Adjoint-Method Retrievals of Low-Altitude Wind Fields from Single-Doppler Reflectivity and Radial-Wind Data

Abstract

The simple adjoint (SA) method is extended to use both the reflectivity equation and the radial-wind equation to retrieve the low-altitude horizontal wind field from single-Doppler reflectivity and radial-wind data. Three extended methods are proposed. The extended method A uses the reflectivity equation and radial-wind equation simultaneously. The extended method B (or method C) uses the reflectivity equation and radial-wind equation alternately with the velocity retrieved from the reflectivity (or radial wind) data first. The first-step retrieved wind is then used to estimate the time-mean residual forcing (or source) term in the radial-wind (or reflectivity) equation, and this estimated forcing (or source) is used as a weak constraint in the second-step retrieval from the radial-wind (or reflectivity) data. The retrieval is expected to be maximally improved when the procedure goes to the third step (and beyond). Tested with the Doppler radar data measured during the Phoenix II field experiment, all three extended methods are found to be better than the previous SA method based on a single (reflectivity or radial wind) equation. Among the three extended methods, method C is found to be slightly better than method A, but slightly worse than method B.