AWIPS images of the GOES-12 and MODIS fog/stratus product

A patch of stratus cloud was easily identifiable on AWIPS images of the GOES-12 and MODIS fog/stratus product (above) across parts of eastern Saskatchewan and western Manitoba in central Canada on 02 October 2008. Note how much sharper the cloud edge appeared on the 1-km resolution MODIS image compared to the 4-km resolution GOES-12 image.

MODIS Cloud Top Temperature, Cloud Phase, and GOES-12 Low Cloud Base products

Other AWIPS satellite products such as the MODIS Cloud Top Temperature and Cloud Phase, and the GOES-12 Low Cloud Base (above) indicated that this particular stratus cloud feature would likely not have posed a hazard to aircraft icing, given that the cloud phase was water droplets which exhibited cloud top temperatures  in the +3 to +6º C range. The lowest cloud bases appeared to be along the western portions of the stratus feature, which was confirmed by a ceiling report of 400 feet above ground level at Key Lake, Saskatchewan (station identifier CYKJ) versus 800 feet at The Pas, Manitoba (station identifier CYQD).

GOES-12 and GOES-13 visible images

The daytime dissipation of this area of stratus cloud could then be monitored using visible channel imagery from GOES-12 and GOES-13 (above). The stratus deck burned off over the Key Lake (CYKJ) area around 18:00 UTC (Noon local time). Note that the surface features on the GOES-13 animations exhibit less image-to-image movement compared to GOES-12 — improvements to the GOES-13 spacecraft Image Navigation and Registration (INR) system  include the use of star trackers to provide more precise image navigation.

Lake Athabasca (which staddles the Alberta/Saskatchewan border region) was seen in the upper left portion of the GOES-12 imagery, due to the different viewing angle from that satellite — note the brighter white features along parts of the southern shore of the lake. The initial question of “Could those bright white features be ice that had formed in the lake?”  was addressed by examining a 4-panel comparison of MODIS Visible, Snow/Ice, Land Surface Temperature, and Sea Surface Temperature (below); ice would have exhibited a darker signal on the 1.6 µm near-IR Snow/Ice image, but this feature was brighter white on both the Visible and the Snow/Ice images. In addition, the MODIS sea surface temperatures in the lake were in the mid 40s F (green colors), which argues against ice formation.

MODIS Visible, Snow/ice, Land Surface Temperature, Sea Surface Temperature

A quick look at a map of the area provided the complete answer: the brighter white features seen along the southern shore of the lake are actually Athabasca Sand Dunes Provincial Park.

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GOES-12 visible images

We received the following question on 02 October 2008:

Hello: I sometimes look at the GOES-12 vis nightime images even though they are usually devoid of any light of course. The 03:15 image tonight, however, is showing a meteor-type streak with a comet-like head and tail. I wonder, though, if GOES can actually detect a rapid transient event such as a meteor – or is this some sort of internal reflection caused by another light source or process? Many thanks! Rob Jackson, Hampton, NH

Excellent question, Rob! A sequence of GOES-12 visible images every day at 03:15 UTC from 27 September through 02 October 2008 (above) revealed that an increasing amount of “stray light”  was finding its way to the satellite’s instrument detectors just prior to the time when the GOES-12 satellite was entering the Fall “eclipse period” (when the satellite passes through the Earth’s shadow). During such Spring and Fall season eclipse periods, imagery from the satellite is interrupted, since the solar panels cannot generate the power needed to operate the various instrument packages.

An example of stray light affecting GOES-12 imagery during a Spring season eclipse period can be seen here.

Beginning with GOES-13, larger batteries on-board the satellite allow the instruments to operate through the eclipse periods (when the satellite is still in the Earth’s shadow). However, while imagery is available through the eclipse period, it is still vulnerable to small amounts of stray light which can affect the accuracy of any images or products. An animation of night-time GOES-13 visible imagery (below) shows the impact of stray light during the eclipse period (during that same time period, no imagery was available from GOES-12 between 03:32 UTC and  06:45 UTC).

GOES-13 visible images

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NOAA-16 11.0 µm IR image + surface reports

A NOAA-16 AVHRR 11.0 µm IR image (above) showed cold brightness temperatures of -10º to -20º C (violet colors) across much of northwestern Alaska on 30 September 2008. The coldest IR brightness temperatures of around -27º C or -17º F (darker blue colors) corresponded to the higher elevations of the Brooks Range which runs from west to east across northern Alaska. The coldest minimum temperature reported in Alaska that morning was -13º C (+9º F) at Anatuvuk Pass (station identifier PAKP, which had a temperature of +16º F at 16 UTC), but the coldest brightness temperatures on the IR image were located well to the west of that station. Two days earlier, Alaska reported their first temperature colder than -18º C  (0º F)  this season: both Chalkyitsik and Denali National Park registered a low temperature of -1º F on the morning of 28 September.

A comparison of MODIS true color images and topography using the Swath Viewer from the Geographic Information Network of Alaska (below) indicated that there was a good deal of snow cover over parts of the higher terrain in northern Alaska, especially across the northern slopes of the Brooks Range (due to a recent period of upslope flow moving inland from the Arctic Ocean, which dropeed several inches of new snow).

MODIS true color images + topography

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AWIPS satellite images + surface analysis

A cold frontal boundary was moving southward across the Pacific Ocean and approaching the Hawaiian Islands on 29 September – 30 September 2008, as seen on a comparison of AWIPS visible, IR, and water vapor satellite imagery and corresponding surface analysis (above). According to the boundary layer Meteorological Assimilation Data Ingest System (MADIS) atmospheric motion vectors (below), the front was moving southward at a speed of around 15-20 knots — IR cloud top temperatures were warmer than 0º C along the frontal cloud band north of Hawaii, suggesting rather shallow cloud features.

AWIPS image of GOES-11 10.7 µm IR channel and MADIS winds

A closer view using GOES-11 visible imagery (below) revealed that a series of mesoscale vorticies had developed along the frontal boundary. Another interesting feature was the persistent volcanic plume downwind of the big island of Hawaii (streaming toward the southwest), due to ongoing activity at the Kilauea volcano since Spring 2008 (see the April 2008 CIMSS satellite blog entry). Also note the long, thin line of cumulus clouds below the volcanic plume, a result of lee-side convergence.

GOES-11 visible images

A comparison of GOES-11 and GOES-13 visible images (below) shows that the volcanic plume was even more apparent with the larger viewing angle and more favorable “forward scattering” geometry from the GOES-13 satellite (positioned at 105º W longitude, vs. 135º W longitude for GOES-11).

GOES-11 and GOES-13 visible images

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