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

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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.