| There are numerous sources of error involved when using radar for meteorological applications. Most of the errors involve the power returned from a hydrometeorological target in a given radar volume aloft. A correction scheme is then applied aloft, but not carried to the surface directly. A major assumption when using radar retrieved precipitation observations in hydrological applications is that the precipitation observed aloft impacts the surface directly below the volume sampled by the radar. However, it is well known that rain may be advected laterally considerable distances, implying that rainfall entered into distributed hydrological models will be inaccurate no matter how accurately the rain is measured aloft. In extreme cases, rain may be observed above one catchment and actually fall in another. This problem has received little attention.; This research presented describes a series of experiments based on data obtained from the Sydney 2000 World Weather Research Programme's Forecast Demonstration Project, wherein the advection of the precipitation below the radar sampled volume is estimated using wind fields derived from Doppler radar and an adjoint model. The experiments show that even at standard resolutions of 2.5 km the error can be extensive, and at higher resolutions and greater ranges (higher beam elevations) the errors become very large. The method is robust and could easily be used to account for wind-drift. |
