Overnight views of Tropical Storm Fred from NOAA-20 and Suomi-NPP

August 16th, 2021 |
Suomi NPP Day Night Band Visible (0.7 µm) and I05 (infrared, 11.5 µm) at 0704 UTC on 16 August 2021 (Click to enlarge)

VIIRS Imagery from Suomi-NPP (the Day Night Band, at 0.7 µm and I05, at 11.5 µm, above, at 0704 UTC) and from NOAA-20 (the Day Night Band, at 0.7 µm and I05, at 11.5 µm, below, at 0754 UTC), show polar orbiting perspectives of Tropical Storm Fred. The Day Night Band shows little detail in the cloud-tops, given the lack of lunar illumination (the moon — about half-illuminated — was below the horizon during these overpasses). The region of coldest cloud tops seems to have decreased from the NPP to the NOAA-20 overpass. The NHC discussion at 0300 UTC suggested that the low-level circulation had emerged from underneath the cirrus canopy, and perhaps that’s detectable in the toggles above and below. The storm does exist under southwesterly shear (morning analysis from the CIMSS Tropical Website).

Suomi NPP Day Night Band Visible (0.7 µm) and I05 (infrared, 11.5 µm) at 0754 UTC on 16 August 2021 (Click to enlarge)

Microwave data from the Advanced Technology Microwave Sounder (ATMS) on board both Suomi-NPP and NOAA-20 can be used to compute a rain rate, as shown below. The Rain Rate snapshots show a decrease in intensity between 0704 (a maximum of about 0.9″/hour) and 0754 UTC (a maximum of 0.5″/hour). That information, combined with the lack of observed lightning in the Day Night Band, might help guide an analyst in their description of the storm strength. Consider, however, that NPP had a near-nadir view whereas NOAA-20 was an edge view.

ATMS Rain Rate derived from Suomi NPP (0704 UTC) and NOAA-20 (0754 UTC) using MIRS Rain Rate algorithm (Click to enlarge)

VIIRS imagery and the ATMS Rain Rate is available in AWIPS-ready tiles via the CIMSS ldm feed. Imagery from Polar Orbiters over Fred (and Grace, and TD #8 (now Henri) in the Atlantic) is also available from the AOML Direct Broadcast link here.

For more information on Tropical Storm Fred, refer to the National Hurricane Center. Fred is forecast to make landfall on the Florida panhandle on 16 August.

Microwave rain estimates with an MCS

July 29th, 2021 |
VIIRS NPP Day Night Band visible (0.70 µm) imagery from Suomi-NPP (0740 UTC) and NOAA-20 (0831 UTC) on 29 July 2021 (Click to enlarge)

Severe thunderstorms developed (in a moderate risk region from the Storm Prediction Center; here are the Storm Reports) over northern Wisconsin late in the day on 28 July 2021 and moved to the southeast (here is an mp4 animation of GOES-16 imagery courtesy of Tim Schmit, NOAA). The Day Night Band imagery, above, from Suomi NPP (0740 UTC) and NOAA-20 (0831 UTC), shows snapshots of the storms as they moved southward into Illinois. The 0740 UTC image include more evidence of lightning — especially in southwestern Wisconsin (the horizontal streaks of light) and just southwest of Dubuque. At 0831 UTC, lightning is not detected in the Day Night Band image.

In addition to carrying the VIIRS (Visible-Infrared Imaging Radiometer Suite) instrument, Suomi-NPP and NOAA-20 also carry the Advanced Technology Microwave Sounder (ATMS), and microwave data from that instrument can be used to infer rain rates (using MIRS — Microwave Integrated Retrieval System — algorithms, that are part of Community Satellite Processing Package — CSPP — software available to use at Direct Broadcast sites). The toggles show the Day Night Band image, the ATMS-derived Rain Rate (the green region at 0742 UTC is >3″/hour!), and the base reflectivity at 0740 UTC (below) and at 0831 UTC (bottom). The MIRS Rain Rate (0742 UTC; 0833 UTC) product does outline regions where rain is likely falling, and gives credible values where the heaviest rains are falling. Note the diminishing rain rate over southwestern WI, for example, between 0740 and 0830 UTC — indicative of weaker convection — an observation echoed in the changes in lightning detection with the Day Night band. Changes in radar to reflect that difference in microwave-estimated rain rate are a little more subtle.

Because microwave estimates of rain rate are affected by background emissivity, and because water has a much lower microwave emissivity than land, you can sometimes view land/water boundaries (as in the 0742 UTC Rain Rate, below).

MIRS Rain Rate gives useful information about rains when radar observations cannot be accessed.

Suomi NPP Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0740 UTC on 29 July 2021 (Click to enlarge)
NOAA-20 Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0830 UTC on 29 July 2021 (Click to enlarge)

MIRS Rain Rate products are available via an LDM feed from CIMSS; they are produced using the Direct Broadcast antenna at CIMSS and are thus very timely.

