Arctic « CIMSS Satellite Blog

Ice leads in the Beaufort Sea

December 20th, 2020 | Scott Bachmeier

Suomi NPP VIIRS Infrared Window (11.45 µm) images [click to play animation]

Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed widespread ice leads in the Beaufort Sea during the 18 December – 20 December 2020 period. Some existing leads increased in width and/or length as they migrated westward, while some new leads were seen to form as land-fast ice fractured off the coasts of Alaska and larger islands of the Canadian Arctic Archipelago.

Suomi NPP VIIRS Infrared images with plots of NAM12 model surface winds on 20 December (below) indicated that the ice lead motion was influenced by surface wind stress — which also played a role in the clockwise flow of the Beaufort Gyre (the primary influence of ice lead motion in that part of the Arctic Ocean).

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of NM12 model surface winds [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of NAM12 model surface winds [click to enlarge]

CIMSS Scientists are working on a Machine-learning Ice Lead detection method, as described here. The toggle below compares the MODIS and VIIRS computations of Ice Leads on 18 December 2020. Leads in this toggle are white; greys are suspected leads, but the detection algorithm ultimately could not confirm their presence. At present, the algorithm is challenged when leads are moving, as in this example. Note that Banks Island, on the right edge of the animation above, is in the lower left corner in the toggle below.

MODIS and VIIRS-derived ice lead information, 18 December 2020 (Click to enlarge)

Posted in Arctic, Suomi NPP, VIIRS | No Comments »

GOES-17 IFR Probability fields are now being created for Alaska

October 15th, 2020 | Scott Lindstrom

GOES-17 IFR Probability fields over Anchorage AK and surroundings, 0200 – 1300 UTC on 15 October 2020 (Click to animate)

CIMSS is now producing IFR Probability fields (and Low IFR Probability, Marginal VFR Probability, and Cloud Thickness fields) using GOES-17 data. (Recall that GOES-16 IFR Probability fields are now produced by NOAA/NESDIS and are distributed via the Satellite Broadcast Network (SBN) to National Weather Service Forecast Offices. GOES-16, however, does not view Alaska). GOES-17 fields will presently be available via an LDM pull. NOAA/NESDIS will likely start processing the fields in 2021.

The animation above shows IFR Probability fields today over the Anchorage region. The animation is preceded by a view of the topographic features, and IFR conditions on 15 October seem centered on topographic features.

GOES-17 can view the North Slope of Alaska. This location is quite far from the GOES-17 sub-satellite point, so resolution is degraded from the nadir 2-km views. However, regions of likely IFR conditions are easily tracked (Again, the animation is preceded by topography), with a large region between the Arctic Ocean and the high terrain of the Brooks Range.

GOES-17 IFR Probability fields over northern Alaska, 0200 -1300 UTC, 15 October 2020 (Click to animate)

GOES-17 views of Alaska southeast, below show probabilities of low clouds and reduced visibility. As over other regions of Alaska today, highest probabilities are over high terrain. GOES-17 IFR Probability for the PACUS domain is available at this website. Work is ongoing to insert IFR Probability (from GOES-16 and GOES-17) into Real Earth.

GOES-17 IFR Probability fields over Alaska Southeast, 0200 -1400 UTC, 15 October 2020 (Click to animate)

GOES-17 fields contain artifacts in the form of horizontal stripes that can be traced to the poorly-functioning Loop Heat Pipe on GOES-17. GOES-17 is now in a reduced-scanning mode between 0600 and 1200 UTC to enhance the ability of the satellite to shed excess heat: fewer Mesoscale sectors are scanned, full disk sectors are not as frequent (every 15 minutes instead of every 10), and the ‘PACUS’ sector is not scanned. This scanning strategy will continue through the end of October.

The Forecast Decision Training Division has a Quick Guide on IFR Probability fields here. A 20-minute YouTube video explaining the product is here.

Posted in Arctic, Fog detection, GOES-17 | No Comments »

Cutoff low over northern Alaska

June 12th, 2020 | Scott Bachmeier

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red [click to play animation | MP4]

GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm) images (above) showed the circulation of an anomalous middle-tropospheric cutoff low over the northwestern portion of Alaska on 12 June 2020. A Potential Vorticity (PV) anomaly associated with this low was causing the dynamic tropopause — represented by the pressure of the PV1.5 surface — to descend as low as the 500 hPa pressure level.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red and available NUCAPS sounding profiles denoted by green/yellow points [click to enlarge]

Just after 21 UTC, an overpass of the Suomi NPP satellite provided NUCAPS soundings (above) within much of the core of the cutoff low — the green NUCAPS sounding profile about 40 miles east/southeast of the 500 hPa PV1.5 pressure contour (below) displayed an apparent tropopause near the 400 hPa pressure level.

NUCAPS sounding profile [click to enlarge]

GOES-17 “Red” Visible (0.64 µm) images (below) revealed the development of numerous showers and thunderstorms across the Brooks Range and North Slope of Alaska, aided by instability beneath the cutoff low.

GOES-17 “Red” Visible (0.64 µm) images, with hourly surface reports plotted in red [click to play animation | MP4]

A higher spatial resolution view of these showers and thunderstorms was provided by a sequence of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP, as viewed using RealEarth (below). A few of these thunderstorms moved toward the Arctic Coast, with one fairly impressive storm just southwest of Katovik which exhibited cloud-top infrared brightness temperatures near -60ºC (red enhancement) around 23 UTC.

VIIRS True Color (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

Summer thunderstorms stretched across the North Slope and near the Arctic Coast today. Data from the GLD360 depicted over 800 Cloud-to-Ground lightning events in the area! Here is the scene at Atqasuk, Utqiagvik, Nuiqsut, and Deadhorse this afternoon and evening. #akwx #lightning pic.twitter.com/tGeqswONW5

— NWS Fairbanks (@NWSFairbanks) June 13, 2020

Posted in Arctic, GOES-17, NOAA-20, NUCAPS, RealEarth, Red-Green-Blue (RGB) images, Suomi NPP, VIIRS | No Comments »

High-altitude waves over the Arctic

March 27th, 2020 | Scott Bachmeier

GOES-17 “Ozone” (9.61 µm) images, with rawinsonde sites plotted in yellow [click to play animation | MP4]

GOES-17 (GOES-West) “Ozone” (9.61 µm) images (above) revealed waves propagating northwestward over northern Alaska, northern Yukon and the adjacent Beaufort Sea during the pre-dawn hours on 27 March 2020. That area was too illuminated by either aurora borealis or the rising sun — so Suomi NPP VIIRS Day/Night Band (0.7 µm) imagery could not confirm the presence of mesospheric airglow waves (see this blog post for some examples).

A plot of the GOES-17 “Ozone” spectral band weighting function — calculated using 12 UTC rawinsonde data from Fairbanks, Alaska — showed a peak contribution from within the stratosphere at the 39 hPa pressure level, corresponding to an altitude around 21 km (below).

Plot of GOES-17 “Ozone” (9.61 um) weighting function, calculated using 12 UTC rawinsonde data from Fairbanks, Alaska [click to enlarge]

The curious aspect of these waves was their northwestward propagation — rawinsonde data from 3 sites across the region (below) indicated that the winds aloft within the upper troposphere and throughout the stratosphere were strong northwesterly, which meant the waves were moving against the ambient flow. Lacking a coherent, science-based explanation for these wave features, this blog post earns its place in the “What the heck is this?” category.