An examination of the effect of wind-drift on radar-derived surface rainfall estimations

The error in location caused by the non-vertical fall of precipitation from the height at which it was observed by radar to the surface has long been remarked upon, but rarely examined. The study described in this paper uses wind fields determined using Doppler radar to estimate the trajectories of falling drops and thereby assess the error induced in surface rainfall rate that is found using radar observations of precipitation aloft. The authors examine real data as well as using that data to simulate changes created by changing resolution and radar beam height.The results show how great the errors could be under certain circumstances. This is particularly the case with high-resolution observations and situations involving low-level directional wind shear. This leads to a comprehension of the complexity of correcting those errors, as determining the trajectory of drops requires detailed knowledge of wind profiles. These profiles may vary on small spatial and temporal scales, especially during the kind of convective episodes for which wind-drift is most likely to cause the greatest uncertainty in retrieved rainfall.