South Sandwich Islands volcanic and orographic cloud signaturesEven though the South Sandwich Islands are near the limb of the GOES-16 (GOES-East) view, Near-Infrared “Cloud Particle Size” (2.24 µm) images (above) were able to display a long volcanic plume (brighter shades of white) originating from Mount Michael on Saunders Island during the daylight hours on 12 March 2020. In addition, smaller/shorter volcanic plumes could also be seen originating from a few of the smaller islands just to the north of Saunders Island. The volcanic plumes were more reflective (brighter white) because they were comprised of smaller droplets compared to the expansive stratus/stratocumulus clouds over the South Atlantic Ocean.
The smaller cloud particles of the volcanic plume were also more efficient reflectors of incoming solar radiation, thus appearing warmer (darker shades of gray) in GOES-16 Shortwave Infrared (3.9 µm) images (below).2 days later, southerly/southwesterly winds interacting with the rugged terrain of the islands created von Kármán vortex streets downwind (north-northeast) of some of the islands (especially Montagu Island, the largest of the South Sandwich chain) — VIIRS True Color Red-Green-Blue (RGB) images from NOAA-20 and Suomi NPP as visualized using RealEarth (below) provided a detailed view of these vortices. In spite of the lower spatial resolution and large satellite viewing angle, the von Karman vortices could also be seen in GOES-16 “Red” Visible (0.64 µm) images (below).