Assimilation system adaptation and maintenance for cloud radar and lidar obs

A key objective of this work package is to ensure that the system developments for cloud radar and lidar observations are maintained along with the evolving operational model at the European Centre for Medium-Range Weather Forecasts (ECMWF). At the first step of this on-going effort, the previous assimilation system developments for these observations were adapted to the Integrated Forecasting System (IFS) model cycle, CY46R1, the cycle used at the beginning of this project in October 2019. After successful moving of those developments to the model cycle CY46R1 and based on experimentation done using this cycle, some adjustments and minor corrections have been required. The porting, debugging and testing required in order to make the updated system with cloud radar and lidar observations functional is described. In the next step, the assimilation system was ported to the higher IFS model cycle, CY47R1, as part of preparations to include these developments in CY48R1 in order to appear passively in the operational code when releasing this cycle in 2022. Basic testing of the developments in CY47R1 has been done. That included a comparison of the analysis increments between cycles CY46R1 and CY47R1, as well as checking the bit reproducibility of the system when cloud radar and lidar observations are switched off (i.e. to ensure that the passive observations do not modify any integration of the operational code). During the project, the system has been updated to use, on top of already included cloud radar reflectivity and lidar backscatter, for other observations such as cloud Doppler velocity, lidar extinction and lidar Rayleigh backscatter. The technical developments and modifications for that are also described in this report. Finally, summary of modifications and corrections to the assimilation system for cloud radar and lidar observation to be able to use it in the most recent IFS model cycle, CY48R1, is provided. These were required because of: (i) starting to use the model cycle running on new computer at ECMWF’S new Data Centre in Bologna, (ii) running IFS Four-Dimensional Variational (4D-Var) data assimilation under the framework of the Object-Oriented Prediction System (OOPS) and (iii) corrections and modifications as outcome of extensive testing for cloud radar and lidar observations done when using still the cycle CY46R1. Basic testing of the system in CY48R1 is also discussed.