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]

Inferring wind speed from ACSPO SSTs

June 17th, 2020 |

ACSPO Sea Surface Temperatures on 16 June 2020 from 1811 UTC (from Suomi NPP), 1903 UTC (from NOAA-20) and 1955 UTC (from Suomi NPP again) on 16 June 2020 (Click to enlarge)

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 at 0727 UTC on 17 June 2020 (from NOAA-20) (Click to enlarge)

ACSPO Sea Surface Temperatures at 1924 UTC on 15 June 2020 (from NOAA-20) (Click to enlarge)

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