Snow melt across the Upper Midwest

March 12th, 2019 |

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm) images, with hourly plots of surface temperature [click to play animation | MP4]

GOES-16 (GOES-East) Near-Infrared “Snow/Ice” (1.61 µm) images (above) revealed a darkening signature resulting from a brief period of snow melt during the daytime hours on 12 March 2019. As a southerly flow of warm air (coupled with abundant solar insolation) began to melt the top surface of the deep snow cover, its “water to ice crystal” ratio increased — making it appear darker, since water is a stronger absorber of radiation at the 1.61 µm wavelength. The northward progression of this snow melt signature was most obvious across eastern South Dakota into eastern North Dakota and far western Minnesota, but was also evident in western parts of the Dakotas as well as downwind of the Turtle Mountains along the North Dakota / Manitoba border.

GOES-16 Snow/Ice images centered over the North Dakota / South Dakota / Minnesota border region (below) provided a closer view of the progressive northward darkening of this snow melt signature. Also of interest was a packet of standing waves to the lee (northeast) of the Coteau des Prairies — downsloping flow contributed to localized warming and melting at that location early in the day. The effect of the arrival of southwesterly downslope flow at Sisseton (located approximately midway between Browns Valley and Veblen) was very apparent in a time series of surface data. In contrast, the warm-up was much more gradual and the wind speeds significantly lighter not far to the west at Aberdeen.

GOES-16 Near-Infrared "Snow/Ice" (1.61 µm) images [click to play animation | MP4]

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm) images [click to play animation | MP4]

An animation that cycles through GOES-16 Low-level Water Vapor (7.3 µm), “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice”  images is shown below — the standing waves were also evident in the Water Vapor imagery.

GOES-16 Low-level Water Vapor (7.3 µm), "Red" Visible (0.64 µm) and Near-Infrared "Snow/Ice" (1.61 µm) images [click to play MP4 animation]

GOES-16 Low-level Water Vapor (7.3 µm), “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images [click to play MP4 animation]

Hat tip to James Hyde for bringing this interesting signature to our attention.

Geo2Grid software package released

March 12th, 2019 |

All sixteen GOES-16 ABI Bands, and a True-Color image, at 1807 UTC on 11 March 2019, created with Geo2Grid (Click to animate)

SSEC and CIMSS have released a processing package that converts GOES-R Level-1b Radiance files to full-resolution imagery. Geo2Grid is part of the CSPP-Geo package and offers a flexible scriptable method to convert data into imagery. It can be downloaded at this site (Free registration may be required). Documentation is available at that site as well.

System requirements include CentOS 6. The software generates GeoTIFF images at full spatial resolution for the given sector; Full-disk Band 2 (0.64 µm) imagery, and generation of True Color imagery is the biggest test of the system. The self-contained software package is downloaded as a gzipped tarball. After uncompressing and untarring the file, it is ready to go. You can order GOES-R Radiance Files from CLASS and then ftp those data into a directory. Converting the Radiance files into imagery is straightforward:

$GEO2GRID_HOME/bin/geo2grid.sh -r abi_l1b -w geotiff -f /data-ssd/CLASS/CSPPCheck

The ‘r’ flag tells the program what data are being read (you can also read AHI data), the ‘w’ flag describes the output (GeoTIFF is the only option at present) and the ‘f’ flag describes where the downloaded data sits. This command will generate imagery at full resolution for all the files, and that means the Band 2 (the 0.5-km “Red” Band”) file will have different dimensions than teh 1-km Bands 1, 3 and 5, and from the other Bands. A flag is available to force all imagery to the same resolution:

-g MIN –match-resolution

Those two flags will generate a series of files with 2-km resolution. (Note that the long dash in front of ‘match-resolution’ is actually two short dashes; -g MAX would force files with 0.5-km resolution).

It’s also possible to subsect imagery by adding something like

–ll-bbox -105 30 -80 50.

Results from that subsecting is shown below. Note that the first image also includes map information that is added with other flags:

–add-coastlines –coastlines-resolution=h –coastlines-outline=red –add-borders –borders-resolution=h –borders-outline=red

See the documentation for more information.

All sixteen GOES-16 ABI Bands, and a True-Color image, at 1807 UTC on 11 March 2019, zoomed in over the midwestern United States, created with Geo2Grid (Click to animate)

At present, the Geo2Grid software does not annotate the image, although the GeoTIFF files typically have Band and Day/Time information within the filename. Imagery in the animations in this blog has been annotated using ImageMagick, a command like this one:

convert -font helvetica -fill yellow -pointsize 32 -draw “text 20,700 ‘GOES-16 ABI Band 05 1807 UTC 11 March 2019′” GOES-16_ABI_RadC_C05_20190311_180712_GOES-East.gif GOES-16_ABI_RadC_C05_20190311_180712_GOES-Eastannotated.gif

Other software packages can do similar annotation, of course.

