Airborne glacial silt over the Gulf of Alaska

November 16th, 2013 |
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

Hat tip to Mark Ruminski (NOAA/NESDIS) for directing our attention to a pair of airborne glacial silt plumes that were being drawn southward over the far northern Gulf of Alaska on 16 November 2013. McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the two distinct hazy plumes as they were being advected offshore east of the Cordova, Alaska (PACV) area. The tight cyclonic circulation of a mesoscale area of low pressure may have helped to increase the speed of the gap winds that were lofting the glacial silt particles from the Copper River Delta and Icy Bay regions.

Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data (above) showed a better view of the 2 plumes at 21:23 and 23:04 UTC. The airborne glacial silt plumes appeared darker on the corresponding 3.74 µm shortwave IR images (below) due to enhanced solar reflection off the small particles.

Suomi NPP VIIRS 3.74 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images

MODIS Volcanic Ash Height product

MODIS Volcanic Ash Height product

MODIS-based products designed to monitor volcanic ash plumes were also able to detect the glacial silt plumes and provide quantitative information about these features. The mean plume height (above) was around 5000 feet, with a maximum around 9000 feet at some locations. The mean particle effective radius (below) was generally in the 4-7 µm range, with a maximum size of 9-10 µm.

MODIS Volcanic Ash Particle Effective Radius product

MODIS Volcanic Ash Particle Effective Radius product

 

Re-suspended ash from the Katmai volcano in Alaska

September 22nd, 2013 |
GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (above; click image to play animation) showed a distinct hazy plume streaming southeastward from the Katmai volcano area in Alaska on 22 September 2013. This was a signature of re-suspended volcanic ash — a deep layer of ash has remained on the ground near the volcano following the massive 1912 eruption — which was carried aloft by strong winds on the back side of a deep area of low pressure over the Gulf of Alaska (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

A closer view using a sequence of four Suomi NPP VIIRS 0.7 µm Day/Night Band images (below) showed the evolution of the ash plume as it moved over southeastward over Kodiak Island and then out over the Gulf of Alaska. Winds at Kodiak (station identifier PADQ) gusted as high as 55 knots or 63 mph. With limited snow cover and strong winds (which were enhanced by local terrain effects), the surface volcanic ash was easily lofted to great heights.

Suomi NPP VIIRS 0.7 µm Day/Night Band images

Suomi NPP VIIRS 0.7 µm Day/Night Band images

An image of a MODIS-based NOAA/STAR/CIMSS Volcanic Ash Height product is shown in combination with the Volcanic Ash Advisory that was issued by the Anchorage Volcanic Ash Advisory Center (below).

MODIS Ash Height product with Volcanic Ash Advisory

MODIS Ash Height product with Volcanic Ash Advisory

MODIS Ash Height product

MODIS Ash Height product

A sequence of three MODIS Volcanic Ash Height product images (above) suggested that the average height of the re-suspended ash plume was around 9,000 – 11,000 feet. A vertical profile of CALIPSO satellite-based lidar data near the source of the ash plume (below; courtesy of Mike Pavolonis, NOAA/NESDIS/STAR) indicated that the top of the plume was around 3.5 km or 11,000 feet (at 12:57 UTC, near latitude/longitude 58 N / 155 W).

CALIPSO total attenuated backscatter

CALIPSO total attenuated backscatter

The corresponding MODIS Ash Mass Loading product (below) indicated values of 2-3 tons per square kilometer existed over much of the ash plume.

MODIS Ash Mass Loading product

MODIS Ash Mass Loading product

Finally, the corresponding MODIS Ash Mass Effective Radius product (below) showed that much of the plume likely consisted of particles with radii in the 4-6 µm range, with a maximum value of 8.33 µm.

MODIS Ash Mass Effective Radius product

MODIS Ash Mass Effective Radius product

Additional information on the NOAA/UW-CIMSS GOES-R Volcanic Ash Products shown above can be found in this Java-based VISITview lesson (a separate Lesson Playback Control window will open to assist in viewing the lesson content).

===== 23 September Update =====

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

On the following day (23 September), a Suomi NPP VIIRS 0.7 µm Day/Night Band image (above) showed that the resuspended Katmai ash plume was still present, but was much less expansive than what was seen on 22 September.

Hat tip to Mark Ruminski of the NOAA/NESDIS Satellite Services Division for bringing this interesting event to our attention!

First snowfall of the season in northeastern Alaska

August 21st, 2013 |
Suomi NPP VIIRS 11.45 µm IR channel images (click image to play animation)

Suomi NPP VIIRS 11.45 µm IR channel images (click image to play animation)

AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel data (above; click image to play animation) showed the development of a cyclonic swirl of middle to high altitude clouds associated with an upper-level shortwave moving northward over northeastern Alaska on 20 August 2013. This disturbance helped to reinforce the northerly to northeasterly flow of unseasonably cold air across the Beaufort Sea and North Slope regions of Alaska, producing upslope winds along the Brooks Range — this scenario led to the first major snowfall of the season in northern Alaska, with eastern portions of the Brooks Range and North Slope regions receiving several inches of accumulation.

The first glimpse of snow cover appeared on a Suomi NPP VIIRS 0.7 µm Day/Night Band image at 11:57 UTC or 3:57 AM local time on 21 August (below), as clouds began to clear in the vicinity of Anaktuvuk Pass (PAKP) to Arctic Village (PARC) and points northward. The long and narrow bright streak seen over land in the western portion of the Day/Night Band image is the glow of the aurora borealis (note the lack of a signal there on the corresponding 11.45 µm IR channel image) — in contrast, the bright features seen over water in the eastern/northeastern portion of the Day/Night Band image were clouds becoming illuminated by the rising sun.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

A mid-day comparison of Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images at 20:14 UTC or 12:14 PM local time (below) revealed the areal extent of the fresh snow on the ground — new snow appeared as darker shades of red across the eastern Brooks Range and North Slope regions (in contrast to supercooled water droplet clouds, which appeared as varying shades of white). Snow depth reports ranged from 2-6 inches at 12 UTC. Note that clouds whose tops were composed of ice crystals also appeared as varying shades of red on the RGB image.

Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images

Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images

A comparison of two consecutive VIIRS false-color RGB images at 20:14 and 21:53 UTC (below) indicated that the outer edges of the snow cover were slowly melting, as surface air temperatures were able to recover into the 30s and 40s F over that region. With the combination of fresh snow cover, clearing skies, and light winds the morning low on 21 August was 23º F at Anaktuvuk Pass (PAKP); their high temperature on 20 August during the period of accumulating snow was just 36º F.

Suomi NPP VIIRS false-color Red/Green/Blue (RGB) images at 20:14 and 21:53 UTC

Suomi NPP VIIRS false-color Red/Green/Blue (RGB) images at 20:14 and 21:53 UTC

 

Summer Solstice in Alaska

June 21st, 2013 |
GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 (GOES-West) 0.63 µm visible channel images (above; click image to play animation) showed the cloud features over much of Alaska on 21 June 2013 (the day of the summer solstice). Record heat had been occurring across much of Alaska during the previous week, and Barrow (BRW) had a daily record high temperature of 62 F on 20 June. Note that there were numerous thunderstorms that developed over the Brooks Range and even over the North Slope regions of Alaska — on 20 June, over 4000 cloud-to-ground lightning strikes were detected. The haziness seen early in the animation was due to widespread smoke from wildfires that had been burning in southwestern Alaska a few days earlier.