Using Polar-Orbiting Satellite Imagery from Direct Broadcast sites to understand Elsa

July 6th, 2021 |

Suomi NPP Adapative Day Night Band imagery, 0636 UTC on 6 July 2021 (Click to enlarge)

AOML (The Atlantic Oceanographic and Meteorological Laboratory) maintains a Direct Broadcast antenna site that holds satellite imagery (created using CSPP — the Community Satellite Processing Package) created when a tropical system — such as Elsa — is within the download footprint of the AOML antenna.  This imagery — particularly in the microwave — is useful to describe the system’s structure. The Day Night Band image above, from Suomi NPP at 0636 UTC, shows a non-symmetric storm with the bulk of clouds to the east and south of the surface center (at that time near 23.9 N, 82.3 W, i.e., in the Florida Straits to the south of Dry Tortuga).  Rainfall, as diagnosed using MIRS algorithms and microwave ATMS (Advanced Technology Microwave Sounder) data from NPP, below, shows the asymmetry of the storm as well:  almost all the diagnosed rain is east of the center. (It’s helpful that both infrared imagers and microwave sounders are on the same satellite!)

Suomi NPP ATMS-derived Rain Rate, 0637 UTC on 6 July 2021 (Click to enlarge)

The GCOM-W1 (supported by JAXA) satellite also scanned Elsa shortly before 0700 UTC on 6 July.  Microwave observations at ~36 GHz, below, and at 89 GHz, farther below, can help to characterize the structure of the storm. Indeed, observations at/around 85-89 GHz are used in the MIMIC TC product as described here.

GCOM AMSR-2 observations at 36.5 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

GCOM AMSR-2 observations at 89.0 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

In addition to the AOML site, the CIMSS Direct Broadcast site contains Polar Orbiting imagery in near-real time. The afternoon 88.2 GHz image from (NOAA-20) ATMS is shown below.  Cold cloud tops associated with strong scattering by ice of the 88.2 GHz signal are apparent.

NOAA-20 ATMS Channel 16 Brightness Temperature, 1845 UTC on 6 July 2021 (Click to enlarge)


There are a multitude of polar orbiters such that observations show up in clusters of time.  However, for a better time animation, it’s still best to rely on GOES-16!  The animation below, from CSPP Geosphere, shows a sheared storm south and west of Ft Myers FL.  Indeed, an 1800 UTC 6 July 2021 shear analysis from the CIMSS Tropical website (here, from this site), shows westerly shear of 25-30 knots.

GOES-16 True-Color imagery, 6 July 2021 from 1730 to 1920 UTC (Click to animate)

For the latest information on Elsa, consult the webpages of the National Hurricane Center, or the SSEC/CIMSS Tropical Weather Page.

Subtropical storm in the South Pacific

May 27th, 2021 |

GOES-17

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

GOES-17 (GOES-West) “Red” Visible (0.64 um) images (above) showed the development of a subtropical storm in the South Pacific Ocean (just northeast of New Zealand) on 27 May 2021. Surface analyses from the New Zealand Met Service are available here.

GOES-17 “Clean” Infrared Window (10.3 um) images (below) highlighted the curved band of cold-topped convection wrapping into the deepening storm.

GOES-17 "Clean" Infrared Window (10.3 um) images [click to play animation | MP4]

GOES-17 “Clean” Infrared Window (10.3 um) images [click to play animation | MP4]

A NOAA-20 Infrared Window (11.45 um) image viewed using RealEarth (below) showed a higher resolution view of the band of cold clouds wrapping into the system at 1206 UTC.

NOAA-20 Infrared Window (11.45 um) image [click to enlarge]

NOAA-20 Infrared Window (11.45 um) image [click to enlarge]

With ample illumination from the Moon — in the Waning Gibbous phase, at 98% of Full — a Suomi NPP VIIRS Day/Night Band (0.7 um) image (below) provided a high-quality “visible image at night” at 1256 UTC (12:56 am NZST).

Suomi NPP VIIRS Day/Night Band (0.7 um) image [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 um) image [click to enlarge]

Suomi NPP ATMS Microwave (183.3 GHz) image

Suomi NPP ATMS Microwave (183.3 GHz) image (credit: Derrick Herndon, CIMSS) [click to enlarge]

A Suomi NPP ATMS Microwave (183.3 GHz) image (above) portrayed the spiral band wrapping into the core of the system at 1256 UTC, while a cross section of Suomi NPP ATMS Brightness Temperature anomaly (below) depicted the deep warm core (shades of green) characteristic of the subtropical cyclone.

Cross section of Suomi NPP ATMS Brightness Temperature anomaly [click to enlarge]

Cross section of Suomi NPP ATMS Brightness Temperature anomaly (credit: Derrick Herndon, CIMSS) [click to enlarge]