The research seeks fundamental understanding in cloud physics, precipitation physics, radar meteorology, and radiative transfer through clouds. To that end, the researcher, in collaboration with graduate students, plans to conduct theoretical investigations, perform numerical experiments, analyze data from a variety of sensors, and suggest novel experiments. The specific objectives are following.

1. Physics of rain: do all raindrops fall at terminal speed? Theoretical investigation and analysis of data from video disdrometers and Doppler radars will be conducted, with emphasis on fluctuations of raindrop fall velocities and deviations from a terminal speed. This study will have implications for retrieval by profilers, Doppler radars and disdrometers.

2. Radar meteorology: the research will search for coherent backscatter data based on new theoretical analyses. Data analysis from short pulse radars, and exploratory signal processing will be conducted. This study will have implications of recently discovered fluctuations in raindrop surface tension in radar polarimetry. Non-Rayleigh signal statistics of radar echoes and in-phase/quadrature signatures of heterogeneous targets will also be investigated.

3. Cloud physics: Is cloud ice "sloppy"? Study of freezing of supercooled water droplets and the resulting "scarred" ice and theoretical investigation of defect number density in ice versus the degree of supercooling will be carried out. Investigation of diffusional growth of cloud droplets with emphasis on the quasi-steady approximation and associated relaxation times in mixed-phase clouds will be conducted.

4. Radiative transfer through clouds: surfactant-caused change in optical properties and the possibility of hyperspectral signatures in cloud albedo will be investigated.

Intellectual merits: The questions above have not been fully addressed previously. Furthermore, fundamental studies of fluctuations in clouds and precipitation are likely to yield insights into the structure of precipitation media, fundamental processes in clouds, radar signal analysis and interpretation, and light attenuation in heterogeneous materials.

Broader impacts: This research is also likely to have broad impacts on cloud physics and development of precipitation. It will improve characterization of rainfall spatial structure for better rainfall estimation with weather radar, and radiative properties of clouds. In addition, insofar as supercooled water is a metastable liquid, the associated irreversible phase transition is of wide interest in material science. Hence, study of the resulting defect riddled ice is likely to contribute to solid state physics as well as to physical meteorology.

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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A. Gannet Hallar
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Michigan Technological University
United States
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