Characterization of the microphysics of precipitation over Amazon region using radar and disdrometer data

摘要

This work presents a characterization of the Amazonian precipitation diurnal cycle through an analysis of radar reflectivity profiles and drop-size distributions attained respectively from a microwave vertical profiler and a disdrometer during the 1999 WET-AMC experiment. In such analysis, precipitation was split in time and classes, which provided information on the daily variation of typical reflectivity profiles and the raindrop spectra associated with them. A clear signature of the diurnal cycle can be observed in the radar profiles and in the raindrop size distribution; for instance, the stratiform rainfall is dominant in the period of 03:00 to 09:00 LST showing the collapse of the convective structures dominant during the afternoon. The time interval centered at 21:00 LST shows the collapse of the ice phase and convective activity, typical of the transition from convective to stratiform precipitation. The size distribution and the reflectivity profiles also depend on the rainfall intensity. The combined analysis of the diurnal cycle and rainfall intensity shows interesting features of the cloud life cycle over the Amazon region, including the initiation of ice and the establishment of the bright band. Statistical analysis revealed that most RDSDs exhibit a single peak around 0.5 mm (48.9%), 1.0 mm (30.7%) or 2.0 mm (2.5%) and that only a few are effectively bimodal, which permitted the use of gamma distributions to fit most of the observed raindrop spectra.