Abstract/Summary

Despite the fundamental contribution of diabatic processes for the evolution of storm tracks, our theoretical understanding of their role is still incomplete. Given that the strongest diabatic forcing is associated with cyclones, fronts, and atmospheric rivers, these synoptic features must exert a significant influence on the evolution of storm tracks. Their relative contribution to the climatological maintenance of baroclinicity, however, has not been investigated. Hence, we quantify the diabatic contribution of cyclones, fronts, and atmospheric rivers to free-tropospheric baroclinicity variability in the North Atlantic storm track in winter using the isentropic slope framework, which discriminates between diabatic and adiabatic contributions to changes in baroclinicity. The total variability of free-tropospheric baroclinicity within the storm track is characterised by diabatic generation followed by adiabatic decay. We find that the largest diabatic generation of baroclinicity takes place within cyclones, both individually and in combination with fronts, which contribute to more than half of this total variability in the storm track, despite their limited spatial extent and temporal occurrence. The contribution from atmospheric rivers, however, is small, confirming that the presence of moisture alone does not necessarily translate into diabatic production of baroclinicity in the absence of a mechanism for ascent. Though the contribution from the background to the variability is coherent with the total variability, there is no clear synoptic evolution associated with the background variability. Thus, the largest diabatic production of free-tropospheric baroclinicity is tightly linked to cyclones and fronts, whereas its adiabatic depletion occurs irrespective of the presence of weather features.