摘要
火星探测是当前国家高科技竞争力的标志,世界航天强国均研制火星大气模式,为登陆探测提供气象环境保障.本文描述了 我国新一代火星大气模式(global open planetary atmospheric model for Mars,缩写GoPlanet-Mars,简称GoMars)的研制,其中的动力框架完全自主研发,具有二阶精度、能保证质量守恒.GoMars引进并耦合了美国宇航局艾姆斯研究中心的火星物理过程,具备模拟沙尘、水和CO2的能力.基于我国"祝融号"、美国"维京1号、2号"的实测数据以及国际火星大气全球数据集评估了GoMars,结果表明:GoMars能成功再现3个探测器记录的火星大气独特的地表气压"两峰两谷"特征;在全球地表温度、纬向急流、极区CO2冰和沙尘方面,GoMars也具备良好的模拟性能,可为我国火星探测计划实施提供新的气象环境保障手段.
Abstract
Mars exploration requires a high degree of scientific and technological capability,particularly in the development of a Martian atmospheric model to provide information on the meteorological conditions for landing.In addition,China has planned to implement the"Tianwen-3"exploration mission,with the goal of completing the human's first sampling return from Mars.Based on these requirements,we developed a new global open planetary atmospheric model for Mars,abbreviated as GoPlanet-Mars(short name:GoMars),in China.We first independently designed the dynamic core of GoMars and then coupled it with the physical parameterizations developed by the National Aeronautics and Space Administration(NASA)'s Ames Research Center in United States of America.Moreover,the dynamic core of GoMars model conserves mass,potential temperature and has second-order accuracy.It solves the fully compressible nonhydrostatic equations of motion using the spherical longitude and latitude grids with mixed finite difference and finite volume discretization.In addition,for the singularity problem caused by the convergence of the meridians of the longitude and latitude grid at the north and south poles,the GoMars model uses a zonal Gaussian convolution filter on the temporal tendency of the predicted quantity.Compared with the traditional zonal fast Fourier transform or digital recursive filtering,the Gaussian convolution kernel width used by GoMars model changes continuously with latitude according to the linear numerical stability condition,which overcomes the problem of computational distortion caused by the discontinuous change,thereby greatly improving the computational stability and efficiency of the explicit scheme.In addition,the GoMars model can stably run without filtering the extremely high Martian topography and has high efficiency for parallel computing.The GoMars model has the ability to simulate the three critical cycles of the Martian atmosphere:Dust,water,and CO2 cycles.We preliminarily validated the GoMars model based on the in situ observations of China's Zhurong rover and the USA's Viking 1 and 2 landers,as well as a common set of global atmospheric reanalysis data for Mars(OpenMARS).Specifically,the GoMars simulation of the global spatial distribution of basic Martian meteorological environmental variables at the annual mean time scale and the diurnal temporal evolution of surface pressure and dust activity were examined.The results showed that the GoMars model successfully reproduced the unique characteristics of surface pressure on Mars as recorded by the Zhurong rover and the two Viking landers,especially in summer in the Northern Hemisphere.The surface pressure simulated by the GoMars model was consistent with the observations of the Zhurong rover.Furthermore,the GoMars model had good performance for the surface temperature,zonal wind,polar CO2 ice cap and dust process compared with the OpenMARS reanalysis data.In particular,the GoMars model alleviated the cold bias of the temperature north of 30°S simulated by the NASA Ames Legacy Mars Global Climate Model(NASA model).Moreover,the westerly jet stream in the upper troposphere was stronger and higher in the results obtained by the GoMars model compared to those in the NASA model;therefore,their spatial structure in the GoMars model was more consistent with the OpenMARS reanalysis data.The independent development of the Martian atmospheric model and the production of Martian weather forecasts are some of the greatest challenges of the international frontier in planetary atmospheric science and some of the necessary conditions for successful Mars exploration,and earth and planetary science researchers must work together to meet these challenges.
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