Exploring the vertical extent and deepening mechanisms of cut-off lows in the Southern Hemisphere: insights from eddy kinetic energy analysis

Abstract. Downstream baroclinic development is a process involving the generation and redistribution of eddy kinetic energy (EKE) from upstream to downstream regions of baroclinic waves. While it is recognized that downstream baroclinic development plays a fundamental role in the development of cut-off lows (COLs), the mechanisms that govern their deepening are not yet fully understood. This study employs a track matching based-approach applied to the ERA-Interim reanalysis to examine the vertical extent of COLs in the Southern Hemisphere and elucidate the potential mechanisms contributing to their deepening. By analyzing the relative contributions within the EKE budget, we reveal that the deepening of COLs is primarily governed by the interplay between baroclinic processes and oriented ageostrophic fluxes. These fluxes act as conduits for importing kinetic energy from the upstream mid-latitude jet into the COL system. While this phenomenon is common across all COLs, our investigation reveals that the dynamical processes are notably more vigorous in deep structure COLs compared to their shallow counterparts. In addition, the COL vertical extent is influenced by diabatic processes and regional factors such as topography that modifies the characteristics of Rossby waves and their breaking. Understanding the key features of the vertical extent and deepening mechanisms of COLs is crucial for accurate forecasting, as it provides valuable information on the dynamics and evolution of these systems.