A Saharan Air Layer (SAL) outbreak is occurring over the eastern Atlantic Ocean on 11-12 March 2019. The animation above shows the Split-Window Difference (10.3 µm – 12.3 µm) (link, from this website) color-enhanced to accentuate in red/pink/white the regions where Saharan Dust has been lofted into the atmosphere. This outbreak has been developing — this animation (courtesy Arunas Kuciauskas, NRL in Monterey) from 0400 UTC on 8 March to 1400 UTC on 11 March of the DEBRA product (now the Dynamic Enhanced Background Reduction Algorithm, from this website) shows the dust originating west of a departing cyclone over northwest Africa).

NUCAPS Profiles sampled a region of the SAL on Tuesday 12 March, and those are shown below. (This has been discussed previously on this blog, here)  The swath of points is shown on top of a GOES-16 Red/Green/Blue image composite designed to highlight dust in pink. Sounding locations shown are denoted by the orange dot, and Precipitable Water associated with the sounding is indicated.  The accentuated mid-level drying associated with the SAL air, inferred by the pink in the RGB, is readily apparent.

============= Update 13 March 2019 ==============

The animation above and the one below are courtesy Arunas Kuciauskas from the Naval Research Lab in Monterey CA. The Dynamic Enhanced Background Reduction Algorithm (DEBRA) dust product animation, above, is a product developed at both NRL and the Cooperate Institute for Research in the Atmosphere (CIRA) by Steve Miller. DEBRA was derived from the MSG SEVIRI dataset. The background is gray-scaled to enhance the yellow-shaded lofted dust. Brighter yellow shades suggest greater confidence that a pixel is dusty.

The animation below shows output from the ICAP model;  this is an Aerosol optical depth (AOD) prediction model that was initialized with data from 0000 UTC 11 March 2019; it provides 6-hourly forecasts of AOD (colored contours) through 0000 UTC on 16 March 2019.   This ICAP Multi Model Ensemble (ICAP MME) is a consensus style 550 nm aerosol optical thickness (AOT) forecast ensemble from the following systems: ECMWF MACC, JMA MASINGAR, NASA GSFC/GMAO, FNMOC/NRL NAAPS, NOAA NGAC,  Barcelona Supercomputing Centre NMMB/BSC-CTM and UK Met office unified model.

Suomi NPP overflew the leading edge of the SAL in the eastern Atlantic around 1500 UTC on 13 March 2019. The animation below shows the NUCAPS points superimposed on the GOES-16 Baseline Total Precipitable Water Product (very dry air is indicated) and on the Dust RGB that highlights the SAL in Red. Additionally, 6 NUCAPS Soundings are shown. They captured the very dry air associated with the SAL.  Total Precipitable Water estimates from the GOES Baseline Product and from the NUCAPS sounding are indicated.  The GOES moisture estimates are heavily constrained by GFS model data as the Advanced Baseline Imager (ABI) has only 3 infrared bands (at 6.19 µm, 6.95 µm and 7.34 µm, Bands 8, 9 and 10) that are sensitive to water vapor.  In contrast, the Cross-track Infrared Sounder (CrIS) on Suomi NPP has many more bands that are sensitive to Water Vapor.  More than 60 are used in the NUCAPS retrieval.

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GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed a narrow filament of dry air over northern Wyoming and western South Dakota on the morning of 11 March 2019. A cold thermal signature of the Bighorn Mountains in northern Wyoming could be seen through this band of dry air — even on the Upper-level 6.2 µm imagery.

At 12 UTC the Rapid City SD (KUNR) sounding sampled this filament of dry air, but the Riverton WY (KRIW) sounding — even though it was closer to the Bighorn Mountains — did not, due to the presence of moist air throughout much of the middle/upper-troposphere over southern and central Wyoming. As a result, the Rapid City water vapor weighting functions peaked at a lower altitude than those for Riverton (below), thus enabling the Bighorn Mountain thermal signature to be seen. In the animation above, note how the mountain signature eventually became masked, especially in the 6.9 µm and 6.2 µm imagery, as the middle/upper-tropospheric moisture moved slowly northward during the day. As was the case over Riverton at 12 UTC, this high-altitude moisture absorbed upwelling surface radiation, then re-radiated it at the colder ambient temperature of the atmospheric layer where it existed.

