Joint Seminar: On the link between decadal-to-multidecadal oceanic and boreal polar stratospheric variability in the MPI Grand Ensemble

The wintertime polar stratosphere is dominated by a region of low geopotential height enclosed by strong westerly winds, called stratospheric polar vortex. The boreal polar vortex may suffer strong disruptions such as major sudden stratospheric warmings (SSWs). During SSWs, the polar temperature increases abruptly, and easterlies prevail in the stratosphere. According to observations, SSWs are not equally distributed over time, with decades with almost no events and decades with SSWs happening almost every winter, suggesting the existence of multidecadal variability of SSWs. Previous studies have indicated that the sources of this low-frequency variability of SSWs should be primarily located in the ocean surface. However, the short observational data record and the requirement of long model simulations with daily output have not enabled a detailed analysis of the influences of these oceanic phenomena on SSWs.
In this study, we investigate the effects of two main modes of low-frequency SST variability in the Pacific and Atlantic Oceans, Pacific Decadal Variability and Atlantic Multidecadal Variability respectively, on SSWs. To do so, we use for the first time a large ensemble of historical experiments (MPI Grand Ensemble, MPI-GE) to examine the modulation of the frequency, tropospheric precursors, and impact of SSWs by the PDV and AMV. We find a strong impact of the PDV on the occurrence of SSWs, with a higher SSW frequency for the PDV positive phase. The PDV influence is mediated by constructive interference of PDV anomalies with tropospheric stationary waves. The main effect of AMV is, instead, a modulation of the tropospheric response to SSWs, a finding that can be useful for predicting the tropospheric fingerprint of SSWs.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Blanca Ayarzaguena


Swantje Bastin

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