NUCAPS Profiles across a Saharan Air Layer (SAL) Outbreak

March 12th, 2019 |

Split Window Difference imagery over the Atlantic Basin, 1800 UTC 11 March through 1800 UTC 12 March 2019 (Click to animate)

A Saharan Air Layer (SAL) outbreak is occurring over the eastern Atlantic Ocean on 11-12 March 2019. The animation above shows the Split-Window Difference (10.3 µm – 12.3 µm) (link, from this website) color-enhanced to accentuate in red/pink/white the regions where Saharan Dust has been lofted into the atmosphere. This outbreak has been developing — this animation (courtesy Arunas Kuciauskas, NRL in Monterey) from 0400 UTC on 8 March to 1400 UTC on 11 March of the DEBRA product (now the Dynamic Enhanced Background Reduction Algorithm, from this website) shows the dust originating west of a departing cyclone over northwest Africa).

NUCAPS Profiles sampled a region of the SAL on Tuesday 12 March, and those are shown below. (This has been discussed previously on this blog, here)  The swath of points is shown on top of a GOES-16 Red/Green/Blue image composite designed to highlight dust in pink. Sounding locations shown are denoted by the orange dot, and Precipitable Water associated with the sounding is indicated.  The accentuated mid-level drying associated with the SAL air, inferred by the pink in the RGB, is readily apparent.

GOES-16 Dust RGB at 1530 UTC on 12 March 2019 superimposed with NUCAPS sounding locations. Inset: NUCAPS Sounding in the location indicated by the orange dot. Total Precipitable Water for the sounding as indicated (Click to enlarge)


============= Update 13 March 2019 ==============

DEBRA dust product from MSG Seviri data, hourly from 0000 UTC on 11 March to 1500 UTC 12 March 2019 (Click to enlarge)

The animation above and the one below are courtesy Arunas Kuciauskas from the Naval Research Lab in Monterey CA. The Dynamic Enhanced Background Reduction Algorithm (DEBRA) dust product animation, above, is a product developed at both NRL and the Cooperate Institute for Research in the Atmosphere (CIRA) by Steve Miller. DEBRA was derived from the MSG SEVIRI dataset. The background is gray-scaled to enhance the yellow-shaded lofted dust. Brighter yellow shades suggest greater confidence that a pixel is dusty.

The animation below shows output from the ICAP model;  this is an Aerosol optical depth (AOD) prediction model that was initialized with data from 0000 UTC 11 March 2019; it provides 6-hourly forecasts of AOD (colored contours) through 0000 UTC on 16 March 2019.   This ICAP Multi Model Ensemble (ICAP MME) is a consensus style 550 nm aerosol optical thickness (AOT) forecast ensemble from the following systems: ECMWF MACC, JMA MASINGAR, NASA GSFC/GMAO, FNMOC/NRL NAAPS, NOAA NGAC,  Barcelona Supercomputing Centre NMMB/BSC-CTM and UK Met office unified model.

Aerosol Optical Depth predictions from the ICAP MME, 0000 UTC 11 March through 0000 UTC 16 March 2019 (Click to enlarge)

Suomi NPP overflew the leading edge of the SAL in the eastern Atlantic around 1500 UTC on 13 March 2019. The animation below shows the NUCAPS points superimposed on the GOES-16 Baseline Total Precipitable Water Product (very dry air is indicated) and on the Dust RGB that highlights the SAL in Red. Additionally, 6 NUCAPS Soundings are shown. They captured the very dry air associated with the SAL.  Total Precipitable Water estimates from the GOES Baseline Product and from the NUCAPS sounding are indicated.  The GOES moisture estimates are heavily constrained by GFS model data as the Advanced Baseline Imager (ABI) has only 3 infrared bands (at 6.19 µm, 6.95 µm and 7.34 µm, Bands 8, 9 and 10) that are sensitive to water vapor.  In contrast, the Cross-track Infrared Sounder (CrIS) on Suomi NPP has many more bands that are sensitive to Water Vapor.  More than 60 are used in the NUCAPS retrieval.

NUCAPS Sounding Points at 1520 UTC on 13 March 2019, along with Baseline Total Precipitable Water and the Dust RGB at 1515 UTC 13 March 2019. NUCAPS soundings at the points indicated are shown. Total Precipitable Water from GOES and from NUCAPS are indicated as well (Click to enlarge)