Linking Northern Hemisphere temperature extremes to Rossby wave packets

This work investigates the statistical linkage between upper-tropospheric transient Rossby wave packets (RWPs) and lower-tropospheric temperature extremes in the Northern Hemisphere during the period 1979-2015. Data from ERA-Interim reanalyses are used for the diagnosis of RWP amplitude and temperature anomalies as well as the systematic examination of their connection. Areas of large RWP amplitude are found to be associated with an increased probability of lower-tropospheric temperature extremes in many regions of the midlatitudes. Although a seasonal and inter-regional variability is apparent, this link is always stronger than in an analysis using a circumglobal waviness metric based on Fourier wavenumber amplitudes. Further insight is gained by complementing the climatological results with an investigation of the two most severe recent heat waves in Europe, viz. during the 2003 and 2010 summers. Both events are found to be associated with conspicuous non-circumglobal RWPs, but differences between the two events suggest that the mechanisms linking RWPs and temperature extremes are case-dependent. The aforementioned results underscore the important role of upper-troposphere dynamics and open up avenues for future research on heat waves and cold spells at both weather and climate time-scales.