Radar and aircraft observations of precipitation evolution in trade wind cumuli
Abstract
Understanding the processes involved in the formation of rain is critical to producing accurate weather forecasts. The process by which droplets large enough to initiate coalescence are created in a realistic time frame is one of the key uncertainties. One potential reason for the accelerated onset of coalescence is the presence of giant aerosol particles. These particles are large enough that coalescence can begin earlier than with smaller aerosol particles, thus initiating the formation of precipitation. Past modeling and observational studies have shown that giant aerosol particles can be important for rain formation in continental clouds, but studies have disagreed regarding the importance of these aerosol particles in maritime clouds. The present study investigates the possible role of giant aerosol in marine trade wind cumuli through the use of extensive data collected during the Rain in Cumulus over the Ocean field campaign and a new three-dimensional visualization tool developed at Purdue. This tool is capable of combining data from different sources at widely varying scales and utilizes new visualization and user interface techniques that offer new perspectives on observational data. Existing giant aerosol particle concentration and cloud droplet number concentration data are used to characterize giant aerosol particle and cloud condensation nuclei for each day in the study, and the evolution of entire lifetimes of selected clouds on each day is tracked with dual-polarization radar data. This study reveals that giant aerosol particles have a varying role in precipitation formation. Comparing the radar echo evolution to measured giant aerosol particle and cloud droplet number concentrations for each day, along with observations of cloud depth and lifetime, the importance of giant aerosol particles to rain formation in trade wind cumuli appears to be modulated by several factors, including cloud depth, giant aerosol particle number concentration, and cloud droplet number concentration. In most cases, giant aerosol particles appeared only to be important to precipitation initiation when some other factor was acting to inhibit it, such as greater droplet concentrations or shallow clouds.
Degree
M.S.
Advisors
Lasher-Trapp, Purdue University.
Subject Area
Atmospheric sciences
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.