Mid-tropospheric vortices over Alaska

November 9th, 2021 |

GOES-17 Mid-level Water Vapor (6.9 µm) images [click to play animated GIF | MP4]

GOES-17 (GOES-West) Mid-level (6.9 µm) Water Vapor images (above) revealed a complex pattern of middle-tropospheric vortices moving slowly west-southwestward over Interior Alaska and the Chukchi / Bering Seas on 09 November 2021. Note that the cold (brighter white) peaks of a few of the higher mountain ranges — including Denali — could be seen.

The presence of a relatively dry air mass across those areas allowed the signature of higher terrain to be evident in Water Vapor images — since a dry air mass has the effect of shifting the peaks of Water Vapor weighting functions to lower altitudes. The weighting function of the 6.9 µm spectral band (calculated from rawinsonde data at 12 UTC on 09 November and 00 UTC on 10 November) is plotted in blue for Fairbanks and Anchorage (below).

GOES-17 water vapor weighting functions for Fairbanks, Alaska [click to enlarge]

GOES-17 water vapor weighting functions for Anchorage, Alaska [click to enlarge]

Plots of GOES-17 parallax direction and magnitude for objects at altitudes of 15,000 feet (4.5 km) and 30,000 feet (9.1 km) are shown below (source), and help to explain the slight north-northwestward shift of the brighter white (colder) high-terrain signature in the Water Vapor imagery.

Plots of GOES-17 parallax direction (green arrows) and parallax magnitude (km, red) for objects at altitudes of 15,000 and 30,000 feet (4.5 and 9.1 km) [click to enlarge]

ACSPO SSTs on 9 November

November 9th, 2021 |
ACSPO SSTs over the northern Gulf of Mexico derived from NOAA-20 VIIRS data, 0800 UTC 09 Nov 2021 (Click to enlarge)

The Advanced Clear Sky Processor for Ocean algorithm is part of the Community Software Processing Package (CSPP), CIMSS-maintained software that can be applied to Direct Broadcast data, such as those data from NOAA-20 and Suomi-NPP (and other satellites) downloaded at two antennae at CIMSS. CSPP will create AWIPS-ready tiles so that SST information can be viewed within AWIPS (as shown above and below) and the AWIPS-ready tiles are available via LDM feed from CIMSS (images — rather large — are also routinely available online: here for the image above, here for the Suomi-NPP-derived image below).

Both SST images show remarkable gradients in sea surface temperature: upper 60s (cyan) to low 80s (yellow) just south of Louisiana in less than 20 miles (above); low 60s (blue) to 80 (chartreuse) to the east of the Outer Banks, also in less than 20 miles (below). The warmest water in the Gulf of Mexico is around 83º F, and shelf water is in the mid-60s. Warmest Gulf Stream waters are around 81º F. Magenta values correspond to temperatures in the 50s.

ACSPO SSTs over the northern Gulf of Mexico derived from Suomi-NPP VIIRS data, 0710 UTC 09 Nov 2021 (Click to enlarge)