GOES-14 SRSO-R imagery: “mystery feature” over eastern Tennessee

May 21st, 2015


 

GOES-14 remained in Super Rapid Scan Operations for GOES-R (SRSO-R) demonstration mode on 21 May 2015, providing 1-minute images for much of the eastern US (see this blog post) — and another interesting feature was seen over eastern Tennessee that was rather perplexing. Since this easily qualified for the “What the heck is this?” blog category, we thought it might be fun to have a contest of sorts and invite readers to submit their wild guesses and/or educated explanations. We will post more imagery later in the day on 22 May as to our explanation — but in the meantime, leave a comment on the blog (comments are moderated, so they will not appear until approved), or send your thoughts to our Twitter account.

—– 22 May Update —–

Thanks to all who submitted their suggestions here and on Twitter of an explanation of the “What the heck is this” feature; Here is our best guess:

GOES-13 (GOES-East) visible, 3.9 µm shortwave IR, 6.5 µm, and 10.7 µm IR images [click to play animation]

GOES-13 (GOES-East) visible, 3.9 µm shortwave IR, 6.5 µm, and 10.7 µm IR images [click to play animation]

The first step in trying to understand what might be causing this interesting feature was to examine 4-panel images showing imagery from other GOES channels (or spectral bands): in this case, the 3.9 µm “shortwave IR” channel, the 6.5 µm “water vapor” channel, and the 10.7 µm “IR window channel” (above; click image to play animation). The 3.9 µm IR brightness temperatures of cloud features were in the +20 to +25º range, while the 10.7 µm IR brightness temperatures were in the +3 to +5º C range — the significantly warmer shortwave IR temperatures indicates that the clouds were comprised of liquid or supercooled cloud droplets. Otherwise, no significant clues were seen on the IR (or the water vapor) images.

However, the METAR surface reports offer an important clue: a rain shower moved from southwest to northeast through the region during the preceding overnight hours with the passage of a weak low pressure system (surface analyses), with Knoxville (station identifier KTYS) receiving 0.23″ and Oak Ridge (KOQT) receiving 0.10″ of rainfall (radar-estimated 24-hour precipitation). Therefore, one plausible explanation of the feature seen on visible imagery is that it was a shallow pool of stable, rain-cooled air near the surface that was spreading out and flowing downslope (westward) into the Great Valley of East Tennessee during the morning and early afternoon hours.

While the outer edges of this rain-cooled stable air feature remained generally cloud-free, the inner core exhibited a good deal of cloud development (including what appeared to be a more dense northwest-to-southeast oriented cloud band through the middle). An overlay of hourly RTMA surface winds (below; click image to play animation) indicated that there was convergence within the feature (to the lee of higher terrain within the Cumberland Plateau), which along with daytime heating of the moist soil would have helped to promote such shallow cloud development.

GOES-13 0.63 µm visible channel images, with RTMA surface winds [click to play animation]

GOES-13 0.63 µm visible channel images, with RTMA surface winds [click to play animation]

For clouds within expanding the rain-cooled boundary at 1534 UTC, the CLAVR-x POES AVHRR Cloud Type was liquid, with Cloud Top Height values of 1-3 km and Cloud Top Temperature values of +2 to +10º C (below).

CLAVR-x POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

CLAVR-x POES AVHRR Cloud Type, Cloud Top Height, and Cloud Top Temperature products

Severe thunderstorm over West Texas, as viewed from 3 GOES satellites

May 19th, 2015

GOES-15 (left), GOES-14 (center), and GOES-13 (right) 0.62 µm visible channel images [click to play animation]

GOES-15 (left), GOES-14 (center), and GOES-13 (right) 0.62 µm visible channel images [click to play animation]

Thunderstorms began to develop across West Texas during the afternoon hours on 19 May 2015, along and ahead of an eastward-moving dryline. One of the storms went on to produce a few brief tornadoes, and hail as large as 3.0 inches in diameter (SPC storm reports). Different views of this storm were provided by GOES-15 (GOES-West), GOES-14 (in SRSO-R mode), and GOES-13 (GOES-East) 0.62 µm visible channel images (above; click image to play 190 MB animated GIF; also available as an MP4 movie file, or on YouTube). This comparison highlights the advantages of 1-minute interval Super Rapid Scan images (which will be available from GOES-R) compared to the standard 15-minute interval Routine Scan images provided by the current generation of GOES.

