Microphysics of raindrop size spectra: Tropical continental and maritime storms
Microphysics of raindrop size spectra: Tropical continental and maritime storms
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DOI：
10.1175/2007jamc1649.1
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发表时间：
2007-11-01
影响因子：
3
通讯作者：
Atlas, David
中科院分区：
文献类型：
--
作者：
Ulbrich, Carlton W.;Atlas, David
这项工作使用在热带大陆风暴表面测量的雨滴尺寸光谱来确定最佳拟合伽马分布的相关参数。然后探讨了影响这些参数的物理过程及其与可测量的雷达反射率 Z 和差分反射率 ZDR 的关系。它们与降雨定量测量的关系也是如此。然后与之前报道的热带海洋制度的相应特征进行比较。在巴西和波多黎各阿雷西博观测到的风暴分为对流 (C)、过渡 (T) 和层状 (S) 部分。雨滴尺寸分布 (DSD) 参数在伽马参数图 (GPD) 上进行了明确定义，该图显示 1) 中值体积雨滴尺寸 D-0 如何从降雨的 S 段到 T 段到 C 段增加，同时 2) 光谱宽度参数 mu 的范围增加，斜率参数 Lambda 的范围以 S 到 C 的相同顺序减小。雨滴生长主要发生在 0 摄氏度以下，通过 C 降雨中的碰撞、合并和分裂。随着更多的水集中在该尺寸附近，中位体积直径 D-0 会增大，因此 DSD 会变窄；也就是说，mu 和 Lambda 都会增加。在海洋和大陆风暴中，风暴对流部分的 DSD 接近平衡。 Z = AR(b) 关系中的系数 A 随着 D-0 的增加而增加，而指数 b 接近 1。 D-0 和 A 对随着上升气流强度的增加而增加，并且似乎很大程度上由上升气流强度决定，从而提供了确定降雨测量的适当算法的可能方法。尽管相对于雷达采样的大体积，表面测速仪测量的小液滴数量样本往往会在小液滴尺寸和大液滴尺寸下截断 DSD，但 mu = 5 至 12 的窄分布不能归因于这种效应。如此狭窄的 DSD 符合对流风暴开始时单分散大水滴的常见经验。 ZDR-Z-D-0 的地面观测结果与英国和其他地方的雷达观测到的从 C 到 T 到 S 雨类型的时空变化也有显着的一致性。由于风暴的 C 区尽管持续时间较短，但通常占降雨量的主要部分，因此更准确地测量该区域尤为重要。海上和大陆风暴之间的广义数参数 N-W 与 D-0 存在独特的集群。遥感和参数化方法必须将暴雨划分为对流段、过渡段和层状段。
This work uses raindrop size spectra measured at the surface in tropical continental storms to determine the associated parameters of the best-fit gamma distributions. The physical processes responsible for those parameters and their relations to the measurable radar reflectivity Z and differential reflectivity ZDR are then explored. So too are their relations to quantitative measurements of rain. Comparison is then made with corresponding features previously reported in tropical maritime regimes. The storms observed in Brazil and Arecibo, Puerto Rico, have been divided into convective (C), transition (T), and stratiform (S) segments. The raindrop size distribution (DSD) parameters are clearly defined on a gamma parameter diagram (GPD) that shows 1) how median volume drop size D-0 increases from S to T to C segments of the rain while 2) the range of the spectrum breadth parameter mu increases, and the range of the slope parameter Lambda decreases in the same sequence of S to C. Drop growth occurs predominantly below the 0 degrees C level by collision, coalescence, and breakup in the C rains. The median volume diameter D-0 grows as more of the water is concentrated near that size and so the DSD narrows; that is, both mu and Lambda increase. In both maritime and continental storms the DSD in the convective portion of the storm approaches equilibrium. The coefficient A in the Z = AR(b) relation increases with D-0 while the exponent b approaches unity. The D-0 and A pair increase with, and appear to be determined largely by, the updraft strength, thus providing a possible means of determining the appropriate algorithms for rainfall measurement. Although the small drop number samples measured by the surface disdrometer relative to the large volumes sampled by a radar tend to truncate the DSD at both small and large drop sizes, narrow distributions with mu = 5 to 12 cannot be attributed to such an effect. Such narrow DSDs accord with common experience of monodispersed large drops at the beginning of a convective storm. There is also remarkable agreement of the surface-based observations of ZDR-Z-D-0 with the time-space variations from C to T to S rain types observed by radar in England and elsewhere. Because the C region of a storm often accounts for a major share of the rain accumulation despite its shorter duration, it is particularly important to measure that region more accurately. There are distinctive clusters of the generalized number parameter N-W versus D-0 between maritime and continental storms. Methods for remote sensing and parameterization must partition the rainstorms into convective, transition, and stratiform segments.