Heat Fluxes by Planetary-scale Stationary and Transient Eddies before Sudden Stratospheric Warming

Traditionally, major sudden stratospheric warming (SSW) events are attributed to the anomalous growth of stationary planetary wave into the stratosphere. This common belief stems from the dominance of stationary waves observed just prior to the most common SSW type, associated with the displaced polar vortex (SSW-D). However, a few studies recently observed enhanced traveling planetary wave activity in the mesosphere, prior to the 2009 SSW associated with a split polar vortex (SSW-S). They suggested that the precursory impact of these waves may play a role in triggering the SSW onset. To examine the importance of traveling waves, a global climate model simulation (nudged with observations below 50 km) between 1979-2014 was used to quantity the eddy heat fluxes for stationary and transient planetary waves, 20 days prior to the onset of 18 SSW-D events and 6 SSW-S events. Along with the composite difference between stationary eddy heat flux and transient eddy heat flux between both SSW types, the corresponding flux anomalies, relative to wintertime climatology, were found. A major finding was the dominance of the anomalous transient eddy heat flux in the stratosphere and mesosphere leading up to SSW-S, as compared to SSW-D. While the transient feature in the stratosphere may be related to non-steady stationary waves, the robust presence of mesospheric transient eddy heat fluxes corroborates the precursory traveling perturbations, observed thus far, in the 2009 SSW-S. Knowing the occurrence and impacts of these mesospheric waves well before SSW may lead to the ability to improve forecasting of SSW and, subsequently, surface weather.