Polarimetric Radar Operation in Support of North American Monsoon Experiment (NAME)

北美季风实验(NAME)是一项多方面的研究工作，致力于提高北美暖季降水的可预报性。目前，由于缺乏对季风内降水系统的了解，以及无法在数值天气预报模式中准确地将这些降水系统参数化，阻碍了对从墨西哥南部延伸到美国的地区在中短期时间尺度上对暖季降水的预测。理解和预测季风系统的几个关键的相互关联的物理过程仍然没有得到很好的量化，包括：季风的整体结构；季风内个别降水系统(包括中尺度对流系统)的结构、运动学、形态和日循环；此外，在西马德雷山脉(SMO)、加利福尼亚州海湾和中间的沿海平原上，降水系统与该地区不同地表属性的相互作用，以及海洋强迫对附近大陆降水(反之亦然)、陆面记忆过程、地表通量和蒸散输送的影响。为了详细研究这些过程，计划在2004年夏季设立一个综合的命名增强观察期(EOP)。EOP名称的核心目标是研究极化多普勒雷达的持续运行，这将补充持续的长期观测和一致的EOP观测，如增强型无线电探空仪、Pibal和剖面仪网络。O根据风暴类型、位置和环境强迫，记录按对流和层状成分划分的降雨量和强度的水平分布；o测量降雨的日周期、对流强度、风暴形态和微观物理，这将是诊断该区域降水背后的物理过程的关键，从而与该区域的可预报性相联系；o识别降水特征内的二维气流，以及其他边界层流，包括微风锋、海湾涌浪及其在对流启动中的作用；O能够评估云解析模式中的微物理参数和数值天气预报模式中的对流参数。将使用几种现有的方法仔细分析NAME提供的多普勒和偏振数据。偏振数据将被用来确定对流和周围层状降水中的主要降水粒子类型。这项研究的学术价值在于探索重要地形附近热带对流的物理和动力学特征。关于热带降水性质的新结果有望从NAME中获得。多普勒数据将通过获取数据来验证季风降水的数值模式，从而对整个科学产生更广泛的影响，特别是提高对进入美国西南部的水汽输送进行建模的能力，这些水汽输送推动了这些地区夏末的降雨。因此，作为一个名义上的结果，预计美国西南部将出现更好的季风降雨预报。

The North American Monsoon Experiment (NAME) is a multi faceted research effort that strives to improve predictability of warm season precipitation over North America. Currently, the prediction of warm season precipitation on short- to medium-range timescales in the region extending from southern Mexico into the United States is hampered by a lack of understanding of precipitating systems within the monsoon, and the inability to accurately parameterize these precipitating systems in numerical weather prediction models. Several key interrelated physical processes fundamental to understanding and predicting the monsoon system remain poorly quantified, including: the bulk structure of the monsoon; the structure, kinematics, morphology, and diurnal cycle of individual precipitating systems (including mesoscale convective systems) within the monsoon; and, the interaction of precipitating systems with the variable surface properties in the region over the Sierra Madre Occidental (SMO), the Gulf of California and the intervening coastal plain, as well as the influence of the oceanic forcing on nearby continental precipitation (and vice versa), land surface memory processes, surface fluxes, and evapotransporation.To study these processes in detail, a comprehensive NAME Enhanced Observing Period (EOP) is planned for the Summer of 2004. Central to the goals of the NAME EOP is the continuous operation of the a research polarimetric Doppler radar, which will complement ongoing, long term observations and coincident EOP observations such as enhanced radiosonde, pibal, and profiler networks. Specific NAME EOP objectives key to the campaign that will be addressed under this research include:o documentation of the horizontal distribution of rainfall amount and intensity partitioned by convective and stratiform components, as a function of storm type, location, and environmental forcing;o measurement of the diurnal cycle of rainfall, convective intensity, storm morphology, and microphysics that will be crucial in diagnosing the physical processes behind precipitation in the region and thus links to predictability in the region;o identification of 2-D airflow within precipitating features, as well as other boundary layer flows including breeze fronts, gulf surges, and their role in convective initiation;o hydrometeor identification allowing evaluation of microphysical parameterizations in cloud resolving models and convective parameterizations in numerical weather prediction models.The Doppler and polarimetric data from NAME will be carefully analyzed using several existing methods. The polarimetric data will be used to identify dominant precipitation particle types in the convection and surrounding stratiform precipitation. The intellectual merit of this research consists of exploring the physical and dynamical characteristics of tropical convection in the immediate vicinity of significant topography. New results on the nature of tropical precipitation are expected to be gained from NAME. The Doppler data will provide for broader impact on the overall science by acquiring data to validate numerical models of the monsoon precipitation, and in particular, improving the ability to model the moisture transport into the southwest U.S. that drives the late summer rainfall in those regions. Hence better forecasts of heavy monsoonal rainfall in the southwest U.S. are expected as an outcome of NAME.