热层大气密度反演与建模研究进展

Recent progress on the retrieval and modeling of thermosphere mass density

热层是位于地球表面大约90 km到近1000 km的大气圈层,它与电离层和低层大气都存在着复杂的耦合关系;同时热层作为人类航天器空间活动的主要区域,其大气直接影响着各类低轨航天器的运行轨迹.近年来,热层大气观测资料的逐步增加推动了热层大气变化特性的研究和大气模式的发展.本文首先综述了基于多源卫星观测数据的热层大气密度反演算法.着重介绍了基于精密轨道数据以及加速度计数据反演密度的主要算法,以及各种反演策略的优缺点.总结了当前工程常用的MSIS、Jacchia以及DTM热层大气模式在数据源、算法实现过程及其适用范围等方面的异同.接着介绍了基于当前最新大气密度观测数据结合已有大气模式,应用多项式、稀疏矩阵拟合以及数据同化等技术的大气模式优化研究进展.最后概述了基于观测数据研究热层大气响应磁暴、耀斑以及日食等空间事件方面的科学进展.

The thermosphere is the atmospheric layer extending from about 90 km to nearly 1000 kilometers,which is an important interreaction area between the Sun and the Earth.Under the effects of solar radiation flux changes,geomagnetic activities,and low atmospheric forcings,the thermosphere could undergo significant changes.On the other hand,the thermospheric molecule flow collides with space objects,leading to the drag effect,which impacts significantly on the trajectories of space objects.In this paper,we first survey multiple density retrieval methods.The space object tracking data has the advantage of a large amount of data and has long been used for density retrieval since the 1960s.However,the density from this method suffers from low accuracy and time resolution.With the development of the Global Navigation Satellite System(GNSS),satellite Precise Orbit Determination(POD)data was utilized to derive thermospheric density with higher accuracy and time resolution.The accelerometers of some geodesic satellites offer the highest accuracy of measurements.Subsequently,three widely-used empirical thermospheric models(Mass Spectrometer Incoherent Scatter MSIS,Jacchia,and Drag Temperature Model DTM)were summarized.The methodologies and data sources were further compared.Based on the derived neutral densities and thermospheric models,several new approaches in improving the previous atmospheric models were overviewed.Since the exospheric temperature is the crucial parameter for empirical models,one of the effective ways to improve models is to modify the exospheric temperature using accelerometer-based densities.The polynomial fitting as well as the Principal Component Analysis(PCA)techniques,were utilized to reconstruct the global density.Other methods such as assimilation and particle filter were also applied to improve atmospheric models.Finally,based on the derived neutral densities,the thermospheric responses to solar and astronomical events such as geomagnetic storms,solar flares,and solar eclipses were further reviewed.