Accurate Characterization of Winter Precipitation Using Multi-Angle Snowflake Camera, Visual Hull, Advanced Scattering Methods, and Polarimetric Radar

Colorado State University, Fort Collins CO

Investigators

Abstract

This award will establish a novel approach to characterization of winter precipitation and modeling of associated polarimetric radar observables, with a longer-term goal to significantly improve the radar-based quantitative precipitation estimation in stronger, more hazardous, winter events. The principal enabling technologies are (i) multi-angle snowflake camera (MASC), (ii) visual hull (VH) geometrical method for reconstruction of 3D hydrometeor shapes, (iii) fast and accurate advanced higher order computational electromagnetics (CEM) scattering methods, and (iv) fully polarimetric data from the advanced CSU-CHILL radar. The main objectives of this research and methods to be employed are: - Microphysical and realistic 3D-geometrical characterization of ice particles using MASC - Combining fall speed and particle geometry to estimate density-"size" power laws, snow rates - Calculations of "particle-by-particle" scattering matrices and polarimetric radar observables - Sensitivity studies of various parameters of scattering models in simulations of radar measurables - Analysis and cross-validation of CSU-CHILL and MASC/VH/CEM data for winter precipitation events - Derivation and validation of radar-based snow rate relations for previously classified particle types Intellectual merit is contained in and warranted by the research objectives described above. Overall, it is in the synergistic use of new research instrumentation (MASC) coupled with accurate, efficient, versatile, and robust CEM scattering methods as well as state-of-the-art polarimetric radar (with exceptional polarization purity) to substantially increase the accuracy of modeling of radar observables and characterization of winter precipitation. This is the first time real (measured) snowflake images will be used with highly accurate and efficient realistic scattering calculations, to obtain radar measurable parameters, which will be validated by a highly precise polarimetric radar. This will be the first set of high-quality multi-year data for scattering matrices and the full set of radar observables for MASC-based classified particle types constituting winter precipitation. The full-wave CEM modeling approach to atmospheric particle scattering based primarily on the higher order method of moments (MoM) will be able to overcome all shortcomings of both the T-matrix and the DDA methods. Snowflake 3D shape reconstruction by the VH method based on three MASC photographs is much more accurate than any other available snowflake shape reconstruction examples. This research will significantly improve, in a longer term, the radar-based estimation of liquid equivalent snow rates near the surface in stronger, more hazardous, winter events by first classification of precipitation type followed by quantification. Winter precipitation studies using the combined MASC and OTT-Pluvio snow gauge will impact microphysical parameterizations used in advanced cloud resolving models. "Look-up tables" with comprehensive scattering properties of ice hydrometeors, obtained by MASC/VH/CEM-methods, at multiple radar/radiometric sensor frequencies from 3-150 GHz, should be of interest and use for many researchers in the field. Radar-based snow rate relations will be directly applicable to improved quantification of winter precipitation by the WSR-88D network. This research is also aimed at establishing and promoting the full-wave CEM modeling approach and the higher order MoM as an enabling resource and technology for future research in atmospheric particle scattering analysis. Applications may be extended to radiometric cloud/snow detection and mm-wave radars. Having potential to change the way characterization of winter precipitation is done; this research is transformative in its nature. Educational and outreach activities include training of two Ph.D. students, a new course on scattering by precipitation particles, advanced workshops with a series of seminars/lectures on the topics of the project for graduate students, faculty, and scientists within the Colorado Front Range, and K-12 outreach workshops on Snowflake Research for high school students.