Solstice images of Antarctica and Alaska

December 21st, 2019 |

GOES-16

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

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed that most of Antarctica experienced 24 hours of full solar illumination during the Southern Hemisphere’s Summer Solstice on 21 December 2019. Through breaks in the cloud cover, a few bright areas of sun glint were also evident, moving from west to east, due to the reflection of sunlight off ice-free water.

In spite of receiving 24 hours of sunlight, interior areas of the continent remained quite cold — due to high elevation and deep snow cover. For example, surface air temperatures at station 8927 near the center of Antarctica remained within the -25 to -35ºF range on 21 December (source).

Surface air temperatures (ºF) at automated weather stations across Antarctica [click to enlarge]

Surface air temperatures (ºF) at automatic weather stations across Antarctica [click to enlarge]

In the Northern Hemisphere, GOES-17 (GOES-West) Visible images (below) revealed a few hours of illumination of the southern summits of Denali and nearby portions of the Alaska Range. Note the presence of much colder surface air temperatures (-20s and -30s F) north of the Alaska Range.

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]

Farther to the north across Interior Alaska, some locations reported minimum air temperatures in the -40s to -50s F. A Suomi NPP VIIRS Infrared image (below) showed surface brightness temperatures as cold as -50ºC or -58ºF (brighter yellow enhancement) in the Yukon Flats area around Fort Yukon (PFYU).

NOAA-20 VIIRS Infrared Window (11.45 µm) image at 2220 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) image at 2220 UTC [click to enlarge]

Stratus clouds affecting surface temperatures in Alaska

December 17th, 2019 |

GOES-17 Nighttime Microphysics RGB and

GOES-17 Nighttime Microphysics RGB and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

A comparison of GOES-17 (GOES-West) Nighttime Microphysics RGB and “Clean” Infrared Window (10.35 µm) images (above) showed the formation and motion of patchy stratus clouds (RGB shades of yellow) over Interior Alaska on 17 December 2019.  Note how the clouds are difficult to detect and track on the 10.35 µm images, since the temperatures of cold land surfaces and stratus cloud tops were similar. Since these high latitudes receive little to no sufficient solar illumination to allow useful visible imagery during the winter season, the RGB product can be a helpful tool for monitoring the evolution of such low clouds.

Plots of surface data from Bettles (PABT) and Fort Yukon (PFYU) (below) showed that the stratus cloud deck — with bases in the 6,000-10,000 feet range — had an impact on surface air temperature trends, with warming occurring as radiational cooling was slowed and/or reversed as the clouds moved overhead. Temperatures continued to rise at Bettles as the cloud coverage remained broken to overcast, while the temperature briefly dropped again at Fort Yukon as the cloud coverage thinned to scattered.

Plot of surface data from Bettles, Alaska [click to enlarge]

Plot of surface data from Bettles, Alaska (PABT) [click to enlarge]

Plot of surface data from Fort Yukon, Alaska [click to enlarge]

Plot of surface data from Fort Yukon, Alaska (PFYU) [click to enlarge]

Snowfall across northern Alaska

September 18th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog RGB and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog Red-Green-Blue (RGB) and and Day Cloud Phase Distinction RGB images (above) showed portions of the Brooks Range and eastern North Slope of Alaska that had significant snow cover on 18 September 2019. Some areas received 4-6 inches of snowfall during the previous day (a Winter Storm Warning had been issued, forecasting accumulations in the 4-8 inch range).

Snow cover appeared brighter white in the Visible images, and darker shades of gray in the Snow/Ice images; in the RGB images, snow was darker shades of red in the Day Snow-Fog, vs brighter shades of green in the Day Cloud Phase Distinction. Note that the Day Cloud Phase Distinction RGB provided sharper images than the Day Snow-Fog RGB (below), since the former makes use of higher spatial resolution 0.64 µm data for its Green component.

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

Although much of the Bettles (PABT) area was masked by cloudiness on 18 September, that site received moderate to heavy snow for a few hours on 17 September (below), and reported a snow depth of 4 inches at 17 UTC (9 am local time).

Time series of surface data from Bettles, Alaska on 17 September [click to enlarge]

Time series of surface observation data from Bettles, Alaska on 17 September [click to enlarge]


VIIRS imagery and NUCAPS profiles near the North Pole

August 22nd, 2019 |

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]

A sequence of 4 consecutive Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.4 µm) images (above) showed a small swirl of clouds associated with a weak area of low pressure near the North Pole — north of Greenland (surface analyses) — on 22 August 2019.

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

There were Suomi NPP NUCAPS soundings available in the vicinity of the surface low (above) — profiles from the 4 squared green dot locations (green dots indicate successful sounding retrievals from both the CrIS and ATMS instruments) which were closest to both the surface low and the North Pole (below) revealed characteristically-low arctic tropopause heights of around 7-8 km, and surface temperatures dropping to below freezing at the 2 most northerly points of 88.28º and 88.57º N latitude. Note: the Suomi NPP (SNPP) CrIS anomaly that began on 24 March 2019 was resolved via a switch to the redundant Side-2 electronics on 24 June — so CrIS data once again became available for incorporation into SNPP NUCAPS soundings beginning on 01 August. Training material for NUCAPS in AWIPS is available here.

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

According to GCOM-W1 AMSR2 data (source), this weak surface low was over a portion of the Arctic Ocean where sea ice concentration was still high (below).

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]