A sequence of 1-km resolution Terra/Aqua MODIS (11.0 µm), 1-km resolution POES AVHRR (12.0 µm) and 375-meter resolution Suomi NPP VIIRS (11.45 µm) Infrared images (below) showed better details of such features as overshooting tops, some of which exhibited IR brightness temperature values as cold as -78º C on MODIS, -81º C on AVHRR and -86º C on VIIRS.A comparison of Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0852 UTC or 3:52 am local time (below) showed the MCS as its core was centered over northern Illinois. Note how the tall, dense cloud mass blocked the view of nearly all city lights over a large area — including the normally very large and very bright lights of the Chicago metroplex. With almost no illumination from the Moon (which was in its Waxing Crescent phase, at 1% of Full), only the faint light of airglow helped to illuminate some cloud features over the northern portion of the satellite scene. In addition, numerous bright white streaks were seen in the Day/Night Band image along the leading (southern) edge of the MCS, due to cloud illumination from intense lightning activity; one lone lightning streak was evident in Wisconsin, whose intensity was bright enough to saturate the Day/Night Band detectors (hence the long “post-saturation recovery” streak as the sensor continued scanning toward the southeast). A few hours earlier at 0339 UTC, the CLAVR-x POES AVHRR Cloud Top Height product (below) showed areas with height values of 16-17 km (lighter cyan color enhancement) — the large amount of water and ice particles contained within such tall clouds was therefore able to effectively block the view of city lights on the VIIRS Day/Night Band image. Note that a Cloud Top Height product will be available from the ABI instrument on GOES-R.
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: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.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).
The animation above (available here as an mp4, and here on YouTube) shows 11.22 µm infrared imagery at 2.5-minute time steps (bottom) and 10-minute time steps (top) from Himawari-8 on 14 May 2015. Category 2 intensity Typhoon Dolphin is approaching Guam, seen at the left edge of both panels in the frame. The 2.5-minute imagery gives a much better indication of the quick rise and decay of overshooting tops (IR brightness temperatures of the storm tops approach -95º C!). A 10-minute time step cannot fully resolve the evolution of these features. The 2.5-minute time step also better captures the divergent flow (and outward-propagating gravity waves) at the top of the central dense overcast. No eye was yet apparent in the infrared imagery, or on DMSP SSMI 85 GHz microwave imagery.
How high are the clouds in the Central Dense Overcast (CDO)? Cloud Heights are available from CLAVR-x (Clouds from AVHRR Extended). Data from Geostationary Satellites are processed and are available to download here. Values from COMS-1 and from MTSAT-2 (displayed with McIDAS-V) suggest maximum cloud heights near 55,500 feet.
The MIMIC Total Precipitable Water (TPW) product, below, showed that Typhoon Dolphin was able to tap rich moisture from the Intertropical Convergence Zone (ITCZ) during the 13-14 May period; TPW values within the tropical cyclone circulation were often in the 60-65 mm or 2.5-2.6 inch range (darker red color enhancement).
Visible Imagery from Himawari-8, just after sunrise on 15 May, show continuous development of short-lived overshooting tops to the east of Guam. More information on the storm is available at the CIMSS Tropical Cyclones site, the JMA Tropical Cyclone site and the Joint Typhoon Warning Center.