Dynamics of concurrent and sequential Central European and Scandinavian heatwaves

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 146; no. 732; pp. 2998 - 3013
• Main Authors: Spensberger, C., Madonna, E., Boettcher, M., Grams, C. M., Papritz, L., Quinting, J. F., Röthlisberger, M., Sprenger, M., Zschenderlein, P.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.10.2020; Wiley Subscription Services, Inc
• Subjects: Air masses; block; Central Europe; Climatology; Dynamics; Heat waves; heatwave; Heatwaves; Pressure gradients; Regions; Scandinavia; weak pressure gradient; Central Europe; Scandinavia
• DOI: 10.1002/qj.3822
• ISSN: 0035-9009

In both 2003 and 2018 a heatwave in Scandinavia in July was followed by a heatwave in Central Europe in August. Whereas the transition occurred abruptly in 2003, it was gradual in 2018 with a 12‐day period of concurrent heatwaves in both regions. This study contrasts these two events in the context of a heatwave climatology to elucidate the dynamics of both concurrent and sequential heatwaves. Central European and, in particular, concurrent heatwaves are climatologically associated with weak pressure gradient (WPG) events over Central Europe, which indicate the absence of synoptic activity over this region. One synoptic pattern associated with such events is Scandinavian blocking. This pattern is at the same time conducive to heatwaves in Scandinavia, thereby providing a mechanism by which Scandinavian and Central European heatwaves can co‐occur. Further, the association of WPG events with Scandinavian blocking constitutes a mechanism that allows heatwaves to grow beyond the perimeter of the synoptic system from which they emanated. A trajectory analysis of the source regions of the low‐level air incorporated in the heatwaves indicates rapidly changing air mass sources throughout the heatwaves in both regions, but no recycling of heat from one heatwave to the other. This finding is line with a composite analysis indicating that transitions between Scandinavian and Central European heatwaves are merely a random coincidence of heatwave onset and decay. We analyse the dynamics of concurrent and sequential heatwaves in Central Europe and Scandinavia. We show that (a) some circulation patterns are conducive to heatwaves in both regions, (b) the sequential occurrence of heatwaves in these regions is merely a random coincidence, and (c) that Central European and concurrent heatwaves are associated with weak pressure gradient situations over Central Europe.