X-Band Radar Precipitation Estimates for the Surface Atmosphere Integrated Field Laboratory (SAIL) Field Experiment

The Surface Atmospheric Integrated Field Laboratory (SAIL) field experiment is designed to advance the understanding of the water cycle within complex terrain, specifically the relationship between precipitation and river runoff within a portion of the Upper Colorado River Basin, known as the East River Watershed. With the goal of accurately estimating precipitation, the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) Second Mobile Facility (AMF2) is stationed in Crested Butte, Colorado from September 2021 to June 2023 collecting observations with a scanning X-Band dual-polarimetric radar provided by Colorado State University (CSU). As the East River Watershed has sparse radar coverage from the National Weather Service (NWS) Next-Generation Weather Radar (NEXRAD) system, the CSU X-Band scanning radar provides high spatiotemporal observations for the calculation of precipitation estimates within the watershed. As the CSU X-Band is located within complex terrain, additional data processing using the Corrected Moments in Antenna Coordinates 2.0 package (CMAC2.0) (DOI:10.5439/1855341) are needed to provide a quality assured dataset. This processing includes corrections due to beam blockage, de-alias doppler velocities, corrected reflectivity for liquid water path attenuation, differential phase corrected for non-uniform beam filling, among others. To estimate precipitation from the CSU X-Band, empirical relationships relating observed equivalent reflectivity factor (Ze) to snowfall rates (S), or rainfall rates (R), will be applied to the CMAC2.0 corrected observations. As these empirical relationships can vary with different hydrometeor characteristics, an ensemble approach with multiple relationships will be used to describe the spread within the calculated precipitation estimates and different environments observed. Utilizing the Python-ARM Radar Toolkit (Py-ART), CSU X-Band precipitation estimates will be collocated with ground instrumentation for various sites of interest within the East River Watershed. Additionally, a gridded dataset will be provided to the SAIL and ARM community to investigate precipitation processes within the watershed.