Interesting “O-shaped clouds” over the Eastern Pacific Ocean

November 18th, 2008 |
GOES-13 visible images

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 IR image + QuikSCAT winds

GOES-11 3.9 µm shortwave IR image + QuikSCAT winds

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

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

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

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

MODIS Sea Surface Temperature product

Snow streaks across the Great Lakes region

November 18th, 2008 |
MODIS true color and false color images

MODIS true color and false color images

MODIS true color and false color images from the SSEC MODIS Today site (above) displayed a number of mesoscale snow streaks across parts of the Great Lakes region on 18 November 2008. The snow on the ground (as well as any clouds) appear as white features on the true color imagery — on the false-color imagery,  any snow cover on the ground (as well as ice crystal clouds aloft) appear as cyan-colored features  (in contrast to supercooled sater droplet clouds, which appear as varying shades of white). Many of the snow streaks across parts of Wisconsin, Michigan, Indiana, and Ohio were on the order of 10 miles (19 km) or less in width.

A surge of cold arctic air on the previous day helped to initiate widespread snow showers across much of the Great Lakes region, which produced the narrow snowfall streaks. There was also significant lake-effect snowfall to the lee of the Greak Lakes –  snowfall amounts were as high as 22.0 inches at Trenary in the Upper Peninsula of Michigan, 10.5 inches at Gile in far northern Wisconsin, and 9.8 inches at Moorestown in the southwestern part of Lower Michigan. Extensive snow cover can be seen across far southwestern Lower Michigan and far northern Indiana on the MODIS images, along with an elongated lake-effect cloud band stretching north to south across Lake Michigan.

GOES-12 visible images

GOES-12 visible images

AWIPS images of the GOES-12 visible channel (above) showed that many of the snow streaks began to melt during the late morning and early afternoon hours.