RAIN RELATIONS INFERRED FROM MICROPHYSICAL DATA IN TOGA COARE AND THEIR USE TO TEST A RAIN-PROFILING METHOD FROM RADAR MEASUREMENTS AT K-U-BAND

The first part of this paper is dedicated to establishing relations am ong rain-integrated parameters representative of west Pacific precipit ation. This is achieved by using airborne microphysical data gathered within a rain event on 6 February 1993 during the Tropical Ocean and G lobal Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA CO ARE). The relations between the rain rate R, the reflectivity factor Z and the attenuation coefficient K are calculated for moderate to heav y precipitation at 13.8 GHz. They give twice as much attenuation for a given Z than the relations obtained for an exponential distribution w ith N-0 = 8 x 10(6) m(-4). This effect is related to the large number of small size particles observed in TOGA COARE convective systems. In the second part of the paper, these relations are used to check the re liability of a rain-profiling method applied to ARMAR (airborne radar- mapping radar) observations at 13.8 GHz in the same rain event. This m ethod provides a bulk correction factor that can be interpreted primar ily in terms of a change of the initial Z-K relation. Then, the algori thm provides modified Z-R and K-R relations while assuming a gamma or an exponential-shaped distribution for raindrops with a constant N-0. For the selected case study, the adjusted relations agree very well wi th those derived from the microphysical measurements. An exponential s hape model with constant N-0 for the DSD is found to provide results t hat are consistent with the microphysical measurements. Moreover, the derived N-0 value is close to that inferred from the radar algorithm. The impact of modifying the initial rain relations in the radar algori thm on the rain-rate estimates is also discussed. The retrieved rain r ates are not very sensitive to the choice of initial relations except for very high values. Finally, the results are found more representati ve of convective rain than stratiform precipitation.