GOES-15 0.63 µm visible channel images (click image to play animation)

As high pressure associated with cold arctic air began to build over the eastern interior of Alaska and the Yukon Territory of Canada, a strong pressure gradient created intense gap winds through the channeled terrain of south-central Alaska on 21 October 2012. These winds stirred up glacial silt and then carried it down the valleys and toward the coast. GOES-15 0.63 µm visible channel images (above; click image to play animation) showed the hazy signature of a particularly large airborne plume of glacial silt as it moved offshore over the adjacent offshore waters of the Gulf of Alaska.

Suomi NPP VIIRS 0.64 µm visible channel images

A more detailed view is provided by Suomi NPP VIIRS 0.64 µm visible channel images (above) and 1.61 µm near-IR “snow/ice channel” images (below). The largest glacial silt plume was blowing southward out of the Copper River valley (just east of Cordova, station identifier PACV) and across Prince William Sound toward Middleton Island (station identifier PAMD). Additional smaller glacial silt plumes could be seen farther east on the 20:08 UTC image, in the vicinity of Yakutat (station identifier PAYA). On the previous day (20 October), northeasterly surface winds gusted to 28 mph at Middleton Island and 20 knots at Cordova — however, the gap winds emerging from the Cooper River valley were likely much stronger.

Suomi NPP VIIRS 1.61 µm “snow/ice channel” images

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Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data (above) showed the hazy signature of a dense plume of blowing dust along the southwestern periphery of a large mid-latitude cyclone that was centered over Minnesota and Wisconsin on 18 October 2012. Surface winds gusted as high as 73 mph in Nebraska and 56 mph in Kansas, reducing visibility to near zero in areas of dense blowing dust.

An animation of AWIPS 4-panel images of GOES-13 0.63 µm visible channel, 6.5 µm water vapor channel, 10.7 µm IR channel, and 3.9 µm shortwave IR data (below; click image to play animation) showed (1) the evolution of the dense plume of blowing dust on visible imagery as it developed and moved southeastward across Nebraska, Kansas, and Oklahoma; (2) a well-defined dry region (yellow color enhancement) on water vapor imagery that highlighted strong middle-tropospheric subsidence that initiated the downward transfer of momentum leading to the subsequent strong winds at the surface; and (3) the appearance of wildfire “hot spots” (black to yellow to red color enhancement) on the shortwave IR imagery in northeastern Colorado and southwestern Nebraska.

GOES-13 0.63 µm visible, 6.5 µm water vapor, 10.7 µm IR, and 3.9 µm shortwave IR images (click image to play animation)

An Aqua MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below) showed the tan/light brown signature of the most dense portion of the blowing dust plume. The blowing dust reduced surface visibility to near zero in a number of areas, forcing road closures across parts of Nebraska and Kansas — including a multiple-vehicle accident that closed Interstate 35 near Blackwell, Oklahoma.

MODIS true color image (displayed using Google Earth)

MODIS 0.64 µm visible channel and 11-12 µm IR brightness temperature difference (BTD) product

A comparison of the MODIS 0.64 µm visible channel data with the corresponding 11-12 µm IR brightness temperature difference (BTD) product (above) demonstrated that the BTD product did a better job at depicting the broad areal extent of the airborne dust (lighter blue to cyan color enhancement) at 20:13 UTC (3:13 PM local time). There was one pilot report of moderate to severe turbulence over northeastern Oklahoma near the leading edge of the dust plume.

===== 19 October Update =====

The MODIS BTD product was then able to follow the movement of the dust plume during the subsequent overnight hours, when visible channel imagery was no longer available — the plume became more narrow and less dense as it continued to move southeastward across Arkansas and then over northern Mississippi and Alabama by 08:10 UTC (4:10 AM local time) on 19 October (below).

MODIS 11-12 µm IR brightness temperature difference (BTD) product

After sunrise on the morning of 19 October, the hazy signature of the airborne dust could be seen on GOES-14 0.63 µm visible channel images over the southeastern US (below). There were pilot reports of flight visibility being restricted to 2 miles at an altitude of 1000 feet over southeastern Tennessee (GOES-13 visible image | MODIS BTD image), and 3 miles at an altitude of 3500 feet over northern Alabama (GOES-13 visible image | MODIS BTD image).

GOES-14 0.63 µm visible channel images

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GOES-13 Imager at 1445 UTC 18 October

GOES-13 replaced GOES-14 as the operational GOES-East satellite at 1444 UTC on 18 October 2012. The image above shows the 5 imager channels at 1445 UTC.

In September of 2012, Imagery from both the GOES-13 Sounder and from the GOES-13 Imager showed increasing amounts of noise. On September 23, 2012, GOES-13 was placed in standby mode after both the Sounder and Imager suffered anomalies. The 1046 UTC image and the 2115 UTC image, both on September 23rd, were the last images produced by the sounder and imager, respectively. GOES-14, which had been switched on for an annual north-south maneuver and for subsequent GOES-R simulations, has been standing in as GOES-East for GOES-13 since 24 September.

An outgas was performed on the GOES-13 Sounder that has improved image quality. During an outgas, the sounder instruments are heated (in this case, for nearly 2 days). This drives off molecules that have condensed onto sensors during the satellite’s lifetime. These volatile molecules originate from the various lacquers and coatings that are on the surfaces of the satellite (a rough analogy is new car smell). Sounder imagery from before and after the outgas shows the improvement in all shortwave channels. Similarly, imagery from the imager (below), shows that GOES-13 and GOES-14 have comparably clean signals.

GOES-13 and GOES-14 Imager data from 1302 UTC 16 October (click to toggle between images)

The reduction in noise for Sounder channels means that sounder-derived products will be cleaner. The imagery below is the Total Precipitable Water product derived from the sounder. Cleaner signals in the shortwave infrared channels means fewer fictitious clouds (a comparison using GOES-14 is available here). It is possible that Channel 15, the noisiest of the shortwave IR channels on the sounder, will soon be excluded from both sounder-derived TPW and cloud-top pressure.

Total Precipitable Water derived from the GOES-13 Sounder

NOAA/NESDIS scientists will continue to monitor GOES-13 performance before GOES-14 is put back into storage. In the meantime, a drift-stop maneuver on GOES-14 will occur at 1356 UTC on 19 October, stopping GOES-14’s eastward drift towards the GOES-East station longitude of 75 W. GOES-14 will be very near 90 W when the drift-stop occurs. This link from the Washington Post Capital Weather Gang blog gives additional information. See also this memo from NOAA SSD. Real-time sounder imagery is available here.

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Suomi NPP VIIRS 11.45 µm IR channel and 0.8 µm Day/Night Band image

Tropical Storm Rafael was slowly intensifying over the Atlantic Ocean north-northeast of Puerto Rico on 15 October 2012. McIDAS-V images of Suomi NPP VIIRS 11.45 µm IR channel and 0.8 µm Day/Night Band data at 05:33 UTC (above; courtesy of William Straka, CIMSS) showed cloud top IR brightness temperatures colder than -85 C (violet color enhancement), as well as city lights from the islands of the Dominican Republic, Puerto Rico, and other nearby islands.

A 08:25 UTC SSMI-15 85 GHz microwave image from the CIMSS Tropical Cyclones site (below) revealed a ragged banding structure that suggested Rafael was trying to form an organized eye.

SSMI-15 85 GHz microwave image

A comparison of AWIPS images of POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel data at 14:08 UTC (below) offered a close-up view of the central dense overcast region of Rafael, with transverse banding forming along the periphery and convective overshooting tops with IR brightness temperatures as cold as -93 C (darker violet color enhancement).

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

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