CIMSS Satellite Blog

AWIPS images of the GOES-12 10.7 µm IR channel (above) revealed 2 separate periods where packets of “transverse banding” (thin, banded cloud elements oriented perpendicular to the ambient flow) were forming over parts of Florida, Alabama, and Georgia on 07 March 2008. These transverse bands were located at high altitudes along the western edge of the large convective cloud mass that was moving across the region; severe thunderstorms along the eastern flank of this line produced several tornadoes in northern Florida and southern Georgia (including a tornado responsible for 2 fatalities near Lake City, Florida).

A comparison of the 4-km resolution GOES-12 IR image at 16:32 UTC with the 1-km resolution NOAA-17 AVHRR IR image at 16:20 UTC (below) shows a closer view of one area of transverse banding moving over the Florida panhandle region, and demonstrates that more accurate identification of this type of small-scale cloud feature is possible with improved spatial resolution satellite imagery. The IR channels available on the Advanced Baseline Imager (ABI) instrument on GOES-R will provide 2-km resolution data, which should improve the ability to detect subtle features such as transverse banding.

There were large areas across the southeastern US that were covered by aviation AIRMET (Airmen’s Meteorological Information) turbulence advisories (outlined in yellow, below), but these advisories were for locations a bit farther to the west than the transverse banding seen on the satellite imagery. In fact, there were indeed a couple of pilot reports of high-altitude turbulence indicated near the regions of transverse banding.

In addition to the AIRMET advisories, there was also a SIGMET (Significant Meteorological Information, outlined in red) that had been issued due to isolated aircraft reports of severe to extreme turbulence at the 28,000-29,000 feet altitude range over northern Alabama and western Tennessee during the 15:00-16:00 UTC period. Note that there were also some transverse banding signatures evident in the patch of cloud that was located over northern Mississippi at that time — once again, the structure of these banded cloud features was much more obvious when viewed using the 1-km resolution NOAA-17 AVHRR IR imagery (below).

On that same day, a Lufthansa Airbus A340 passenger jet flying from Frankfurt, Germany to Atlanta, Georgia encountered severe turbulence around 19:15 UTC, at an altitude of 36,300 feet (while over the Atlantic Ocean, about 80 nautical miles southeast of Charleston, South Carolina):

CHS UUA /OV 80SE CHS/TM 1915/FL363/TP HA343/TB SEV FL350-FL363/RM CLIMB 130 FT ZJX=

The aircraft apparently lost about 1300 feet of altitude after encountering the severe turbulence. Ten persons aboard that flight received injuries (with a few requiring hospitalization), and the plane landed with priority clearance at Atlanta around 20:07 UTC. While the GOES-12 10.7 µm IR imagery in the vicinity of the incident (below) did not exhibit any of the transverse banding signatures that were seen farther inland, there were some rapidly developing thunderstorms in the vicinity (around 80 nautical miles southeast of Charleston, CHS) that likely contributed to the high-altitude turbulence. Note that the Lufthansa pilot report of turbulence did not show up in the database that was plotted by the McIDAS software shown below, but it was plotted by the AWIPS software (although in the wrong location, directly over Charleston, instead of 80 miles southeast of CHS).

With a dome of high pressure centered over the southeastern US early in the day on 25 February 2008, the Gulf Coast of Texas began to experience a southeasterly onshore flow during the pre-dawn hours. AWIPS images of the GOES-12 10.7µm IR channel (above) revealed a subtle signature of slightly warmer cloud top temperatures (darker gray enhancements) associated with the “return flow” of fog and stratus as moisture over the Gulf of Mexico began to move inland across Texas.

The GOES-12 fog/stratus product (above) was better able to detect the inland progression of the leading edge of the fog/stratus features (darker yellow to orange enhancements), as well as the development of separate areas of radiation fog further inland (lighter yellow enhancement).

A new satellite product that has recently been added to AWIPS (beginning with Operational Build 8.2) is the GOES Low Cloud Base product (above), which provides an indicator of whether the base (or bottom) of a cloud/fog feature meets the aviation criteria of Instrument Flight Rules (IFR) with bases less than 1000 feet above ground level (red enhancement), or Marginal Visual Flight Rules (MVFR) with bases greater than 1000 feet but less than 3000 feet above ground level (green enhancement), or cirrus cloud (blue enhancement). Note that the GOES Low Cloud Base product is only valid during night-time hours; this is also true of the GOES fog/stratus product (due to the fact the the 3.9µm shortwave IR channel used for those satellite products is very sensitive to reflected solar radiation during daylight hours).

A comparison of the 4-km resolution GOES-12 IR image, fog/stratus product, and low cloud base product with the 1-km resolution MODIS fog/stratus product (above) shows the advantage of better spatial resolution for detecting the leading edge of the inland-moving fog/stratus features, and also for estimating what portions of the areas of fog/stratus might be vertically deeper (denoted by the darker orange to red enhancements). The spatial resolution of the IR channels on the Advanced Baseline Imager (ABI) instrument aboard the GOES-R satellite (planned to be launched in 2014) will be 2 km, which will provide improved detection of mesoscale features compared to the 4 km IR channels and products now available from the current generation of GOES imagers. And what about the Sounder instrument aboard GOES-R and beyond? We refer you to the VISIT Meteorological Interpretation Blog for a discussion of that particular topic…

Severe thunderstorms developed over northwestern Kansas on 19 June 2007. An AWIPS image of the MODIS 11.0µm InfraRed (IR) channel (above) revealed an “enhanced-v” and a “warm trench” IR signature on adjacent storm tops. The coldest cloud top brightness temperature values were -77º C on both signatures; the warmest IR temperature associated with the “enhanced-v” was -58º C, while the warmest IR temperature in the “warm trench” was -61º C. You can get a sense that such a “trench” can surround an overshooting top by examining astronaut photography of thunderstorms taken from the space shuttle (image courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center).

A closer view of the MODIS IR image with a different color enhancement (above) shows that both IR signatures were surrounded by clusters of negative (yellow) and positive (red) cloud-to-ground (CG) lightning strikes. SPC storm reports listed hail (up to 1.75 inches in diameter) within 1 hour of the MODIS image in the region of both IR signatures, but only the southernmost enhanced-v storm produced a tornado; however, higher radar reflectivity values (65-70 dBz) were seen with the northernmost “warm trench” storm.

A comparison of the GOES-12 and MODIS IR images (above) demonstrates the better detection capability of these types of IR signatures using 1-km resolution MODIS IR imagery (vs 4-km resolution GOES IR imagery). The IR channels on the next-generation GOES-R Advanced Baseline Imager (ABI) will have a 2-km resolution.

GOES-12 10.7µm IR imagery (above; 100-image QuickTime animation) showed that these severe thunderstorms in Kansas persisted into the nighttime hours, and eventually became part of a very large Mesoscale Convective Complex (MCC) farther to the south over Oklahoma and Texas. Note the large number of IR pixels exhibiting brightness temperatures of -80º C or colder (violet enhancement) after 02:02 UTC; IR brightness temperatures were as cold as -93º C on a 23:22 UTC NOAA-12 AVHRR IR image, and as cold as -84º C on 05:10/05:13 UTC GOES / MODIS IR images (with 4159 negative and 334 positive CG lightning strikes at that time). Later SPC storm reports included hail up to 4.25 inches in diameter in Kansas (at around 00:05 UTC), and wind gusts to 94 mph in Texas (at around 07:09 UTC).