Comparison of Thermodynamic Retrieval by the Adjoint Method with the Traditional Retrieval Method

Abstract

The adjoint technique for retrieval of the thermodynamic fields is compared with the traditional technique of Gal-Chen and Hane. The comparison is performed using both Doppler radar observations and simulated data. The real dataset is a gust-front case observed during the Phoenix II experiment. The simulated data are from a numerical experiment of a collapsing cold pool. In the simulated data study, we assume that observations of the horizontal velocity are available, either from a dual-Doppler synthesis or from a single-Doppler retrieval. Tests are performed on data that have been degraded in various ways to replicate real data. These tests include the sensitivity to the temporal sampling frequency, random error, spatially correlated error, and divergent/rotational error in the forcing terms. In most of the cases examined, it is found that the adjoint method is able to retrieve the buoyancy field more accurately than the traditional technique.