Shear Instabilities over the Gulf of Alaska

April 4th, 2011 |

Water vapor imagery from Monday 4 April 2011 over the Gulf of Alaska shows the development of what appears to be Kelvin-Helmholtz instability, an instability that occurs in regions of strong shear. In this case, the shear zone occurs within a gradient of moisture along the edge of a polar vortex, so the developing vortex deforms the water vapor field as detected by the GOES-11 Imager. The vertical circulation associated with the roll vortex can also change the detected moisture field: infer descent in the regions where the water vapor signal decreases with time, and ascent in regions where the water vapor signal increases with time. When these vortices are sampled by the GOES Sounder, it is common to see an enhanced ozone signal in the driest part of the developing vortex, suggesting the entrainment of dry stratospheric air into the vortex circulation.

The vortices have a signal only in the water vapor imagery. Visible imagery from AVHRR (here) show no evidence of wrapped-up vortices.

Note that the GOES-11 Imager was in eclipse between 0800 UTC and 1030 UTC and so no images were received then.