Deep orographic storms over the Sierra Nevada. Part I: thermodynamic and kinematic structure.

Abstract

Two deep, orographic storms were documented over the Sierra Nevada with an instrumented aircraft and with a single Doppler radar. In both storms the geostrophic winds were normal to the barrier with speeds of 15 to 30m s-1. Because of blocking the measured wind component normal to the barrier was substantially less than the geostrophic wind component, especially below barrier crest height. The forced ascent of stable air plus the diabatic process of melting caused the isotherms to descend near the barrier. The barrier yet can be explained by the thermal wind relation and is, therefore, a quasi-geostrophic phenomenon. The derived vertical velocities were estimated to be 0.2 to 0.4m s-1.-from Author