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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-17
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-17
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 May 2020

Submitted as: research article | 04 May 2020

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This preprint is currently under review for the journal WCD.

Mechanisms and predictability of Sudden Stratospheric Warming in winter 2018

Irina A. Statnaia1,2, Alexey Y. Karpechko1, and Heikki J. Järvinen2 Irina A. Statnaia et al.
  • 1Finnish Meteorological Institute, 00560 Helsinki, Finland
  • 2Institute for Atmospheric and Earth System Research, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland

Abstract. In the beginning of February 2018 a rapid deceleration of the westerly circulation in the polar Northern Hemisphere stratosphere took place and on 12 February the zonal mean zonal wind at 60° N and 10 hPa reversed to easterly in a Sudden Stratospheric Warming (SSW) event. We investigate the role of the tropospheric forcing in the occurrence of the SSW, its predictability and teleconnection with the Madden-Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The SSW was preceded by significant synoptic wave activity over the Pacific and Atlantic basins, which led to the upward propagation of wave packets and resulted in the amplification of a stratospheric wavenumber 2 planetary wave. The dynamical and statistical analyses indicate that the main tropospheric forcing resulted from an anticyclonic Rossby wave breaking, subsequent blocking and upward wave propagation in the Ural Mountains region, in agreement with some previous studies. The ensemble members which predicted the wind reversal, also reasonably reproduced this chain of events, from the horizontal propagation of individual wave packets to upward wave activity fluxes and the amplification of wavenumber 2. On the other hand, the ensemble members which failed to predict the wind reversal, also failed to properly capture the blocking event in the key region of the Urals and the associated intensification of upward propagating wave activity. Finally, a composite analysis suggests that teleconnections associated with the record-breaking MJO phase 6 observed in the late January 2018 likely played a role in triggering this SSW event.

Irina A. Statnaia et al.

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Irina A. Statnaia et al.

Irina A. Statnaia et al.

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Short summary
In this paper we investigate the role of the tropospheric forcing in the occurrence of the Sudden Stratospheric Warming (SSW) that took place in February 2018, its predictability and teleconnection with the Madden-Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The purpose of the paper is to present the results of the analysis of the atmospheric circulation before and during the SSW and clarify the driving mechanisms.
In this paper we investigate the role of the tropospheric forcing in the occurrence of the...
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