Evaluation of the variational soil moisture assimilation scheme at Deutscher Wetterdienst

✍ Scribed by Reinhold Hess; Martin Lange; Werner Wergen

• Book ID: 104565029
• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 969 KB
• Volume: 134
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.306

✦ Synopsis

Abstract

A two‐dimensional, variational soil moisture assimilation scheme has been in operational use at DWD since 2000. The same scheme was also used and evaluated in the EU‐funded project ELDAS. By design, the scheme leads to improved forecasts of screen level parameters. The present paper discusses if this is achieved in a physically consistent way so that the assimilation process results in more realistic soil water contents. It is shown that overall the scheme behaves well, both in the longer‐term mean and in individual cases. A remarkable result is that the assimilation process for soil moisture also leads to improved quality of precipitation forecasts. Nevertheless, erroneous precipitation forecasts remain the largest error source for soil moisture. The assimilation scheme can successfully compensate for these errors. Using observed precipitation would be better still.

The diagnostics also revealed some unwanted features. They include sometimes large and frequent assimilation changes in the lower layer of the soil model. Reasons for this are discussed and possible remedies suggested. Copyright © 2008 Royal Meteorological Society