|TITLE||THE KEY ROLE OF BLOCKING IN DRIVING THE COLD SPELLS OVER SOUTHEASTERN EUROPE IN WINTER 2016 - 2017|
|AUTHORS||E Tyrlis (1), D Matei (1), J Bader (1,2), E Manzini (1), K Lohmann (1)|
- Max Planck Institute for Meteorology, Hamburg, Germany
- Uni Climate, Uni Research & Bjerknes Centre for Climate Research, Bergen, Norway
|ABSTRACT||Winter cold extremes over the Mediterranean can have a significant financial and societal impact. In this work we investigate the dynamical environment that led to the extremely cold conditions that affected southeastern Europe in winter 2016-2017. We study the hemispheric scale circulation that was associated with this regional climate anomaly and we conclude that the latter was not an isolated event but rather it pertained to a series of cold spells that affected large parts of Eurasia during autumn and winter 2016-2017. The possibility of a link between the recently observed increasing trend of mid-latitude cold extremes, which can also affect the Mediterranean, and Arctic Amplification has become a topic of heated debate. Specifically, the role of sea ice loss over the Barents-Kara Seas (BKS) into driving cold episodes over Eurasia has been highlighted in the relevant literature. Here, we use ERA-Interim reanalysis data to investigate the daily evolution of the atmospheric state with view to trace the pathways that led to these extreme conditions.
Abundant blocking over most of the Northern Hemisphere was the key circulation pattern in autumn 2016 when a nearly four-fold increase in blocking activity was observed over Eurasia. We identify distinct and successive blocking episodes over central Asia; each of them induced a pair of cold air advection to its south and warm advection over the Arctic. The resulting warm and cold anomalies over the BKS and central Asia, respectively, featured large concurrent variability on synoptic timescales whose pace was set by blocking. Subsequently, blocking activity spread towards Europe in early winter 2017. This favored the development of successive equatorward surges of cold air masses towards the Mediterranean that severely affected the Balkans.
This work has been undertaken in the framework of the InterDec project funded under the 2015 joint JPI Climate-Belmont Forum call.|