Radar/rain-gauge comparisons on squall lines in Niamey, Niger for the AMMA

Abstract : Massachusetts Institute of Technology C-band radar observations are integrated with rainfall measurements from an extensive network of gauges in Niamey, Niger, West Africa, for the African Monsoon and Multidisciplinary Analysis (AMMA). The large number of gauges available enabled Z e-R power-law relationships for the convective and stratiform regions of individual squall lines. The Z e-R relationships based solely on radar measurements directly over the gauges were developed for the estimate of rainfall and attendant latent heat release (by other AMMA investigators) where gauges were unavailable. The low prefactor values of the Z e-R power laws relative to like values for Z-R disdrometer power laws have contributions of order 1-2 dB from the use of the lowest beam tilt (0.57 •) and ∼1-2 dB by the radar reading low. (The sphere calibration and the Tropical Rainfall Measuring Mission TRMM-radar calibration are inconsistent at the 1-2 dB level for unknown reasons.) Radar/gauge comparisons are also shown for individual storms. Accurate, unbiased results for the convective regime require adjustment of the radar-to-gauge radials for attenuation. Beam filling problems and aliasing issues can often be identified in the case of outlier points.