A Linear Analysis of the Footprints of Heating from U.S. Mesoscale Convective Systems on Springtime Extratropical Synoptic Variability

This study employs a two-layer Quasi-Geostrophic (QG) model with a linear, empirical parameterization of diabatic heating to investigate the impact of springtime Mesoscale Convective Systems (MCSs) over the U.S. on Northern Hemispheric extratropical synoptic variability. The inclusion of diabatic heating enhances the overall intensity of synoptic variability and significantly improves the structure of synoptic-scale disturbances, as characterized by “moist” nonmodal growth within a climatological springtime background flow. Specifically, MCS-induced heating over the U.S. not only amplifies local synoptic variability but also extends its influence to planetary and hemispheric scales. Further analysis of local nonmodal disturbance growth over the North America-North Atlantic sector reveals that while the North Atlantic storm track heating is crucial in shaping the overall structure of synoptic variability in the region, MCS heating over the U.S. substantially energizes these disturbances. This intensification has the potential to generate pronounced impact on downstream low-frequency variability, thereby influencing circumglobal teleconnections. Finally, doubling the strength of MCS heating in the model leads to the evolution of synoptic disturbances into structures reminiscent of the LC1-type baroclinic lifecycle, which favors anticyclonic wave breaking and tends to trigger a transition to the positive phase of the North Atlantic Oscillation (NAO). The implications of this idealized analysis are further discussed in the context of documented MCS variability and its coupling with regional and global circulation changes.