suggesting a transition from subtropical storm to tropical storm status. Reconnaissance aircraft data confirmed this trend, and Olga was named a Tropical Storm late in the day. Olga produced nearly 10 inches of rain across the island of Puerto Rico.

GOES-10 IR image + ASCAT winds

A NOAA-17 AVHRR 3-channel red/green/blue (RGB) false-color image (below) revealed that the center of Olga was partially exposed as the storm began to interact with the rugged terrain on the island of Hispaniola, with some convection around the core of the storm (primarily within the northern quadrant).

NOAA-17 AVHRR RGB image

Subtropical Storm Olga

December 10th, 2007 |

GOES-10 IR images (Animated GIF)

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.

GOES-10 IR image + deep layer mean winds

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.

GOES-10 IR image + model forecast tracks

“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.