Cyclone–Anticyclone Asymmetry Concerning the Height of the Thermal and the Dynamical Tropopause

Abstract

The differences between upper-tropospheric cyclones and anticyclones are investigated regarding the height of the thermal and the dynamical tropopause. The problem is addressed in an idealized framework by analyzing axisymmetric balanced flows, which are characterized by a radial scale ?R and a tropopause potential temperature anomaly ??, where cyclones and anticyclones differ only by the sign of ??. The height of the thermal tropopause significantly differs from the height of the dynamical tropopause unless the anomaly is shallow. There is a pronounced asymmetry in that the differences are much larger and more likely to occur in the case of cyclones. Two factors contribute to this asymmetry. First, for a given amplitude |??|, cyclones and anticyclones have different aspect ratios in geometric space; second, for a high-latitude winter scenario the critical lapse rate of the WMO thermal tropopause is asymmetric with respect to typical tropospheric and stratospheric lapse rates. Simulated station statistics regarding the height of the two tropopauses share essential qualitative features with similar statistics from observations. The asymmetry in the model sensitively depends on the lower-stratospheric lapse rate. Multiple tropopauses may greatly enhance the asymmetry.