Heatwaves in Europe: Areas of homogeneous variability and links with the regional to large-scale atmospheric and SSTs anomalies

CARRIL A. F., S. GUALDI, A. CHERCHI AND A. NAVARRA

CLIMATE DYNAMICS

Springer

Lugar: Hamburg; Año: 2008 vol. 30 p. 77 - 98

0930-7575

This work presents a methodology to study theinterannual variability associated with summertime monthsin which extremely hot temperatures are frequent. Dailytime series of maximum and minimum temperature fields(Tmax and Tmin, respectively) are used to define indexes ofextreme months based on the number of days crossingthresholds. An empirical orthogonal function (EOF) analysisis applied to the monthly indexes. EOF loadings giveinformation about the geographical areas where the numberof days per month with extreme temperatures has thelargest variability. Correlations between the EOF principalcomponents and the time series of other fields allow plottingmaps highlighting the anomalies in the large scalecirculation and in the SSTs that are associated with theoccurrence of extreme events. The methodology is used toconstruct the ‘‘climatology’’ of the extremely hot summertimemonths over Europe. In terms of both interannualand intraseasonal variability, there are three regions inwhich the frequency of the extremely hot days per monthhomogeneously varies: north-west Europe, Euro-Mediterraneanand Eurasia region. Although extremes over thoseregions occur during the whole summer (June to August),the anomalous climatic conditions associated with frequentheatwaves present some intraseasonal variability. Extremeclimate events over the north-west Europe and Eurasia aretypically related to the occurrence of blocking situations.The intraseasonal variability of those patterns is related tothe amplitude of the blocking, the relative location of theaction centre and the wavetrain of anomalies downstreamor upstream of the blocking. During June and July,blocking situations which give extremely hot climateconditions over north-west Europe are also associated withcold conditions over the eastern Mediterranean sector. TheEuro-Mediterranean region is a transition area in whichextratropical and tropical systems compete, influencing theoccurrence of climate events: blockings tend to be relatedto extremely hot months during June while baroclinicanomalies dominate the variability of the climate events inJuly and August. We highlight that our method could beeasily applied to other regions of the world, to other fieldsas well as to model outputs to assess, e.g. the potentialchange of extreme climate events in a warmer climate.