Polarimetric Radar Observation of the Melting Layer in a Convective Rainfall System during the Rainy Season over the East China Sea
Polarimetric Radar Observation of the Melting Layer in a Convective Rainfall System during the Rainy Season over the East China Sea
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DOI：
10.1175/2010jamc2469.1
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发表时间：
2011-03
影响因子：
3
通讯作者：
Y. Shusse;N. Takahashi;K. Nakagawa;S. Satoh;T. Iguchi
中科院分区：
文献类型：
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作者：
Y. Shusse;N. Takahashi;K. Nakagawa;S. Satoh;T. Iguchi
中国东海雨季期间，对流降水在极化雷达变星中往往表现为融化层(ML)特征。本文利用C波段偏振雷达观测了2006年6月2日中国东海对流降水区的ML(降雨面积与极化ML信号的比值)和ML信号极大值(MLSM层，由ML中的相对湿度极小值定义)层高度的变化。对于这种分析，发展了一种降雨类型分类方法，除了利用距离高度指示器(RHI)观测资料提供常规的对流-层状分类外，还可以评估ML的存在。这种降水类型的分类包括两个步骤：利用2公里高度上ZH的水平分布进行常规的对流-层状分离，以及利用每个水平网格点上的HV垂直廓线进行ML检测。将这两种分类结合起来，识别出以下四种降雨类型：1)有ML的对流性降雨，2)无ML的对流性降雨，3)有ML的层状降雨，4)无ML的层状降雨。在降水系统的对流区中，有53.9%的区域出现了ML。使用相同的定义，83.1%的层状区可检测到ML。在08C附近，对流区的对流层高度显著减小，ZDR增大，层状区的对流区也是如此。积雪融化是对流区ML特征的可能原因。对流区MLSM平均高度为4.64公里，比层状区(4.18公里)高0.46公里，比周围08C层(4.37公里)高0.27公里。
During the rainy season over the East China Sea, convective rainfalls often show melting layer (ML) characteristics in polarimetric radar variables. In this research, the appearance ratio of the ML (the ratio of rainfall area accompanied by polarimetric ML signatures) and the variation in height of the level of the ML signature maximum (MLSM level; defined by the level of the rhv minimum in the ML) in a convective rainfall region in a rainfall system over the East China Sea observed on 2 June 2006 were studied using C-band polarimetric radar (COBRA). For this analysis, a method of rainfall type classification that evaluates the presence of an ML in addition to providing conventional convective‐stratiform classification using range‐ height indicator (RHI) observation data was developed. This rainfall type classification includes two steps: conventional convective‐stratiform separation using the horizontal distribution of Zh at 2-km altitude, and ML detection using the vertical profile of rhv at each horizontal grid point. Using a combination of these two classifications, the following four rainfall types were identified: 1) convective rainfall with an ML, 2) convective rainfall with no ML, 3) stratiform rainfall with an ML, and 4) stratiform rainfall with no ML. An ML was detected in 53.9% of the convective region in the rainfall system. Using the same definition, an ML was detected in 83.1% of the stratiform region. The ML in the convective region showed a marked decrease in rhv coincident with an increase in ZDR around the ambient 08C level, as did that in the stratiform region. Melting aggregated snow was the likely cause of the ML signature in the convective region. The average height of the MLSM level in the convective region was 4.64 km, which is 0.46 km higher than that in the stratiform region (4.18 km) and 0.27 km higher than the ambient 08C level (4.37 km).