Dual-frequency profiler study of hydrometeor fall speeds in tropical deep convection

This study investigates hydrometeor fall speeds using a dual-frequency profiling radar operating during the 2005–2006 monsoon season near Darwin, Australia. Our focus is on tropical deep convection where the observations provide a new perspective on hydrometeor fall speeds within and near intense drafts having mixed-phase media. The techniques we employ avoid undue assumptions on the air motion or media distributions, offering a convenient path to estimate bulk radar reflectivity( Z )-weighted hydrometeor fall speed ( V t ). While these mixed-phase media estimates are not specific to size or density, they may be replicated by models and are practical for radar-based retrievals that necessitate V t assumptions. Tests performed under rain and snow conditions show comparable performance to disdrometer and other references. The standard deviation of residuals for rain and snow relationships are ≅1 and ≅0.4 m s −1 , respectively. In convective core regions aloft, Darwin observations align with existing graupel V t - Z treatments, however mixed-phase media typically falls faster (>1–2 m s −1 ) for Z <35 dBZ than prior relationships. Breakdowns suggest that Active and Break monsoon conditions favor a similar V t - Z behavior in strong cores. However, Break conditions – those more favorable to intense daytime tropical convection – potentially indicate the presence of additional lofted liquid or melting media mixed in volumes at convective core peripheries Z <35 dBZ. Break events also show higher variability in V t - Z pairs, with select samples having V t faster than rain for a given Z that argues for partially-melted graupel coupled with size-sorting.