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 potential
vorticity (PV) along the tropopause, impacting Rossby wave evolution. This study explores how
mesoscale heating not only perturbs the mid-latitude circulation but may also catalyze Rossby
wave breaking along the jet stream.

A forecast bust of a Rossby wave breaking event over the North Atlantic in April 2020 is
examined. The case involves a warm conveyor belt (WCB) with embedded convection and
upstream thunderstorms over North America. The case is evaluated using archived forecast data
from various weather centers and reforecasts conducted with the Model for Prediction Across
Scales (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 Rossby
wave predictability. Higher-resolution simulations capture a more persistent WCB and stronger
PV reduction along the tropopause due to microphysics, amplifying the Rossby wave. In
contrast, coarser simulations failed to sustain WCB persistence, favoring cyclonic wave breaking
regardless of initial conditions.

Ensemble members with persistent mesoscale convective systems over North America were
associated with slowed Rossby wave packet progression, leading to anticyclonic wave breaking
over the Atlantic, and the most accurate forecasts. This outcome was sensitive to initial
conditions and to the persistence of the adjacent WCB.

The presented findings highlight the importance of faithfully simulating mesoscale heating
across a RWP to successfully forecast an individual Rossby wave breaking event. Implications of
these results for ongoing global convection-resolving MPAS simulations at the National Center
for Atmospheric Research are also discussed.