Dynamics of Extreme Negative Planetary Wave Heat Flux Events in an Idealized Model

Extreme total (climatology plus anomaly) stratospheric planetary wave-1 heat flux events are coupled to significant tropospheric impacts. In particular, extreme negative heat flux events are associated with a poleward shift of the tropospheric jet in the Atlantic basin, near surface warming over Eurasia and cooling over Northern Canada. Here a dry dynamical core is used to investigate the dynamics of negative stratospheric heat flux events. Ensemble spectral nudging experiments are performed to isolate the roles of i) the upward propagating wave-1 precursor, ii) the zonal-mean waveguide and iii) higher order planetary wavenumbers. The events are partially reproduced when simultaneously nudging the upward propagating wave-1 precursor and the zonal-mean waveguide whereas weaker responses are found when nudging either in isolation. The events are almost entirely reproduced when nudging the wave-1 precursor and the higher-order wavenumbers. Idealized experiments with wave 2-4 eddy forcing imposed on the zonal-mean flow show that higher wavenumbers impact the events by shaping the stratospheric zonal-mean waveguide, including the vertical reflecting surface. Wavenumbers 2-4 also play a role during negative heat flux events in reanalysis data. Taken together, the nudging and eddy forcing experiments support the role of wave reflection during extreme negative stratospheric heat flux events.