As a follow-up to this 15 June blog post, GOES-16 (GOES-East) Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB (Red-Green-Blue) images (above) displayed signatures of another dense plume of Saharan Air Layer dust — which appeared as shades of yellow in the Split Window Difference images, and shades of magenta in the Dust RGB images — that was streaming westward off the coast of Africa and moving over the Cape Verde Islands and the eastern Atlantic Ocean from 0600 UTC on 17 June to 0020 UTC on 18 June 2020. This renewed pulse of dust was caused by an anomalously strong easterly wind burst within the lower troposphere.

GOES-16 True Color RGB images created using Geo2Grid (below) showed the characteristic tan hues of the dust plume during daylight hours (0800-1850 UTC).

True Color RGB images from NOAA-20 and Suomi NPP as viewed using RealEarth (below) provided views of the dust plume at 14 UTC and 15 UTC. Note that the core of the dust plume moved directly over the Cape Verde Islands.

Plots of surface report data from Sal, Cape Verde (GVAC) and Nauackchott, Mauritania (GQNO) are shown below. The surface visibility dropped below 1 mile at Sal, Cape Verde from 16-18 UTC — and along the coast of Africa at Nauackchott, Mauritania the arrival of the dry easterly winds was very evident in the sharp drop of dewpoint temperatures after 09 UTC.

===== 18 June Update =====

On the following day, GOES-16 True Color RGB images (above) showed that the dust plume had moved a bit farther west and northwest. A longer 2-day (17-18 June) animation of GOES-16 Split Window Difference and Dust RGB images is shown below.

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The animation above shows Advanced Clear-Sky Processor for Ocean (ACSPO) sea-surface temperatures at three different times on 16 June: 1811 UTC (using data from Suomi NPP), 1903 UTC (using data from NOAA-20) and 1955 UTC (using data, again from Suomi NPP). (Orbit paths for the satellites can be viewed here). Note that the default color map bounds for these images has been changed to be from 50º F to 90º F.

Compare the 3 images above to the 0727 UTC 17 June SST analysis, below, or to the SST analysis from 1924 UTC on 15 June 2020, at bottom. In all the analyses, mid-Gulf SSTs are fairly constant around 82º F. Shoal waters south of Louisiana or off the coast of southwest Florida show very warm temperatures on the 16th. This kind of near-shore warming can occur during the day when winds are weak and wave action is small. (The 3 surface charts from 1800 UTC on 14, 15 and 16 June, shown here, show a weakening in the winds with time over the northern Gulf of Mexico.) As winds and wind-driven waves slacken, the amount of turbulent mixing at the ocean surface decreases, allowing for the surface skin of the ocean to become very warm; that warmth is detected by the satellite. Winds and waves do not slacken in the central Gulf; vertical mixing in the top of the ocean in that region does not change. (The relationship between winds and sea surface temperatures has been discussed on this blog in the past; see here, for example.)

Large diurnal changes in near-shore sea-surface temperatures very often indicate slack winds and small waves.

ACSPO Sea-Surface Temperatures are available via an LDM feed from CIMSS. They are computed from Direct-Broadcast data downloaded via antennas in Madison.

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GOES-16 Split Window difference (SWD) fields, above, and Meteosat Dust RGB imagery (both from 1500 UTC on 15 June 2020, and available at this site) suggest that a Saharan Air Layer (SAL) event is developing in the eastern Atlantic Ocean.  (Click here to see an animation of the Split Window Difference; AWIPS note: the default SWD enhancement has been replaced in the animation by the Grid/Low-Range Enhanced field) The dry, dusty air associated with SALs has an impact on air quality in the Caribbean, and it also suppresses tropical cyclone activity.  What other satellite products can be used to track this feature?

The 4-panel images below includes GOES-16 Aerosol Detection (upper left), GOES-16 Dust RGB (upper right), GOES-16 Split-Window Difference (10.3 µm – 12.3 µm) (lower left), and gridded NOAA-Unique Combined Atmospheric Processing System (NUCAPS) 850-700 mb Relative Humidity at 1550 UTC`and 1600 UTC. GOES-16 Aerosol Detection can detect SAL layers because of the suspended dust in the atmosphere. Both the Dust RGB and Split Window difference fields detect the SAL because of the differential absorption of infrared radiation at 10.3 µm and 12.3 µm by silicates within the dust. 

The bright pink in the Dust RGB is characteristic of dust detection with that product, and it shows a strong feature emerging from Africa.  The Split Window difference (SWD) field shows the SAL region to be blue to brown;  note that SAL air is indicated over the central Atlantic as well.  The yellow/orange/red enhancement in the SWD (bracketed by blue regions in the enhancement that suggest dry air) between 30º and 40º W Longitude, and 10º and 20º N Latitude, suggests more moisture in the air there.

Aerosol Optical Depth is higher in the SAL air because of the suspended dust.  Relatively cleaner air is north and south of the feature.  The low-level Relative Humidity in the SAL air is low.  This is more easily seen in the later image — 1600 UTC with this ascending NOAA-20 pass — than in the earlier (1550 UTC) image.  (Click here to see a toggle of both gridded NUCAPS fields).

GOES-16 Aerosol Products, below, identify both the region of higher Aerosol Optical Depth (AOD), and the type of Aerosol (in this case:  Dust) that is responsible for the higher AOD values.

The plot below shows the location of the NUCAPS points for the early afternoon swath in the eastern Atlantic. The points overlay the 850 mb – 700 mb relative humidity fields. Note the dryness at the eastern edge of the image, near 30º W; a skinny tongue of moisture (cyan in the moisture enhancement) extends to the north (corresponding to the region in the SWD where yellow/orange/red colors suggest more moisture), with dry air north and west of that moisture, near 45º W.

The three soundings below show the dry air to the north and west (13º N, 42.5º W), the relative moisture in the middle (13.5º N, 36.5º W), and the dry air to the east (13.5º N, 31º W).

True-color imagery (an example computed using CSPP-Geo is shown below from 1710 UTC) can also be used to track dust.  Dust in true color has a much different presentation than adjacent clear(er) skies.

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1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed the smoke plume and thermal anomaly (cluster of hot pixels) associated with the Magnum Fire in northern Arizona on 12 June 2020. The hottest Shortwave Infrared brightness temperatures observed were 138.7ºC (411.9 K), which is the saturation temperature for those ABI detectors. Near and immediately downwind of the fire source region, brighter-white pyrocumulus clouds were seen penetrating the top of the darker gray smoke plume. About 50-60 miles north of the fire, the smoke plume drifted over Bryce Canyon, Utah (KBYC) — but the surface visibility there remained at 10 miles, indicating that the smoke remained aloft (and automated hourly reports listed an overcast layer at 9-12 kft from 03-05 UTC).

At 2112 UTC, the Suomi NPP VIIRS Fire Radiative Power product as viewed using RealEarth (below) revealed a maximum FRP value of 142.3 MW, and a band I4 (3.74 µm) infrared brightness temperature of 367 K.

On the following day (13 June), a veil of broken to overcast cirrus moved over the Magnum Fire for much of the day — but in 1-minute GOES-17 3.9 µm imagery, the fire’thermal anomaly was only completely masked for very brief periods when the clouds were at their maximum thickness (below).

Another view of the fire using 5-minute imagery from GOES-16 (GOES-East) provided quantitative products such as Fire Power, Fire Temperature and Fire Area (below) — these 3 products are components of the GOES Fire Detection and Characterization Algorithm (FDCA). These FDCA products are still being tested and evaluated using GOES-17 data before being released.

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