Experimental 1D + 4D‐Var assimilation of CloudSat observations

Observations providing three‐dimensional information on clouds from space‐borne active instruments on board CloudSat and CALIPSO are already available and new satellites, such as EarthCARE, should appear in the near future. This opens new possibilities for exploring the usefulness of this kind of observation, not only for improving model parametrizations but also for investigating their usage in data assimilation to extract information from the data so as to improve the initial atmospheric state. In this study, a 1D + 4D‐Var technique has been selected to study the impact of observations related to clouds on 4D‐Var analyses and subsequent forecasts. Using this two‐step approach, temperature and specific humidity profiles retrieved from 1D‐Var assimilation of CloudSat observations have been included in the 4D‐Var system. Several experiments have been run for a couple of selected meteorological situations.