Blowing dust across the Canary Islands and Atlantic Ocean

February 23rd, 2020 |

GOES-16

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]

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]

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]

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 [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 Dust RGB animation from 08 UTC on 22 February to 18 UTC on 24 February is available here.

In addition to the Dust RGB, signatures of the airborne sand/dust were also evident in GOES-16 Split Window Difference (10.3-12.3 µm) and Split Cloud Top Phase (11.2-8.4 µm) imagery (below). This arises from the fact that silicates (sand/dust particles) have different energy absorption characteristics at varying wavelengths.

GOES-16 Dust RGB, Split Window Difference (10.3-12.3 µm) and Split Cloud Top Phase (11.2-8.4 µm) [click to play animation | MP4]

GOES-16 Dust RGB, Split Window Difference (10.3-12.3 µm) and Split Cloud Top Phase (11.2-8.4 µm) images [click to play animation | MP4]

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 image, with plots of available NUCAPS profile points [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]

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

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