Connecting Atmospheric Blocking to European Temperature Extremes in Spring

Lukas Brunner,Andrea K Steiner,Gabriele C Hegerl

doi:10.1175/jcli-d-16-0518.1

Lukas Brunner, Andrea K Steiner + Show 1 more

Open Access

https://doi.org/10.1175/jcli-d-16-0518.1

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Abstract

Atmospheric blocking is an important contributor to European temperature variability. It can trigger cold and warm spells, which is of specific relevance in spring because vegetation is particularly vulnerable to extreme temperatures in the growing season. The spring season is investigated as a transition period from predominant connections of blocking with cold spells in winter to predominant connections of blocking with warm spells in summer. Extreme temperatures are termed cold or warm spells if temperature stays outside the 10th to 90th percentile range for at least six consecutive days. Cold and warm spells in Europe over 1979–2014 are analyzed in observations from the European daily high-resolution gridded dataset (E-OBS) and the connection to blocking is examined in geopotential height fields from ERA-Interim. A highly significant link between blocking and cold and warm spells is found that changes during spring. Blocking over the northeastern Atlantic and Scandinavia is correlated with the occurrence of cold spells in Europe, particularly early in spring, whereas blocking over central Europe is associated with warmer conditions, particularly from March onward. The location of the block also impacts the spatial distribution of temperature extremes. More than 80% of cold spells in southeastern Europe occur during blocking whereas warm spells are correlated with blocking mainly in northern Europe. Over the analysis period, substantial interannual variability is found but also a decrease in cold spells and an increase in warm spells. The long-term change to a warmer climate holds the potential for even higher vulnerability to spring cold extremes.

Highlights

European weather and climate is strongly influenced by large-scale circulation patterns such as the Atlantic storm tracks, the jet stream, and atmospheric blocking (e.g., Woollings 2010).Atmospheric blocking describes a meteorological situation in which a persistent and stationary high pressure system blocks the climatological westerly flow at mid-latitudes for several days to weeks (Rex 1950; Tibaldi and Molteni 1990; Pelly and Hoskins 2003; Barriopedro et al 2006; Croci-Maspoli et al 2007).Extremes on both ends of the temperature distribution are especially closely connected to atmospheric blocking
If the trend is not removed from the underlying temperature time series (Fig. 1d, bottom) an increase of the number of warm spell day (WSD) in the investigated period from 1979 to 2014 is evident, consistent with the detection of changes in the number of temperature extremes in Europe (Zwiers et al 2011; IPCC 2013; Morak et al 2013)
We found blocking in winter and early spring to be stronger connected to cold conditions while blocking in late spring and summer is stronger connected to warm conditions

Summary

Introduction

European weather and climate is strongly influenced by large-scale circulation patterns such as the Atlantic storm tracks, the jet stream, and atmospheric blocking (e.g., Woollings 2010). Atmospheric blocking describes a meteorological situation in which a persistent and stationary high pressure system blocks the climatological westerly flow at mid-latitudes for several days to weeks (Rex 1950; Tibaldi and Molteni 1990; Pelly and Hoskins 2003; Barriopedro et al 2006; Croci-Maspoli et al 2007) Extremes on both ends of the temperature distribution are especially closely connected to atmospheric blocking. We investigate the link between atmospheric blocking and European cold and warm spells during spring to provide better insight into the shifting role of blocking for extremes during this transition period.

Data and Methods

Results

Summary and discussion