Mars Thermospheric Neutral Winds: Mars Global Ionosphere-Thermosphere Model (M-GITM) Simulated Datasets for Comparison to MAVEN Spacecraft Measurements

The NASA MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft, which is currently in orbit around Mars, has been taking monthly measurements of the speed and direction of the winds in the upper atmosphere of Mars between about 140 to 240 km above the surface. The observed wind speeds and directions change with time and location, and sometimes fluctuate quickly. These measurements are compared to simulations from a computer model of the Mars atmosphere called M-GITM (Mars Global Ionosphere-Thermosphere Model), developed at U. of Michigan. This is the first comparison between direct measurements of the winds in the upper atmosphere of Mars and simulated winds and is important because it can help to inform us what physical processes are acting on the observed winds. Some wind measurements have similar wind speeds or directions to those predicted by the M-GITM model, but sometimes, there are large differences between the simulated and measured winds. The disagreements between wind observations and model simulations suggest that processes other than normal solar forcing may become relatively more important during these observations and alter the expected circulation pattern. Since the global circulation plays a role in the structure, variability, and evolution of the atmosphere, understanding the processes that drive the winds in the upper atmosphere of Mars provides key context for understanding how the atmosphere behaves as a whole system.

A basic version of the M-GITM code can be found on Github as follows:
https:/github.com/dpawlows/MGITM
;About 30 Neutral Gas and Ion Mass Spectrometer (NGIMS) wind campaigns (of 5 to 10 orbits each) have been conducted by the MAVEN team (Benna et al., 2019). Five of these campaigns are selected for detailed study (Roeten et al. 2019). The Mars conditions for these five campaigns have been used to launch corresponding M-GITM code simulations, yielding 3-D neutral wind fields for comparison to these NGIMS wind observations. The M-GITM datacubes used to extract the zonal and meridional neutral winds, along the trajectory of each orbit path between 140 and 240 km, are provided in this Deep Blue Data archive. README files are provided for each datacube, detailing the contents of each file. A general README file is also provided that summarizes the inputs and outputs of the M-GITM code simulations for this study.

当前在轨环绕火星运行的美国国家航空航天局（NASA）火星大气与挥发物演化（Mars Atmosphere and Volatile Evolution, MAVEN）航天器，正对火星表面140至240公里高度的高层大气风速与风向开展月度观测。实测风速与风向会随时间与空间位置发生变化，部分时段甚至会出现快速波动。本次观测数据将与密歇根大学开发的火星大气计算机模型——M-GITM（火星全球电离层-热层模型，Mars Global Ionosphere-Thermosphere Model）的模拟结果进行比对。这是首次将火星高层大气直接风速观测数据与模拟风场进行对比，该研究具有重要意义：其可帮助我们厘清调控实测风场的物理过程。部分实测风速与风向与M-GITM模型的预测结果吻合，但部分时段模拟与实测风场之间也存在显著差异。观测与模拟结果之间的偏差表明，在本次观测周期内，除常规太阳强迫之外的其他物理过程的相对重要性有所提升，并改变了预期的大气环流模式。由于全球环流对火星大气的结构、变异性与演化均存在调控作用，阐明火星高层大气风场的驱动过程，可为理解火星大气作为整体系统的运行机制提供关键依据。

M-GITM代码的基础版本可在GitHub上获取，链接如下：
https://github.com/dpawlows/MGITM
MAVEN科研团队（Benna等人，2019）已开展约30次中性气体与离子质谱仪（Neutral Gas and Ion Mass Spectrometer, NGIMS）风场观测任务（单次任务包含5至10个轨道周期），其中5次任务被选为详细研究对象（Roeten等人，2019）。研究人员基于这5次任务对应的火星环境参数，启动了对应的M-GITM代码模拟，生成了可与NGIMS实测风场比对的三维中性风场数据。本Deep Blue Data归档中提供了M-GITM数据立方体，可用于提取140至240公里高度区间内各轨道轨迹上的纬向与经向中性风场。每个数据立方体均附带README文档，详述了各文件的内容；此外还提供了通用README文档，汇总了本次研究中M-GITM代码模拟的输入与输出参数。