Interactive comment on Retrieval of three-dimensional wind fields from Doppler radar data using an efficient two-step approach by C
This manuscript is concerned with the description and testing of a variational dualDoppler radar wind retrieval algorithm. The constraints imposed in the analysis procedure are: observational constraints, which incorporate data from two or more Doppler radars (and possibly other data sources, e.g., dropsonde or sounding observations), a mass conservation constraint (sometimes referred to in the literature as a mass continuity constraint), and spatial smoothness constraints. The procedure is general enough to incorporate data from two or more stationary Doppler radars or from a so-called "pseudo-dual-Doppler radar", that is, data from an airborne-radar that, when appropriately processed, are equivalent to data gathered from two stationary Doppler radars. The observational and mass conservation constraints are standard in dual-Doppler analysis procedures. The use of smoothness constraints is standard in variational (e.g., 3DVAR) analysis techniques. The new aspect of this study is a data gridding/reduction step designed to minimize loss of information and to generate estimates of the variances of the reduced velocities. Any improvements made in these directions would be of interest to radar and mesoscale meteorologists as it could potentially improve dualDoppler analyses of a variety of convective and non-convective weather phenomena. The new retrieval is tested with pseudo-dual-Doppler radar data from a tropical depression. Unfortunately, the results from these tests are inconclusive. A comparison of the retrieved horizontal wind vectors with the horizontal wind vectors from an independent data source (dropsondes) does indicate a qualitatively good agreement (Fig. 8). But there is relatively little challenge in obtaining qualitatively reasonable horizontal wind components from dual-Doppler or pseudo-dual Doppler data, especially on the coarse analysis grid indicated on that figure. A more challenging problem and one of prime interest to mesoscale meteorologists is the analysis of the vertical wind component. Apparently it was not possible to evaluate the accuracy of the retrieved vertical wind component in this test case. In the future it would probably be better to consider a more stringent test of the algorithm, perhaps
A Variational Multiple–Doppler Radar Three-Dimensional Wind Synthesis Method and Its Impacts on Thermodynamic Retrieval
Abstract A multiple–Doppler radar synthesis method is developed to recover the three-dimensional wind field. In this method the solutions are obtained by variationally adjusting the winds to satisfy a series of constraints in weak formats. Among them, the primary ones are multiple-radar radial velocity observations, the anelastic continuity equation, the vertical vorticity equation, the background wind, and spatial smoothness terms. The retrieved wind products are at two time levels, and can be readily applied to deduce the information about the pressure and temperature through the use of the thermodynamic retrieval algorithm, in which the temporal derivatives of the wind fields are required. Experiments using model-simulated data are conducted, from which two major findings are obtained. First, the wind field along and near the radar baseline can still be recovered. This is a major advantage over the traditional approach. Therefore, the proposed method is capable of providing uninterrupted observations o...
Three-Dimensional Wind Field Analysis from Dual-Doppler Radar Data. Part II: Minimizing the Error due to Temporal Variation
Abstract One of the major problems in three-dimensional wind field analysis from dual (or multiple) Doppler radar data resides in the non-stationary of the observed air flow within the volume sampling time which ranges typically from 2 to 5 min. The present part II is focused on this problem. Most often, the storm moves horizontally at a speed of 5–25 m s−1.Therefore, the temporal variation for a fixed observer at ground level results from the superposition of two effects: 1) the intrinsic temporal variation (or variation seen in a frame moving with the storm) and 2) the effect of horizontal advection. The first contribution of the paper concerns the development of an algorithm for correcting for the advection effect in the case of a dual-Doppler radar observation. This algorithm, which provides a mathematically exact solution to the problem of correcting for advection, can be very easily implemented in a computer program. The second contribution deals with the errors that may arise from an accurate (or l...