Gale-force low in the Gulf of Alaska

November 19th, 2018 |
GOES-17 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

GOES-17 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

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

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed the circulation associated with an occluded gale-force low in the Gulf of Alaska (surface analyses) which moved northward to a position just south of the Kenai Peninsula on 19 November 2018.

The 3 GOES-17 ABI Water Vapor bands sample radiation from different layers within the troposphere — the height and depth of these individual layers varies with changes in (1) the temperature/moisture profile of the atmosphere and (2) the satellite viewing angle (or zenith angle). The 3 water vapor weighting functions — calculated using 12 UTC rawinsonde data from Anchorage (PANC) — provide information on the height and depth of the radiating layers in the vicinity of the storm  (below).

GOES-17 Water Vapor weighting function plots for Anchorage, Alaska [click to enlarge]

GOES-17 Water Vapor weighting function plots for Anchorage, Alaska [click to enlarge]

Eruption of Volcán de Fuego in Guatemala

November 19th, 2018 |

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, center) and Low-level (7.3 µm, bottom) Water Vapor images [click to play animation | MP4]

GOES-16 Upper-level (6.2 µm, top), Mid-level (6.9 µm, center) and Low-level (7.3 µm, bottom) Water Vapor images [click to play animation | MP4]

Following several days of unrest, there was a moderate eruption of Volcán de Fuego in Guatemala beginning around 0630 UTC on 19 November 2018. GOES-16 (GOES-East) Upper-level (6.2 µm), Mid-level (6.9 µm) and Low-level (7.3 µm) Water Vapor images (above) displayed a signature of the volcanic plume, which drifted slowly northward and eastward for several hours. Since the 7.3 µm spectral band is also affected by SO2 absorption, the longer-lasting signal in the Low-level Water Vapor imagery suggests the plume contained SO2 as well as ash.

A GOES-16 multiispectral Ash/Dust Cloud Height product from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) indicated that the ash reached a maximum height of 7-8 km in the general vicinity of the summit between 1100-1200 UTC. A low-altitude plume of ash was seen drifting westward at heights of 1-5 km.

GOES-16 Ash Height product [click to play animation | MP4]

GOES-16 Ash/Dust Cloud Height product [click to play animation | MP4]

Along the southern coast of Guatemala, a 1400 UTC METAR from San Jose (MGSJ) reported a surface visibility of 5 statute miles with Volcanic Ash in the vicinity (VCVA) as the current weather type (below). At that time, the GOES-16 Split Window (10.3-12.3 µm) Brightness Temperature Difference was highlighting  concentrations of middle-tropospheric volcanic ash (yellow enhancement) farther inland closer to the volcano.

GOES-16 Split Window difference (10.3-12.3 µm) image, with METAR surface reports [click to enlarge]

GOES-16 Split Window difference (10.3-12.3 µm) image, with METAR surface reports [click to enlarge]

Thermal signature of an Antares rocket launch

November 17th, 2018 |

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm, left), Near-Infrared “Cloud Particle Size” (2.24 µm, center) and Shortwave Infrared (3.9 µm, right) images [click to play animation | MP4]

An Antares rocket was launched from the NASA Wallops Flight Facility on the Eastern Shore of Virginia (Space.com article) at 0901 UTC (4:01 AM local time) on 17 November 2018. At 0902 UTC a subtle thermal signature was seen just southeast of the launch site on GOES-16 (GOES-East) Near-Infrared “Snow/Ice” (1.61 µm). Near-Infrared “Cloud Particle Size” (2.24 µm) and Shortwave Infrared (3.9 µm) images (above). The thermal signature appeared at the center of each 0902 UTC image (where map outlines have been erased for clarity).

A corresponding thermal signature was also evident on 0902 UTC GOES-16 Low-level (7.3 µm). Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below) — since the Water Vapor spectral bands are essentially Infrared bands, the signal was due to superheated air from the powerful First Stage rocket (which burned for 3.5 minutes after launch).

GOES-16 Low-level (7.3 µm, left). Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

Taking a closer look with AWIPS, similar thermal signatures could be seen. Note that for the hottest pixel southeast of Wallops KWAL, the 3.9 µm Shortwave Infrared brightness temperature increased from 3.4ºC to 7.3ºC between 0857 and 0902 UTC — while the corresponding 10.3 µm “Clean” Infrared Window brightness temperature only increased from 3.7ºC to 4.0ºC.

GOES-16 Near-Infrared "Snow/Ice" (1.61 µm, left). Near-Infrared "Cloud Particle Size" (2.24 µm, center), Shortwave Infrared (3.9 µm, right) and "Clean" Infrared Window (10.3 µm) images [click to play animation | MP4]

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm, top left),. Near-Infrared “Cloud Particle Size” (2.24 µm, top right), Shortwave Infrared (3.9 µm, bottom left) and “Clean” Infrared Window (10.3 µm, bottom right) images [click to play animation | MP4]

A 4-panel comparison of Near-Infrared and Water Vapor bands is shown below. The difference between spatial resolution is quite evident: 1 km at satellite sub-point for the 1.61 µm band vs 2 km for the Water Vapor (and all other Infrared) spectral bands.

GOES-16 Near-Infrared "Snow/Ice" (1.61 µm, top left). Low-level Water Vapor (7.3 µm, top right), Mid-level Water Vapor (6.9 µm, bottom left) and Upper-level Water Vapor (6.2 µm, bottom right) images [click to play animation | MP4]

GOES-16 Near-Infrared “Snow/Ice” (1.61 µm, top left), Low-level Water Vapor (7.3 µm, top right), Mid-level Water Vapor (6.9 µm, bottom left) and Upper-level Water Vapor (6.2 µm, bottom right) images [click to play animation | MP4]

A thermal signature was also apparent using the Split Water Vapor (6.2-7.3 µm) and Split Fire (2.24-1.61 µm) band differences.

Dry air within an Atlantic subtropical ridge

November 16th, 2018 |

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a large region of very dry air within a subtropical ridge over the central North Atlantic Ocean on 16 November 2018. Infrared brightness temperatures were unusually warm (brighter yellow to red enhancement) on all 3 Water Vapor bands, especially along the western edge of the dry air.

A GOES-16 Upper-level Water Vapor image at 1700 UTC (below) showed a swath of NUCAPS sounding availability close to that time. The swath passed directly over the driest air within the subtropical ridge.

GOES-16 Upper-level (6.2 µm) Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

GOES-16 Upper-level Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

One of the green (high-quality) NUCAPS soundings within the arc of driest air (below) revealed a remarkably dry profile above the trade wind inversion — dewpoint values were -50ºC and colder within the 500-620 hPa layer, and dewpoint depressions were about 50ºC near the 550 hPa level.

NUCAPS sounding profile within the driest air [click to enlarge]

NUCAPS sounding profile within the driest air [click to enlarge]

Even though the middle to upper tropozphere was quite dry, note that the Total Precipitale Water (TPW) value calculated from the NUCAPS profile was 0.73 inch — there was still abundant tropical moisture within the marine boundary layer of the warm central Atlantic. The GOES-16 TPW product (below) showed minimum values of 0.6-0.8 inch in the region of driest air on the Water Vapor imagery (1800 UTC comparison). In contrast, TPW values over a large portion of the Lower 48 states were 0.6 inch or less, even in regions that appeared to be “moist” on the Water Vapor imagery.

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]