AWIPS images of the MODIS sea surface temperature (SST) product on 16 April 2008 (above) displayed some interesting warm water eddy structures (green to yellow colors) over the western Atlantic Ocean, not far off the coast of the Mid-Atlantic states. A comparison with the SST analysis field from the High Resolution Real Time Global (RTG_SST_HR) model less than 6 hours later (at 00:00 UTC on 17 April) demonstrated the advantage of the 1-km resolution MODIS data for resolving the small-scale detail in the structure of warm water eddies; even the magnitude and placement of the largest warm eddy (in the middle 60s F or 18-20º C, light green colors) was incorrectly depicted by the RGT_SST_HR model. On the other hand, the model did do a fairly good job of portraying the warm plume of the Gulf Stream (denoted by the yellow to orange colors in the bottom center of the image).

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An animation of GOES-12 (GOES-East) visible channel imagery (above) showed the development of an elongated plume of blowing dust over the south-central US on 10 April 2008. The dust plume originated in eastern New Mexico and western Texas, and was being drawn northeastward into the circulation of a large and powerful mid-latitude cyclone that was centered over the central Plains states.

Also note the haziness that was seen moving northward across the western Gulf of Mexico — this was due to smoke from widespread fires that had been burning in parts of southern Mexico and Central America (NOAA Hazard Mapping System fire and smoke product).

AWIPS images of the MODIS visible and “cirrus detection” channels (above) showed the early stages of formation of the dust plume over the Texas / New Mexico border region at 17:20 UTC (11:20 AM local time) on 10 April. At that particular time, the blowing dust was not yet readily identifiable on 1-km resolution MODIS visible imagery (nor on 250-meter resolution MODIS true color imagery); however, a subtle light gray “dust signal” was evident on the 1.4 µm near-IR “cirrus detection” image (since that channel is very sensitive to the presence of particles that are efficient scatterers of light).

The conventional method used to detect airborne dust or sand is to calculate the difference in brightness temperatures between the 11.0 and 12.0 µm IR channels; higher concentrations of dust exhibit a brighter yellow signal (a more negative temperature difference) on such a MODIS IR difference product (above). The dust feature was obvious over New Mexico and Texas on the first image (17:25 UTC on 10 April), with the second image (08:42 UTC on 11 April) showing the dust reaching from northeastern Texas to far southern Wisconsin. Note that a “false positive” dust signal (lighter yellow colors) appears over parts of the western US on the IR difference product, due to the high emissivity of the soils found over certain regions.

The GOES-West (GOES-11) imager has the 11.0 µm and 12.0 µm IR channels used to calculate this type of IR difference product, but the GOES-East (GOES-12 ) imager lacks the 12.0 µm channel — so using this IR brightness temperature difference technique to detect airborne dust (or volcanic ash) over the eastern US is only possible using data from either the GOES sounder or the polar-orbiting NOAA AVHRR and Terra/Aqua MODIS instruments.

The strong winds associated with the large storm system in the central US transported the dust rapidly northeastward, helping it to reach northern Illinois and southern Wisconsin. Backward air mass trajectories calculated using the NOAA Air Resources Laboratoty HYSPLIT model (above) verified the rapid transport of dust from New Mexico and Texas all the way to southern Wisconsin during the 24-hour period from 12 UTC on 10 April to 12 UTC on 11 April. In fact, there were public reports of dust-laden moisture seen on cars in southern Wisconsin (in the La Crosse, Madison, and Racine areas) on the morning of 11 April — some of the dust aloft was scavenged by falling precipitation overnight and brought down to the surface.

A similar event of blowing dust from Texas reaching southern Wisconsin occurred back in December of 2003 (CIMSS GOES Gallery | National Weather Service Milwaukee/Sullivan).

UPDATE: The National Weather Service forecast office at Green Bay, Wisconsin received photos of “dirty snow” (below) that fell near Lac du Flambeau in far northern Wisconsin on 11-12 April. In addition, the NWS forecast office at Marquette, Michigan passed along a report of “brown snow” that fell on 11 April at Marenisco in the Upper Peninsula of Michigan.

(Photos courtesy of Linda Albers, NWS Cooperative Observer at Lac du Flambeau, Wisconsin)

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Explosive events from the Kilauea Volcano (located on the Big Island of Hawai’i) 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 (GOES-West) 0.63 µm 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 Hawai’i. 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 Hawai’i Volcanoes National Park on 08 April. GOES-11 visible imagery (below) revealed two separate plumes, emanating from the Halema`uma`u and the 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 7.4 µm 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 Hawai’i toward the smaller islands of Maui/Kahoolawe/Lanai/Molokai (below). Unfortunately, GOES-11 sounder data over the Hawai’i 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 Hawai’i, 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 (images every 5 minutes 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 11.0 µm – 8.5 µm 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 Hawai’i) and the larger steam plume (evident as the hazy area on the visible image, moving westward and northwestward from the island).

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An AWIPS image of the GOES-12 10.7 µm “IR window” channel (above) showed a large cluster of convection that developed in the vicinity an inverted surface trough axis over the Gulf of Mexico on 07 April 2008.

An animation of AWIPS images of the GOES-12 6.5 µm “water vapor channel” (above) suggested that much of the middle to upper troposphere was quite dry (yellow to orange colors) over the Gulf of Mexico region on that particular day.

However, AWIPS images of the POES AMSU total precipitable water (above) and the DMSP SSM/I total precipitable water (below) revealed that a plume of significant moisture was moving northward into the central Gulf of Mexico during 06-07 April, providing a necessary ingredient for the development of the convection.

A comparison of the GOES water vapor channel image with total precipitable water products from the GOES sounder, POES AMSU, and DMSP SSM/I (below) demonstrates how misleading it would be to simply interpret the GOES vapor image alone and conclude that the entire Gulf of Mexico region was generally “very dry” (aside from the cluster of convection that had developed). The bulk of the precipitable water plume existed at lower levels of the atmosphere, below the layer that was being sensed by the GOES imager water vapor channel (which, according to the GOES water vapor weighting function plot for Brownsville, Texas at 12 UTC on 07 April was centered around 500 hPa).

An animation of hourly composites of the CIMSS MIMIC total precipitable water product (below) showed the evolution of the moist plume as it emerged into the southwestern Gulf of Mexico and then moved northeastward into the central Gulf during the 06-07 April period. The MIMIC product blends microwave total precipitable water data from the DMSP SSM/I and the Aqua AMSR-E polar orbiting instruments, and advects the blended moisture fields using lower-tropospheric mean layer wind derived from the GFS model.

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