|Title||Observing system impact assessment using a data assimilation ensemble technique: application to the ADM-Aeolus wind profiling mission|
|Publication Type||Technical memorandum|
|Secondary Title||ECMWF Technical Memoranda|
|Authors||Tan, DGH, Andersson, E, Fisher, M, Isaksen, L|
Ensembles of parallel 4D-Var data assimilation cycles have been used to assess the impact of two observing systems: (1) the exisiting network of radiosonde and wind profilers and (2) the future spaceborne ADM-Aeolus wind-profiling lidar. We demonstrate that this new technique for impact assessment provides a practical alternative to the traditional observing system simulation experiments (OSSE), with the particular advantage that real existing observations are assimilated exactly as in operational practise, and do not need to be simulated artificially. It is only the future observing system(s) under test (ADM-Aeolus in our case) that are generated through simulation. Unlike OSSEs, there is also no need to generate an artificial reference atmosphere ('proxy truth' or 'Nature Run'), and the problems normally associated with identical-twin experiments are thus avoided. Based on detailed simulation of the ADM-Aeolus wind-measuring capabilities and expected data quality, our results show that ADM-Aeolus will provide benefit comparable to the radiosonde and wind-profiler network, with analysis impact particularly over ocean, and in the tropics. The impact is retained to the medium range (e.g. day 5) of forecast. Our results for radiosonde and wind-profiler impact qualitatively agree with those obtained with the well-established observing system experiment (OSE) technique, which gives reason for some confidence in the usefulness of the ensemble-based technique for impact assessment.