Rope cloud in the East Pacific Ocean
* GOES-17 images shown here are preliminary and non-operational *
An 1802 UTC GOES-17 “Red” Visible (0.64 µm) image with an overlay of the 12 UTC surface analysis (above) revealed a well-defined rope cloud which stretched for nearly 1000 miles, marking the cold front position at the time of the image. Rope clouds can therefore be used to diagnose the exact location of the leading edge of a cold frontal boundary between times when surface analyses are available. In this case, the cold front was associated with a Hurricane Force low over the East Pacific Ocean on 16 January 2019 (surface analyses).An animation of GOES-17 Visible images is shown above, with a zoomed-in version closer to the rope cloud displayed below. An even closer look (below) showed that the rope cloud was only about 2-3 miles wide. When the 18 UTC surface analysis later became available, a close-up comparison with the 1802 UTC GOES-17 Visible image (below) indicated that the northern portion of the cold front (as indicated by the rope cloud) was slightly ahead of — and the southern portion slightly behind — the smoothed cold frontal position of the surface analysis product. 1-km resolution AVHRR Visible (0.63 µm) and Infrared Window (10.8 µm) images of the rope cloud were captured by NOAA-15 at 1617 UTC (above) and by NOAA-18 at 1710 UTC (below). Along the northeastern portion of the rope cloud, there were a few convective clouds which exhibited cloud-top infrared brightness temperatures as cold as -55 to -60ºC (darker shades of red) and were tall enough to be casting shadows due to the low morning sun angle.
Check out this “rope cloud” in this morning’s MN2 pass. Pretty defined. UltraTrack with Doppler compensation along with XHRPT. pic.twitter.com/Bc1xtk4hGj
— ??? ???¢?? (@usa_satcom) January 16, 2019
===== 17 January Update =====On the following day, another rope cloud (one that was more fractured) was seen moving across Hawai’i as a cold front passed the island of Kaua’i — the southeastward progression of the rope cloud was evident on GOES-17 True Color Red-Green-Blue (RGB) images (above) from the UW AOS site.
Surface observations plotted on GOES-17 Visible images (below) showed the wind shift from southwest to north as the cold front moved through Lihue on Kauwa’i around 00 UTC.
===== 18 January Update =====Not all rope clouds are associated with cold fronts; with ample illumination from the Moon — in the Waxing Gibbous phase, at 90% of Full — a Suomi NPP VIIRS Day/Night Band (0.7 µm) image (above) provided a “visible image at night” of a rope cloud in the northern Gulf of Mexico which highlighted a surface wind shift axis.
A sequence of VIIRS Day/Night Band images from NOAA-20 and Suomi NPP (below) showed the movement of the rope cloud during a time span of about 1.5 hours.