Rainfall assimilation into limited area models

A physical assimilation technique based on humidity nudging has been developed for application to satellite-derived rainfall fields, in the framework of the European project "EURAINSAT". The aim of the forcing procedure is to improve the short-range precipitation forecasts with particular attention to specific meteorological phenomena, such as heavy orographic precipitation and small-scale "hurricane-like" cyclones in the Mediterranean area. The nudging scheme forces the model humidity profile in order to get model precipitation closer to the observed precipitation. The forcing is a function of the difference between the rain rates, observed and forecasted, and of precipitation type, convective, or stratiform. In addition, a modelling tool to reproduce the idealised development of midlatitude baroclinic unstable modes, including humidity in the atomsphere and a full water cycle, has been developed with the purpose of investigating the effects and capabilities of assimilation of precipitation in an idealised frame. More realistic experiments have been also performed by implementing a lagged forecast procedure, in order to evaluate, with an observing system simulation experiment(OSSE)-type strategy, the scheme's performance in terms of improvements of short-range precipitation forecasts and impact on the dynamics of the meteorological evolution. Finally, satellite rain estimates, based on combined microwave (MW) and infrared (IR) techniques, have been assimilated into the limited area meteorological model trying to improve the short-range precipitation forecasts.