GOES-11 10.7 µm IR images

The first tropical depression of the East Pacific season (Tropical Depression 1E) formed off the southwest coast of Mexico on 18 June 2009 — this was the latest date of the start of the tropical cyclone season in that particular ocean basin since reliable records began in 1970. The previous record for the latest start of the season in the East Pacific basin was the development of Tropical Storm Aletta on 19 June in 1994.

GOES-11 10.7 µm IR images (above) showed that the tropical depression exhibited some very cold cloud tops early in the day on 18 June (IR brightness temperature values as low as -87º C, darker purple color enhancement), but then the cold cloud canopy collapsed fairly quickly later in the day, with cloud top temperatures warming from -86º C at 19:00 UTC on 18 June to -64º C at 01:00 UTC on 19 June. A new series of convective bursts then developed in the northern quadrant of the tropical depression after about 03:00 UTC on 19 June.

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GOES-11 "split window" IR difference product (10.7 - 12.0 µm)

A series of volcanic eruptions from Sarychev Peak (located in the central Kiril Islands) began on 10-11 June 2009, and GOES-11 “split window” IR difference images (above) showed a good signature of one of the ash plumes (yellow to cyan color enhancement) as it began to move eastward across the North Pacific Ocean on 16 June 2009.

AWIPS images of the MTSAT + GOES-11 IR channel with overlays of the MTSAT high density winds (below) showed the high-altitude flow that was helping the volcanic ash plume features to move southeastward around 40-60 knots (according to the Volcanic Ash Advisories that were issued on 16 June).

GOES-11 is the last of the current GOES series to have the 12.0 µm IR channel on the imager instrument package, which allows the calculation of such a “split window” IR difference product for volcanic ash detection. Once GOES-11 is replaced by either GOES-13 or GOES-14 as the operational GOES-West satellite, the geostationary volcanic ash detection ability will be greatly diminished over the eastern North Pacific Ocean…until the launch of the Advanced Baseline Imagery (ABI) on the GOES-R satellite.

MTSAT + GOES-11 IR images, MTSAT high density winds

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NOAA-15 visible and 10.8 µm IR images

A large severe thunderstorm that was developing in southern Kansas during the afternoon hours on 15 June 2009 had a very nice satellite presentation on NOAA-15 visible and 10.8 µm IR imagery (above). A “warm trench” signature appeared to be surrounding the cluster of coldest pixels associated with the strongest overshooting top located to the northeast of Dodge City, Kansas (station identifier KDDC). Around the time of these images, SPC storm reports included a tornado, hail of 1.75 inch in diameter, and wind gusts to 60 mph just to the east of Dodge City.

A comparison of the 1-km resolution NOAA-15 10.8 µm IR and the 4-km resolution GOES-12 10.7 µm IR data (below) showed that the coldest cloud top IR brightness temperature was -86º C on the NOAA-15 image (versus -73º C on the corresponding GOES-12 image). In addition, a significant parallax shift was seen on the GOES-12 image, due to the large viewing angle of the geostationary satellite — image features were located several miles to the north-northwest on the GOES-12 image.

NOAA-15 10.8 µm and GOES-12 10.7 µm IR images

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GOES-11 visible images

Well, not really — but a very interesting cloud plume formed yesterday and streamed off the 20,318-ft (6194-m) summit of Denali (“Mt. McKinley”) in southern Alaska on 10 June 2009, which almost had the  appearance of a volcanic eruption plume. GOES-11 visible images (above) showed this thin cloud plume spreading out as it curved to the southeast and then to the south, eventually moving over Anchorage and then the Kenai Peninsula.

A 1-km resolution NOAA-18 AVHRR 10.8 µm IR image (below) indicated that IR brightness temperatures were quite warm for such a high-altitude cirrus plume, barely reaching the -15 to -20º C range. Due to the thin nature of this cloud plume, a significant amount of radiation from the warmer ground surfaces below was bleeding upward through the thin cloud layer and reaching the satellite detectors.

NOAA-18 AVHRR 10.8 µm IR image

A false-color NOAA-18 Red/Green/Blue (RGB) image (below) showed the “transparent” nature of the cloud plume, with snow cover features on the ground clearly recognizable beneath the cloud.

NOAA-18 AVHRR false color RGB image

Tracking the location of the leading edge of the thin cloud plume feature was difficult using single-channel satellite imagery, which underscores the importance of using multi-spectral satellite products such as the 10.8 – 12.0 µm IR difference  (below) to correctly analyze the cloud location. Areas where the IR difference product reached +7 to +10 K (cyan colors) corresponded to the thicker portions of the cloud plume.

NOAA-18 IR difference product (10.8 - 12.0 µm, channel 04 - 05)

The cloud plume was curving to the southeast and then to the south due to the presence of a ridge of high pressure aloft over southern Alaska, as seen on an AWIPS image of the GOES-11 IR channel with an overlay of the GFS model 500 hPa winds (below).

GOES-11 10.7 µm IR image + GSF 500 hPa winds

A tip of the hat to Emily Niebuhr, UW-Madison / AOS graduate student, who is currently up in Alaska and brought this to our attention!

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