Blowing dust in the Arabian Sea

November 3rd, 2018 |

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Strong winds across southern Iran and Pakistan were lofting plumes of blowing sand/dust offshore over the Gulf of Oman and the Arabian Sea during 01 November, 02 November and 03 November 2018 — a sequence of daily composites of True Color Red-Green-Blue (RGB) images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS from RealEarth (above) showed the increase in dust transport during that 3-day period.

A comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November is shown below.

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Metop-A and Metop-B ASCAT data (source) showed surface wind speeds in the 20-25 knot range emerging from the coast where plumes of blowing dust were located (below).

Meop ASCAT surface scatteromete winds [click to enlarge]

Meop ASCAT surface scatteromete winds [click to enlarge]

EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm) images from 02 November and 03 November (below) showed the daily evolution of the dust plumes.

Meteosat-11 Visible (0.8 µm) images [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 02 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Blowing dust from the Copper River Valley in Alaska

November 1st, 2018 |

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Strong gap winds accelerating out of the Copper River Valley along the southern coast of Alaska were lofting fine particles of glacial silt/sand and transporting those aerosols southwestward across the Gulf of Alaska on 31 October and 01 November 2018. A sequence of NOAA-20 VIIRS True Color Red-Green-Blue (RGB) images viewed using RealEarth (above) showed that the plume was more widespread on 01 November.

A comparison of Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images (below) showed the plume at 2022 UTC on 01 November. The map overlay has been removed from one set of images, to better reveal the dust plume source region. Note that the plume appeared much warmer (darker shades of red)  in the Shortwave Infrared image — this is due to enhanced solar reflectance off the small dust particles. Since airborne dust is generally transparent at longer infrared wavelengths, only the thickest portion of the plume exhibited a subtle signature on the 11.45 µm image.

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

The surface visibility briefly dropped to 3 miles at Middleton Island (PAMD) around the time of the Suomi NPP VIIRS images. as gusty north-northeasterly winds carried the plume over that location (below). Although Cordova (station identifier PACV) is only about 20 miles northwest of the Copper River Delta, the localized gap winds did not affect that site (where wind speeds were 3 knots or less the entire day).

Time series plot of surface observations at Middleton Island [click to enlarge]

Time series of surface observations at Middleton Island [click to enlarge]

ASCAT surface scatterometer winds (source) from Metop-A and Metop-B (below) showed speeds in the 25-30 knot range where the gap winds were exiting the Copper River Delta.

Metop-A and Metop-B ASCAT surface scatterometer winds [click to enlarge]

Metop-A and Metop-B ASCAT surface scatterometer winds [click to enlarge]

A toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images (source) at 2204 UTC on 01 November (below) showed a subtle BTD signal within the more dense center portion of the plume, due to the silicate composition of some of the airborne particulate matter.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images [click to enlarge]

VIIRS Aerosol Optical Thickness (AOT) products from the eIDEA site (below) revealed larger AOT values on 01 November.

VIIRS Aerosol Optical Thickness product [click to enlarge]

VIIRS Aerosol Optical Thickness product [click to enlarge]

The gap winds were caused by a strong gradient between cold high pressure over Interior Alaska/Yukon and an occluding gale force low pressure system in the Gulf of Alaska (surface analyses: WPC)| OPC). GOES-15 (GOES-West) Visible (0.63 µm) images (below) showed the circulation of the low, and surface observations highlighted the cold air over snow-covered inland areas. While the dust plume was faintly apparent, it did not show up as well with the lower spatial resolution and large viewing angle of GOES-15.

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

A similar — though more prolonged and intense — event was noted in October 2016.

Blowing dust along the southwest coast of Greenland

October 14th, 2018 |

As noted by Santiago Gassó, a long and very narrow plume of airborne dust was evident just off the southwest coast of Greenland on 14 October 2018. Terra MODIS and Suomi NPP VIIRS True Color Red-Green-Blue (RGB) images as viewed using RealEarth are shown below. An exposed (free of snow cover) glacial outlet between Qeqertarsuatsiaat and Paamiut was the point source of the dust plume — the change in water colors (shades of cyan) highlighted the offshore flow of meltwater from this glacier into the Labrador Sea, which then began to curve northward within the West Greenland Current. The strong pressure gradient between high pressure over southern Greenland and a low pressure southeast of the island (surface analyses) along with a passing trough axis caused brisk northerly winds, which lofted the aerosols into the boundary layer.

Terra MODIS and Suomi NPP VIIRS True Color RGB images [click to enlarge]

Terra MODIS and Suomi NPP VIIRS True Color RGB images [click to enlarge]

The plume of aerosols was also apparent on GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (below). The appearance of the plume on 1.61 µm imagery was due to the bright color of the “glacial flour” particles, which were efficient reflectors of incoming solar radiation — this brighter signature showed up well against the dark appearance of the water (which strongly absorbs radiation at the 1.61 µm wavelength).

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm) images [click to play animation | MP4]

The plume of airborne dust was also seen on GOES-17 Visible and Near-Infrared images (below), although the viewing angle was less favorable than from GOES-16.

* GOES-17 images shown here are preliminary and non-operational *

GOES-17 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 Near-Infrared "Snow/Ice" (1.61 µm) images [click to play animation | MP4]

GOES-17 Near-Infrared “Snow/Ice” (1.61 µm) images [click to play animation | MP4]

Unfortunately, there were no surface observations in the vicinity of the plume source to indicate how strong the surface winds were blowing; the closest active reporting sites along the southwest coast of Greenland were Godthaab/Nuuk to the distant north and Narsarsuaq to the distant south (large-scale Near-Infrared image). However, Metop-B ASCAT winds (source) just offshore of the plume origin area were in the 30-40 knots range around 1440 UTC (below).

Metop-B ASCAT surface scatterometer winds [click to enlarge]

Metop-B ASCAT surface scatterometer winds [click to enlarge]

Hurricane Michael reaches Category 3 intensity

October 9th, 2018 |

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) image, with Metop-A ASCAT surface scatterometer winds [click to enlarge]

Metop-A ASCAT scatterometer data (above) showed surface wind speeds as high as 64 knots near the storm center while Michael was at Category 2 intensity just northwest of Cuba at 0307 UTC on 09 October 2018.

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0752 UTC (below; courtesy of William Straka, CIMSS) revealed transverse banding north of the storm center on the Infrared image, and mesospheric airglow waves propagating westward away from Michael on the Day/Night Band image.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

5-minute GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images from 0517-1332 UTC (below) showed a series of relatively brief convective bursts around the storm center, but in general Michael exhibited a somewhat disorganized appearance during that time period.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

After sunrise, 1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (below) revealed the gradual formation of a more well-defined eye during the day, with episodic clusters of convective “hot towers” developing in the southeastern and eastern portions of the eyewall — which then rotated around to the north and northwest of the eye. By 18 UTC Michael had intensified to a Category 3 storm.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

1-minute GOES-16 “Clean” Infrared Window images (below) indicated that infrared brightness temperatures associated with these hot towers were often as cold as -80º to -89ºC (violet to darker purple enhancement).

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

Michael had been encountering unfavorable deep-layer wind shear and had also been moving over a pocket of water with low Ocean Heat Content northwest of Cuba (below). However, once the hurricane began to move over waters having higher OHC in addition to warm Sea Surface Temperature, it gradually began to intensify from a Category 2 to a Category 3.

Ocean Heat Content and Sea Surface Temperature, with a plot of the track of Michael [click to enlarge]

Ocean Heat Content and Sea Surface Temperature, with the track of Michael [click to enlarge]