Using the concept of the Dynamic State Index for a scale-dependent analysis of atmospheric blocking

Abstract

The present study investigates the phenomenon of atmospheric blocking using a cascade of Dynamic State Indices. The different DSI variants signalize model dependent aspects of atmospheric blockings, which allows for a scale-dependent analysis of the corresponding flow pattern. Starting from the primitive equations, approximations lead to the reduced equations of the quasi-geostrophic model and the further approximated barotropic Rossby model. For each model a corresponding Dynamic State Index can be derived. All DSI variants underlie the same concept, such that the three variants capture the stationary and adiabatic state as well as their local deviations. The DSI variants are investigated in the framework of a case study of the atmospheric blocking phenomenon over the European part of Russia in summer 2010. Two main results are presented: (i) The anticyclone of the block is characterized by a large area with nearly vanishing DSI values in all three models. In contrast, the typical DSI dipoles along the jet that surrounds the block differ, dependent on the level of the model reduction, not only in the spatial extent but also in the amplitude. (ii) The DSI variants shows the difference of the impact of the diabatic processes related to precipitation concerning the back and front side of the high. The amplitudes of the negative mean of DSI values on the back side of the high, respectively the amplitudes of the positive DSI mean on the front side, is larger for the primitive equations than for the quasi-geostrophic model. Thus, the DSI is a unified concept for atmospheric dynamics designed to diagnose the scale-dependent footprints of the steady and adiabatic conditions as well as non-steady and diabatic processes depending on the level of the model reduction.