One interesting feature seen on the visible channel images above was the apparent merger of the large dominant dryline storm and a smaller northward-moving storm that had formed in Mexico (radar animation). In GOES-13 10.7 µm IR imagery with an overlay of SPC storm reports (below; click image to play animation), one report of 2.0-inch diameter hail was seen around or shortly after the time of the storm merger.

GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

With higher spatial resolution IR imagery from MODIS (1-km), VIIRS (375-meter), and AVHRR (1-km), much colder cloud-top IR brightness temperatures were seen (below) compared to the corresponding 4-km resolution GOES IR imagery at those times — especially during the early formative stages of the thunderstorms captured with MODIS and VIIRS. The coldest cloud-top IR brightness temperature on the 2128 UTC AVHHRR image was -80º C, compared to -67º C on the 2130 UTC GOES image.

Terra and Aqua MODIS 11.0 µm, Suomi NPP VIIRS 11.45 µm, and POES AVHRR 12.0 µm IR channel images

Terra and Aqua MODIS 11.0 µm, Suomi NPP VIIRS 11.45 µm, and POES AVHRR 12.0 µm IR channel images

A more detailed discussion of this event can be found on the RAMMB GOES-R Proving Ground Blog.

Atmospheric Bore between the Grand Banks and New England

May 8th, 2015
GOES-13 0.63 µm Visible images (click to play animation)

GOES-13 0.63 µm Visible images (click to play animation)

Atmospheric Bores form in stable air and create horizontal cloud bands that propagate perpendicular to the along-band direction. The feature seen above in GOES-13 visible imagery formed in stable air south of a High Pressure system that pushed a backdoor cold front into New England (surface analyses). The southern edge of this bore was likely eroding as it became influenced by warmer less-stable air over with the Gulf Stream — the warm waters of the Gulf Stream were apparent in the toggle, below, of POES AVHRR 0.86 µm visible and 12.0 µm infrared imagery at 1055 UTC. The bore was apparently moving over the top of a shallow layer of sea fog that had formed in the colder waters north of the Gulf Stream.

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

POES AVHRR 0.86 µm Visible image and 12.0 µm Infrared image at 1055 UTC on 8 May 2015 (click to enlarge)

Suomi NPP overflew the area at ~1800 UTC, affording a very high resolution view of the bore structures with the VIIRS 0.65 µm visible channel, below.

SNPP_DNB_1807UTC_08May2015

Suomi NPP VIIRS Visible (0.65 µm) imagery, 1807 UTC on 8 May 2015 (Click to enlarge)

The daytime propagation of the bore feature could also be followed on POES AVHRR 0.86 µm visible channel images, shown below.

POES AVHRR 0.86 µm visible images (click to enlarge)

POES AVHRR 0.86 µm visible images (click to enlarge)

Dust storm in southern Nevada and California

April 14th, 2015
GOES-13 0.63 µm visible channel images (click o play animation)

GOES-13 0.63 µm visible channel images (click o play animation)

GOES-13 (GOES-East) 0.63 µm visible channel images (click image to play animation; also available as an MP4 movie file) showed the hazy signature of a cloud of thick blowing dust moving southward across southern Nevada and parts of southern California, along and behind a strong cold frontal boundary on 14 April 2015.

Areas where the dust cloud was more dense could be identified using the Terra and Aqua MODIS 11-12 µm IR brightness temperature difference (BTD) product (below). The 12 µm IR channel is no longer available on the imager instrument of the current series of GOES satellites — however, the ABI instrument on the upcoming GOES-R satellite will have a 12 µm IR channel, allowing the creation of such BTD products to aid in the identification and tracking of similar dust features.

Terra and Aqua MODIS 11-12 µm IR brightness temperature difference

Terra and Aqua MODIS 11-12 µm IR brightness temperature difference

At 1833 UTC, a pilot reported that the top of the dust cloud was at 11,500 feet near its leading edge (below). Farther to the south, strong winds interacting with the terrain were causing pockets of moderate to severe turbulence.

Terra MODIS 11-12 µm IR brightness temperature difference, with pilot reports

Terra MODIS 11-12 µm IR brightness temperature difference, with pilot reports

The blowing dust cloud was also evident on true-color Red/Green/Blue (RGB) images from MODIS and VIIRS, as visualized using the SSEC RealEarth web map server (below).

MODIS and VIIRS true-color RGB images

MODIS and VIIRS true-color RGB images