GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images (above) showed widespread elevated convective banding that was helping to enhance snowfall rates — with some locations reporting 1.5 to 2.0 inches per hour — across parts of Minnesota, Wisconsin, Lower Michigan, Iowa and Illinois on 16 February 2023. There was no GLM indication of lightning activity associated with any of these convective bands.

On the Day Cloud Phase Distinction RGB images, shades of yellow to green suggested that cloud tops along many of the convective bands were either glaciated or were mixed phase (composed of ice crystals and supercooled water droplets). The ability to load select GOES RGB images combined with various GOES Level 2 Derived Products (using Satellite > Local Menu Items > Satellite Sector) provides the ability to use AWIPS cursor sampling to determine specific quantitative properties associated with the various RGB shades — for example, the GOES-16 Day Cloud Phase Distinction RGB image at 1731 UTC (below) includes cursor sampling of the individual RGB components in addition to the associated Cloud Top Phase (Ice) and Cloud Top Height (19,658 feet) derived products at that cursor location, which was along a convective band that was enhancing snowfall rates and reducing the surface visibility to 1/4 mile at Middleton (KC29) just west of Madison, Wisconsin (KMSN). The GOES-16 “Clean” Infrared Window (10.3 µm) cloud-top infrared brightness temperature — the Red component of the RGB image — at that particular cursor location was -24.73ºC.

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NOAA’s newest satellite, NOAA-21, has started sending data to Earth with each overpass. The satellite launched 3 months ago as JPSS-2, and was renamed NOAA-21 once in orbit. NOAA-21 joins the Suomi-NPP and NOAA-20 satellites in polar orbit around Earth.

CIMSS acquires NOAA-21 views of North America via Direct Broadcast from the satellite to a receiver on our roof when NOAA-21 flies overhead. NOAA is receiving global NOAA-21 data and shared the following images.

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RADARSAT-2 and RCM-1 had two closely-spaced overpasses over Cyclone Freddy in the Indian Ocean early on 16 February 2023, as shown above. Eyewall speeds exceed 130 knots in the RCM-1 data! (Imagery and data are available here). The quadrant analyses for RCM-1 and for RADARSAT-2 show hurricane-force winds extending out about 40 nautical miles from the storm center. The toggle below shows 0000 UTC Himawari-9 clean window imagery overlain with the 0004 UTC RADARSAT-2 SAR Winds. Because Freddy now is almost at the limb of the Himawari-9 imagery (as shown here), there is a noticeable parallax shift in the Himawari-9 clouds — away from the sub-satellite point (for Himawari-9, that’s at 140.7^o E longitude; Freddy was at 82.2^o E Longitude!)

The toggle below compares 0000 UTC Clean Window imagery from Himawari-9 (AHI data) and from GEOKOMPSAT-2 (over the Equator at 128.2^o E) (AMI data). The parallax shift in the AMI data is smaller than with AHI because Freddy is closer to GEOKOMPSAT-2’s subsatellite point. (Himawari HSD and Geokompsat-2 Level 1b files were processed with geo2grid software for these images). However, both satellites show an eye to the west of its SAR-derived location. Note also the degradation in Himawari-9 image acuity over the western part of the domain; brightness temperatures are also cooler over the western quarter of the domain, likely due to limb cooling (also discussed in this blog post): radiation from the edge of a Full-Disk scan (compared to radiation from the sub-satellite point) will pass through more of the colder upper troposphere (because of the much more slanted path towards the satellite) before reaching the satellite detectors, and a cooler temperature will be perceived.

Earlier SAR captures of Freddy’s eye with comparisons to Himawari-9 imagery are available here. Thanks to JMA and KMAs for the data!

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The toggle below compares EWS-G1 infrared imagery (4-km resolution) with AHI data remapped to the EWS-G1 projection. Both satellites were sampling the eye near 0000 UTC on 16 February. EWS-G1 is over the equator near 66^oE, so any eye displacement due to parallax will be to the east of the eye, i.e. in the opposite direction of the Himawari-9 parallax displacement.

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Cyclone Freddy was at its strongest at around 0000 UTC on 16 February, as noted here.

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Two more SAR data collections occurred over American Samoa waters on 16 February, as shown above. (This is part of an ongoing special collection that extends through early March). As with most previous observations, winds around American Samoa were light. Consider these ASCAT observations from MetopC at ca. 2040 UTC on 16 February 2023, for example, taken from this site. Observed winds are uniformly around 10 knots.

The most notable feature in the 0550 UTC winds above is the arc of showers to the northeast of American Samoa, shown below. Imagery from this time is also available at this website, both wind fields and Normalized Radar Cross Section (NRCS) fields. NRCS data suggests that the peak winds — those values exceeding 20 knots — might be where SAR energy is reflecting off ice in clouds, leading to a SAR-derived wind that is too strong.

How long do the winds in the SAR field above persist? The mp4 animation below (click here for an animated gif) from 0000 UTC to 2000 UTC tracks the cloud feature associated with the SAR observations at 0548 UTC to the east, but that feature is very difficult to discern in the second SAR overpass at 1650 UTC.

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