Last updated: 2008
See also: final report | workshops
Quantitative precipitation forecasting (QPF) is one of the most important reasons to utilize and pay for a numerical weather prediction model, both for forecasters and customers. Unfortunately, it is also among the most difficult parameters to quantitatively forecast for an NWP model, and the COSMO is not doing a particularly good job at it (other models may not be much better, though).
This project aims at looking into the COSMO deficiencies concerning QPF by running sensitivity experiments on a series of well chosen cases which have verified very poorly. If successful, the outcome of these sensitivity experiments will be a more effective set of COSMO namelist or model parameters for QPF, or a clear idea of what parts of the model need to be reformulated and improved most urgently to obtain better quantitative precipitation forecasts.
There are various indications, both from verification (WG5) and from forecasters in various COSMO countries, that the COSMO has serious deficiencies in forecasting precipitation. Some of these problems are longstanding (and not necessarily unique to the COSMO), some others seem fairly recent. This project aims at collecting, consolidating, and highlighting these deficiencies in order to then investigate, understand, and possibly improve some of them (for more details on the individual tasks, see the respective section below).
This task is focused on getting a better and quantitative idea of the COSMO problems related to precipitation. This will include a consolidation of the available problem reports from all the COSMO member states and all the 7 COSMO implementations (i.e., LM-DWD/LME, aLMo, LAMI, EuroLM, LM-HNMS, LM-IMGW, LM-NMA) , as well as a thorough assessment of the existing verification results from all the partners.
This will result in a first list of test cases. To ensure that the observed COSMO problems are not due to an old version of the model (or a very specific COSMO implementation), the test cases will then be run with a LM reference version, and the test cases, for which the COSMO reference version reproduces the QPF deficiencies, will constitute a final list of test cases recommended for sensitivity studies.
The second task will be to establish a standardized set of model changes for sensitivity studies, starting from the suggestions of the experts from working groups 1 to 3 (i.e., data assimilation, dynamics and numerics, physics).
This task is to investigate the sensitivity of the COSMO for the weather situations and test cases identified as error prone by the verification efforts (task 1) with respect to the standardized set of model changes (task 2).
This fourth task is to run idealized moist benchmark cases for the same set of standardized model changes. Additionally, the benchmark cases can also be used to determine the most sensitive parameters of the model to define the set of standardized model changes in the first place.
Finally the results of the project will be published in a peer-reviewed journal.
The project was completed in 2007 and only reporting and publication (task 5) were left for 2008. The Final Report was prepared in March 2008. It is available as a pdf file (download (6.2Mb))