Statistical Relations between Precipitation Formation and Quantities of Synoptic Field
Statistical Relations between Precipitation Formation and Quantities of Synoptic Field
复制标题
降水形成与天气场数量的统计关系
DOI：
--
复制
发表时间：
1978
期刊：
影响因子：
--
通讯作者：
H. Sakakibara
中科院分区：
文献类型：
--
作者：
H. Sakakibara
冰晶在过冷云中通过升华而生长，云滴在水云中通过捕获小水滴而生长，被认为是降水形成的主要机制。前者取决于过冷程度和冰晶浓度，后者取决于云滴的大小分布、液态水含量和云中的上升气流。由于在整个云层中对这些元素的观测是困难的，并且它们之间的物理关系是高度复杂的，因此从上述微物理参数来确定地预测某一云是否会产生降水仍然是困难的。在预测降水时，利用降水与更容易观测到的云层量（如云顶温度和云厚度）之间的统计关系是合适的，至少在业务上是这样。采用云顶温度作为冰过程降水形成的指标，因为大致说来，冰晶的浓度和升华生长速率都取决于温度。由于液态水含量和上升气流都与云的厚度相关，尤其是对流云，因此采用云的厚度作为聚并过程降水形成的指标。许多研究者通过对单个云的详细观测，研究了云顶温度与降水形成的关系，以及云厚与降水形成的关系(如Braham et al. (1951), Battan and Braham (1956), Mason and Howorth （1952), Stewart(1964)）。根据这些关系，他们试图确定哪种过程，即冰过程或合并过程，是各种降水情况的主要原因。然而，在本文中，我们打算在探空、雷达和地面观测资料的基础上，从天气学的角度来讨论降水的形成，以期对某天气场的降水形成诊断有所贡献。
Growth of ice crystals by sublimation in supercooled clouds and that of cloud droplets by capturing smaller droplets in water clouds are considered to be the main mechanisms in precipitation formation. The former depends on the degree of supercooling and the concentration of ice crystals while the latter depends on the size distribution of cloud droplets, liquid water content and updraft in clouds. It would be still difficult to predict decisively whether or not precipitation will result from a certain cloud from the aforementioned microphysical parameters, because the observations of such elements throughout the cloud layer are difficult and the physical relationships among them are highly complicated. For predicting precipitation, it will be suitable to make use of statistical relations among the precipitation and more easily observable quantities about the cloud layer, such as cloud-top temperature and cloud thickness, at least for the operational purposes. The temperature at cloud top is adopted as an index of precipitation formation by the ice process, because, roughly speaking, both the concentration of ice crystals and the growth rate by sublimation depend on temperature. The cloud thickness is adopted as an index of precipitation formation by the coalescence process, because both of liquid water content and updraft are correlated with the cloud thickness, especially in the case of convective clouds. Many researchers have studied the relation between the temperature at cloud top and precipitation formation, and that between the cloud thickness and precipitation formation basing on the detailed observation for individual clouds (e.g. Braham et al. (1951), Battan and Braham (1956), Mason and Howorth (1952), Stewart (1964)). From the relations they tried to decide which process, that is, the ice process or the coalescence process, is principal for various cases of precipitations. In this paper, however, we intend to discuss precipitation formation from the synoptic view point on the basis of the radiosonde, radar and surface observation data and to contribute to the diagnosis of precipitation formation in a certain synoptic field.