How much does diabatic heating affect storm track activity?

We examine regional and seasonal variations of extratropical storm tracks and their maintenance in terms of a column-mean local wave activity budget.  Seasonal climatology of wave activity in ERA5 reveals spatial and temporal variations of storm tracks in both hemispheres broadly consistent with previous studies based on other metrics. The seasonal-mean budget consists of horizontal convergence of wave activity fluxes, input from the surface (the upward Eliassen-Palm flux), a small storage, and the residual. When averaged hemispherically, surface injection of wave activity due to baroclinic instability and forced stationary waves is balanced by a negative residual (dissipation) due to mixing and radiative damping.

However, the budget terms show considerable zonal, meridional and seasonal variations, especially in the Northern Hemisphere. Wave activity migrates downstream from a source region to a sink, where the residual is negative and largely balanced by flux convergence. In addition to the surface sources in the regions of strong baroclinicity, the residual term, though negative on average, shows significant positive values where cloud water abounds, suggesting diabatic (and/or nonquasigeostrophic) sources of wave activity.

By reconstructing the budget driven by a fixed transport velocity and damping rate evaluated from the seasonal climatology but suppressing the positive residual values, we estimate the impact of diabatic sources on the mean wave activity. It is found that the diabatic sources contribute to 26% and 20%, respectively, of North Atlantic and North Pacific storm track activities in winter, 28% of wave activity over the Pacific Northwest in summer, and 34% of activity in the Indo-western Pacific sector of the austral storm track in summer.