Sentinel-1A overflew Samoan waters just around sunset on 25 April in American Samoa (as it does every 12 days at this time). At the overpass time, strong convection was moving slowly northward just to the east of the Sentinal SAR wind swath. The SAR Winds (shown below) show a wind speed boundary with strongest winds close to the eastern edge of the swath. The strongest winds — isolated spots of very strong winds (red and white in the enhancement) — in the scene below likely arise from a reflection of the SAR signal off abundant ice in the cloud. When the SAR Normalized Radar Cross Section is viewed, the ice “contamination” appears as a feathery structure. That’s shown in the NRCS figure at the bottom, taken from this ESA site; ice features are bright white, and if you zoom in, they’ll have a feathery structure. Sentinel-1A data fields are also available here, including, for this day, winds and NRCS.

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The recent Solar Eclipse that extended from the south Indian Ocean to the central north Pacific Ocean (Blog Post) traversed a region that is routinely monitored by different geostationary satellites — Himawari-9, GEOKOMPSAT-2A (GK2A) and FY-4A/FY-4B. Himawari-9 and GK2A have sub-satellite points on the Equator that are separated by only 12.5 degrees of Longitude (140.7^oE for Himawari-9, 128.2^oE for GK2A)! If you create full-disk imagery from the two satellites, stereoscopic views are achieved if one is able to cross their eyes and focus on the image in the middle. The Himawari-9 True-color imagery, above left, and the GK2A imagery, above right, were created using geo2grid (downloadable here). Geo2grid includes readers for both AHI HSD (Himawari Standard Data) data, and for AMI Level 1b data. If data are available (AHI HSD and AMI Le1b files are available at the SSEC Data Center, for example), the following two commands create images that lead to stereoscopy:

../geo2grid.sh -r ami_l1b -w geotiff -p true_color -f /path_to_AMIdata/2023_04_20_110/ami/le1b/fd*ge/*0440.nc../geo2grid.sh -r ahi_hsd -w geotiff -p true_color -f /path_to_AHIdata/ahi/2023/2023_04_20_110/0440/*FLDK*

These two commands will create native-resolution (22000×22000!) True-Color images at 0440 UTC on 20 April 2023. The animation above shows data from 0200 through 0700 UTC. All images created images were resized and annotated, and placed side-by-side, with Himawari data to the left, and GK2A data to the right. The resultant animation can be viewed in three dimensions.

Thanks to Bodo Zeschke (ABoM) for noting that “easy” stereoscopic imagery could be created for this event. Thanks also to both KMA and JMA for the data.

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Sentinel-1A’s overpass just east of North Carolina right after sunset on 23 April 2023, above, shows a sharp delineation in wind speeds, with wind speeds at the western edge of the SAR winds dropping from around 8-9 knots (cyan enhancement) to 2-3 knots (magenta enhancement). The animation below includes the SAR footprints north and south of the footprint shown above — taken within 1 second of each other. There are multiple features in the SAR data that have underlying signals in the SST field. The warmth of the sea surface here is affecting the wind strength; stability changes will change the amount of vertical mixing after all. The North Wall is also apparent in the Normalized Radar Cross Section (NRCS) data (from this site).

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The toggle below shows the SAR data overlain on top of GOES-16 Shortwave Infrared (Band 7, 3.9 µm) imagery. A cleaner view of the temperature gradients is apparent. The SST Level 2 product shown above is computed only in regions that are confidently cloud-free.

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This European Space Agency SAR Data viewer will give you hours of SAR data viewing pleasure (in addition to this NOAA/STAR link!)

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10-minute Full Disk sector GOES-18 (GOES-West) Nighttime Microphysics RGB + daytime True Color RGB images from the CSPP GeoSphere site (above) showed a plume of resuspended ash (from the 1912 Novarupta-Katmai eruption in Alaska) that was being transported offshore across the Shelikof Strait toward Kodiak Island — and wrapping into an eddy circulation within the Strait on 23 April 2023.

The entrainment of resuspended ash within the eddy circulation was more apparent in 1-minute Mesoscale Domain Sector GOES-18 Nighttime Microphysics + daytime True Color RGB images (below).

1-minute GOES-18 Dust RGB images (below) include plots of surface/buoy/ship reports and GOES-18 Derived Motion Winds — note how the wind direction at Shelikof Strait Buoy 46077 changed as the eddy circulation developed. Derived Motion Winds indicated that portions of the offshore resuspended ash plume were moving at speeds up to 20 knots.

A toggle between GOES-18 Dust RGB and Topography images (below) showed that the plume was emerging from the ash-filled Valley Of Ten Thousand Smokes.

Since this particular plume was composed of a mixture of aged ash and more recent sediment from glacial melt (rather than purely fresh volcanic ash), the Dust RGB did a better job at highlighting the plume — as seen in a comparison of Ash RGB and Dust RGB images at 1500 UTC and 1600 UTC (below). Although the two RGBs use the same spectral bands, they are scaled differently (in order to better depict typical ash or dust features).

RCM-1 Synthetic Aperture Radar (SAR) winds (source) at 1646 UTC (below) revealed the area of lighter wind speeds (darker shades of blue) within the eddy circulation over the Shelikof Strait.

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