CAREER: An A Priori Test of Retrieval of Coherent Structures in the Atmospheric Boundary Layer Using an Adjoint Model

靠近地面的风主要是湍流和不规则的，但其中经常嵌入漩涡、漩涡或漩涡，这些漩涡持续的时间足够长，可以被识别为形成、成长和最终消散的实体。这些被称为相干结构，是一类重要的小尺度大气运动。它们造成大量的热量、动量、水蒸气和污染物的输送，并产生小规模的湍流。大气遥感的新方法，特别是激光雷达，由于其良好的空间分辨率，有希望观测和研究相干结构。然而，基于多普勒原理的激光雷达等仪器仅限于观察空间中给定点的速度径向分量，而不是三维速度矢量。一个具有挑战性的问题是仅从径向分量的测量中推导出三维速度场。解决方案不是唯一的：不止一种风模式可以有相同的径向速度模式。解决这个问题的方法是通过要求三维的、随时间变化的流型符合已知的大气动力学定律来限制可能解的数量。这被称为四维数据同化的伴随方法。本项目将FDDA应用于激光雷达数据，观测和研究相干结构。最初它将基于模拟。大涡模拟（LES）模型将产生具有相干结构的湍流风场。通过确定从风场中一个或多个规定观测点观测到的速度的径向分量来模拟激光雷达测量。然后应用FDDA来恢复整个风场。通过降低合成观测的分辨率和增加测量误差来模拟真实观测。这些研究将表明真实激光雷达测量的准确性和局限性，并有助于确定具有实际能力的激光雷达系统的最佳观测条件。基于从模拟中获得的理解，利用真实激光雷达数据观测相干结构的实验将随后进行。对于实验部分的工作，PI将与他的家乡机构和科罗拉多州博尔德实验室的激光雷达专家合作。职业生涯补助金的教育部分将侧重于开发工程课程的教学材料，其中包括气象学和地球物理流体动力学的例子。

The wind near the ground is mainly turbulent and irregular but imbedded in it are often eddies, vortices, or swirls that persist long enough to be recognizable as entities that form, grow, and eventually dissipate. These are called coherent structures and are an important class of small-scale atmospheric motions. They account for substantial transports of heat, momentum, water vapor, and pollutants, and generate small-scale turbulence. New methods of atmospheric remote sensing, in particular lidar because of its fine spatial resolution, hold the promise of observing and studying coherent structures. However, instruments like lidar that are based on the Doppler principle are limited to observing only the radial component of velocity at a given point in space, not the three-dimensional velocity vector. A challenging problem is the deduction of the three-dimensional velocity field from measurements of only the radial component. The solution is not unique: more than one wind pattern can have the same pattern of radial velocity. The approach to the problem is to constrain the number of possible solutions by requiring that the three-dimensional, time-evolving flow pattern conform to the known laws of atmospheric dynamics. This is called the adjoint method of four-dimensional data assimilation (FDDA). This project will apply FDDA to lidar data to observe and study coherent structures. Initially it will be based on simulations. A large-eddy simulation (LES) model will generate a turbulent wind field with coherent structures. Lidar measurements will be simulated by determining the radial components of velocity observable from one or more prescribed observing points in the wind field. Then FDDA will be applied to recover the complete wind field. Real observations will be simulated by degrading the resolution of the synthetic observations and adding measurement errors. These studies will indicate the accuracy and limitations of real lidar measurements and serve to define the optimum observing conditions for lidar systems of realistic capabilities. Based on the understanding gained from the simulations, experiments on observing coherent structures using real lidar data will then be undertaken. For the experimental portion of the work, the PI will collaborate with lidar specialists at his home institution and at the laboratories in Boulder, Colorado. The educational component of the CAREER grant will focus on developing instructional material for an engineering curriculum with examples from meteorology and geophysical fluid dynamics.