Dynamical Forcing of Stratospheric Planetary Waves by Tropospheric Baroclinic Eddies

Abstract

Abstract The forcing of planetary wave variability in the stratosphere by synoptic-scale baroclinic eddies in the troposphere is considered. Simple forced–dissipative numerical experiments are performed in a primitive equation model using a deep hemispheric model domain. The flow is thermally relaxed toward zonally symmetric notional wintertime conditions. No zonally asymmetric thermal or topographic forcing is applied. All planetary-scale zonal asymmetry arises solely through the nonlinear wave–wave interaction of the baroclinic eddies in the troposphere. The numerical experiments indicate that realistic stratospheric planetary wave amplitudes and variability, comparable to those observed in the Southern Hemisphere, can be forced through this mechanism. No evidence is found in these simulations for planetary-scale disturbances arising through in situ instability in the stratosphere. The nonlinear tropospheric forcing mechanism in the numerical simulations is further investigated by reproducing the strato...