CIMSS Satellite Blog

As noted in the previous Blog entry, Tropical Storm Bertha became the Atlantic Basin’s second tropical storm on 03 July 2008. Meteosat-9 IR images with overlays of QuikSCAT and ASCAT satellite winds (above) from the CIMSS Tropical Cyclones site on following day (04 July 2008) showed some bursts of convection around the tropical cyclone, and verified the presence of tropical storm force winds. The CIMSS wind shear product (below) indicated that Bertha existed in an environment of low wind shear, which was favorable for continued intensification.

Meanwhile, on the previous day (03 July 2008), the afternoon MODIS visible image and Land Surface Temperature product (below) showed mostly cloud-free conditions and very hot surface temperatures across much of the Desert Southwest region of the United States. Death Valley in California reached a high temperature of 122º F, the hottest day so far this summer season (121º F had been reached at that location a few times in June 2008); other high temperatures in the region that day included 118º F at Bullhead City, Arizona and 115º F at Laughlin, Nevada. While the MODIS LST values were generally about 20-30º F higher than the actual air temperatures that were measured in instrument shelters about 5 feet off the ground — the highest LST values seen on this day were near 150º F (darker red colors) in parts of California, Nevada, and Arizona — the LST product is still useful for depicting where the hottest areas might be (since the coverage of stations that report air temperature over any given region might be somewhat sparse).

Wildfire activity began to increase across the northern portions of Saskatchewan and Manitoba in Canada on 30 June 2008. GOES-11 visible and 3.9 µm “shortwave IR” images (above) showed a number of thick smoke plumes (lighter gray features on the visible images) drifting southeastward from a large cluster of active fire “hot spots” (darker black pixels on the IR images). GOES-11 was placed into Rapid Scan Operations (RSO) during the afternoon hours, so images near the end of the animation were available at 5-7 minute intervals.

The largest fire was located between Pelican Narrows and Sandy Bay in Saskatchewan, as seen in an AVHRR false color image (below, viewed using Google Earth). A close-up view reveals that the fire had actually jumped the only road that was in that area (the seasonal road which connects Sandy Bay and Pelican Narrows). The GOES-11 shortwave IR brightness temperatures associated with this particular fire were as high as 341º K (68º C, 158º F), which is the saturation temperature of the 3.9 µm detectors on the GOES-11 satellite. Note that some small pyrocumulus clouds could be seen developing over this large and very hot fire on the GOES-11 visible imagery (above) as well as on the AVHRR false color image (below).

A closer view of the largest fire using AWIPS images of the 1-km resolution MODIS 3.7 µm and the 4-km resolution GOES-12 3.9 µm IR channels (below) shows the advantage of higher spatial resolution for displaying the shape and coverage of not only the largest fire cluster (located near the center of the image), but also the smaller fires in outlying areas. Many of the pixels were so hot that the IR brightness temperatures exceeded the 54.5º C upper threshold for AWIPS display, and showed up as black pixels (registered as “NO DATA“) on the imagery. The smoke from this fire was restricting surface visibility to 1 mile at Flin Flon (CYFO) and 3 miles at The Pas (CYQD) in Manitoba, even though those 2 sites were not in the direct path of the thickest portion of the smoke plume.

Some clues as to the locations of the hottest portion of the fire — which happened to be located within the eastern half of the active fire area, where the black “NO DATA” pixels were seen on the MODIS shortwave IR image — could be found by examining other MODIS images and products: note the darker black pixels on the 11.0 µm “IR Window” channel, the brighter white pixels on the 2.1 µm near-IR “Snow/Ice” channel, and the darker red pixels on the Land Surface Temperature (LST) product (below). AWIPS cursor sampling indicated that the hottest pixel on the IR Window image was 52º C (126º F), while the hottest pixel on the LST image was significantly warmer at 145º F (63º C).

Today’s CIMSS Satellite Blog entry will take a step back and focus on the larger scale. We’ll begin with an animation of GOES-12 visible images from 25 June 2008 (above). Several items of interest are apparent in addition to the normal diurnal development of thunderstorms across parts of North and Central America: (1) the very large area of haziness that occupies the lower right quarter of the images is due to airborne dust from Africa; (2) thick smoke from wildfires is evident over much of northern California and Nevada; (3) a good deal of Hudson Bay in Canada is still frozen. Such is the diversity of meteorological phenomena that can be seen on satellite imagery in late June!

(1) To confirm that the haziness seen on the visible imagery above is due to African dust, we examine the Meteosat-9 Saharan Air Layer (SAL) tracking product (above). The westward progression of a large Saharan dust outbreak (orange to red color enhancement) can be clearly seen during the 21-25 June period. The areal coverage of the airborne dust over the Atlantic Ocean could also be seen on a composite of AVHRR false-color imagery from 23 June (below, displayed using Google Earth).

(2) To explore the impacts of the thick smoke over northern California, it is interesting to view an AWIPS image comparison of the MODIS Land Surface Temperature (LST) product and the MODIS visible channel (below). Note that the LST values seemed to be about 20º F cooler under the areas of thickest smoke (in the 100-110º F range, orange to light red colors) compared to areas farther to the north and to the south of the smoke (where LST values were in the 120-130º F range, darker red colors). The actual air temperatures were not affected by such a drastic amount, although air temperatures in the Sacramento Valley were in the mid-upper 80s F under the thickest smoke (compared to low to mid 90s F farther to the south in the San Joaquin Valley. At Red Bluff in northern California (KRBL) the maximum temperature on 25 June was 87º F (the surface visibility was 2.5 miles or less the entire day due to smoke), several degrees below the daytime maximum temperatures of 98º F, 95º F, and 96º F on the previous 3 days (KRBL 96-hour meteorogram).

(3) Finally, to confirm that ice still remained in much of Hudson Bay, we next turn to MODIS true color and false color images from the SSEC MODIS Direct Broadcast site (below). The majority of the bright features seen over Hudson Bay on the true color image are indeed ice, which appears as a darker red color on the false color image (in contrast to supercooled water droplet clouds, which appear as varying shades of white).