Precipitation Processes in Convection and over Mountains

在先前NSF的支持下，首席研究员对中纬度、大平原、中尺度对流系统的降水过程有了更深入的科学认识。 除了继续这项研究，首席研究员将专注于地形对流风暴的降水过程。 这种风暴以其产生极端洪水事件的潜力而闻名，但由于大气动力学的复杂性和野外工作的困难环境，对这些系统仍有许多未知之处。 将对已经完成的实地项目的偏振雷达数据进行分析，以确定构成大多数对流系统组成部分的浮力、夹带、膨胀气泡（“粒子喷泉”）中发生的微物理过程。 目前的研究已发展出一个概念模式，有助于解释对流降水过程，并作为检验数值预报模式的基础。除了改进和完善对流降水系统概念模式外，本项目还将重点研究地形背景下的降水过程。气象学研究中的野外观测往往强调非地形条件下的降水云系，通过消除在复杂地形中进行雷达和飞机研究的困难来简化观测，通过消除气流、降水增长和沉降物的复杂地形变化来简化分析。 这项研究解决了地形的问题，利用所有上述的雷达气象学的进步，并利用复杂的理论和地形上的干流模型，这在过去几年中已经发展起来。一个需要研究的地区是北方沿海的加州。 在山脊内是以洪水而闻名的重要河谷。 主要研究员将利用业务数据集和特殊数据集，合成反射率和径向速度数据，从而在气候学的基础上，中尺度阿尔卑斯山计划（MAP）的野外阶段将进一步研究地形降水过程在北方意大利和周围国家在1999年秋季。 该地区是研究地形降水的天然实验室，首席研究员将受益于其他研究人员收集的数据。 这项研究的成功完成将有助于更好地了解和预报山区的局部强降水。

Under prior NSF support, the Principal Investigator has advanced scientific understanding of precipitation processes in mid-latitude, Great Plains, mesoscale convective systems. In addition to continuing this research, the Principal Investigator will focus on precipitation processes in orographic convective storms. Such storms are known for their potential to produce extreme flooding events, but due to complexities of the atmospheric dynamics and the difficult environment for field work, much is still unknown about these systems. Polarimetric radar data from already completed field projects will be analyzed to identify microphysical processes occurring in the buoyant, entraining, expand-ing, bubbles ("particle fountains") that constitute the building blocks of most convective systems. Ongoing studies have developed a con-ceptual model that helps explain the convective precipitation process and serves as a basis for testing numerical forecast models.In addition to advancing and refining the convec-tive precipitation system conceptual model, this project will focus on precipitation processes in orographic set-tings. Field observations in research meteorology have tended to emphasize precipitating cloud systems in non-orographic situations, to simplify the observations by eliminating the difficulties of carrying out radar and air-craft studies in complex terrain and to simplify the anal-ysis by eliminating the complex orographic modifications of the airflow, precipitation growth, and fallout. This study addresses the orographic problem by using all of the above-mentioned advances in radar meteorology and by taking advantage of the sophisticated theory and modeling of dry flow over terrain, which has developed over the last several years. One regime to be studied is coastal northern California. Within the mountain ridges are important river valleys known for their flooding. Using both operational and special data sets, the Principal Investigator will construct composites of the reflectivity and radial velocity data which will lead to identification, on a climatologi-cal basis, of the orographic modification of the dynamics and microphysics of frontal rainstorms moving onshore from the Pacific.The studies of orographic precipitation processes will be furthered by the field phase of the Mesoscale Alpine Programme (MAP) in northern Italy and sur-rounding countries in the Fall of 1999. This region is a natural laboratory for studying orographic precipitation and the Principal Investigator will benefit from the data to be collected by other researchers. Successful completion of this research should lead to a better understanding and forecasting of very heavy, localized precipitation in mountains.