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 northeast of Hawai’i) 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 3 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 3 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.

Actinoform clouds (or actinae) in the central Pacific Ocean

May 30th, 2019 |

GOES-17 “Red” Visible (0.64 µm) images, with 3-hourly plots of ship wind reports [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images, with 3-hourly plots of ship wind reports [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) revealed the mesoscale cyclonic circulations of actinoform clouds (or “actinae“) within the marine boundary layer stratocumulus cloud field over the central Pacific Ocean on 30 May 2019.

This type of cloud feature was originally identified in TIROS-V imagery over the Pacific Ocean in 1962 (below), and was featured in the first Monthly Weather Review “Picture of the Month” series in January 1963.

TIROS-V image of actinoform clouds over the western Pacific Ocean on 07 October 1962 [click to enlarge]

TIROS-V image of actinoform clouds over the western Pacific Ocean on 07 October 1962 [click to enlarge]

Actinoform Clouds (Actinae) in the Eastern Pacific Ocean

March 13th, 2007 |

GOES-11 Visible (0.65 µm) and Shortwave Infrared (3.9 µm) images [click to play animation]

GOES-11 Visible (0.65 µm) and Shortwave Infrared (3.9 µm) images [click to play animation]

GOES-11 (GOES-West) Visible (daytime) and 3.9 µm Shortwave Infrared (nighttime) imagery (above) revealed an interesting cyclonic vortex which was propagating westward across the eastern North Pacific Ocean on 13-14 March 2007. The radial banded cloud features that form such a cloud “swirl” are known as actinae or actinoform clouds, and they are occasionally seen in the marine stratocumulus cloud field over the Pacific Ocean (one such case was June 1997). This type of cloud pattern was first observed back in 1962 on TIROS V imagery near Hawaii.