Investigating Raindrop Evaporation, Breakup, and Coalescence in GoAmazon Observations

Poster PDF

Description

This poster will describe a three-step process investigating evaporation, breakup, and coalescence processes acting upon falling raindrops in stratiform rain during the GoAmazon field campaign. The first step of this study exploits the Rayleigh and non-Rayleigh scattering signatures in 1.29- and 94-GHz (UHF and W-band) vertically pointing radar Doppler velocity spectra observations to retrieve profiles of vertical air motion and raindrop size distributions (DSDs) during stratiform rain observed during GoAmazon. These DSD retrievals are referenced to surface disdrometer observations and extend throughout the liquid rain layer below the mixed-phase melting layer. The second step of this study quantifies the intensity of the precipitation using liquid water content (LWC) and describes the DSD using the total number concentration (Nt) and characteristic mean size and breadth. Using decomposition diagrams (Williams 2016), evaporation is quantified by the change in LWC with height. If evaporation is negligible, then changes in Nt and DSD shape on the decomposition diagram provides net signatures of breakup and coalescence processes. If evaporation is not negligible, then changes in the DSD with height are too complex to isolate evaporation, breakup, and coalescence processes. Thus, modeling of the DSD evolution is needed to infer the relative roles of the individual processes. The last step of this study will address the relative roles of evaporation, breakup, and coalescence processes by embedding a single-column collision-induced breakup model into a radar simulator. While this third step is still under development, the plan is to adjust the single-column model parameters at each range gate so that the simulated 1.29- and 94-GHz Doppler spectra match the observed spectra. The output of these simulations will be profiles of model parameters that quantify the microphysical processes. Williams, C.R., 2016: Reflectivity and liquid water content vertical decomposition diagrams to diagnose vertical evolution of raindrop size distributions. J. Atmos. Oceanic Technol., 33, 579-595, doi: 10.1175/JTECH-D-15-0208.1.