Arctic « CIMSS Satellite Blog

Thunderstorms over the Chukchi Sea and Beaufort Sea north of Alaska

July 12th, 2021 | Scott Bachmeier

Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images [click to play animation | MP4]

A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images (above) showed snapshots of thunderstorms over parts of the Chukchi Sea and the Beaufort Sea off the northern coast of Alaska on 12 July 2021. The coldest convective cloud-top infrared brightness temperatures were in the -30 to -40ºC range. Unusual aspects of these thunderstorms included their high latitude location over ice-covered waters — as far north as 75ºN latitude — and the large amount of cloud-to-surface lightning strikes that they produced.

There were 6 lightning strikes in Alaska today, and 159 over the sea ice in the Beaufort Sea. #akwx @AlaskaWx pic.twitter.com/PL8i17gR3Z

— Brian Brettschneider (@Climatologist49) July 13, 2021

Update on thunderstorms rumbling across across the Chukchi & Beaufort Seas on July 12. All this is occurring over high concentration sea ice as unstable air from Siberia is pushed eastward by a deep storm center farther north. #akwx #Arctic #lightning @Climatologist49 pic.twitter.com/8Ef78IOJRF

— Rick Thoman (@AlaskaWx) July 13, 2021

These thunderstorms were not surface-based — instead, they were forced by an approaching cold front (surface analyses) which helped to release elevated instability within the 500-300 hPa layer (below).

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with contours of NAM40 lapse rate within the 500-300 hPa layer [click to enlarge]

Rawnsonde data from Utqiagvik (PABR) were not available (due to ongoing equipment malfunction at that site) — but a NUCAPS profile near the southernmost cluster of convection around 15 UTC (below) showed the layer of instability aloft.

NUCAPS profile near thunderstorms off the northern coast of Alaska [click to enlarge]

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

Ice motion in Norton Sound, and an aircraft dissipation trail over the North Slope of Alaska

May 28th, 2021 | Scott Bachmeier

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

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

GOES-17 (GOES-West) “Red” Visible (0.64 um) images (above) showed the motion of ice within Norton Sound — inbound early in the day, transitioning to outbound later in the day — on 28 May 2021. This ice motion was likely driven primarily by tidal motions within the Sound; for example, a plot of tide height for Unalakeet (below) depicted rising tide (water moving into the Sound) from 04-20 UTC followed by falling tide (water moving out of the Sound) after 20 UTC.

Plot of tide height at Unalakeet, Alaska on 28 May [click to enlarge]

Farther inland over the Alaska North Slope, comparisons of Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images at 1838 and 2015 UTC (below) revealed the formation and subsequent expansion of an “aircraft dissipation trail”. As an aircraft — likely headed to or from Prudhoe Bay — flew through a relatively thin cloud layer composed of supercooled water droplets, it caused glaciation of supercooled water droplets along its flight path (which then fell out of the cloud as snow).

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

1-minute GOES-17 Day Cloud Phase Distinction RGB images created using Geo2Grid (below) showed the formation and growth of the aircraft dissipation trail.

GOES-17 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

===== 29 May Update =====

GOES-17 “Red” Visible (0.64 um) images, with plots of NAM12 model winds (green barbs) and Metop-A ASCAT winds (red bars) [ click to play animation | MP4]

GOES-17 “Red” Visible (0.64 um) images, with plots of NAM12 model surface winds (green barbs) and Metop-A ASCAT winds (red barbs) [click to play animation | MP4]

On the following day, 1-minute GOES-17 Visible images (above) showed a similar inbound/outbound diurnal shift in the direction of ice flow within Norton Sound. Plots of NAM12 model surface winds and Metop-A ASCAT surface scatterometer winds indicated that the ice motion was generally orthogonal to surface wind direction — which reaffirmed that tides were the primary factor influencing ice motion during those 2 days.

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

Cold temperatures across the North Slope of Alaska

February 4th, 2021 | Scott Bachmeier

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

Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) revealed a large area of cold surface infrared brightness temperatures across much of the North Slope of Alaska on 04 February 2021 — with the coldest IR temperature being -56ºC (darker shades of violet) about 30 miles south-southeast of Umiat (PAUM) on the 1221 UTC image. The surface air temperature at the nearby Umiat RAWS site around that time was -55ºF (-48.3ºC). Narrow fingers of cold air drainage into some of the river valleys along the northern slopes of the Brooks Range (topography) were also apparent.

The corresponding GOES-17 “Clean” Infrared Window (10.35 µm) images (below) also showed the large area of cold surface IR brightness temperatures, but the temperatures were not as cold (in the -40 to -50ºC range), and the small-scale signatures of various topographical features were not depicted.

GOES-17 “Clean” Infrared Window (10.35 µm) images [click to enlarge]

A toggle between Infrared Window images from Suomi NPP VIIRS and GOES-17 (10.35 µm) at 1223 UTC is shown below.

Infrared Window images from Suomi NPP VIIRS and GOES-17 (10.35 µm) at 1223 UTC [click to enlarge]

Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 (10.35 µm) at 1223 UTC [click to enlarge]

Posted in Arctic, GOES-17, Suomi NPP, VIIRS, Winter weather | No Comments »

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.