The temporal mean of transient Rossby wave packets

Extremes of temperature or precipitation on intra-seasonal time scales are commonly structured in a circumglobal wave with a synoptic-scale zonal wavenumber. The mechanism that determines this wavenumber and the relationship with processes on shorter timescales, such as Rossby wave packets, are not fully understood. We employ a simple kinematic model to demonstrate how a transient Rossby wave packet produces significant temporal mean circulation anomalies with a wavelength that is larger than the wavelength of the instantaneous wave packet itself. This demonstration is verified by comparison with a linear, quasi-geostrophic channel model where we can assess sensitivities to the latitude and the meridional extent of the wave packet. These two highly idealized models help us to better understand the role of Rossby wave packets in concurrent and compound weather extremes.