新一代天气雷达降水估算的区域覆盖能力评估

Assessment of CINRAD Regional Coverage for Quantitative Precipitation Estimation

准确分析雷达的覆盖能力是应用新一代天气雷观测数据的重要基础,本文提出依据0℃层高度和雷达波束阻挡来分析雷达降水估算有效覆盖范围的方法,并以浙江为例,客观评估了新一代天气雷达针对降水估算的区域覆盖能力。分别评估雷达网当前业务中默认的降水估算混合扫描方法和考虑地形影响的混合扫描方法的覆盖效果,结果表明:相对SA雷达230 km的降水估算半径,本地主汛期内有17%的区域因波束太高而不适宜于降水估算;而在适宜高度范围内的有效覆盖与波束阻挡直接相关;无论哪种方法,因波束阻挡产生的盲区都较小;而业务默认方法由于未处理波束阻挡,导致35%的降水低估风险区,浙江大部分地区都存在低估风险;而考虑波束阻挡后有效覆盖区达82%以上,且对全年绝大部分降水的区域覆盖效果都相当好。鉴于浙江雷达网良好的覆盖能力,提出改进的雷达降水估算混合扫描方法,即在应用波束阻挡的同时,以本地0℃层为波束高度约束,从所有仰角中提取混合扫描数据。对比分析表明,该方法不仅满足区域覆盖的要求,而且估算的降水空间分布与地面观测实况的一致性最好。

Accurate analysis of coverage of weather radar is important for using CINRAD observations,and flooding is one of the main meteorological disasters in China.In this paper,a method considering terrains' occultation and according to local distribution of melting layer height is supported to assess coverage of weather radar for quantitative precipitation estimation(QPE).Taking Zhejiang province as an example,objective assessment of CINRAD regional coverage is presented respectively for CINRAD operational QPE and algorithm considering terrains' occultation to radar beam.The results are:during the flood season,17%of the maximum covered area is invalid as the result of the limit of melting layer.And coverage capability of beam below melting layer is directly related to beam blockage,blind area is very small for both QPE regions.For default operational CINRAD QPE,35%of the maximum covered area faces the risk of underestimation due to partial beam blockage,which covers most region of the province.When considering terrains' occultation,most of the region,more than 82%,is valid coverage,including the whole province.Regional coverage is good to most rainfall of a year too.Finally,a improved method of getting hybrid scan from all elevation cuts with both the restriction of melting layer height and beam blockage is presented,in addition to good coverage,it's QPE results agree with actual precipitation distribution best when comparing with operational CINRAD method and hybrid scan method below averaged rain top.