Diabatic Dynamic Initialization with an Iterative Time Integration Scheme as a Filter

Abstract

A new diabatic dynamic initialization technique using an iterative time filter has been developed for an intermittent global data assimilation system. The diabatic dynamic initialization procedure has been implemented within the Goddard Earth Observing System (GEOS) Data Assimilation System employing the GEOS General Circulation Model. The initialization method employs only the forward full diabatic model integration as the initial balancing procedure. The initial balancing is accomplished efficiently by using a new iterative Euler scheme as a filter. The iterative Euler scheme converges rapidly after only a few iterations. It provides a filter most effective for the high-frequency and small-scale modes. The initial spinup effect is almost entirely eliminated, and initially disturbed external and internal modes are balanced by the initialization procedure during the first few time steps. After the short initialization procedure is completed, the standard model integration is continued with the resulting initialized fields, which are now free of noise and spinup effects. Using the new initialization technique, monthly mean analysis and diagnostic fields have been calculated for January and February 1989. The results obtained show the positive impact of the initialization procedure. In particular, the Hadley circulation has been improved. Most importantly, the global rms height and wind errors calculated against the radiosonde data at station locations are significantly reduced. A set of five comparative 10-day forecasts calculated from initialized and uninitialized analyses show that the scores are moderately to marginally better for the initialized cases. The initialization procedure is computationally efficient and can be easily applied to various large-scale and mesoscale models/systems.