Satellite winds « CIMSS Satellite Blog

Mesovortex formation in northwestern Wisconsin

March 26th, 2013

GOES-13 0.63 µm visible channel images (click image to play animation)

AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed the formation of a mesoscale vortex over far northwestern Wisconsin during the day on 26 March 2013. Overlays of MADIS 1-hour interval atmospheric motion vectors (below) showed that the satellite-derived winds were indicating some degree of cyclonic flow into the western portion of the mesovortex.

GOES-13 0.63 µm visible channel images with MADIS 1-hour interval atmospheric motion vectors

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below) showed that the cloud elements comprising the mesoscale vortex appeared convective in nature, with many exhibiting IR cloud top brightness temperatures of -20º C or colder (light blue color enhancement). The morning rawinsonde data from Minneapolis, Minnesota indicated that a very unstable layer was present just above the surface between 950 and 750 hPa — so with a convective temperature of only 36º F the convective elements were quick to develop once surface temperatures began to warm after sunrise.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

===== 27 April Update =====

During the following overnight hours, the cyclonic swirl signature of the mesoscale vortex could still be seen over northwestern Wisconsin at 07:53 UTC or 2:53 AM local time on the Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” (below). Due to ample illumination by a full Moon, a “night-time visible image” provided by the corresponding 0.7 µm Day/Night Band (DNB) showed that city lights could still be seen through the low cloud deck; other features of interest on the DNB image included ice in Green Bay and a few areas along the south shore of Lake Superior, and the southern extent of the snow cover from far eastern South Dakota into southern Minnesota.

Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” + 0.7 µm Day/Night Band image

Posted in General interpretation, GOES-13, Satellite winds, Suomi NPP, VIIRS | No Comments »

Wave features seen on water vapor imagery

January 7th, 2013

MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

AWIPS images of 1-km resolution 6.7 µm water vapor channel data (above) revealed interesting wave patterns over parts of southern California, Baja California, and the adjacent offshore waters of the Pacific Ocean on 07 January 2013. A comparison with the corresponding 0.65 µm MODIS visible image showed that there were no clouds associated with any of these water vapor wave features. The mountain waves over southern California and northern Baja California were caused by strong winds on the western periphery of an upper-level low pressure system — and there were isolated pilot reports of moderate turbulence over southern California at the 30,000-34.000 foot altitude range.

Also of interest is the “bow shock wave” feature seen on the water vapor image, which fans out downwind (southward) of Guadalupe Island (station identifier 76151). These waves were caused by the interaction of lower-tropospheric winds from the north interacting with the high terrain of the volcanic island (whose highest point is Mount Augusta at 4257 feet or 1298 meters). Lower-tropospheric satellite winds off the west coast of Baja California were as strong as 37 knots at the 812 hPa pressure level.

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (below; click image to play animation) suggested that there was strong middle-tropospheric subsidence over the region surrounding Guadalupe Island — as seen by the warming/drying trend (the transition to brighter yellow colors) — which allowed the weighting function of the water vapor channel to peak at lower altitudes in order to detect the lower-level signature of the bow shock wave.

GOES-15 6.5 µm water vapor channel images (click image to play animation)

Posted in Aviation, GOES-15, MODIS, Satellite winds | No Comments »

Ice motion in the Bering Sea off the coast of Alaska

December 18th, 2012

Suomi NPP VIIRS 0.7 µm Day/Night Band image with overlay of surface analysis

A large and intense area of low pressure was located in the Gulf of Alaska on 18 December 2012 (above), which was forecast to produce areas of hurricane-force winds west and southwest of the storm center.

A comparison of AWIPS images of Suomi NPP VIIRS 0.7 µm Day/Night Band images (below) revealed a large amount of Bering Sea ice motion just off the southwest coast of Alaska in the 101 minutes between the two images (21:59 UTC and 23:40 UTC), due to the strong northwesterly winds of 30-40 knots that had existed over that region.

Suomi NPP VIIRS 0.7 µm Day/Night Band images with surface observations and GOES cloud-tracked atmospheric motion vectors

The image comparison below shows false-color Red/Green/Blue (RGB) composites created using the 0.64 µm VIIRS visible channel (Red) and the 1.61 µm “snow/ice channel” (Green and Blue) which allowed an easier discrimination between the ice (which appeared as darker shades of red) and supercooled water droplet clouds (which appeared as shades of white).