ATMOSPHERIC DATA ASSIMILATION ON THE EQUATORIAL BETA-PLANE

Kalman filter theory shows great promise when applied to the assimilat ion of atmospheric observations. Previous work has concentrated on ext ratropical dynamics, and tropical aspects have not yet been seriously tackled. In this article, a Kalman filter is applied to the linearized shallow water equations on an equatorial beta plane. The system or mo del error is constructed from the slow eigenmodes of the model and is based on an expansion in parabolic cylinder functions. The resulting s econd-moment statistics are discussed in some detail. The Kalman filte r is applied to a special observation network that allows the diagonal ization of the system. Following Daley and Menard (1993), it is then p ossible to obtain the complete space and time solution for the second- moment forecast and analysis error statistics. The slow (low-frequency ) and fast (high-frequency) error statistics are examined separately f or both the optimal and suboptimal cases.