If you see something, like a blog post for example (link, this shows an airmass high in Total Precipitable Water crossing the North Pole) and you’re curious what JPSS satellite imagery might look like with that something, how can you proceed? If the data are in the recent past, one could, for example, refer to the CIRA Polar slider and download an image, like this one that is time-stamped 0452 UTC on 7 March. That image, however, will not be full-resolution, and there are limits to what can be created. This blog post steps you through ways to figure out which JPSS data to download, and how to access it via NOAA CLASS, and how to display it with Polar2Grid (version 3.0, discussed in this previous blog post).

The first step is to find the times that Suomi NPP, or NOAA-20, or (eventually) NOAA-21 overflew the region. Satellite orbits are available here. The date in question is 7 March, and there are archived images for NPP, NOAA-20 and NOAA-21. Paths over the Arctic for NPP are shown below (link, here’s the similar image for NOAA-20), and the path from 1425 through 1445 UTC from Suomi NPP looks appropriate.

The next step is to access data at NOAA CLASS. We will request ‘JPSS VIIRS Sensor Data Record Operational (VIIRS_SDR)’ data. That takes you to a page that looks like this, where I have selected NPP data from 14:25 to 14:45 on 7 March 2023, from either ascending or descending passes. The Data I selected were Day Night Band (SVDNB) and I05 (SVI05) SDRs, as well as the navigation files that are needed: GDNBO, GIMGO and GITGO files. After some time, an email announces that the files are ready for download. Here is the listing after they’d been placed on my machine with the Polar2Grid software. There are eight files each of GDNBO, GIMGO, GITCO, SVDNB and SVI05 files, i.e., eight granules of data and navigation information within one directory. Note: As part of my NOAA CLASS preferences/profile, I have ‘No’ clicked for ‘Package Geolocation with JPSS Data Products’ and ‘Yes’ clicked for ‘De-aggregate JPSS Data Products’. Now it’s time to create imagery using Polar2Grid.

As always, I first interrogate to see what kind of imagery can be created with the data/navigation files that I have, i.e., I execute this command: ./polar2grid.sh -r viirs_sdr -w geotiff --list-products-all -f ../../data/Arctic/*.h5 and this command returns a list (under ### Standard Available Polar2Grid Products) of what I can request using the product flag (-p), including I05 and different flavors of Day Night Band imagery: adaptive_dnb, dyanmic_dnb, histogram_dnb, hncc_dnb (hncc: high and near-constant contrast). I then invoked the Polar2Grid command (1. and 2.) to create this imagery, (3.) to color-enhance the Infrared image, and then (4. and 5.) add coastlines and lat/lon lines. The flags in the add_coastlines.sh shell script are explained in the Polar2Grid online documentation under Section 7: Utility Scripts.

1:  ./polar2grid.sh -r viirs_sdr -w geotiff -p I05 -g polar_canada -f ../../data/Arctic/*.h5
2:  ./polar2grid.sh -r viirs_sdr -w geotiff -p adaptive_dnb dynamic_dnb histogram_dnb hncc_dnb -g polar_canada -f ../../data/Arctic/*.h5
3:  ./add_colormap.sh /home/scottl/CSPPGeo/enhancements/IR13_AWIPSAPPROXnew.txt npp_viirs_I05_20230307_142958_polar_canada.tif
4:  ./add_coastlines.sh --add-coastlines  --coastlines-outline black --coastlines-width 2 --add-grid --grid-D 10.0 10.0 --grid-d 10.0 10.0 --add-colorbar --colorbar-align bottom --colorbar-text-size 1 --colorbar-tick-marks 255 --colorbar-height 50 npp_viirs_I05_20230307_142958_polar_canada.tif
5:  ./add_coastlines.sh --add-coastlines  --coastlines-outline black --coastlines-width 2 --add-grid --grid-D 10.0 10.0 --grid-d 10.0 10.0 *dnb*20230307_142958_polar_canada.tif

Note in the polar2grid call above I have referenced one of the ‘built-in’ grids with -g, i.e., the ‘polar_canada’ grid. In this way I did not have to use the p2g_grid_helper.sh script to create a yaml file that holds gridding information. Imagery created are shown below. The toggle includes the ‘hncc’ Day Night Band image — on this day it had the best look — and the 11.45 µm I05 image both reprojected onto the ‘polar_canada’ map. The cloud feature that you might expect given the cross-polar motion of the relatively high Total Precipitable Water airmass is apparent.

View only this post Read Less

GOES-18 infrared imagery (Band 13, 10.3 µm) and derived Total Precipitable Water, above, shows tropical Invest 91P several hundred miles south of American Samoa within a corridor of moisture associated with the South Pacific Convergence Zone (SPCZ). (Note that the default color scale for Total Precipitable Water (TPW) has been rescaled so the “dryest” value is 1.0 inches). The Samoan islands are just at the northern edge of the deepest moisture — observed TPW at the Pago Pago sounding has decreased from 55 mm at 1200 UTC on 12 March to 44 mm at 1200 UTC on 14 March, the start of the animation above. MIMIC Total Precipitable water for the 24 hours ending 1300 UTC on 14 March, below, (source) shows dryer air very slowly moving over the Samoan islands from the north and northeast. (SAR and Scatterometry surface winds are all northerly around Samoa, as shown in this blog post).

---

A Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1252 UTC is shown below — ample illumination from the Moon (in the Waning Gibbous phase, at 56% of Full) provided a useful “visible image at night”. No bright lightning streaks were seen within the convective cluster associated with Invest 91P.

