Idealised simulations of polar low development in an Arctic moist‐baroclinic environment

Abstract

This study examines the influence of moisture, baroclinicity, and static stability on developing disturbances at high latitudes by utilising an idealised baroclinic channel model. The set‐up is composed of environmental baroclinicity defined by a zonally uniform jet in thermal wind balance with a meridional temperature gradient and moisture content defined by relative humidity profiles. Initiation of disturbance growth is achieved by superimposing a weak, surface‐based warm‐cored cyclonic disturbance to the set‐up. The experiments show that the disturbance is able to amplify within such an environment in the absence of an upper‐level perturbation, surface fluxes, friction, or radiation. Separation between developing and non‐developing disturbances is feasible by considering the baroclinic and diabatic contributions to eddy available potential energy. Developing disturbances show a clear diabatic dominance during the early stage of development, whereas experiments lacking this diabatic boost fail to intensify within a 3‐day time window. A comparison with the conceptual framework of the Diabatic Rossby Vortex (DRV) growth mechanism provides insight into the dynamical pathway potentially underlying the enhanced amplification. The emerging disturbance qualitatively resembles the postulated DRV structure, the major difference being a decreased depth in comparison with simulated and observed DRVs in midlatitudes. A suit of sensitivity experiments examines the range of atmospheric conditions in which enhanced amplification by diabatic processes is possible. Threshold values for moisture content and isentropic slopes are identified.