Synthetic Observations of the Planetary Boundary Layer from Space: An Observing System Simulation Experiment Framework

To address critical gaps identified by the National Academies of Sciences, Engineering and Medicine in the current Earth system observation strategy, the 2017-2027 Decadal Survey for Earth Science and Applications from Space recommended incubating concepts for future targeted observables including the atmospheric planetary boundary layer (PBL). A subsequent NASA PBL Study Team Report identified measurement requirements and activities for advancing the maturity of the technologies applicable to the PBL targeted observables and their associated science and applications priorities.While the PBL is the critical layer where humans live and surface energy, moisture, and mass exchanges drive the Earth system, it is also the farthest and most inaccessible layer for spaceborne instruments. Here we document a PBL Observing System Simulation Experiments (OSSEs) framework suitable for assessing existing and new measurement techniques and determining their accuracy and improvements needed for addressing the elevated Decadal Survey requirements. In particular, the benefits of Large-Eddy Simulation (LES) are emphasized as a key source of high-resolution synthetic observations for key PBL regimes: from the tropics, through sub-tropics and mid-latitudes, to subpolar and polar regions. The potential of LES-based PBL OSSEs is explored using six instrument simulators: global navigation satellite system-radio occultation, differential absorption radar, visible to shortwave infrared spectrometer, infrared sounder, multi-angle imaging radio spectrometer, and microwave sounder. The crucial role of LES in PBL OSSEs and some perspectives for instrument developments are discussed.

为弥补美国国家科学院、工程院及医学院（National Academies of Sciences, Engineering and Medicine）在当前地球系统观测战略中指出的关键空白，2017-2027年《空间地球科学与应用十年调查》（Decadal Survey for Earth Science and Applications from Space）提出，需为未来针对性观测开展概念孵化工作，其中涵盖大气行星边界层（atmospheric planetary boundary layer, PBL）。后续美国国家航空航天局（National Aeronautics and Space Administration, NASA）PBL研究小组发布的报告明确了相关测量需求与推进举措，以提升适配PBL针对性观测的技术成熟度，并明确其关联的科学与应用优先级。尽管行星边界层是人类赖以生存的关键圈层，地表能量、水汽与物质交换正是在此驱动地球系统运行，但它同时也是星载仪器观测距离最远、最难抵达的圈层。在此背景下，本文构建了一套行星边界层观测系统模拟实验（Observing System Simulation Experiments, OSSEs）框架，可用于评估现有及新型测量技术，并确定为满足更高标准的十年调查需求所需达到的测量精度与改进方向。尤为重要的是，大涡模拟（Large-Eddy Simulation, LES）作为获取关键PBL区域高分辨率合成观测数据的核心手段，其优势得到重点强调——这些区域涵盖热带、亚热带、中纬度，直至亚极地与极地地区。本研究依托六类仪器模拟器，对基于大涡模拟的PBL OSSEs的应用潜力展开探索，这六类模拟器分别为：全球导航卫星系统无线电掩星（global navigation satellite system-radio occultation）、差分吸收雷达、可见光至短波红外光谱仪、红外测深仪、多角度成像辐射光谱仪以及微波测深仪。本文最后探讨了大涡模拟在PBL观测系统模拟实验中的关键作用，以及相关仪器研发的若干前瞻性视角。