Analysis of Tropical Rainfall Properties during GoAmazon2014/5 using Radar and Disdrometer Observations

The relationships between tropical convection and local and large-scale environments involve complicated feedbacks between clouds, aerosols, and precipitation. Due to the lack of detailed knowledge concerning these interactions, accurate simulations of convection and the aforementioned feedbacks are extremely difficult. GoAmazon2014/5, a DOE sponsored field campaign, provides a unique opportunity to advance research in this area using data collected near Manacapuru, Brazil (3°S, 60°W) in the central Amazon from 2014-15. The region experiences distinct wet and dry seasons, during which large mesoscale convective systems (MCSs) and isolated thunderstorms, respectively, are predominant. Furthermore, the diurnal cycle in precipitation has been shown to influence the atmospheric boundary layer and chemical transport during the wet and dry seasons. Given these characteristics, along with the close proximity of the Manaus pollution plume to the main DOE observation site in Manacapuru, the GoAmazon campaign allows for the relationships between tropical clouds, precipitation, and aerosols to be explored.
This study will analyze radar and disdrometer observations to highlight variations in rain properties during GoAmazon over a variety of time and space scales. Parsivel and Joss-Waldvogel disdrometers will be used to assess drop size distributions (DSDs) near Manacapuru, while the Brazilian military (SIPAM) operational S-band radar in Manaus will be used to provide a broader context of rain patterns. The two-year time series of the campaign allows for a thorough comparison to be made between tropical MCS and isolated thunderstorm activity, thus highlighting any seasonal and diurnal differences in rain characteristics. The disdrometer observations will also be analyzed alongside the outputs of a new technique based on observations made by the SIPAM radar. This technique (termed the ‘descending arm’) was first introduced by Gerken et al. (2016) and involves using localized (i.e., 22 km x 22 km) reflectivity patterns from approximately 7 km to the surface to deduce the presence of a strong, localized downdraft. The descending arm has been linked to enhancements of ozone at the surface, indicative of vertical chemical transport during the GoAmazon campaign. This study will present analyses of the aforementioned parameters during case studies where a descending arm and/or an ozone spike are both present and absent. Convective downdrafts are also precursors for convective cold pools, which play an integral role in the initiation and organization of convection. Understanding how rainfall and DSD parameters change in the vicinity of these downdrafts, and how these relate to the presence of descending arms, will provide a useful foundation for further research on tropical cold pools. The presence of the Manaus pollution plume will further allow for comparisons of these parameters between polluted and non-polluted tropical environments, and to what extent rainfall is altered in the region when pollution is present.