Kármán vortex streets and an actinoform cloud feature off the coast of Chile

March 11th, 2022 |

GOES-16 True Color RGB images [click to play animated GIF | MP4]

GOES-16 (GOES-East) True Color RGB images created using Geo2Grid (above) showed (1) Kármán vortex streets extending downwind (to the north) of Isla Alejandro Selkirk and Robinson Crusoe — part of the Juan Fernández Islands off the coast of Chile, and (2) an actinoform cloud feature farther to the west (which was also moving northward) on 11 March 2022.

In the corresponding Day Cloud Phase Distinction RGB images (below), the light shades of green exhibited by the narrow cloud bands within the actinoform feature suggested that they were beginning to glaciate — similar to what was observed in this example.

GOES-16 Day Cloud Phase Distinction RGB images [click to play animated GIF | MP4]

A toggle between GOES-16 True Color RGB and Day Cloud Phase Distinction RGB images at 1600 UTC is show below.

GOES-16 True Color RGB and Day Cloud Phase Distinction RGB images at 1600 UTC [click to enlarge]

It is interesting to note that as a ship was passing through the northern portion of the Kármán vortex street about 100 miles north of Isla Alejandro Selkirk at 16 UTC, it reported moderate showers (below) — which would not be expected from a typical field of marine stratocumulus clouds. 

GOES-16 “Red” Visible (0.64 µm) images, with ship reports plotted in cyan [click to play animated GIF | MP4]

Kudos to the NWS Spaceflight Meteorology Group and UW-CIMSS for bringing these phenomena to our attention:

Actinoform clouds near Bermuda

February 5th, 2022 |

GOES-16 “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images [click to play animated GIF |MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images (above) displayed actinoform clouds (reference) near Bermuda on 05 February 2022. The light shades of green exhibited by the narrow cloud bands within the actinoform features suggested that they were beginning to glaciate — and as one of those cloud bands (associated with a dissipating actinoform feature) moved across the island of Bermuda, it briefly produced light rain showers at the airport (TXKF). It should be noted that this is an unusual location to see actinform clouds; most examples tend to form over the Pacific Ocean.

A toggle between GOES-16 Visible and RGB images at 1401 UTC is shown below.

GOES-16 “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images at 1401 UTC [click to enlarge]

Another example of actinoform clouds producing precipitation — over the Pacific Ocean, near Hawai`i — can be seen here.

Thanks to Margaret Mooney (CIMSS) for bringing these features in the Atlantic to our attention:

Actinoform cloud in the East Pacific

November 16th, 2021 |

GOES-17 True Color RGB images [click to play animated GIF | MP4]

GOES-17 (GOES-West) True Color RGB images created using Geo2Grid (above) showed a cyclonically-rotating actinoform cloud feature that was moving west-southwestward across the East Pacific Ocean (about midway between Hawai’i and California) on 16 November 2021.

In GOES-17 Day Cloud Phase Distinction RGB images (below), the increasing shades of green exhibited by the curved bands of shallow convection suggested that those features were likely mixed-phase clouds — composed of a combination of liquid/supercooled water droplets and ice particles. 

GOES-17 Day Cloud Phase Distinction RGB images [click to play animated GIF | MP4]

Similarly, in a toggle between NOAA-20 VIIRS True Color and False Color RGB images viewed using RealEarth (below), darker shades of cyan suggested the presence of mixed-phase banded cloud elements within the core of the actinoform feature.

NOAA-20 VIIRS True Color and False Color images at 2218 UTC [click to enlarge]

Other examples of actinoform clouds can be examined by scrolling through this link.

Actinoform clouds near Hawai’i

June 30th, 2020 |

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) revealed 3 cyclonically-rotating actinoform cloud structures that were moving west-southwestward toward the Hawaiian Islands on 30 June 2020 (surface analyses).

A closer look at the northernmost actinoform feature showed it moving over Buoy 51000 (located 245 miles northeast of Honlulu) around 04 UTC on 01 July — there was somewhat of an increase in 1-minute wind speeds and wind gusts as it approached, but no obvious perturbation was seen in the air pressure (it appeared to have arrived during the typical ~12-hourly drop in pressure).

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

A sequence of three hourly (at 0010, 0110 and 0210 UTC) panoramic camera views from Buoy 51000 (below) suggested that there were rain showers reaching the ocean surface beneath one of the actinoform’s radial arms at 0210 UTC (GOES-17 Visible image).

Sequence of 3 hourly (at 0010, 0110 and 0210 UTC) panoramic camera views from Buoy 51000 [click to enlarge]

Sequence of three hourly panoramic camera views from Buoy 51000 —  at 0010, 0110 and 0210 UTC [click to enlarge]

True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) VIIRS images from NOAA-20 and Suomi NPP as visualized using RealEarth (below) provided a detailed view of 2 of the actinoform clouds. The radial arms that comprised the cloud features remained within the marine boundary layer, so they exhibited fairly warm cloud-top infrared brightness temperatures.

True Color RGB and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

True Color RGB and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

Plots of rawinsonde data from Hilo, Hawai’i (below) indicated that the marine boundary layer was strongly capped by a temperature inversion at an altitude of 1.3-1.5 km (where the air temperature was around +15ºC — which was very close to the minimum cloud-top infrared brightness temperatures exhibited by the actinoform clouds).

Plots of rawinsonde data from Hilo, Hawai'i [click to enlarge]

Plots of rawinsonde data from Hilo, Hawai’i [click to enlarge]

Other examples of actinoform clouds have been shown in May 2019, March 2008, March 2007 and June 1997.