_________

What does the future hold for Invest 91P? The toggle below shows imagery from the SSEC/CIMSS tropical weather site (link). Shear values are low and Sea Surface Temperatures are warm. However, winds in the atmosphere (shown below, from here) are moving the invest area to the south, towards a less favorable environment.

For more information on Invest 91P (or 90P to its west!), refer to the SSEC/CIMSS Tropical Weather website (link) or the webpages of the Joint Typhoon Warning Center (link).

View only this post Read Less

The special SAR observation period over American Samoa, allowing extra observations from RADARSAT and RCM satellites (see CIMSS Blog posts here, here, here, here, here, here, here and here!) has ended, but Sentinel-1A will still routinely send back SAR observations over the Samoan Island chain. The pass above show GOES-18 Clean window imagery (10.3 µm) with SAR winds overlain.

A zoomed-in view of the SAR winds to the west of Samoa shows how parallax must be considered. GOES-18 navigation assumes clear skies, and if a tall (GOES-18 cloud-top heights — not shown — diagnose heights exceeding 44000 feet) cumulonimbus cloud is present, it will be navigated such that it is displayed farther from the sub-satellite point (0^oN, 137.2^oW) than its true position. Ice within that cumulonimbus cloud is likely altering the SAR return so that stronger winds are diagnosed. As noted in previous SAR blog posts, the presence of ice can be inferred by feathery features within the Normalized Radar Cross Section (NRCS).

The image below toggles between the NRCS and Wind Speed (from this page) and highlights the feathery structures (suggestive of thick ice within the cumulonimbus cloud) in the regions of strongest diagnosed winds. Note that the wind direction is northerly, and a wind shadow is obvious to the south of Savai’i (Salafai).

Part of the earlier of the SAR observations on this ascending Sentinel-1A pass is shown below. The coldest cloud top, in the northeastern part of the domain (orange/red enhancement) also shows a parallax shift away from the GOES-18 sub-satellite point (at about 137.2^oW) such that the cold cloud top is shifted west of the strong SAR winds (40-50 knots in the white enhancement) that are likely an artifact of the ice within that cloud. The large area of strong winds (20-25 knots, yellow/green in the color enhancement) over the center of the domain do not arise from cloud ice.

A toggle between NRCS and wind speed at 06:00:18 is shown below.

MetopC ascended over the Samoan islands after 0900 UTC on 13 March 2023, and Advanced Scatterometer (ASCAT) winds from that pass are shown below. ASCAT also diagnoses relatively weak winds just south of Western Samoa, 20-25 knot winds south of the lighter winds.

---

Dora Meredith from the NWS Forecast Office in Pago Pago asked the excellent question: Would the Parallax shift be different from Himawari-9? GOES-18 is over the equator at 137^oW, about 35^o east of the Samoan Islands, and Himawari-9 is over the equator at 140.7^oE, about 45^o west of the Samoan Islands. The toggles below shows two examples of SAR winds south of Samoa in three panels; the right panel also showing GOES-18 Band 13 infrared imagery — and a parallax shift in the imagery to the west, away from GOES-18’s sub-satellite point is apparent; the left panel shows Himawari-9 Band 13 infrared imagery — and a parallax shift in the imagery to the east, away from Himawari-9’s sub-satellite point is likewise apparent.

View only this post Read Less

1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) included an overlay of GLM Flash Extent Density — which showed thunderstorms that produced flash flooding, hail and an EF-1 tornado (SPC Storm Reports) in the Central Valley of California on 11 March 2023. At 2236 UTC (1 minute prior to the Tornado Warning being issued), an overshooting top along the Calaveras/Tuolumne County line exhibited an infrared brightness temperature of -53.3ºC — which roughly corresponded to the altitude of a Most Unstable Maximum Parcel Level (MU MPL) as analyzed from the 0000 UTC Oakland rawinsonde (source).  Note that for the relatively low-topped convection over California on this day, the coldest value of the default infrared enhancement was modified to -70ºC, to aid in the identification of colder overshooting tops (shades of white embedded within dark black regions).

The corresponding GOES-18 Cloud Top Height derived product at 2236 UTC — just before the issuance of the Tornado Warning — was around 32,482 feet (below). For this storm, the maximum value of the default Cloud Top Height enhancement was set to 35,000 feet.

During the period leading up to convective initiation of the hail/tornado-producing thunderstorm, 1-minute GOES-18 Visible and Infrared images (below) include contours of LightningCast Probability — a >50% LightningCast Probability (green contour) over western San Joaquin County at 2009 UTC provided a 17-minute lead time to the start of a prolonged period of GLM-indicated lightning activity for that storm, which commenced at 2026 UTC (2000 – 0100 UTC animation).

These thunderstorms developed in an environment of modest moisture and instability, as shown by 1-minute GOES-18 Visible and Infrared images combined with Total Preciptitable Water (TPW) and Convective Available Potential Energy (CAPE) derived products in cloud-free areas (below). Satellite-derived TPW values up to 0.90 inch and CAPE values as high as 400 J/kg were observed in the general vicinity of the strongest convection. Note that the default enhancements for TPW and CAPE were also modified for use with these particular storms — the maximum TPW value was set at 1.1 inches, while the maximum CAPE value was set at 500 J/kg.

We have determined a brief EF-1 tornado touched down 6SW of Tuttletown in Tuolumne County during yesterday's severe thunderstorms that also produced 1" hail and significant flash flooding. See map and press release for more info. #CAwx pic.twitter.com/bEHYHzolI4

— NWS Sacramento (@NWSSacramento) March 12, 2023

View only this post Read Less