Precipitation Processes in Convection and over Mountains

在之前国家科学基金会的支持下，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理解。除了继续这项研究外，首席调查员还将重点研究地形对流风暴中的降水过程。这类风暴以可能产生极端洪水事件而闻名，但由于大气动力学的复杂性和野外工作的困难环境，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，以确定浮力、夹带、膨胀、气泡(“粒子喷泉”)中发生的微物理过程，这些气泡构成了大多数对流系统的组成部分。正在进行的研究开发了一个概念模式，它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。除了提出和完善传输性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。研究气象学的野外观测倾向于强调非地形情况下的降水云系，通过消除在复杂地形上进行雷达和飞机研究的困难来简化观测，并通过消除气流、降水增长和落尘的复杂地形修改来简化分析。这项研究利用上述雷达气象学的所有进展，并利用近几年发展起来的地形干流的复杂理论和模型，解决了地形问题。一个需要研究的制度是加利福尼亚州北部的沿海地区。在山脊内是以洪水闻名的重要河谷。首席调查员将利用业务和特殊的数据集，建立反射率和径向速度数据的合成，这将导致在气候学的基础上识别从太平洋移动到陆地上的锋面暴雨的动力学和微物理的地形修正。地形降水过程的研究将通过1999年秋季在意大利北部和周边国家的中尺度阿尔卑斯计划(MAP)的实地阶段而得到进一步的发展。该地区是研究地形降水的天然实验室，首席调查员将从其他研究人员收集的数据中受益。这项研究的成功完成将有助于更好地理解和预报山区非常大的局部降水。

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.