Raman Lidar Applications in Mesoscale Studies

虽然在过去十年中，在了解恶劣天气系统的结构特征方面取得了很大进展，但在引发深对流的关键因素方面，许多问题仍然没有得到回答。最近的研究表明，干线是一种急剧的水平湿度梯度，经常在春季和初夏出现在美国中南部，为引发对流创造了有利的环境。这一中尺度现象意义重大，因为它经常与恶劣天气的发生有关，而恶劣天气往往沿着干线发展并向东发展。在冷锋进场时尤其如此，冷锋进场提供了一种提升潮湿空气的机制。然而，到目前为止，对干线的水分结构和演变的详细研究还很少。首席调查员将进行一项为期三年的研究，利用拉曼激光雷达系统的能力，量化雷暴前环境和干线的详细垂直和水平水汽层结，以及湿度在对流风暴的发展和启动中的潜在作用。他们将使用拉曼激光雷达来验证干线特性、干线-锋面相互作用和相关对流的理论和数值预测。该项目依赖于获取和利用1994年至2000年在美国不同地区的几次实地任务期间观测到的水蒸气混合比和气溶胶剖面的拉曼激光雷达观测数据。计划于2002年5月至6月在美国大平原南部进行的国际H20项目(IHOP)和由能源部(DOE)大气辐射测量(ARM)计划实施的水蒸气密集型作业(WVIOP)的数据也将被利用。将结合对拉曼激光雷达、探空仪、雷达、微波辐射计、风廓线仪和其他常规数据集的现有数据进行分析，并使用数值模型来实现本研究的目标。将分析辐合区、锋面和干线的动力、热力和水汽结构以及边界层的时间发展。重点领域包括干线和冷锋期间水汽垂直结构的小范围变化对风暴启动和对流的影响，以及对流层中层结构在风暴动力学和启动和/或抑制中的作用。研究内容包括对流有效势能和对流抑制的计算，以及对选定个例的简单模式模拟，以更好地了解风切变在对流启动中的作用。研究结果将有助于更好地了解干线的日特征，通过证明或反驳预测量来补充对流启动的理论预测，并最终有助于改进恶劣天气条件的预测技术。

While much progress has been made over the last decade in understanding the structural characteristics of severe weather systems, many questions remain unanswered on the critical factors that trigger deep convection. Recent work has shown that the dryline, a sharp horizontal gradient in moisture and often found over the south central United States in spring and early summer, creates a favorable environment for initiation of convection. This mesoscale phenomenon is significant because it is often linked to the occurrence of severe weather, which tends to develop along and to the east of the dryline. This is particularly true during a cold frontal approach, which furnishes a mechanism for the lifting of the moist air. To date however, there have been very few detailed studies of the moisture structure and evolution of the dryline.The Principal Investigators will perform a three year study to quantify the detailed vertical and horizontal moisture stratification of the pre-thunderstorm environment and drylines as well as the potential role of humidity in the development and initiation of convective storms using the capability of Raman lidar systems. They will use the Raman lidar to verify theoretical as well as numerical predictions of dryline characteristics dryline-front interactions and associated convection. This project relies on acquiring and utilizing Raman lidar observations of water vapor mixing ratio and aerosol profile data observed between 1994 and 2000 during several field missions at different parts of the U.S.A. Data from the International H20 Project (IHOP), planned for May-June 2002 in the southern Great Plains of the United states, and the Water Vapor Intensive Operations (WVIOP) conducted by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program, also will be utilized. A combination of analyses of existing data from Raman lidars, rawinsonde, radars, microwave radiometers, wind profilers and other conventional data sets and a numerical model will be used to achieve the objectives of this research. Dynamic, thermodynamic and moisture structure of convergence zones, frontal surfaces, and drylines as well as the temporal development of the boundary layer will be analyzed. Areas of focus include the effects of small-scale variations in the vertical structure of moisture during drylines and cold fronts on storm initiation and convection and the role of the structure of the mid-tropospheric layer in storm dynamics and initiation and/or inhibition. The calculation of convective available potential energy and convective inhibition as well as simple model simulations of selected case studies to better understand the role of wind shear in the initiation of convection are included.The results of the research should provide a better understanding of the diurnal characteristics of the dryline, complement the theoretical predictions of convective initiation by proving or disproving the predicted quantities and eventually contribute towards improvements in the forecasting skills of severe weather conditions.