Abstract
AbstractIn 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.
Highlights
The 2018 summer was amongst the hottest in the recorded history of Europe (Magnusson et al, 2018), with large parts of Scandinavia (Sinclair et al, 2019) and Central Europe affected by a heatwave (e.g., Vogel et al, 2019).Long periods of high temperatures with reduced precipitation are a threat for human life (e.g., Robine et al, 2008), but can cause crop failure and increase the hazard of forest fires (e.g., De Bono et al, 2004; Lesk et al, 2016)
Concurrent Central European and Scandinavian heatwaves can to some extent be related to Scandinavian blocking, both in the sense of a synoptic feature and a weather regime
A strong Scandinavian block coincided with the 2018 concurrent heatwaves, and constituted part of a larger-scale flow configuration that suppressed synoptic activity over Central Europe
Summary
The 2018 summer was amongst the hottest in the recorded history of Europe (Magnusson et al, 2018), with large parts of Scandinavia (Sinclair et al, 2019) and Central Europe affected by a heatwave (e.g., Vogel et al, 2019).Long periods of high temperatures with reduced precipitation are a threat for human life (e.g., Robine et al, 2008), but can cause crop failure and increase the hazard of forest fires (e.g., De Bono et al, 2004; Lesk et al, 2016). Wileyonlinelibrary.com/journal/qj 2998 amplitude, persistence, and spatial extent, the 2018 heatwaves were comparable to the two prominent heatwaves in 2003 and 2010 over Europe and Russia, respectively (Barriopedro et al, 2011; Fischer, 2014) In those summers, more than one million square kilometres were simultaneously affected by a heatwave (Barriopedro et al, 2011). Some studies consider the average over a season of all grid points that fulfill the chosen criteria, but do not require the affected areas to be connected in space and time (e.g., Coumou and Robinson, 2013; Vogel et al, 2019) In such a case, several spatially and temporally unrelated heat extremes can account for the seasonal signal. For this study we are interested in heatwaves that are spatially and temporally related, meaning that they have to occur in the vicinity of each other, and be separated by at most a few days
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