Mean state and day-to-day variability of tropospheric circulation in planetary-scale barotropic Rossby waves during Eurasian heat extremes in CMIP5 models

Abstract

Surface Eurasian heat waves (EHWs) in reanalysis datasets exhibit distinct signatures in the planetary Rossby wave circulation during extended boreal summer, particularly evident in the day-to-day variability. The representation of these signatures continues to be a challenge for climate models, despite significant advancements. This study demonstrates uncertainties in the simulated EHW-related variability in planetary-scale Rossby waves for the present-day climate and the future scenario RCP4.5 in a subset of CMIP5 models. The historical simulations represent surface EHW and the associated mean pattern of Rossby waves reasonably well, in particular the uncoupled simulations. However, the EHW signatures in day-to-day tropospheric circulation variability are not adequately reproduced. For the RCP4.5 scenario and future EHWs defined with respect to the future mean climate, models do not suggest an increase in EHWs. There is considerable uncertainty in how climate models represent the associated Rossby wave circulation, with a particular lack of consistent representation of day-to-day variability. These uncertainties and inconsistencies further limit confidence in future projections of changes in EHWs. Our results suggest that intrinsic variability should be an additional component of the metrics evaluating the simulation of EHWs and their related circulation.