Field Studies of Raindrop Axis Ratio Distributions Using an Improved 2D-Video Disdrometer and Dual-Polarized Radar

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This grant is a continuation of the NSF supported work performed by this research group, utilizing data, analyses procedures and results acquired under that grant. New aspects of this study is to characterize drop axis ratio distributions with a profile 2D-Video Disdrometer (2DVD) under a wide variety of rain conditions, while using simultaneous scanning dual polarization and vertically pointing Doppler radar observations to characterize the vertical profiles of the same rain events. The combined data on sizes, shapes and vertical profiles are necessary for understanding variability in existing polarimetric radar rain-retrieval and attenuation-correction algorithms. In addition, they will also investigate collisional-forcing of drop oscillations in strong rainfall and its subsequent effect on the axis ratio distributions.The existing data sets will be augmented through field campaigns at three well-instrumented sites that cover a range of rain climatologies. These sites include (i) Colorado (Platteville site 30 km S of CSU CHILL radar), (ii) Okinawa Sub-Tropical Research Center (Ogimi wind profiler site 15 km NE of the polarimetric C-band COBRA radar) and (iii) Sumatra (Koto Tabang).The field campaigns and data analysis procedures will be focused on achieving the following objectives:a. rain type and regime dependence of drop axis ratio distributionsb. implications for attenuation-correction and polarization radar-based rain retrieval algorithmsc. evaluation of collisionally-forced drop oscillations via observations and modeling, and impact on radar algorithms.The broader impact will be in two areas: (i) the assessment of rain retrieval algorithms, including attenuation-correction schemes for operational weather radars which will be upgraded for polarimetric capability; and (ii) implications of drop shapes and size distributions for propagation of radio waves along line-of-sight terrestrial systems as well as earth-space systems.