Radiative decay of idealized stratospheric filaments in the troposphere

The radiative decay of idealized stratospheric filaments embedded in a reference midlatitude troposphere is investigated. The filaments are characterized by typical lower stratospheric values of potential vorticity (PV), ozone, and humidity. The evolution of the filaments is obtained numerically in the framework of a plane symmetric balanced model. Diabatic heating due to radiation is accounted for by using a realistic parameterization scheme. The control parameter for the numerical experiments is the aspect ratio of the initial PV anomaly, which determines the partitioning into a thermal and a dynamical anomaly. For shallow filaments, both the temperature and the humidity anomaly are radiatively relevant. Initially, the decay of the filament is independent on whether or not the moisture anomaly is accounted for. At later times the effect of the moisture anomaly slows down the evolution significantly. For intermediate and tall filaments the humidity anomaly dominates the evolution from the beginning, leading to an enhancement rather than a decay of the PV anomaly. In addition, for tall filaments the advection by the induced Sawyer-Eliassen circulation has a significant impact on the evolution of the anomaly. In all experiments, ozone plays a minor role. The characteristic timescale of the evolution scales somewhat less than linearly with the filament thickness and shows only weak sensitivity to the aspect ratio.