Assimilating Rain-Affected Microwave Radiances Withing Tropical Cyclones Using the COAMPS Adjoint Model

This work focuses on some of the issues related to directly assimilating rain-affected radiances. The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) adjoint model and an adjoint radiative transfer model that accounts for scattering from hydrometeors are utilized for these experiments. The COAMPS adjoint model includes an explicit moist physics parameterization so that hydrometeor concentrations are a prognostic variable.

Results from tests of the COAMPS tangent linear model with meaningful perturbations will be shown to demonstrate the validity of the linear assumption in the presence of moist physics. Additionally, rain-affected microwave radiances were assimilated in four-dimensional variational (4D-Var) experiments to improve the initial representation of hydrometeor fields associated with tropical cyclones. The best analysis results were obtained in assimilating lower frequency channels and producing analyses of liquid hydrometeors. Improving the assimilation of higher frequency channels (which have better spatial resolution than the lower frequency channels) and the analyses of frozen hydrometeors remains a challenge. Furthermore, more work is needed to demonstrate that these observations can have a positive forecast impact on both precipitation and conventional model variables such and wind and temperature.