Blowing dust in southern Bolivia

July 4th, 2020 |

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

GOES-16 True Color RGB images (credit: Tim Schmit, ASPB/CIMSS) [click to play animation | MP4]

GOES-16 (GOES-East) True Color Red-Green-Blue (RGB) images created using Geo2Grid (above) showed plumes of blowing dust originating from dry river beds along portions of the Río Grande O Guapay and Río Parapetí in southern Bolivia on 04 July 2020. Strong northerly winds developed across that region, just east of the axis of a deepening trough of low pressure.

VIIRS True Color RGB images from Suomi NPP and NOAA-20 as visualized using RealEarth (below) provided a more detailed view at the blowing dust plumes.

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]

A plot of surface report data from Viro Viru International Airport, Santa Cruz de la Sierra — located not far to the north of the blowing dust plumes — showed northerly winds gusting as high as 36 knots (41 mph) at 20 UTC (below).

Plot of surface report data from Viro Viru International Airport [click to enlarge]

Plot of surface report data from Viro Viru International Airport [click to enlarge]

Thanks to Santiago Gassó for pointing out these dust features.

Saharan Air Layer dust reaches the Lesser Antilles, Puerto Rico and the Gulf of Mexico

June 21st, 2020 |

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in white [click to play animation | MP4]

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in white [click to play animation | MP4]

The major Saharan Air Layer dust outbreak (previously discussed here and here) continued its westward progression — and on 21 June 2020, GOES-16 (GOES-East) Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images (above) showed signatures of the dust (shades of tan to light brown in Split Window Difference, and shades of magenta in Dust RGB images) as it moved over the Lesser Antilles, the eastern  Caribbean Sea and Puerto Rico. Surface reports at Port of Spain, Trinidad and Tobago (plot | data) indicated a drop in visibility below 1/2 mile for several hours, until some of the airborne dust was scavenged by convective precipitation; farther to the north, dust restricted the visibility to 3 miles at Barbados (plot | data). At San Juan, Puerto Rico (plot | data) the surface visibility only dropped to 7 miles, as most of dust remained aloft.

GOES-16 True Color RGB images created using Geo2Grid (below) showed the characteristic tan hues of the dust plume during daylight hours (1000-2200 UTC).

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

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

===== 22 June Update =====

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth images, with surface reports plotted in white [click to play animation | MP4]

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth images, with surface reports plotted in white [click to play animation | MP4]

On 22 June, GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth (AOD) images (above) showed that the SAL dust had continued moving west, overspreading Puerto Rico, Hispaniola and much of the Caribbean Sea. Widespread AOD values of 1.0 to 1.8 were seen across that region.

A closer look at GOES-16 Split Window Difference and AOD images centered over Puerto Rico (below) revealed that the surface visibility was reduced to 3 miles at two sites in eastern Puerto Rico — and an AOD value of 2.0 was noted just south of San Juan TJSJ at 2201 UTC. The visibility was further reduced to 2-3 miles at nearby islands.

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth images, with surface reports plotted in white [click to play animation | MP4]

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Aerosol Optical Depth images, with surface reports plotted in white [click to play animation | MP4]



GOES-16 True Color RGB images (below) depicted the thick plume of dust.

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

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

A 9-day animation of a GOES-16 Split Window Difference “Saharan Air Layer product” covering the period 13-22 June 2020 (below) displayed the westward progress of the SAL plume (darker red to shades of white) across the Atlantic Ocean.

GOES-16 Split Window Difference "Saharan Air Layer product", 13-22 June [click to play animation | MP4]

GOES-16 Split Window Difference “Saharan Air Layer product”, 13-22 June [click to play animation | MP4]

===== 24 June Update =====

GOES-16 True Color RGB (daytime) and Dust RGB (nighttime) images, 08-24 June [click to play MP4 animation]

GOES-16 True Color RGB (daytime) and Dust RGB (nighttime) images, 08-24 June (credit: Tim Schmit, ASPB/CIMSS)  [click to play MP4 animation]

A 17-day animation of GOES-16 True Color RGB (daytime) and Dust RGB (nighttime) images during the period from 08-24 June (above) showed that (1) the primary strong SAL dust plume eventually reached the Gulf of Mexico on 24 June, (2) a second SAL dust plume emerged off the northwest coast of Africa on 22-23 June, and (3) the Dust RGB only exhibited a strong signature (brighter shades of magenta) for the most highly-concentrated areas of dust as they began to move westward off the coast of Africa — once the dust became more diffuse over the middle Atlantic, it lost a recognizable signature in the Dust RGB (while still retaining a good daytime signature in the True Color RGB).

A 12-day animation of GOES-16 Split Window Difference “Saharan Air Layer product” covering the period 13-24 June (below) also displayed the primary SAL plume reaching the Gulf of Mexico on 24 June, in addition to the secondary SAL plume emerging on 22-23 June.

GOES-16 Split Window Difference "Saharan Air Layer product", 13-24 June [click to play animation | MP4]

GOES-16 Split Window Difference “Saharan Air Layer product”, 13-24 June [click to play animation | MP4]

Saharan Air Layer dust continues to stream over the Atlantic Ocean

June 17th, 2020 |

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in blue [click to play animation | MP4]

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in blue [click to play animation | MP4]

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).

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

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

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.

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

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

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.

Plot of surface report data from Sal, Cape Verde [click to enlarge]

Plot of surface report data from Sal, Cape Verde [click to enlarge]

Plot of surface report data from Nauackchott, Mauritania [click to enlarge]

Plot of surface report data from Nauackchott, Mauritania [click to enlarge]

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

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

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

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.

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in blue [click to play animation | MP4]

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) and Dust RGB images, with surface reports plotted in blue [click to play animation | MP4]

Detection of Saharan Air Layer in the eastern Atlantic

June 15th, 2020 |

Color-enhanced GOES-16 Split Window Difference field, 1500 UTC on 15 June 2020 (Click to enlarge)

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 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 (Click to enlarge)

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 1600 UTC (Click to enlarge)

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.

GOES-16 Aerosol Optical Depth and GOES-16 Aerosol Type, 1600 UTC on 15 June 2020 (Click to enlarge)

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.

NUCAPS Sounding Locations overlain on top of Gridded NUCAPS field of 850 mb – 700 mb relative humidity (Click to enlarge)

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).

NUCAPS soundings at 1600 UTC in dry air, in the ribbon of moist air, and in dry air at the eastern edge of the NUCAPS swath.

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.

GOES-16 True Color imagery, 1730 UTC on 15 June 2020 (Click to enlarge)