The Importance of Mesoscale Heating Along a Rossby Wave Packet for the Predictability of a Rossby Wave Breaking Event

Mesoscale heating can influence the mid-latitude large-scale flow by redistributing potentialvorticity (PV) along the tropopause, impacting Rossby wave evolution. This study explores howmesoscale heating not only perturbs the mid-latitude circulation but may also catalyze Rossbywave breaking along the jet stream.A forecast bust of a Rossby wave breaking event over the North Atlantic in April 2020 isexamined. The case involves a warm conveyor belt (WCB) with embedded convection andupstream thunderstorms over North America. The case is evaluated using archived forecast datafrom various weather centers and reforecasts conducted with the Model for Prediction AcrossScales (MPAS) at horizontal resolutions from 60 to 3.75 km. Potential vorticity tendencies (i.e.,microphysics, convection, radiation) are output to diagnose multi-scale interactions.Key findings show mesoscale heating on the jet stream's equatorward side is critical for Rossbywave predictability. Higher-resolution simulations capture a more persistent WCB and strongerPV reduction along the tropopause due to microphysics, amplifying the Rossby wave. Incontrast, coarser simulations failed to sustain WCB persistence, favoring cyclonic wave breakingregardless of initial conditions.Ensemble members with persistent mesoscale convective systems over North America wereassociated with slowed Rossby wave packet progression, leading to anticyclonic wave breakingover the Atlantic, and the most accurate forecasts. This outcome was sensitive to initialconditions and to the persistence of the adjacent WCB.The presented findings highlight the importance of faithfully simulating mesoscale heatingacross a RWP to successfully forecast an individual Rossby wave breaking event. Implications ofthese results for ongoing global convection-resolving MPAS simulations at the National Centerfor Atmospheric Research are also discussed.