The fog above sea problem in Harmonie: Part 1 Analysis

A few years ago the Harmonie model was gradually introduced in our operational practice at KNMI. Since the start it has proven its value, especially in cases of extreme weather. There are however still important deficiencies. During the cloud and convection workshop in Norrköping October 2012, high priority was given to the fog above sea problem. Several times and at different institutes, Harmonie produced large and persistent fog fields above sea, which were not observed. Especially in The Netherlands these unrealistic fog fields are problematic as our main airport is located close to the coast. Besides, these erroneous fog fields decrease the credibility of the model to customers and forecasters. Several physical processes and parameterizations can contribute to the formation of fog. Here we present an analysis of some of the most plausible processes related to the production of excessive fog.