The impact of geomagnetic activity on thermospheric composition and circulation, and its coupling to the middle and upper atmosphere

最近的研究表明，在极地冬季，中层大气（10至90公里）的臭氧收支可以通过来自低层热层（90至120公里）的NOx （N， NO, NO2）的入侵与高层大气耦合。由于臭氧是大气中层辐射加热的主要种类之一，臭氧收支的变化会影响大气温度和地表环流。由于这些氮氧化物入侵的强度随地磁活动的变化而变化，因此这些冬季氮氧化物增强原则上是太阳变率对气候系统可能影响的另一种机制。然而，目前最先进的化学-气候模型还不能正确地描述氮氧化物的来源区域和被输送到大气中层的数量。为了正确地模拟从高层大气到中低层大气的这种耦合，需要对低层热层的源区域进行良好的描述，描述与高纬度地磁活动相关的基本过程：由于极光电子的沉降、焦耳加热以及随后由NO增强和引力波激发引起的红外冷却增加而导致的化学成分的变化。由于已知在高纬度低热层激发的重力波既向上传播也向赤道传播，因此后一过程也会影响低地球轨道卫星的环境。在这个项目中，我们将使用扩展到低层热层的耦合化学-气候模型xEMAC，以以下方式解决这个问题：与我们在不来梅雅各布斯大学的合作伙伴合作，模型中的焦耳加热和粒子降水将受到Swarm仪器观测结果的时间和空间限制。地磁安静期和非常活跃期都将被研究。该模型将向上扩展，以调查卫星环境，作为优先方案第二阶段后续研究的先导。在可能的情况下，将根据观测结果对模式响应进行验证，并对模式结果进行分析，以研究焦耳加热和颗粒降水对低层热层的化学成分、温度和环流的影响，以及它们与中低层大气和高层大气的耦合。通过这个项目，我们将有助于更好地理解太阳-气候耦合，并改进其在当前最先进的化学-气候模型中的表现，以及更好地理解通过低层热层地磁活动对卫星环境的太阳强迫。

Recent research has shown that the ozone budget in the middle atmosphere (10 to 90 km) can be coupled to the upper atmosphere via intrusions of NOx (N, NO, NO2) from its source region in the lower thermosphere (90 to 120 km) during polar winter. As ozone is one of the key species of radiative heating in the middle atmosphere, changes to the ozone budget there can affect atmospheric temperatures and circulation down to the surface. As the strength of these NOx intrusions varies with geomagnetic activity, these winter-time NOx enhancements are therefore in principle another mechanism for the possible impact of solar variability on the climate system. However, state-of-the-art chemistry-climate models are currently not able to correctly describe the source region and the amount of NOx which is transported down to the middle atmosphere. To correctly model this coupling from the upper atmosphere down to the middle and lower atmosphere, a good description of the source region in the lower thermosphere is needed, describing the principle processes related to geomagnetic activity at high latitudes: changes to the chemical composition due to precipitating auroral electrons, Joule heating, and subsequent increased infrared cooling from enhanced NO as well as excitation of gravity waves. As gravity waves excited in the lower thermosphere at high latitudes are known to propagate equatorwards as well as upwards, the latter process can also affect the environment of low-Earth orbit satellites. In this project, we will address this issue using the coupled chemistry-climate model xEMAC extending into the lower thermosphere in the following way: Joule heating and particle precipitation in the model will be constrained temporally and spatially by observations from the Swarm instruments, in cooperation with our partner at the Jacobs University of Bremen. Both geomagnetically quiet times and very active periods will be investigated. The model will be extended upward to investigate the satellite environment as a precursor for follow-up studies in the second phase of the priority program. The model response will be validated against observations where possible, and model results will be analyzed to investigate the impact of Joule heating and particle precipitation on the chemical composition, temperature, and circulation of the lower thermosphere separately and combined, as well as its coupling to the middle and lower atmosphere, and to the upper atmosphere. With this project, we will contribute to a better understanding of the solar-climate coupling, and improve its representation in current state-of-the art chemistry-climate models, as well as to a better understanding of solar forcing of the satellite environment via geomagnetic activity in the lower thermosphere.