The adjoint method is applied to tropical rainfall events measured during the TOGA-COARE IOP(Tropical Ocea-Global Atmosphere, Coupled Ocean Atmosphere Response Experiment) to retrieve wind fields from single-Doppler radars. The method is used for rainfall echo not for clean-air echo because radars used in TOGA-COARE can not detect clean-air echo. The effects of cost function and initial guess field on the retrieval fields are examined. Comparing the results with dual-Doppler analysis fields indicated, this method can retrieve the horizontal wind fields more accurately than vertical and the radial velocity defined by the model output, u,v, and w, is not valid in real radar data. Therefore, the difference between model output and initial guess is added to cost function. Several initial guess fields are tested because the results are highly influenced by initial guess field and the best initial guess field is achieved by synthesis of VAD and observed radial velocity.