Short-term variability of the equatorial ionosphere and its association with planetary-scale waves

电离层，即，地球上层大气的电离部分。海拔100-600公里，每天、每小时都有很大变化。了解电离层的短期变化或“天气”变得越来越重要，因为它影响到现代无线电通信和导航技术。在日照面，太阳辐射是电离层电导率高的原因，在低到中纬度电离的全球分布主要是由赤道电动力学。因此，它是非常重要的，以确定赤道电场和电流的可变性的来源。在过去十年中，观测和数值研究确定，来自低层大气层的波强迫是电离层变化的一个重要来源。然而，目前还没有全面了解哪些大气波起作用以及有多重要。我们的最新研究显示，赤道电射流的强度，这是一个纬向电离层电流沿着日侧磁赤道流动，可以直接调制向西传播的行星波，这代表了正常模式，或共振振荡，大气。我们的研究仅限于由单个卫星检测到的几个事件，我们只考虑了周期为6天的波。我们受到这一成功的激励，现在将进行广泛的研究，以充分量化大气行星波对赤道电离层电动力学变化的贡献。为此，我们将联合收割机结合多个卫星和地面站最近对赤道电射流的广泛观测，并将观测结果与日本最近开发的最先进的全大气层物理模型GAIA进行比较。所有项目任务都需要德国和日本团队共同努力，以最好地实现观测和模拟结果相结合的新结果。德国小组将利用其在卫星和地面磁数据分析方面的专门知识，而日本小组将通过分析GAIA模拟数据以及进行受控数值实验作出贡献。这一联合项目将解决的科学问题有三个方面：第一，行星波对赤道电急流的气候影响是什么，包括季节性、年际和太阳周期变化？第二，在中层大气中经常观测到的周期为~2天、~6天、~10天和~16天的行星波的相对重要性如何？最后，行星波调制赤道电动力学的机制是什么？我们的目标是提供新的，详细的和基本的知识，行星波的作用之间的低层大气和电离层的垂直大气耦合过程。

The ionosphere, i.e., the ionized part of the Earth's upper atmosphere in ca. 100-600 km altitude, varies significantly from day to day, from hour to hour. Understanding the short-term variability, or "weather", of the ionosphere becomes increasingly crucial as it affects modern radio communication and navigation technology. On the dayside, where insolation is responsible for high ionospheric conductivity, the global distribution of ionization at low to mid latitudes is dominated by the equatorial electrodynamics. Thus, it is highly important to identify sources of variability of equatorial electric fields and currents. During the last decade, observational and numerical investigations identified wave forcing from lower atmospheric layers as a significant source of variability for the ionosphere. However, it is yet to be comprehensively understood which atmospheric waves contribute and how significantly. Our latest study revealed evidence that the intensity of the equatorial electrojet, which is a flow of zonal ionospheric current along the dayside magnetic equator, can be directly modulated by a westward-propagating planetary wave, which represents the normal mode, or resonant oscillation, of the atmosphere. Our study was limited to a few events detected by a single satellite and we considered only waves with a period of ~6 days. We are motivated by this success and will now conduct an extensive study to fully quantify the contributions of atmospheric planetary waves to the variability of the electrodynamics in the equatorial ionosphere. To this end, we will combine extensive and recently available observations of the equatorial electrojet from multiple satellites as well as ground-based stations, and compare the observational results with the state-of-the-art physics-based model of the whole atmosphere, GAIA, that has been recently developed in Japan. All project tasks will need to be joint efforts between the German and Japanese teams to best achieve the novel results from combining observational and simulation results. The German team will exploit its expertise in satellite and ground magnetic data analyses, while the Japanese team will contribute by analyzing GAIA simulation data as well as by performing controlled numerical experiments. The scientific questions that will be addressed in this joint project are threefold: Firstly, what is the climatology of the planetary-wave effect on the equatorial electrojet, including seasonality, interannual and solar-cycle variability? Secondly, what is the relative importance of the planetary waves with periods at ~2 days, ~6 days, ~10 days, and ~16 days, which are commonly observed in the middle atmosphere? Finally, what is the mechanism by which planetary waves modulate the equatorial electrodynamics? Our aim is to provide new, detailed and fundamental knowledge on the role of planetary waves for vertical atmospheric coupling processes between the lower atmosphere ad the ionosphere.