Impact of the Microphysics in HARMONIE-AROME on Fog

Abstract

This study concerns the impact of microphysics on the HARMONIE-AROME NWP model. In particular, the representation of cloud droplets in the single-moment bulk microphysics scheme is examined in relation to fog forecasting. We focus on the shape parameters of the cloud droplet size distribution and recent changes to the representation of the cloud droplet number concentration (CDNC). Two configurations of CDNC are considered: a profile that varies with height and a constant one. These aspects are examined together since few studies have considered their combined impact during fog situations. We present a set of six experiments performed for two non-idealised three-dimensional case studies over the Iberian Peninsula and the North Sea. One case displays both low clouds and fog, and the other shows a persistent fog field above sea. The experiments highlight the importance of the considered parameters that affect droplet sedimentation, which plays a key role in modelled fog. We show that none of the considered configurations can simultaneously represent all aspects of both cases. Hence, continued efforts are needed to introduce relationships between the governing parameters and the relevant atmospheric conditions.

Use of CAMS near Real-Time Aerosols in the HARMONIE-AROME NWP Model

“…In general, a reduction in N d compared with the reference values increases the terminal velocity, υ, and sedimentation. For a comprehensive study of the different cloud droplet configurations in the model, see [45].…”

Fog Decision Support Systems: A Review of the Current Perspectives

“…As such, Ref. [7] describes the limitations associated with the use of fixed parameters in microphysical parameterizations that do not take the regional variability in aerosol conditions properly into account. The authors highlight the fact that use of existing parameterizations and their parameters to predict fog in contrasting environments is a flawed approach.…”