Can you remember the extraordinary summer of 2003? The unprecedented heat wave in Russia 2010? Or the record-breaking temperatures of summer 2019? These high impact events were accompanied by dried out soils, crop failures, water shortages, and humans being on the brink of a heat stroke. – Periods of unusually and uncomfortably hot weather, heat waves, pose a threat to natural ecosystems and society and appear to be an inescapable weather hazard in the course of global warming.
Heat waves are often associated with persistent high pressure systems hovering over an area. But there seems to be little knowledge about which mechanisms and what scales are particularly important for the establishment of heat waves. Which factors determine their onset, their intensity, and their duration? And which role do local effects play compared to the upper-tropospheric flow? Our aim is to understand more about the drivers of heat waves in order to improve their forecasts. Therefore, we want to disentangle the various processes which lead to the formation of heat waves. This in turn will help people to prepare and will mitigate most severe impacts.
In our research we mostly focus on the role of the large-scale circulation for the establishment of heat waves. Recent analysis has shown that strong heat waves in Europe are often associated with pronounced and localized undulations in the jet-stream, so-called Rossby wave packets (see figure below). Linking to this, we analyze ensemble forecasts and model simulations in order to better understand the predictability of European heat waves. Moreover, we use a quasi-Lagrangian approach on reanalysis data to investigate whether air masses during heat waves warm mainly by advection or diabatic heating and how the large-scale circulation contributes to that.
The right image shows a snapshot of the European heat wave in 2003. The colors indicate the temperature anomaly at about 1500 m above ground. The contour lines depict the upper-tropospheric flow.
- Fragkoulidis G. and Wirth V. (2018): Synoptic circulation patterns during temperature extremes in
southeastern Europe. COMECAP 2018 Proceedings.
- Zschenderlein .P, Fragkoulidis G., Fink A. H. and Wirth V. (2018): Large-scale Rossby wave and
synoptic-scale dynamic analyses of the unusually late 2016 heatwave over Europe. Weather, 73, pp.
- Fragkoulidis G., Wirth V., Bossmann P. and Fink A. H. (2018): Linking Northern Hemisphere temperature extremes to Rossby wave packets. Q. J. R. Meteorol. Soc., 144, pp. 553-566. doi:10.1002/qj.3228