Towards 3D prediction of supercooled liquid water for aircraft icing: Modifications of the microphysics in COSMO-EU

Abstract

Supercooled liquid water (SLW) in the atmosphere is responsible for aircraft icing which can cause severe accidents. To date, the microphysics scheme in the model of the Deutscher Wetterdienst (DWD) for the European scale (COSMO-EU; due to be replaced by ICON-EU in 2015) has been optimised to forecast precipitation on the ground but not the water phase in the atmosphere. As a consequence, prediction of SLW is rather poor, as was shown in a series of case studies by the Aeronautical Meteorology department at DWD. ADWICE – the tool used by the DWD to predict aircraft icing – therefore does not rely on COSMO model SLW output, but predicts SLW by itself using a simple parcel method. In an effort to improve ADWICE it has been found that this algorithm has its limits and that it should be replaced by SLW prediction from a 3D weather prediction model. To this end it is necessary to improve the SLW prediction in the COSMO model. In this paper we analyse the microphysics scheme of COSMO-EU with respect to SLW production and depletion and present modifications that greatly improve SLW prediction. As reference for two case studies we use radar-lidar-radiometer products from the Meteorological Observatory Lindenberg to verify the change in SLW prediction.

Keywords

• supercooled liquid water
• aircraft icing
• COSMO-EU
• cloud microphysics
• Cloudnet retrieval