Impacts of Jet Stream Structure on Cyclone Merging and Persistent Anticyclones: Insights from Dry Idealized Simulations
Midlatitude jet streams exhibit substantial variability in latitude, width, and vertical depth on synoptic to multi-decadal timescales. While the upper-level dynamics of baroclinic waves have been extensively studied, the sensitivity of the extreme-generating, low-level phenomena to these variations remains underexplored. Here, we systematically investigate this sensitivity using dry, adiabatic idealized experiments with the GFDL FV3 dry dynamical core initialized with analytically specified jets. We identify jet variations that control synoptic-scale features of interest. Results indicate that poleward-shifted jets accelerate initial cyclone intensification and favor anticyclonic Rossby Wave Breaking (RWB). These wave-breaking tendencies are consistent with established baroclinic paradigms, validating the newly configured idealized simulations. Additionally, jet width regulates the likelihood of surface cyclone merging. Poleward-shifted, broader, and higher jets produce more frequent cyclone merging, generating intense wind extremes. Finally, we show that poleward-shifted, broad, deep jets dynamically precondition the flow for persistent stationary anticyclones in the absence of diabatic contributions. Together, these findings illustrate how changes in jet stream structure may modulate midlatitude weather extremes.