A toggle between 6.2 µm Water Vapor images from GOES-17 (GOES-West) and GOES-16 at 1202 UTC  (above) showed that while the filament of dry air appeared very similar from both satellites, there was a bit of noise in the GOES-17 image. In a plot of the mean 6.2 µm brightness temperature difference between GOES-17 and GOES-16 (below), note that the difference began to increase shortly before 12 UTC as GOES-17 ABI Loop Heat Pipe cooling issues started to adversely affect instrument performance. The GOES-17/GOES-16 brightness temperature difference and GOES-17 ABI Focal Plane Module temperature can be monitored in real time here.

A comparison of Water Vapor weighting functions for GOES-17 vs GOES-16 (computed using Rapid City SD rawinsonde data) is shown below — the peak pressure (or altitude) of the weighting functions remained constant, but the infrared brightness temperature sensed from GOES-17 was slightly colder (a result of the slightly larger satellite viewing angle or zenith angle).

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A persistent northward transport of anomalously-warm air across the Bering Sea during the month of February 2019 led to an unusual loss of sea ice there — daily images of GCOM-W1 AMSR2 Sea Ice Concentration (source) from 01 February to 09 March (above) showed the northward retreat of ice from the Bering Sea into the Chukchi Sea. The ice reached its maximum northward extent on 04 March; northward ice motion was very pronounced during the 25-26 February and 27-28 February periods. In early March a synoptic pattern change then allowed cold arctic air to flow back toward the south, helping the ice concentration to begin increasing again in the northern portion of the Bering Sea.

Minimal cloudiness on 28 February allowed the northward flow of ice through the Bering Strait to be seen on GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (below).

Bering Sea ice extent for Mar 02 from @NSIDC data (210000 km²) is the lowest daily #seaice extent of record for the entire month of March & only 29% of 1981-2010 average. Previous lowest 214000 km² on Mar 09, 2018. #Arctic #akwx @Climatologist49 @ZLabe @YJRosen @ArcticResearch pic.twitter.com/IzjwGXELCL

— Rick Thoman (@AlaskaWx) March 3, 2019

Sea ice in the Bering Sea began the month of February with a near record low extent, and then near record southerly winds blew from a region of much above normal SSTs. On the left panel, red is southerly winds > +2.5 std. dev. above average. @AlaskaWx @IARC_Alaska pic.twitter.com/cUh6CdQqhd

— Brian Brettschneider (@Climatologist49) March 8, 2019

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GOES-16 (GOES-East) “Red” Visible (0.64 µm), “Clean” Infrared Window (10.3 µm), Cloud Top Height, Cloud Particle Size Distribution, and Cloud Phase (above) helped to characterize standing wave clouds that developed to the lee of the Appalachian Mountains on 07 March 2019. The primary standing wave rotor clouds were composed of smaller supercooled water droplets,  with “banner clouds” composed of larger/colder ice crystals forming downwind of the rotor clouds. For example, at 1637 UTC cloud particle sizes associated with the rotor clouds were as small as 3-10 µm (darker shades of purple).

GOES-16 Day Cloud Phase Distinction Red-Green-Blue (RGB) images from the AOS site (below) also identified the rotor clouds as supercooled water droplet features (brighter shades of white), with the banner clouds being identified as high-level ice (shades of pink) or glaciating (shades of green) features. An unrelated phenomena was the brief brightening of the bare ground across much of the Southeast US midway through the animation — a result of transient solar reflectance that is seen around the Spring and Autumn equinox.

In a comparison of 1-km resolution Terra MODIS Visible (0.65 µm), Near-Infrared “Cirrus” (1.37 µm), Shortwave Infrared (3.7 µm) and Infrared Window (11.0 µm) images at 1631 UTC (below), note that the standing wave rotor clouds appeared much warmer (darker gray) in the Shortwave Infrared images — this is due to the fact that small supercooled water droplets are very efficient reflectors of incoming solar radiation.

There were a few pilot reports of light to moderate turbulence in the general vicinity of the standing waves, especially around 14 UTC (below).

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