EMS Annual Meeting Abstracts
Vol. 18, EMS2021-42, 2021, updated on 18 Jun 2021
EMS Annual Meeting 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Predictions of the boreal winter stratosphere with the C3S multi-model seasonal forecast system

Alice Portal1,2, Paolo Ruggieri3,4, Froila M. Palmeiro5, Javier Garcı́a-Serrano5, Daniela I. V. Domeisen6, and Silvio Gualdi4,7
Alice Portal et al.
  • 1University of Milano-Bicocca, Department of Earth and Environmental Sciences, Milan, Italy (a.portal@campus.unimib.it)
  • 2Laboratoire de Météorologie Dynamique/IPSL, Ecole Normale Superieure, PSL Research University, Sorbonne Université, École Polytechnique, IP Paris, CNRS, Paris, France
  • 3Department of Physics and Astronomy, University of Bologna, Bologna, Italy
  • 4Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Bologna, Italy
  • 5Group of Meteorology, Universitat de Barcelona (UB), Barcelona, Spain
  • 6Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 7Istituto Nazionale di Geofisica e Vulcanologia (INGV), Bologna, Italy

As a result of the recent progress in the performance of seasonal prediction systems, forecasts of the mid-latitude weather at seasonal time scales are becoming increasingly important for societal decision making, as in risk estimate and management of meteorological extreme events. The predictability of the Northern-Hemisphere winter troposphere, especially in the Euro-Atlantic region, stems from the representation of a number of sources of predictability, notably El Nino Southern Oscillation, the stratospheric polar vortex, Arctic sea-ice extent, Eurasian snow cover. Among these, the stratospheric polar vortex is known to play a paramount role in seasonal forecasts of the winter tropospheric flow.

Here, we investigate the performance in the stratosphere of five seasonal prediction systems taking part in the Copernicus Climate Change Service (C3S), with a focus on the seasonal forecast skill and variability, and on the assessment of stratospheric processes. We show that dynamical forecasts of the stratosphere initialised at the beginning of November are considerably more skilful than empirical forecasts based on observed October or November anomalies. Advances in the representation of stratospheric seasonal variability and extremes, i.e. sudden stratospheric warming frequency, are identified with respect to previous generations of climate models running roughly a decade ago. Such results display, however, a large model dependence. Finally, we stress the importance of the relation between the stratospheric wave activity and the stratospheric polar vortex (i.e. the wave—mean-flow interaction), applied both to the variability and to the predictability of the stratospheric mean flow. Indeed, forecasts of the winter stratospheric polar vortex are closely connected to the prediction of November-to-February stratospheric wave activity, in particular in the Eurasian sector.

How to cite: Portal, A., Ruggieri, P., Palmeiro, F. M., Garcı́a-Serrano, J., Domeisen, D. I. V., and Gualdi, S.: Predictions of the boreal winter stratosphere with the C3S multi-model seasonal forecast system, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-42, https://doi.org/10.5194/ems2021-42, 2021.

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