P7.1 Study on the Optimal Scanning Strategies of Phase-array Radar through Ensemble Kalman Filter Assimilation of Simulated Data

1 The phased-array radar (PAR) of the National Weather Radar Testbed (NWRT) in Norman, Oklahoma represents a paradigm shift for weather radar observations. The PAR with abilities such as a higher data update rate through beam multiplexing (Yu et al. 2007) offers not only an opportunity but also a challenge for meteorologists to exploit its potentials for helping us improve convective storm analysis and prediction. In this paper, the ensemble Kalman filter (EnKF) data assimilation technique is used to study the impact of different scanning strategies and to provide scientific guidance for the design and use of optimal scanning strategies for PAR. The EnKF method has shown great promise in a number of recent studies with simulated data within the Observation Simulation System Experiments, (OSSE, Snyder and Zhang 2003; Zhang et al. 2004; Tong and Xue 2005, TX05 hereafter; Xue et al. 2006, XTD06 hereafter). These OSSE studies, especially the earlier ones, make several simplifying assumptions about radar observations. For example, radar data are assumed to be available on the regular model grid points in the first three studies referenced. XTD06 assumes that radar data are available in the PPI planes but at vertical columns that coincides with columns of the analysis grid. In this study, the ARPS (Advanced Regional Prediction System) EnKF data assimilation system is upgraded to directly assimilate flexible forms of radar data, such as those on individual radials, and to apply more realistic observation operators that include beam weighting in all three directions. A companion radar emulator has been developed to simulate various scanning modes of PAR and produce realistically simulated data. As a result, in this system, OSSE for different scanning strategies can be easily implemented. In the experiments reported here, in both the truth simulation and data analysis, the same grid is used with a horizontal grid spacing of 1 km and a stretched vertical grid of 100 m at the surface while increasing