GOES-11/GOES-12 water vapor composite image + GFS 500 hPa height

An anomalous ridge of high pressure developed across western North America on 23 September 2009, bringing hot and dry conditions to parts of the Pacific Northwest states — high temperatures at many locations in Oregon were in the 90s and low 100s F for two consecutive days. The effect of this large ridge could be seen quite well on an AWIPS composite image of the GOES-11 and GOES-12 water vapor channels (above). Stu Ostro at The Weather Channel pointed out that the 5950 meter geopotential height at Spokane, Washington at 00 UTC on 23 September is the record highest value for so far north in the US so late in the season (since the beginning of the NCEP reanalysis dataset, which goes back though 1948).

A pair of large wildfires were burning in southwestern Oregon — the “hot spots” from these 2 fires could be seen on MODIS 3.7 µm and GOES-11 3.9 µm shortwave IR images (below), located to the east of Roseburg (station identifier KRBG). The location and areal coverage of these wildfire hot spots was better depicted on the 1-km resolution MODIS image, compared to the 4-km resolution GOES-11 image; in addition, the leading edge of the marine fog/stratus that was moving inland was more accurately shown on the higher-resolution MODIS imagery.

MODIS 3.7 µm + GOES-11 3.9 µm shortwave IR images

250-meter resolution MODIS true color and false color images from the SSEC MODIS Today site (below) show even better details of the smoke plumes and the marine fog/stratus. There was also evidence of  some smoke remaining in a few of the valleys near the fire activity. The MODIS false color image also displays the larger active fire “hot spots” as pink-colored features at the source of the smoke plumes.

MODIS true color and false color images

GOES-12 (GOES East) visible images

The large plumes of smoke from these Oregon fires could be seen moving northward across western Oregon and western Washington, even drifting as far to the north as southern British Columbia and Alberta in Canada. Note that the leading (northern) edge of the smoke plume was easier to identify on GOES-12 (GOES East) visible imagery (above) compared to GOES-11 (GOES West) visible imagery (below) — this is a result of the more favorable forward scattering geometry with the GOES-12 satellite. However, the more direct viewing angle of GOES-11 made it easier to see the marine fog/stratus that was moving inland along coastal sections of Washington, Oregon, and California.

GOES-11 (GOES West) visible images

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MTSAT-1R visible images

One of the worst dust storms in the past 70 years swept across a large part of eastern Australia on 22 September – 23 September 2009 (Daily Mail Online photos). A sequence of MTSAT-1R visible images (above) showed the progression of the large dust cloud as it moved eastward during the daylight hours. Note the appearance of “lee waves” along the top of the dust cloud, as the strong winds interacted with the high terrain of the Great Dividing Range. An undular bore could also be seen forming out ahead of the cold front, over the offshore waters of the South Pacific Ocean.

The surface meteorogram for Brisbane, Australia (station identifier YBBN) is shown below; note that the surface visibility dropped to 0.2 km (0.1 mile) as the cold front passed, and following the frontal passage the dew point dropped from +16º C (61º F) to -16º C (+3º F).

Brisbane, Australia surface meteorogram

A larger-scale view of the dust cloud feature could be seen using MODIS true color imagery from the NASA MODIS Rapid Response site (below, viewed using Google Maps). See also the NASA  MODIS Image of the Day.

MODIS true color image

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GOES-12 10.7 µm IR images

Madison, Wisconsin received 3.63 inches (92 mm) of rainfall on 22 September 2009 — much of it within a 4 hour period — which set a record for the highest rainfall amount for any day during the month of September (additional details are available from the NWS Milwaukee/Sullivan). AWIPS images of the GOES-12 10.7 µm IR Window channel (above) showed that the cloud top IR brightness temperatures were rather unremarkable, with only a few areas exhibiting temperatures colder than -50º C (yellow color enhancement) during the heavy rainfall event. The 1-km resolution AVHRR Cloud Top Temperature values were only slightly colder, at -54º C — this corresponded to a AVHRR Cloud Top Height of 11-12 km.

GOES-12 visible images (below) did not show any pronounced cloud top texture or shadowing that would indicate strong convective elements over southern Wisconsin — in fact, there were no cloud-to-ground lightning strikes seen during the day, and no thunder was reported at any of the first order observing stations.

GOES-12 visible images

Blended Total Precipitable Water product

The Blended Total Precipitable Water (TPW) product (above) did reveal that an area of TPW values of 40 mm and greater (red colors) developed across northern Illinois and far eastern Iowa after about 08 UTC — this seemed to be associated with a disturbance that developed and moved northward along and ahead of a frontal boundary that was moving slowly eastward across the region. It should be noted that these TPW values were about 175-200% above normal.

However, about 5 hours earlier the MODIS TPW product displayed TPW values of 40 mm and higher (red colors) over parts of northwestern Illinois, at a time when the Blended TPW product was still only indicating TPW values of 30-35 mm (below). This area of higher TPW values over northern Illinois was then advected northward during the day, and lifted along and ahead of a developing warm frontal boundary. A cross section oriented north to south showed a deep column of upward vertical motion (omega values of 10 µbars per second, red colors) over southern Wisconsin.

Blended TPW + MODIS TPW products

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Night-time MTSAT-1R 3.75 µm shortwave IR image (14:30 UTC)

A curious image artifact was noted on MTSAT-1R 3.75 µm shortwave IR imagery, in the form of a very cold “false eye” appearing  just to the right of the actual eye of Typhoon Choi-Wan (17W) in the western North Pacific Ocean . The “ghost” of the eye exhibited a satellite radiance of zero (very cold, appearing bright white on the image), and was offset from the true eye by 16 pixels in the horizontal and 1-2 pixels in the vertical. This false eye was most apparent on MTSAT-1R imagery during the local night-time hours, as was seen on 16 September 2009 at 14:30 UTC (above) and 15:30 UTC (below).

Night-time MTSAT-1R 3.75 µm shortwave IR image (15:30 UTC)

This false eye artifact was also evident during local daytime hours, but the “ghost” did not exhibit zero radiance — the feature could be seen better on the shortwave IR imagery once a contrast stretch  enhancement was applied (below). The offsets of the false eye were the same as seen during local night-time hours.

Daytime MTSAT-1R shortwave IR (original and enhanced) + MTSAT-1R visible images

A similar (but less obvious) image artifact could be seen on a night-time shortwave IR image over China (below) — there was a bright white “ghost”  to the  right of the warm area that was between the two colder cloud features (again, the ghost feature was offset to the east by 16 pixels with a vertical displacement of 1-2 pixels).

Night-time MTSAT-1R 3.75 µm shortwave IR image (over China)

The exact cause of these image artifacts is not known; however, since the MTSAT-1R satellite scans from left to right using a Charge-Coupled Device (CCD) array,  the satellite sensor may be overcompensating for the CCD “quantum wells” losing more charge faster than expected, subtracting more of a bias than it should (this could also be a side-effect of sensor aging). Instrument cross-talk could be another source of this type of image anomaly.

Kudos to Chris Schmidt at CIMSS for processing and analyzing these MTSAT-1R images, and supplying the explanations of possible causes of such an image artifact.

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