Alaska: a thunderstorm, single digits and a volcano

September 25th, 2018 |

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

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

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images (above) captured an unusually late thunderstorm that produced small hail at Anchorage PANC (surface observations) on 24 September 2018. The coldest cloud-top infrared brightness temperature was -53.8ºC, which was colder than the -46.3ºC tropopause temperature on the 00 UTC Anchorage sounding. This particular thunderstorm (Anchorage averages only 1-2 per year) even featured a wall cloud:



In far northeastern Alaska, snow cover across the North Slope and Brooks Range was evident in a sequence of Suomi NPP VIIRS Visible (0.64 µm) images (below). Since there were also areas of low cloud present (both north and south of the primary snow cover), the VIIRS Shortwave Infrared (3.74 µm) images could be used to discriminate between these low clouds — whose supercooled water droplets were effective reflectors of solar radiation, making then appear warmer or darker gray — and the cloud-free areas of snow cover.

Sequence of 4 Suomi NPP VIIRS Visible (0.64 µm) and Shortwave Infrared (3.74 µm) images [click to enlarge]

Sequence of 4 Suomi NPP VIIRS Visible (0.64 µm) and Shortwave Infrared (3.74 µm) images [click to enlarge]

The presence of this snow cover aided strong nighttime radiational cooling as a ridge of high pressure moved over the North Slope (surface analyses), and on the following morning temperatures dropped as low as 4ºF (the temperature later reached 3ºF at Toolik Lake):

Finally, along the Alaska Peninsula, Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images revealed the bright glow and hot thermal signature of the ongoing eruption of Mount Veniaminof at 1204 UTC and 1344 UTC (below).

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 1204 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 1204 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 1344 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 1344 UTC [click to enlarge]

Coincidentally, on this day GOES-17 began a test of Mode 6 operation which performs a Full Disk scan every 10 minutes. Although the Alaska Peninsula was on the extreme northwest limb of the Full Disk scan, Veniaminof’s thermal anomaly or “hot spot” (darker black pixels) could still be detected and monitored at 10 minute intervals using Shortwave Infrared (3.9 µm) imagery (below). However, an increase in layered cloud cover southeast of that area later in the day (in tandem with the extreme satellite view angle) eventually masked the warm thermal signature — a more direct view from overhead with Suomi NPP VIIRS still showed a very hot volcano summit (96.9ºC) at 2156 UTC.

GOES-17 Shortwave Infrared (3.74 µm) images [click to play animation | MP4]

GOES-17 Shortwave Infrared (3.74 µm) images [click to play animation | MP4]

Since there were no significant ash emissions from Mount Veniaminof on this day, no volcanic signature was evident on GOES-17 “Red” Visible (0.64 µm) imagery (below).

GOES-17

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

* GOES-17 images shown here are preliminary and non-operational *

Eruption of the Sierra Negra volcano in the Galapagos

July 1st, 2018 |

GOES-16 False Color RGB images [click to play animation]

GOES-16 False Color RGB images [click to play animation]

GOES-16 (GOES-East) False Color Red-Green-Blue (RGB) images from the NOAA/CIMSS Volcanic Cloud Monitoring site (above) showed another eruption of the Sierra Negra volcano on the Galapagos, which began late in the day on 01 July 2018. Since the volcanic plume was rich in SO2, it exhibited a cyan appearance in the RGB imagery.

As was demonstrated following the 26 June eruption, GOES-16 Low-level Water Vapor (7.3 µm) imagery (below) can also be used to initially track volcanic plumes that have high concentrations of SO2.

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play animation | MP4]

GOES-16 Low-level Water Vapor (7.3 µm) images [click to play animation | MP4]

Eruption of the Sierra Negra volcano in the Galapagos

June 26th, 2018 |


GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm), Mid-level Water Vapor (6.9 µm) and Low-level Water Vapor (7.3 µm) images beginning late in the day on 26 June 2018 (below) showed that a signature of the volcanic plume was evident in the 7.3 µm imagery for several hours after it was no longer seen in the 10.3 µm or 6.9 µm imagery — this is due to the fact that the 7.3 µm spectral band is also sensitive to SO2 absorption (and this volcanic eruption produced large amounts of SO2).

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm, top), Mid-level Water Vapor (6.9 µm, middle) and Low-level Water Vapor (7.3 µm, bottom) images [click to play animation | MP4]



Lava flows continue from Kilauea’s Lower East Rift Zone

June 18th, 2018 |

NOAA-20 VIIRS Day/Night Band (0.7 µm), Shortwave Infrared I04 (3.75 µm), Shortwave Infrared M13 (4.05 µm) and Longwave Infrared (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm), Shortwave Infrared I04 (3.75 µm), Shortwave Infrared M13 (4.05 µm) and Longwave Infrared (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm), Shortwave Infrared I04 (3.75 µm), Shortwave Infrared M13 (4.05 µm) and Longwave Infrared (11.45 µm) images (above) showed signatures of the ongoing lava flows from the Lower East Rift Zone of the Kilauea volcano on the Big Island of Hawai’i at 1225 UTC (2:25 am local time) on 18 June 2018.

Note how the central ribbon of hottest lava flow (which continues its active ocean entry) saturated the I04 3.75 µm image, causing a “wrap-around” effect to display cold brightness temperatures (white pixels) — although the M13 4.05 µm band has a lower spatial resolution, it saturates at much higher temperatures, and sensed brightness temperatures in the 480 to 557 K range. The Infrared images also showed evidence of steam clouds flowing southward over the adjacent offshore waters.

A webcam image from near Kapoho (PGcam) around the time of the NOAA-20 VIIRS images is shown below. The active Fissure 8 is near the center of the image.

Webcam image from near Kapoho [click to enlarge]

Webcam image from near Kapoho [click to enlarge]

VIIRS imagery and webcam capture courtesy of William Straka (CIMSS).