As noted in the past blog post, the NWS Water Surface Conditions / Synthetic Aperture Radar Science Team has arranged for observations over the Samoan Islands on 9 dates between 30 January 2023 and 5 March 2023 (imagery is available online here). The image above shows both the derived winds and the Normalized Radar Cross Section (NRCS) from 0556 UTC on 2 February 2023; Derived winds and NRCS at 1700 UTC on 2 February 2023 are shown below. At both times, north or northeast winds are indicated. (Advanced Scatterometer — ASCAT — winds from the descending pass of MetopC at ca. 2030 UTC on 2 February 2023 show the same wind direction).

GOES-18 Clean Window infrared imagery (Band 13, 10.3 µm) from 1630 to 1730 UTC, below, (bracketing the SAR observation at 1700 UTC), shows cloud motions from south to north, suggesting considerable shear over the region. (This 1800 UTC/2 February 2023 shear analysis from the SSEC/CIMSS Tropical website shows the strong southwesterly shear).

The image below overlays RADARSAT-2 winds on top of the GOES-18 Clean window imagery. This animation shows the infrared imagery with and without the wind analysis (with two different enhancements), and one thing is apparent: it’s very difficult to pair the wind perturbations with brightness temperature features in the GOES-18 imagery!

The difficulty in attributing a Band 13 feature to the wind field features is also shown in the zoomed-in scene shown in the slider comparison below.

Some of the stronger SAR winds in the convective storms in the southern part of this scene (shown in the comparison above and in the image below) likely arise because of ice within convective clouds. Such ice strongly reflects microwave energy from the SAR satellite and that strong signal is misinterpreted as a strong wind return from the ocean surface. The NRCS imagery from that time will show a diffuse/feathery structure in regions where ice is present in the clouds.

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Should you believe the winds over the ocean? Yes. This study compared SAR winds to ocean buoys in the Atlantic. See in particular Figure 2 in Section 3, also available here.

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A NOAA-20 overpass across the Great Lakes on 2 February showed primarily clear skies over Lake Erie and western Lake Ontario, allowing for computation of ACSPO (Advanced Clear-Sky Processor for Ocean) Sea-Surface Temperatures. (Note that the colorbar has been rescaled from its default so that only values between 32 and 41^o F (i.e., 0 and 5^o C) are shown). The warmest lake surface temperatures over Lake Erie are around 37.5^oF; those over Lake Ontario are around 40.8^oF. The image below shows False Color imagery rather than True Color, allowing better identification of snow-covered surfaces over land, and better identification of clouds holding liquid cloud droplets.

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VIIRS True- and False-Color imagery and ACSPO SSTs were created using CSPP Software and data from the Direct Broadcast antenna at CIMSS. They are available as AWIPS tiles via LDM, and are also viewable at this website, in RealEarth, and at the VIIRS viewer.

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The Lightning Imaging Sensor (LIS) that flies on the International Space Station (ISS) observed about 20 individual flashes in about a minute to the east of Japan on 1 February 2023, as shown in the animation above. Himawari-9 Band 13 clean window infrared (10.41 µm) imagery, below, bracketing the lightning observation times above shows a developing storm system moving out over the Pacific — the comma head of the system is over southern Hokkaido Island. Convective development can be inferred between 35^o and 40^o N off the coast of Honshu.

Did this system intensify, as one might expect given the presence of lightning? It did. The imagery below, from this site, shows the storm forecast to strengthen from 999 hPa at 0600 UTC to 989 hPa at 1800 UTC on 1 February. LIS data, though infrequent, can give useful information about convection.

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JMA Himawari-9 False Color RGB images from the NOAA/CIMSS Volcanic Cloud Monitoring site (above) showed plumes of SO2 (brighter shades of cyan) drifting northward, westward and southeastward from the East Epi submarine volcano, following its eruption on 01 February 2023 (local time).  The differences in SO2 transport were due to directional wind shear with height. No signatures of significant concentrations of volcanic ash were seen in other types of multispectral satellite imagery.

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