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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GOES-12 IR image + QuikSCAT WindSat wind vectors

An image of the GOES-12 10.7 µm IR channel (with an overlay of QuikSCAT WindSat wind vectors) from the CIMSS Tropical Cyclones site (above) revealed that wind speeds were near 50 knots within a curved band of deep convection located just to the east of the center of Subtropical Storm Laura on 29 September 2008.

Animations of the GOES-12 10.7 µm IR channel and visible channel images (below) showed the curved band of deep convection developing further and wrapping around the northern and then the western quadrants of the storm during the hours that followed; small-scale swirls were also seen on the visible imagery, rotating around the low-level center of Laura.

GOES-12 10.7 µm IR images

GOES-12 visible images

Laura was eventually classified as a Tropical Storm on the following day (30 September).

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