Role of diabatic processes in the dynamics and predictability of extra-tropical cyclones

English

Role of diabatic processes in the dynamics and predictability of extra-tropical cyclones

Heini Wernli, Jana Campa, Maxi Boettcher

Institut für Physik der Atmosphäre, Universität Mainz

Phase 2: DIAP

Completed work

Maxi Boettcher and Heini Wernli: "Investigation of diabatic Rossby-wave dynamics"

Jana Campa and Heini Wernli:

Summary

Baroclinic instability is the basic mechanism responsible for the growth of extratropical cyclones. Most frequently, tropopause-level disturbances act as cyclogenesis precursors. However, it is known from several case studies that the release of latent heat due to condensation can significantly enhance cyclone growth and alter the structure of storms. In certain cases, it has been hypothesized that diabatically generated, low-level potential vorticity anomalies (so-called diabatic Rossby waves, DRWs) triggered the explosive development. In this project, the role of diabatic processes for extratropical cyclones will be investigated for the first time in a systematic way. Using reanalysis data, diabatic contributions to the intensification of individual cyclones will be quantified in order to obtain a statistical relationship between storm intensification and the along track latent heat release and surface fluxes. Application of the diagnostic to deterministic and ensemble forecasts will allow quantify the role of diabatic processes for cyclone forecast errors. A refined tracking algorithm will be developed to identify DRW-like cyclones, to build a climatology and assess the predictability of this feature. A selection of cases will be simulated with a high resolution numerical model for gaining a deeper understanding of the physical processes that are involved in the evolution of potentially hazardous cyclones in the North Atlantic / European region.

Aims

To investigate the role of diabatic processes (latent heat release due to cloud condensation, surface fluxes) for the genesis, intensification and predictability of extratropical cyclones. A particular focus will be on the analysis of diabatically driven cyclones, so-called diabatic Rossby waves. During the first phase we will conduct a climatological evaluation of the link between moist processes and cyclone intensity using reanalysis data and operational and ensemble forecasts and will study diabatic Rossby waves in analysis and forecast data. High-resolution numerical experiments with the COSMO model will serve for an in-depth analysis of the physical processes at play for a selection of case studies. Results from these climatological and model-based studies will contribute essentially to the set-up of the planned European THORPEX experiment T-NAWDEX that will take place during the second phase.