Abstract
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 spatial
scales, from planetary to synoptic. We use the 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 the weather regime structures associated with these heat wave
events are typical for extremely large poleward-energy-transport events.
Funder
H2020 European Research Council
Cited by
5 articles.
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