CIMSS Satellite Blog

GOES-13 visible images

We created the “What the heck is this?” category just for the type of case that is shown here: GOES-13 visible images (above) displayed an interesting cluster of O-shaped clouds forming over the Eastern Pacific Ocean (near Isla Guadalupe, off the coast of Baja California) on 18 November 2008. A few hours later, an overpass of the QuikSCAT satellite allowed an overlay of WindSat surface wind data on a GOES-11 3.9 µm shortwave IR image  (below) — and the QuikSCAT wind data seemed to suggest that these O-shaped clouds were actually perturbing the general northwesterly marine boundary layer flow to some extent.

GOES-11 3.9 µm shortwave IR image + QuikSCAT winds

MODIS visible, 3.7 µm IR, and 11.0 µm IR images

AWIPS images of the MODIS visible, 3.7 µm shortwave IR, and 11.0 µm IR window channels (above, with an overlay of lower-tropospheric MADIS atmospheric motion vectors) provided two important clues about these cloud features: (1) they were composed of supercooled water droplets, which reflected large amounts of solar radiation leading to a display of very warm (> 30º C, darker gray shades) 3.7 µm brightness temperatures, and (2) they were shallow clouds within the marine boundary layer, with fairly warm cloud top IR window brightness temperatures in the 13-14º C range. These points were further confirmed by examining additional MODIS images (below): the MODIS Cloud Top Temperature (CTT) product showed CTT values of 16-17º C (red color enhancement); the MODIS Cloud Phase product indicated these clouds were composed of supercooled water droplets (blue color enhancement); and the GOES-11 Sounder Cloud Top Height product placed the cloud tops in the 3000-5000 foot range (tan to orange color enhancement).

MODIS visible, Cloud Top Temperature, Cloud Phase + GOES Cloud Top Height

A closer view using 250-meter resolution MODIS true color image from the SSEC MODIS Today site (below) showed impressive structure to the O-shaped clouds, with hints of fine-scale outflow boundaries along the outer edges of some of the cloud features. These cloud features somewhat resemble  Pockets of Open Cells that have been previously documented — these open cells are apparently related to the formation of areas of precipitation (in this case, drizzle) that then act to dissipate a portion of the cloud to the point that a hole forms in the cloud feature. The downdrafts created by the formation of these pockets of open cells may indeed have had enough of an impact on the surface winds to be apparent in the QuikSCAT surface wind data seen above.

250-m resolution MODIS true color image

As an aside, the MODIS Sea Surface Temperature (SST) product (below) showed that SST values were generally in the mid 60s F (darker green colors) over the area where the O-shaped clouds were forming — and there was a well-defined SST gradient just to the south, where SST values rose into the lower 70s F (lighter green to yellow colors).

MODIS Sea Surface Temperature product

GOES-12 visible and 3.9 µm shortwave IR images

GOES-12 visible (daytime) and 3.9 µm shortwave IR (night-time) images (above) showed a distinct swirl of clouds drifting northward across the Gulf of Mexico on 13 November - 14 November 2008. This cloud swirl was actually the remnants of Hurricane Paloma, which had intensified to a Category 4 hurricane and made landfall over Cuba on 08 November. Note that there were a few weak convective bursts forming near the center of the swirl, but these were fairly short-lived.

AWIPS images of the 1-km resolution MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR images (below) indicated that the swirl was comprised of primarily low-level clouds at 18:54 UTC, with IR brightness temperatures considerably warmer  than -20º C — in fact, the MODIS Cloud Top Temperature product displayed values that were generally in the 0º C to +10º C range.

MODIS visible + 11.0 µm IR + 3.7 µm IR images

The MIMIC Total Precipitable Water product (below) showed that the remnants of Paloma (which initially had drifted back southwestward over Cuba on 12 November) were embedded within a plume of higher precipitable water (30-45 mm, or 1.2-1.8 inches) as it moved northward across the eastern Gulf of Mexico.

MIMIC Total Precipitable Water

As the remnants of Paloma reached the coast of the Florida panhandle on the morning of 14 November, explosive convective development was seen. This convection actually displayed a well-defined “enhanced-v” storm top signature on the GOES-12 10.7 µm IR imagery (below). Some back-building of the convection was also evident on the IR imagery — this convection produced a swath of heavy rainfall and flash flooding across parts of the Florida panhandle region, with a report of 9.25 inches of rain at Bloxham (located to the southwest of Tallahassee), and 2.61 inches falling at Tallahassee (setting a new rainfall record for the date). Radar-estimated storm total precipitation exceeded 14 inches.

GOES-12 10.7 µm IR images

A comparison of 1-km resolution NOAA-18 and 4-km resolution GOES-12 IR images (below) demonstrated the superior enhanced-v detection capability of higher spatial resolution data. The enhanced-v “delta-t” value (the difference between the coldest overshooting top and the warmest portion of the downstream warm wake) was an impressive 22.8º C, which would be a large delta-t value for a tornado or hail-producing supercell over the Great Plains region! This convection was also producing a good deal of cloud to ground lightning, as was noted on the early morning NWS Tallahassee Area Forecast Discussion:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
410 AM EST FRI NOV 14 2008

…SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEEN DEVELOPING OVER OUR AREA…WITH A FEW OF THESE STORMS ALREADY EXHIBITING MARGINAL ROTATING UPDRAFTS AND IMPRESSIVE CLOUD TO GROUND LIGHTNING. THE LATEST RUC INDICATES MUCAPE FROM 350 J/KG OVER CENTRAL GA TO 1500 J/KG ALONG THE FL GULF COAST. THIS IS RATHER IMPRESSIVE FOR THIS TIME OF YEAR…

GOES-12 10.7 µm + NOAA-18 10.8 µm IR images

A blog post by Stu Ostro at the Weather Channel raises the interesting question of whether the energy associated with the remnants of Paloma played a role in the additional development of deadly tornadoes across North and South Carolina about 24 hours later?