Shear vorticies over the western US

November 9th, 2020 |

GOES-16 Upper-level Water Vapor (6.2 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 Upper-level Water Vapor (6.2 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm) and Air Mass Red-Green-Blue (RGB) images (above) displayed a series of shear vortices migrating southwestward over the western US on 09 November 2020. The “dynamic tropopause” — taken to be the pressure of the PV1.5 surface — descended to the 500-600 hPa level within the largest and most well-defined vortex that was moving over Montana and Idaho. These features displayed hues of red to orange in the Air Mass RGB images (for example, at 2101 UTC), indicative of the dry and ozone-rich stratospheric air within the vortices. Aircraft reports of turbulence are sometimes seen in the general vicinity of these shear vortices, as the local tropopause is deformed (such as on 07 June 2017); in this case, there were only two instances of turbulence reported (at 1545 UTC and 0200 UTC).

GOES-16 Upper-level Water Vapor (6.2 µm) image at 2101 UTC, with contours of PV1.5 pressure (red) and the orientation of cross section I-I' (cyan) [click to enlarge]

GOES-16 Upper-level Water Vapor (6.2 µm) image at 2101 UTC, with contours of PV1.5 pressure (red) and the orientation of cross section line I-I’ (cyan) [click to enlarge]

The GOES-16 Water Vapor image at 2101 UTC (above) showed the northwest-to-southeast oriented cross section line I-I’ — and RAP40 model fields along that line (below) revealed the descent of stratospheric air (characterized by low values specific humidity along with high values of potential vorticity) within the shear vortex when it was located near the Idaho/Montana border.

Cross section of RAP40 model Potential Vorticity (color image + red contours), Specific Humidity (green contours) and wind barbs (cyan) [click to enlarge]

Cross section of RAP40 model Potential Vorticity (color image + red contours), Specific Humidity (green contours) and Wind (cyan) [click to enlarge]