Using Dual-Polarization Radar Observations to Detect Entrainment Zone Depth and Verify Model Forecasts of Convective Boundary Layer Evolution

最接近地表的大气层称为行星边界层。在白天，当太阳使地表变暖，空气上升并变得湍急时，气象学家将这一层称为对流边界层(CBL)。CBL顶部离地面的高度是可变的，与雷暴发生、降水和污染物浓度有关。然而，没有一种简单的方法可以连续测量大面积CBL的高度。该项目将进一步研究一种利用国家气象局运行的雷达网来提取CBL顶部高度的方法。这些天气雷达足够灵敏，可以探测到不同气团中的梯度，例如更潮湿的对流边界层和上面更干燥的空气。这项工作的意义在于开发了一个数据集，可以用来评估数值模式模拟对流边界层的能力，从而评估实际的天气现象。该项目还有一个重要的教育和推广部分，包括培训多名研究生，为一个公共电视节目制作专题节目，以及实施教师研究体验节目。该项目的总体目标是利用运行中的WSR-88D雷达网的晴空遥感能力，增进对对流边界层顶高度(CBLH)演变的了解。S波段天气雷达在非降水情况下，可以通过使用不同的反射率来定义CBLH来区分生物返回(如昆虫)和布拉格散射(折射率梯度)。由于WSR-88D网络的快速更新和覆盖全国，这项技术将显著增加CBLH的观测值。五个主要活动是：1)在两个不同的年份(2014年和2022年)从美国至少50个雷达获得观测到的每小时日间CBLH的月平均值，以探索CBLH演变中的相似和不同，2)从运行的快速刷新(RAP)模型得出预测的每小时日间CBLH的月平均值，3)计算雷达观测的CBLH和RAP预测的CBLH之间的差异，并使用所有可用的观测来探索差异的原因，4)通过将它们与新的雷暴探空仪观测进行比较来探索差异反射率观测估计夹带深度的能力，5)利用上述观测和模型研究下午晚些时候的逆温层分离和CBL下降。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The layer of the atmosphere closest to the surface is known as the planetary boundary layer. During the daytime, when the sun warms the surface and air rises and becomes turbulent, meteorologists refer to this layer as the convective boundary layer (CBL). The height above the ground of the top of the CBL is variable and has relevance to thunderstorm initiation, precipitation, and pollutant concentration. However, there is no simple way to provide continuous measurements of the height of the CBL over large areas. This project will further investigate a method to retrieve the CBL top height by using the operational National Weather Service radar network. These weather radars are sensitive enough to detect gradients in different airmasses, such as the more humid convective boundary layer and the drier air above that. The significance of the work is through the development of a dataset that can be used to assess the ability of numerical models to simulate the convective boundary layer, and therefore practical weather phenomena. The project also has a significant education and outreach component, with training for multiple graduate students, creation of features for a public television program, and implementation of a Research Experience for Teachers program.The overarching goal of this project is to improve understanding of the evolution of the convective boundary layer top height (CBLH) using the clear-air remote sensing capabilities of the operational WSR-88D radar network. S-band weather radar, in non-precipitating situations, can differentiate between biological returns (e.g. insects) and Bragg scatter (refractive index gradients) by using differential reflectivity to define the CBLH. This technique would provide a significant increase in observations of CBLH due to the rapid updates and nationwide footprint of the WSR-88D network. Five main activities are: 1) Develop monthly mean values of observed hourly daytime CBLH from at least 50 radars across the US over two distinct years (2014 and 2022) to explore similarities and differences in CBLH evolution, 2) Develop monthly mean values of predicted hourly daytime CBLH from the operational Rapid Refresh (RAP) model, 3) Calculate the difference between the radar observed CBLH and the RAP predicted CBLH, and explore reasons for the differences using all available observations, 4) Explore the ability of the differential reflectivity observations to estimate entrainment zone depth by comparing them to new rawinsonde observations, and 5) Study the late afternoon inversion layer separation and CBL descent using the observations and modeling derived above.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.