Snowfall Observations at NASA Wallops FLight Facility

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Wednesday, 7 January 2015
Jorel Torres, Department of Atmospheric and Environmental Sciences, Rapid City, SD; and A. Tokay, D. Kliche, D. B. Wolff, L. F. Bliven, and W. A. Petersen

The National Aeronautics and Space Administration (NASA) Global Precipitation Measurement (GPM) Mission ground validation program has been conducting a field study of precipitation observations at the NASA Wallops Flight Facility (WFF) during the past year. The purpose of the study is to provide a better parameterization of the microphysics of precipitation including falling snow for the GPM algorithm developers. Under the umbrella of physical validation, GPM algorithm developers use the disdrometer based hydrometeor size distributions to test parametric form of the size distribution from dual frequency radar measurements on board the GPM core satellite. In the presence of snow, GPM algorithm developers seek additional information on fall velocity and snow density. There is also need to quantify the partial beam filling within the satellite footprint. In addition, developing alternative methods for snow detection and snow accumulation is imperative since instruments can report snowfall when it is not snowing or when precipitation is ambiguous and difficult to distinguish within microphysical processes that occur during snowstorms. With ground validation, measurements from snow events will allow researchers to improve methods of measuring the precipitation type and then integrating these datasets into hydrological modeling. This will enhance techniques and or algorithms, deciphering the rain-to-snow transitions; assessing the accurate liquid water content produced from snow events that affect flooding characteristics. The main objective of this study is to investigate the microphysical characteristics of falling snow and its spatial variability within the GPM core satellite footprint. To accomplish this goal, eight snow events that occurred at WFF were analyzed. The WFF network had an above average snow precipitation year for the 2013-2014 winter season and recorded more snowy days and accumulation with respect to the long-term climatology. The network comprises of six sites encompassing a variety of instruments: automated parsivel units (APU's), two-dimensional video disdrometers (2DVD's), a precipitation imaging probe (PIP) and pluvio200 weighing bucket rain gauges. These respective instruments have the ability to detect particle size and velocity of both solid and liquid precipitation with the pluvio200 measuring the melted equivalent of snow accumulation. The distances between sites ranged from 0.5-2.3 kilometers. The following steps are taken to accomplish this objective: 1) Comparison of the event snowfall and snow rates between different instruments, 2) Parameterization of the snow size distribution and snowfall velocity, 3) Determination of snow density and spatial variability of falling snow and its microphysical characteristics, 4) Comparison of disdrometer derived and radar observed reflectivity and derivation of reflectivity and snow rate relationships. Preliminary results will be provided with the poster presentation.