CIMSS Satellite Blog

Comparisons of the 1-km resolution MODIS fog/stratus product with the 4-km resolution GOES fog/stratus product help to underscore the improved ability to detect subtle features using higher spatial resolution satellite data. AWIPS images of the MODIS and GOES-11 fog/stratus products (plus topography) covering the Monterey and Fresno, California regions on 19 May 2008 (above) showed a patch of fog over Monterey (KMRY), Watsonville (KWVI), and Salinas (KSNS), with a narrow finger of fog that extended southeastward into the Salinas River Valley.

Farther inland over central California, the MODIS fog/stratus product imagery revealed a noisy “false fog/stratus signal” over parts of the San Joaquin Valley, due to the high emissivity of desert soils that covered the non-agricultural portions of the valley (the contrasting patchwork of green agricultural fields versus brown to gray non-agricultural areas was very evident on 250-m resolution MODIS true color imagery from the previous day) — regions with a lower MODIS Normalized Difference Vegetation Index (NDVI) generally corresponded with regions that exhibited a more pronounced “false fog/stratus signal” (below).

Images centered off the coast of Southern California and Baja California on 20 May 2008 (below) revealed several ship tracks in the marine stratocumulus cloud deck that was offshore. Once again, such small-scale features showed up with greater clarity on the MODIS fog/stratus product imagery. These comparisons give a bit of a preview of the types of improved products that will be available using the Advanced Baseline Imager (ABI) instrument on the upcoming GOES-R satellite (scheduled to be launched in 2014), which will offer IR imagery and products at a 2-km spatial resolution (at 5-minute intervals on a routine basis).

Explosive events from the Kilauea Volcano (located on the Big Island of Hawaii) began to occur in mid-March of 2008 — these were the first explosive events from that particular volcano since 1927. Activity from Kilauea then continued for several weeks; GOES-11 visible imagery from 07 April 2008 (above) showed the hazy signature of a long volcanic plume (composed primarily of steam, but possibly containing small amounts of ash) streaming southwestward from Hawaii. With the typical northeasterly trade winds that often persist over that region, this was the common scenario seen on many days during late March into early April.

However, the northeasterly trade wind flow regime was interrupted by a surface trough of low pressure on 08 April 2008, and southerly to southeasterly winds began to advect the Kilauea plume to the north and northwest during the day (photo). The volcanic plume at that time contained significantly elevated amounts of sulfur dioxide (SO2), which forced the closure of Hawaii Volcanoes National Park on 08 April. GOES-11 visible imagery (below) revealed two separate plumes, emanating from the Halema`uma`u and Pu`u `O`o vents of the Kilauea volcano.

The volcanic SO2 plume on 08 April could be tracked using a GOES-11 sounder brightness temperature difference product (subtracting the 13.4 µm band 5 temperature from the 7.4µm band 10 temperature) — a small “bubble” of elevated SO2 concentration (brightness temperature difference values of 0º to +5º K, yellow to orange colors) was seen to move slowly northwestward from the Big Island of Hawaii toward the smaller islands of Maui/Kahoolawe/Lanai/Molokai (below). Unfortunately, GOES-11 sounder data over the Hawaii region is only available 7 times a day (not once per hour, as it is over the continental US), so the motion of the SO2 feature was more difficult to follow compared to using the more frequent 15-minute visible imagery from the GOES-11 imager.

The surface visibility at Lahaina / West Maui (station identifier PHJH, below) decreased from 15 miles to 7 miles (with haze reported) as southerly winds blew the volcanic plume and SO2 cloud over the island of Maui on 08 April. On the Big Island of Hawaii, volcanic fog (sometimes referred to as “vog”) reduced visibility to less than 1 mile at Hilo.

The 7.4 µm band 10 of the GOES sounder is primarily a “water vapor absorption” band, but this particular sounder channel is also sensitive to high SO2 loadings in the atmosphere (as shown by the figure shown below, taken from Ackerman, S. A., A. J. Schreiner, T. J. Schmit, H. M. Woolf, J. Li1, and M. Pavolonis, 2008: Using the GOES Sounder to Monitor Upper-level SO2 from Volcanic Eruptions, submitted to Journal of Geophysical Research). The plot also shows that high SO2 loading could be detected using a channel located within the 8.4-9.0 µm band.

The Advanced Baseline Imager (ABI) on the future GOES-R satellite will have a similar 7.3 µm channel (at a 2 km spatial resolution, compared to the 10 km spatial resolution on the current GOES sounder), and with ABI imagery available at more frequent time intervals (4 images per hour over the full disk), the detection of these types of volcanic SO2 plumes will be significantly improved in the GOES-R era.

Terra MODIS images at 20:55 UTC on 08 April (below; courtesy of Mat Gunshor, CIMSS) demonstrate the utility of using the 11.0µm - 8.5µm brightness temperature difference product to help discriminate between the SO2 plume (darker blue enhancement on the difference product image, moving north from the Big Island of Hawaii) and the larger steam plume (evident as the hazy area on the visible image, moving westward and northwestward from the island).

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).