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]

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