RW-FCST

English

Phase 1: Sensitivity of severe weather over Europe to upstream wave trains and related processes

Volkmar Wirth, Hartmut Borth, Ilona Türschmann

Institut für Physik der Atmosphäre, Universität Mainz

Phase 2: Diagnosing Rossby wave train errors in numerical weather forecasts

Volkmar Wirth, Gabriel Wolf

Institut für Physik der Atmosphäre, Universität Mainz

Summary

Severe weather over Europe is known to be occasionally associated with long-lived wave trains. This suggests potential predictability on the time-scale of a week and even longer — a potential which is far from being exploited today. As a prerequisite for improved forecasts this project in its second phase aims to diagnose deficiencies in current weather forecast systems regarding the generation, propagation, and decay of such long-lived wave trains. During phase 1 we demonstrated that in a climatological sense severe weather over Europe is associated with distinct long-lived wave trains. We developed a novel diagnostic to automatically identify Rossby wave trains from a Hovmöller Diagram using an envelope of the meridional wind. Further, we used this method to quantify the predictive skill of a numerical weather prediction model regarding Rossby wave trains. The project will be continued during phase 2 by significantly advancing and extending the analysis. First, we shall apply our new diagnostic to systematically quantify forecast errors in long data sets. In addition, we shall explore and develop the utility of so-called “wave activity flux” diagnostics, which are distinct from and partly complementary to the more conventional diagnostics including our own one. We shall apply our diagnostics to ensembles of forecasts in order to learn how well these are able to quantify forecast uncertainty regarding long-lived wave trains. Overall, this project pursues similar goals as RW-GUIDE, but uses vastly different and largely complementary methods.

Work done in phase I:

  • Development of a novel method to automatically identify Rossby wave trains as well as their properties
  • With this method we:
    -  Investigated the predictive skill of a NWP model regarding a special Rossby wave train
    -  Created a climatology on Rossby wave trains
  • Comparison of the novel method to several other methods for the identification and quanification of Rossby wave trains

Detailed information of phase I

Outline of phase 2