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

电离层，即地球上层大气中约100-600公里高度的电离部分，每天、每小时都有很大的变化。了解电离层的短期变化或“天气”变得越来越重要，因为它影响着现代无线电通信和导航技术。在白天，电离层电导率高是由太阳辐射造成的，中低纬度地区电离的全球分布主要受赤道电动力学的影响。因此，确定赤道电场和电流的可变性来源是非常重要的。在过去十年中，观测和数值调查发现，来自低层大气的波强迫是电离层可变性的一个重要来源。然而，目前尚不能全面了解大气波对大气的哪些贡献以及贡献有多大。我们最新的研究表明，赤道电喷流的强度可以直接受到向西传播的行星波的调制，行星波代表大气的正常模式或共振振荡。赤道电喷流是沿日侧磁赤道的纬向电离层电流。我们的研究仅限于由一颗卫星探测到的几个事件，我们只考虑了周期为~6天的波。我们受到这一成功的鼓舞，现在将进行一项广泛的研究，以充分量化大气行星波对赤道电离层电动力学变异性的贡献。为此，我们将结合从多颗卫星和地面站对赤道电喷流进行的广泛和最近可用的观测，并将观测结果与日本最近开发的最先进的基于物理的全大气模型GAIA进行比较。所有的项目任务将需要德国和日本团队的共同努力，以最好地通过结合观测和模拟结果来实现新的结果。德国团队将利用其在卫星和地面磁数据分析方面的专业知识，而日本团队将通过分析GAIA模拟数据以及执行受控的数值实验来做出贡献。这一联合项目将涉及三个科学问题：第一，行星波对赤道电喷流的影响的气候学，包括季节性、年际变化和太阳周期变化？其次，在中层大气中常见的周期为~2天、~6天、~10天和~16天的行星波的相对重要性是什么？最后，行星波调制赤道电动力学的机制是什么？我们的目标是提供关于行星波在低层大气和电离层之间垂直大气耦合过程中的作用的新的、详细的和基本的知识。

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.