Diabatic Dynamic Initialization

Abstract

A generalized dynamical adjustment procedure has been applied to a diabatic model to produce balanced initial conditions. Namely, backward adiabatic model integration is followed by forward diabatic model integration, with a high-frequency (low-pass) filter in the form of the Euler backward time-differencing scheme being applied throughout the whole integration. As a result of the application of such a diabatic dynamic initialization procedure within the Goddard Laboratory for Atmospheres (GLA) 4D data-assimilation system, the following properties of forecasts from initialized fields are achieved right from the beginning of the usual forecast integration: 1) the forecast tendencies (and fields) are free of any noise due to imbalance in initial conditions, and 2) the shocks related to an initial imbalance between model physics and dynamics (and especially the substantial initial imbalance of precipitation and evaporation fields), or the initial spinup effect, are practically removed. Diabatic dynamic initialization has been compared with implicit nonlinear normal-mode initialization and found to be superior in removing the initial spinup effect and in improving the tropical structure. The diabatic dynamic initialization procedure has been successfully tested for the GLA system with the use of all conventional data and the GLA satellite data retrievals. It allows a smooth data insertion without any shocks or imbalances, which is highly desirable for efficient functioning of 4D data-assimilation systems. The developed initialization procedure is computationally efficient and in principle easily applicable to different large-scale and mesoscale forecast models.