Rainfall Assimilation through an Optimal Control of Initial and Boundary Conditions in a Limited-Area Mesoscale Model

Abstract

To assess the impact of rainfall observations on short-range forecasts of precipitation, and to improve our understanding of the physical processes responsible for the development of a mesoscale convective system (MCS) associated with the dryline that occurred on 10 April 1979 in the midwestern United States, a series of four-dimensional variational data assimilation experiments was conducted based on the special dataset collected in the Severe Environmental Storm and Mesoscale Experiment. A nonhydrostatic mesoscale model (MM5) with a relatively simple moist physics and its adjoint were used for both the model simulation and data assimilation. A previous numerical simulation of this MCS, based on conventional initialization procedures, failed to correctly simulate the location and intensity of the observed rainfall. This is attributed to the lack of mesoscale details in the model's initial conditions for the low-level moisture convergence and the upper-level disturbances related to the upper-leve... Abstract To assess the impact of rainfall observations on short-range forecasts of precipitation, and to improve our understanding of the physical processes responsible for the development of a mesoscale convective system (MCS) associated with the dryline that occurred on 10 April 1979 in the midwestern United States, a series of four-dimensional variational data assimilation experiments was conducted based on the special dataset collected in the Severe Environmental Storm and Mesoscale Experiment. A nonhydrostatic mesoscale model (MM5) with a relatively simple moist physics and its adjoint were used for both the model simulation and data assimilation. A previous numerical simulation of this MCS, based on conventional initialization procedures, failed to correctly simulate the location and intensity of the observed rainfall. This is attributed to the lack of mesoscale details in the model's initial conditions for the low-level moisture convergence and the upper-level disturbances related to the upper-leve...