A New Concept in Diagnosing Large-Scale Vertical Motion

The February 7-8, 1980 heavy snow case written up by Mike Akulow in the previous TA will be discussed from a different angle in this TA. In the following discussion it will be shown how PVA and warm advection (the latter often seen in the context of "overrunning") can, by and large, be replaced by PIVA-- Positive Isothermal Vorticity Advection. The opposite of PIVA is NIVA (Negative replaces Positive). For a complete discussion of the concept about to be presented here, the reader is referred to a Monthly Weather Review article by Kevin Trenberth which appeared in the January 1978 issue.