Improved 3D-Var Wind Retrieval Method for Rainy Conditions

The traditional three-dimensional variational (3DVar) method for wind retrieval is mainly based on the measured radial velocity and continuity equation of the wind field, which is unsuitable for radar data under rainy conditions because of the difference between the velocity of raindrops and the background wind. To address that issue, this paper analyzes the relationship between wind-driven raindrops, background wind velocity, and radar data, and a new constraint equation for the improved 3D-Var method is developed based on the convective diffusion equation. To verify the feasibility of the new method, the trajectories of wind-driven raindrops and corresponding radar detection data are simulated with the aircraft wake vortex as the background wind. Results show that the improved 3D-Var method can directly retrieve the background wind velocity from radar data in rainy areas, and the retrieved wind field exhibits the basic characteristics of the aircraft wake vortex. For the whole simulation area, the root-mean-square errors of the retrieval results in horizontal and vertical directions are 1.25 m/s and 1.60 m/s, respectively.