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）中的臭氧收支可以通过来自低热层（90至120公里）源区的NOx（N，NO，NO2）侵入耦合到高层大气。由于臭氧是中层大气辐射加热的关键物质之一，那里臭氧收支的变化会影响大气温度和向下到地面的环流。由于这些氮氧化物侵入的强度随地磁活动而变化，因此，这些冬季氮氧化物的增强原则上是太阳变化对气候系统可能产生影响的另一种机制。然而，目前最先进的化学气候模型无法正确描述源区域和被输送到中层大气的NOx的量。为了正确地模拟这种从高层大气到中层和低层大气的耦合，需要对低热层的源区进行良好的描述，描述与高纬度地磁活动有关的主要过程：由于极光电子沉淀而导致的化学成分变化，焦耳加热，以及随后由于NO增强而增加的红外冷却以及重力波的激发。由于已知在高纬度低热层激发的重力波既可以向上传播也可以向赤道传播，后一过程也会影响低地球轨道卫星的环境。在这个项目中，我们将解决这个问题，使用耦合的化学-气候模式xEMAC延伸到较低的热层以下方式：焦耳加热和粒子沉淀在模型中将被限制在时间和空间上的观察从群仪器，与我们的合作伙伴在不莱梅的雅各布斯大学。地磁平静时间和非常活跃的时期都将被调查。该模型将向上扩展，以调查卫星环境，作为优先计划第二阶段后续研究的先驱。在可能的情况下，将根据观测结果对模型响应进行验证，并将对模型结果进行分析，以调查焦耳加热和粒子沉降对低热层的化学成分、温度和环流的单独和组合的影响，以及其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了解太阳-气候耦合，并改善其在当前最先进的化学-气候模型中的表现，以及通过低热层的地磁活动更好地了解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.