SLS Seminar: Erik Lindgren (MIT)

The role of zonal wavenumbers and eddy-eddy interactions in sudden stratospheric warming formation

Sudden stratospheric warmings (SSWs) are the dominant sources of variability in the Northern Hemisphere winter stratosphere and influence surface climate on monthly timescales, but exactly what causes SSWs is not fully understood. SSWs have traditionally been thought to be caused by the breaking of upward propagating planetary-scale waves originating in the troposphere, but more recent research has shown that SSWs and other similar vortex deceleration events found in reanalysis data often occur without any preceding anomalous upward propagating tropospheric wave activity. An improved understanding of the mechanisms behind SSW generation is required in order to better forecast SSWs and other abrupt polar vortex decelerations.

Here I investigate the extent to which SSWs in an idealized atmospheric GCM are forced by anomalous tropospheric wave fluxes, and if there are any differences between the forcing of displacements (wave-1 SSWs) and splits (wave-2 SSWs). By varying the type and wavenumber of the tropospheric forcing used to produce planetary-scale waves in model, I show that while the fraction of SSWs forced by anomalous tropospheric wave flux is comparable to fractions found in reanalysis data, the processes by which SSWs form can be heavily dependent on the wavenumber of the forcing and the type of SSW. The results also indicate that eddy-eddy interactions (EEI) play an important role in SSW formation, and the effects of EEI on SSWs is further investigated by analyzing model runs where EEI is “turned off” in different regions of the atmosphere. The no-EEI runs show that SSWs can form without EEI, but that EEI is necessary to reproduce the structure of SSWs in the observed atmosphere.

About the Series

The Atmosphere, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmosphere, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm in 54-915. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.