Inter and intraseasonal variations of cloud and precipiation characteristics over the Amazon Basin, observed with TRMM PR and Cloudsat CPR data

Various observational studies have suggested that convection over the Amazon Basin changes its characteristics between monsoon and premonsoon seasons, as well as between the LBA westerly and easterly regimes. Convections in the former conditions are considered to have more oceanic characteristics compared to those in the latters in which convections are purely continental. In this study, we utilize Cloudsat CPR 2B_GEOPROF data and TRMM PR2A25 data to investigate the inter- and intra-seasonal variations of cloud and preciptation characteristics over the Amazon Basin in comparison with convections over the warm pool and over the African Continent as typical oceanic and continental convections, respectively. We quantify how far convections in the monsoon and in the LBA westerly regimes are of oceanic characteristics compared to their counterparts in the premonsoon and in the easterly regimes, respectively, and how far they still retain continental characteristics.

As a result, frequency distributions of precipitation signals are more oceanic in former conditions in a sense that larger frequencies are observed for convective precipitation lower than 5 km and weaker than 40 dBZ, and less beyond. They are also very oceanic with larger frequencies for most ranges of stratiform precipitation except for very high and weaker than 30 dBZ ranges. On the other hand, diurnal variations of convective and stratiform precipitaion reveal that the former cases are more oceanic in a sense that stratiform fraction is very large but they are still continental in a sense that convective precipitation amount has a large afternoon peak. As for the cloud characteristics, size analyses of CPR-detected cloud systems reveal that while dominant horizontal scale is found in 10-30 km range in all conditions over the Amazon Basin as well as typical oceanic and continental conditions during the daytime, convection over all continental cases including the Amazon are organized into ~100 km scales in the nighttime. Environmental conditions related to these changes in cloud and precipitation characteristics are also discussed.