Collaborative Research: Development of a Phase Doppler Interferometer for Characterization of Particle-Turbulence Interactions in Clouds

Michigan Technological University, Houghton MI

Investigators

Abstract

This grant supports the development of a phase Doppler interferometer (PDI) to observe the interaction of fine-scale turbulence and droplets in clouds. The scientific goal is to evaluate the extent to which turbulence influences collisions and coalescence, the processes whereby cloud droplets can interact with each other and grow to produce rain. Phase Doppler interferometry is an optical technique for measuring both the size of individual particles in the small volume defined by the intersection of two laser beams and the velocity of the particles relative to the instrument. The PI will work with Dr. Patrick Chuang of the University of California-Santa Cruz and Dr. William Bachalo of Artium Technologies to design and build a PDI especially suited for measuring cloud droplets. The plan is to develop an instrument capable of measuring the size, velocity, and spacing between droplets with diameters between 2 and 200 micrometers. Special attention will be given to problems common to optical detection devices, such as coincidence errors and the dependence of the volume sampled on the drop size. Testing the instrument in laboratory conditions, using existing wind tunnels and cloud chambers, will be an important part of validating its performance. Although the ultimate goal is to mount the PDI in an airplane for in-cloud measurements, the investigators will carry out initial experiments on laboratory clouds and in field deployments on towers or suspended from tethered balloons. There has long been speculation about the possible effects of turbulence on the collision-coalescence process of rain production. This instrument will fill an important gap in knowledge by actually observing the turbulent motions of cloud droplets at the small scales relevant for the process.