CIMSS Satellite Blog

Comparing Gridded NUCAPS data to model fields

February 24th, 2020 | Scott Lindstrom

NUCAPS fields of 850-mb dewpoint Temperature toggled with NAM40 and RAP40 estimates at approximately the same time, ~1800 UTC on 24 February 2020 (Click to enlarge)

Gridded NUCAPS fields include 850-mb dewpoint temperature fields, and this blog post compares the NUCAPS fields to model fields, and this is part of an ongoing series of blog posts on these horizontal fields. The imagery above compares NUCAPS fields at 850 mb with NAM40 and RAP40 data over the southeastern part of the United States. Very dry air is indicated over the western Atlantic Ocean north and west of the Gulf Stream. There is generally good agreement between the NUCAPS and model fields. Model fields appear dryer (or NUCAPS fields are more moist). Model fields show a pronounced gradient over the upper midwest that, at this scan time, were too far west to be viewed by NUCAPS. (Click here to view the NUCAPS points — green, yellow and red — for this time, to show something about the data that has been input into the gridded fields).

However, the following pass from NOAA-20 (click here to view NOAA-20 orbit paths) included midwestern data. Again, the general good agreement is obvious, especially with regard to the placement of the gradient. Is the atmosphere as dry as the model suggests at 850 mb? That’s a hard question to answer given 1200 UTC Soundings at Omaha, Minneapolis/Chanhassen, and Green Bay. Note that NAM12 and RAP13 data are being shown in this example; they gave mostly the same answer as NAM40/RAP40 used above.

NUCAPS fields of 850-mb dewpoint Temperature toggled with NAM12 and RAP13 estimates at approximately the same time, ~1900 UTC on 24 February 2020 (Click to enlarge)

Posted in NOAA-20, NUCAPS, Training | No Comments »

Blowing dust across the Canary Islands and Atlantic Ocean

February 23rd, 2020 | Scott Bachmeier

GOES-16 “Red” Visible (0.64 µm) images, with plots of hourly surface reports [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the onset of a 2-day event of dense plumes of blowing sand/dust known locally as a Calima — with Western Sahara and Morocco being the primary source regions — which moved across the Canary Islands and the adjacent East Atlantic Ocean on 22 February 2020. Along the coast of Morocco, surface visibility was reduced to 1/8 mile at Tan-Tan (GMAT); over the Canary Islands, visibility dropped to 1/4 mile at Gran Canaria (GCLP).

GOES-16 Dust Red-Green-Blue (RGB) images spanning the period 0800 UTC on 22 February to 2100 UTC on 23 February (below) provided a continuous day/night visualization of the first dust plume (shades of pink/magenta). During the day on 23 February, a second dust plume could be seen emerging from below a patch of mid/high-altitude clouds. The RGB images were created using Geo2Grid.

GOES-16 Dust RGB images [click to play animation | MP4]

VIIRS True Color RGB images from Suomi NPP and NOAA-20 as viewed using RealEarth (below) revealed orographic waves in the airborne sand/dust downwind (northwest) of some of the Canary Islands on 23 February.

VIIRS True Color RGB images from Suomi NPP and NOAA-20 [click to enlarge]

This sand/dust was being lofted by anomalously-strong lower-tropospheric winds — which were up to 5 standard deviations above the mean at the 925 hPa pressure level (below).

925 hPa wind speed anomaly during the period 00 UTC on 22 February to 00 UTC on 24 February [click to enlarge]

===== 24 February Update =====

GOES-16 Dust RGB images [click to play animation | MP4]

GOES-16 Dust RGB images on 24 February (above) showed the second major pulse of sand/dust curling around the northern periphery of the offshore cutoff low pressure system. Toward the end of the animation, another minor pulse could be seen streaming northwestward off the coast of Western Sahara. A longer animation from 08 UTC on 22 February to 18 UTC on 24 February is available here.

A comparison of TROPOMI Aerosol Index, TROPOMI Aerosol layer height (meters), Meteosat-11 Natural Color RGB and Meteosat-11 Dust RGB images at 1515 UTC is shown below (credit: Bob Carp, SSEC). Note that the height of the center of the aerosol layer near the western tip of the plume was generally in the 500-1000 meter range (shades of blue to cyan).

