Mobile trough genesis over the Mongolian Plateau

Abstract

The purpose of this study is to understand the mechanisms responsible for formation of mobile troughs over the large source region in Mongolia. Three winter season mobile troughs which intensified rapidly after formation were analyzed. An objective method developed by Lefevre and Nielsen-Gammon (1995) was used to track the mobile troughs-a quasigeostrophic potential vorticity (QGPV) and associated piecewise tendency diagnosis (PTD) technique developed by Lefevre (1995) was used to analyze the formation mechanisms. Through the PTD technique, which involves in the inversion of QGPV and QGPV advection, it was determined that the mobile troughs developed from a combination of deformation / superposition and downstream development. Baroclinic processes were not evident near the time of formation, but were important as the troughs moved over the Sea of Japan. Two troughs interacted with surface cyclones, but in both cases only minor development occurred. As the troughs moved underneath a climatological mean long wave trough, all three troughs weakened from deformation. There was evidence of orographic masking in one of the cases as the mobile trough existed at upper-levels (above 500 mb) prior to formation by the objective method. However, as the trough moved to the lee-side of the Altai-Sayan mountains, the trough lowered to 500 mb and was initialized by the objective method.