Stratospheric Influences on Tropospheric Weather Systems

Abstract

Four cases of tropospheric weather systems (two sea level cyclones, one sea level anticyclone, and one blocking midtropospheric anticyclone) are investigated with the goal of understanding the role of stratospheric versus tropospheric processes in their developments. The relative contributions of the stratosphere and troposphere to geopotential height tendency fields (1000 mb for the sea level systems, 500 mb for the midtropospheric system) are quantified through vertical integration of thermodynamic processes (advective, adiabatic, and diabatic) over and following tendency centers associated with these systems. Previously known or suspected tropospheric contributions to system development, as well as the influence of stratospheric warm-air advection in the sea level cyclogenesis cases, are confirmed by the diagnoses. New findings include identification of the influence of stratospheric adiabatic cooling in the sea level and midtropospheric anticyclogenesis cases. It is further found that the stratospheric contribution to tropospheric development can be larger in magnitude than the tropospheric contribution and can even overwhelm an opposing tropospheric effect. In particular, it is shown that the midtropospheric anticyclogenesis associated with the blocking case critically depended on the stratospheric contribution and could not be solely explained by tropospheric processes. The 500-mb height tendencies associated with quasigeostrophic potential vorticity (QGPV) changes above the 500-mb level in this case were twice as large those associated with QGPV changes at and below 500 mb during blocking onset.