Panel 1: TROPOMI Aerosol Index Panel 2: TROPOMI Aerosol layer height (meters) Panel 3: Meteosat-11 Natural Color RGB Panel 4: Meteosat-11 Dust RGB [click to enlarge]

TROPOMI Aerosol Index (top left), TROPOMI Aerosol layer height in meters (top right), Meteosat-11 Natural Color RGB (bottom left) and Meteosat-11 Dust RGB (bottom right) [click to enlarge]

GOES-16 Split Window Difference (10.3-12.3 µm) image, with plots of available NUCAPS profile points [click to enlarge]

A GOES-16 Split Window Difference (10.3-12.3 µm) image with plots of available NUCAPS profile points at 1600 UTC (above) denoted the locations of a sequence of 9 consecutive north-to-south sounding points through the western tip of the dust plume. Profiles of NUCAPS temperature and dew point data for those 9 points are shown below — the strong temperature inversion and dry air below 1 km at Points 6, 7 and 8 showed the presence of this dry, dust-laden air (and the Total Precipitable Water value dropped to a minimum value of 0.34 inch at Point 7).

Profiles of NUCAPS temperature and dew point data for Points 1-9 [click to enlarge]

Posted in Air quality, GOES-16, McIDAS-V, Meteosat, NOAA-20, NUCAPS, Other Satellites, RealEarth, Red-Green-Blue (RGB) images, Suomi NPP, VIIRS | No Comments »

Global True-Color Visible Imagery Animated

February 21st, 2020 | Scott Lindstrom

Prediction: this is the best animation you’ll see this week! SSEC is creating daily global composites of True-Color visible imagery. (Previous Blog Post) The animation below shows 1 image from each day between 6 March and 4 April 2019. The animation is also available as an animated gif, or as a YouTube video. Also, Tim Schmit has placed the animation within a container.

True-color visible imagery global montage from 6 March – 4 April 2019 (Click to play mp4 animation)

Posted in General interpretation, Red-Green-Blue (RGB) images | No Comments »

Gridded NUCAPS over the southeast United States

February 21st, 2020 | Scott Lindstrom

Analyzed snow depth at 0600 UTC on 21 February 2020 from the NOHRSC (Click to enlarge)

Snow fell over the southeastern United States, principally North and South Carolina, late on 20 February/early on 21 February 2020. This blog post, one in a series, investigates how gridded NUCAPS thermal fields perform in analyzing the rain/snow line. The snow totals are shown above, an image that was taken from this website at the National Operational Hydrologic Remote Sensing Center (NOHRSC).

NOAA-20 overflew the Carolinas shortly after 0700 UTC on 21 February, and gridded values of 950-mb, 900-mb and 850-mb Temperatures are shown below. (Note how the 950-mb field intersects the ground at the western edge of the Piedmont). The 0º C isotherm at 850 and 900 mb is close to the coast; it is sub-freezing over most of the land at those levels. The analysis from 950-mb shows cold air stretching southwestward from southeastern Virginia, and that region is also where the accumulating snow was focused. This is an argument in favor of the temperature fields in NUCAPS giving useful information about the rain/snow line.

850-mb, 900-mb, and 950-mb analyses of temperature derived from NUCAPS vertical profiles of temperature, 0723 UTC on 21 February 2020. The same color enhancement is used for each level, spanning -40º C to 30º C; 0º C is highlighted by the black line (Click to enlarge)

One of the gridded NUCAPS fields available in AWIPS via the Product Browser (there are many!) is the binary probability of a temperature occurring. The 850-mb binary probability of 0º C is close to the coast, at 900-mb, just slightly inland. The 950-mb values also suggest cold air is more likely over the region where snow fell. There are also some embedded cold pockets at 950 mb over interior North/South Carolina.

Conditional Probability of 0 C at 850, 900 and 950 mb, 0723 UTC on 21 February 2020 (Click to enlarge)

Note that gridded NUCAPS fields include data from infrared retrievals, microwave-only retrievals, and from retrievals that do not converge. The gridding can mask behavior in the vertical profiles that might not necessarily engender confidence in a meteorological analyst. The plot below shows NUCAPS points (Green points are infrared retrievals that successfully converged, yellow points are microwave-only retrievals, and red points occur where the microwave-only and infrared retrievals failed to converge; this is typically where precipitation is falling) plotted on top of the 850-mb temperature analysis. Note, however, that values do show up everywhere! Users of the gridded data should keep in mind the quality of the data that goes into the analysis when they use it. Two vertical soundings from which gridded data are derived are shown at bottom. Users can decide if they would use those vertical soundings in isolation.

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020 (Click to enlarge)

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020. Two soundings are also shown, from a green point and from a yellow point. Note that the plot also shows the binary probability of a temperature at 0º C (Click to enlarge)

Posted in NOAA-20, NUCAPS, Training, Winter weather | No Comments »