HARMONIE-AROME 4D-Var

Abstract

The status of CY43 HARMONIE-AROME 4D-Var is presented. Central to the HARMONIE-AROME 4D-Var implementation is the multi-incremental approach and the current setup comprises two outer loops at six and three times the main forecast grid resolution of 2.5 km. This setup is flexible though, as is the length of the observation window. Results will be given for 4D-Var in comparison to 3D-Var for three domains, centered around Scandinavia, the Iberian Peninsula and the Netherlands. The starting point here is that both 3D-Var and 4D-Var are using identical observations types. Generally speaking it can be concluded that 4DVar forecasts are superior. The paper also gives an extensive list of opportunities from which particularly HARMONIE-AROME 4D-Var can benefit. For example, increasing the observation set, improving the treatment of observations during the observation window and new algorithmic avenues.