Monitoring climatic changes in the thermosphere and ionosphere and understanding their causes is important for practical purposes. To support this effort and facilitate comparisons between observations and model results, a long transient simulation with the Whole Atmosphere Community Climate Model eXtension (WACCM‐X) from 1950 to 2015 was conducted. This simulation used realistic variations in solar and geomagnetic activity, main magnetic field changes, and trace gas emissions, including CO₂, thereby including all known drivers of upper atmosphere climate change. Analysis of the full 1950–2015 interval with a standard multilinear regression approach demonstrated difficulties in removing solar cycle effects sufficiently to obtain reliable trends. Results improved when an (F10.7a)² was included in the regression model, in addition to terms for F10.7a, K_P, and the trend itself. Comparisons with previous studies and analysis of spatial variations in trend estimates confirmed that the increase in CO₂ concentration is the main driver of trends in thermosphere temperature and density, but at high (magnetic) latitudes effects of main magnetic field changes play a role as well, especially in the Northern Hemisphere. Spatial patterns of trends in h_mF₂, N_mF₂, and total electron content indicate a superposition of CO₂ and geomagnetic field effects, with the latter dominating trends in the region of ∼50–20°N, ∼60°W to 20°E. Additional model experiments to investigate the indirect dynamical effects of climate change in the lower atmosphere (<50 km) on the upper atmosphere (>100 km) suggested that these effects are small and insignificant. However, current model limitations could mean that these effects are underestimated.

中文翻译：

---

WACCM‐X模拟的1950年至2015年高层大气气候变化的分析和归因

监测热层和电离层的气候变化并了解其原因对于实际目的很重要。为了支持这项工作并促进观测结果与模型结果之间的比较，我们使用1950年至2015年的整个大气群落气候模型扩展（WACCM‐X）进行了长期瞬态模拟。该模拟使用了太阳和地磁活动，主要磁场的变化以及痕量气体排放（包括CO _2）的实际变化，从而包括了所有已知的高层大气气候变化的驱动因素。使用标准的多线性回归方法对整个1950-2015年的时间间隔进行分析表明，难以充分消除太阳周期效应以获得可靠的趋势。当（F 10.7除了F 10.7 a， K _P和趋势本身的术语外，回归模型还包括a）²。与先前研究的比较以及趋势估计值的空间变化分析证实，CO ₂浓度的增加是热层温度和密度趋势的主要驱动因素，但在高（磁）纬度，主要磁场变化的影响也起着作用。 ，尤其是在北半球。h _m F ₂， N _m F ₂和总电子含量趋势的空间格局表明CO ₂的叠加地磁场效应，后者占主导地位的趋势是在约50–20°N，约60°W至20°E的范围内。其他模式实验研究了低层大气（<50 km）对高层大气（> 100 km）的气候变化的间接动力学影响，表明这些影响很小且微不足道。但是，当前模型的局限性可能意味着这些影响被低估了。