Gaoyuan qixiang (Feb 2024)
Study on Precipitation Observation and Retrieval Methods of X-band Phased Array Polarization Weather Radar in Motuo， Xizang
Abstract
The variation in precipitation in Motuo is closely associated with the transport of water vapor from the India Ocean and the Bay of Bengal to inland China， the Asia summer monsoon， and the progression of the rain band in eastern China.A rain band with an average annual precipitation of more than 2000 mm has been formed due to the interaction of the distinctive topography of Motuo and the southwest air flow.However， it has been challenging to observe precipitation in Motuo due to the peculiar topography， insufficient electricity， and inadequate traffic conditions.An X-band dual-polarization phased array radar （XPAR） is installed during the Second Qinghai-Xizang Plateau Scientific Expedition and Research Program.The advanced dual-polarization phased array radar is used to continuously observe the precipitation in Motuo and is of great significance to the research of the local ecological environment and cloud water resources， and the impact on downstream.Based on XPAR data collected for the period from June to August 2020， we selected the radial precipitation echoes using a statistical method， and after integrating the precipitation echoes， we created the hybrid elevation angle that tallied with the topography of Motuo.Using DSD data from Motuo in 2019， we calculated radar parameters and obtained the localized QPE （Quantitative Precipitation Estimation） formulas of X-band weather radar.We selected three processes of precipitation with different cumulative precipitation， duration， and average rain rate from July to August 2020， calculated ΦDP （Differential Propagation Phase Shift） using the linear programming method， KDP （Differential Propagation Phase Shift Rate） using the ordinary least square method， and corrected ZH （Reflectivity Factor） using the “ZPHI” rain profiling algorithm.Using ZH and KDP as thresholds， we estimated precipitation piecewise utilizing R（ZH） and R（KDP）， and contrasted results with the QPE results from the R（ZH） and R（KDP） methods， respectively.And explored the relationship between precipitation distribution and the topography of Motuo based on the QPE results.The quality of ZH and KDP had been significantly improved.The hybrid elevation angle constructed using a statistical method had a larger echo area than the hybrid elevation angle constructed using STRM1 v3.0 data.The PPI （Plane Position Indicator） diagrams of three precipitation （radar parameters at typical times， and average radar parameters） processes can show the relationship between the variation in precipitation and the topography of Motuo.The QPE formulas and Piecewise Estimation Method （PEM） used in the research functioned well， and each evaluation parameter performed well.The following conclusions are drawn： （1） The hybrid elevation angle constructed using the statistical method outperformed the hybrid elevation angle constructed using topography data in QPE， due to the drastic variation of the topography around the XPAR in Motuo； （2） The data quality control method， the QPE formulas， and the PEM utilized in the research all performed well at precipitation retrieval.The estimation error of the QPE results was significantly reduced， without causing significant changes in CC and RMSE； （3） Precipitation in Motuo may occur and grow as a result of the lifting of the southwest air flow by northern slopes of the valley.Clouds with higher rain rates and smaller drops are found near the level bottom of the valley.
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