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，在极地冬季期间，中层大气(10~90公里)的臭氧收支可以通过来自热层下层(90~120公里)源区的NOx(N，NO，NO2)的侵入而耦合到高层大气。由于臭氧是中层大气辐射加热的关键物种之一，那里臭氧收支的变化会影响大气温度和向下到地表的环流。由于这些NOx侵入的强度随着地磁活动的不同而不同，因此，这些冬季NOx的增强在原则上是太阳变率可能影响气候系统的另一种机制。然而，目前最先进的化学-气候模型无法正确描述氮氧化物的来源区域和向下输送到中层大气的量。为了正确地模拟从上层大气向下到中层和下层大气的这种耦合，需要很好地描述低热层中的源区，描述与高纬度地磁活动有关的主要过程：极光电子沉淀引起的化学成分的变化，焦耳加热，以及随后增强的NO导致的红外冷却增加以及重力波的激发。由于已知在高纬度较低的热层中激发的重力波既向赤道方向传播，也向上传播，后一过程也会影响低地球轨道卫星的环境。在这个项目中，我们将使用扩展到低热层的化学-气候耦合模式XEMAC来解决这个问题，方法如下：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Sarm仪器的观测在时间和空间上的限制。地磁平静时期和非常活跃时期都将被调查。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，将根据观测值验证模式的响应，并将分析模式结果，以研究焦耳加热和粒子降水对低热层的化学成分、温度和环流的影响，以及它与中低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，以及更好地理解太阳通过较低热层中的地磁活动对卫星环境的强迫。

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.