Preprints
https://doi.org/10.5194/wcd-2021-85
https://doi.org/10.5194/wcd-2021-85

  04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal WCD.

Meridional energy transport extremes and the general circulation of NH mid-latitudes: dominant weather regimes and preferred zonal wavenumbers

Valerio Lembo1, Federico Fabiano1, Vera Melinda Galfi2, Rune Graversen3,4, Valerio Lucarini5, and Gabriele Messori2,6 Valerio Lembo et al.
  • 1CNR-ISAC, Bologna, Italy
  • 2Department of Earth Sciences and Centre of Natural Hazards and Disaster Science (CNDS), Uppsala University, Uppsala, Sweden
  • 3Department of Physics and Technology, UiT – The Arctic University of Norway, Tromsø, Norway
  • 4Norwegian Meteorological Institute, Tromsø, Norway
  • 5Department of Mathematics and Statistics and Centre for the Mathematics of Planet Earth, University of Reading, Reading, UK
  • 6Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden

Abstract. The extratropical meridional energy transport in the atmosphere is fundamentally intermittent in nature, having extremes large enough to affect the net seasonal transport. Here, we investigate how these extreme transports are associated with the dynamics of the atmosphere at multiple scales, from planetary to synoptic. We use ERA5 reanalysis data to perform a wavenumber decomposition of meridional energy transport in the Northern Hemisphere mid-latitudes during winter and summer. We then relate extreme transport events to atmospheric circulation anomalies and dominant weather regimes, identified by clustering 500 hPa geopotential height fields. In general, planetary-scale waves determine the strength and meridional position of the synoptic-scale baroclinic activity with their phase and amplitude, but important differences emerge between seasons. During winter, large wavenumbers (k = 2 − 3) are key drivers of the meridional energy transport extremes, and planetary and synoptic-scale transport extremes virtually never co-occur. In summer, extremes are associated with higher wavenumbers (k = 4 − 6), identified as synoptic-scale motions. We link these waves and the transport extremes to recent results on exceptionally strong and persistent co-occurring summertime heat waves across the Northern Hemisphere mid-latitudes. We show that these events are typical, in terms of dominant regime patterns associated with extremely strong meridional energy transports.

Valerio Lembo et al.

Status: open (until 27 Feb 2022)

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Valerio Lembo et al.

Valerio Lembo et al.

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Short summary
Eddies in mid-latitudes characterize the exchange of heat between the Tropics and the Poles. This exchange is largely uneven, with a few extreme events bearing most of the heat transported across latitudes in a season. It is thus important to understand what are the dynamical mechanisms behind these events. Here, we identify recurrent weather regime patterns associated with extreme transports, and we identify scales of mid-latitudinal eddies that are mostly responsible for the transport.