The Role of Climatological State in Supporting US Heat Waves Through Rossby Waves Packets

Abstract

While heat waves are local extreme weather events, a slowly propagating planetary-scale Rossby wave pattern is statistically correlated to the occurrence of heat waves in the US. However, whether this correlation indicates that such planetary wave patterns physically cause the enhanced statistics of local heat waves is debatable. In this work, we hypothesize that the atmospheric climatological state controls the slowly propagating wave pattern, setting up a conducive large-scale environment for local US heat waves. We implement an idealized dry dynamic core model with an iterative approach to simulate the realistic North American summer climatological state. As the idealized atmospheric model can generate similar zonal wavenumber five planetary wave patterns propagating throughout North America, significantly more heat waves are generated, and the statistics of heat waves become consistent with those estimated in reanalysis products. The slowly propagating Rossby wave packets with a timescale of 20–30 days may serve as a new source of intraseasonal predictability in the midlatitudes.