The Application of Specific Attenuation for Rainfall Estimation in Complex Terrain in Taiwan

To improve the accuracy of quantitative precipitation estimation (QPE) in complex terrain, a new rainfall rate estimation algorithm was developed and applied on two C-band dual-polarization radars in Taiwan. In this algorithm, the specific attenuation (A) was utilized in the rainfall rate estimation, and several parameters involved in the A field calculation were derived using the local drop size distribution (DSD) and drop shape relation (DSR) observations. In areas of complex terrain where the lowest tilts are completely blocked and data from higher tilt is used in the QPE, a vertical profile of specific attenuation (VPA) correction was applied to account for the vertical variations in the A field. The VPA correction was shown to provide positive impact on the accuracy of estimated rainfall in severely blocked areas. The R(A)-VPA scheme was tested on different precipitation cases including typhoon, stratiform and convective storms. Compared to existing rainfall estimation approaches such as R(Z) and R(KDP), the new method was able to provide more accurate and robust rainfall estimates when the radar was miscalibrated, its radar signal was significantly attenuated, and when the lower tilts of the radar beam were totally blocked.