PV‐Q Perspective of Cyclogenesis and Vertical Velocity Development Downstream of the Tibetan Plateau

Abstract

AbstractThis study reviews the development of the omega equation and the relation between omega and potential vorticity (PV) advection and considers the application of PV theory to investigate the impact of large‐scale mountains on downstream weather development. A diabatic quasi‐geostrophic omega equation is introduced to reveal the feedback of diabatic heating (Q) on PV advection and vertical velocity. A challenge therein concerning the use of the diagnostic omega equation to interpret weather system development is considered from the PV‐Q perspective based on a severe weather event that occurred downstream of the Tibetan Plateau (TP) on 17–21 January 2008. Results demonstrate that owing to PV restructuring, positive PV was generated over the eastern flank of the TP, and its eastward advection triggered development of isentropic displacement vertical velocity and cyclogenesis in the lower troposphere. A converging southeasterly wind accompanied with ascending isentropic gliding vertical velocity in the lower troposphere was induced to the east of the cyclone center, which transported not only warm moist air but also negative PV from the south, contributing to developments of both local diabatic ascent and precipitation and eastward migration of the cyclone. During the cyclone life cycle, three omega components induced by different processes interacted with each other, and diabatic heating associated with precipitation exerted considerable feedback to vertical motion as well as PV advection. It is the vertical differential PV advection and feedback from diabatic heating that control the evolution of the circulation and the associated precipitation downstream of the TP.