Thermosphere-Ionosphere Variability induced by Planetary Waves and Tides due to Earth's magnetic field

In recent years observations and modeling studies have shown that tides and planetary waves (PW) can generate significant ionosphere-thermosphere (IT) variability. The wave sources vary, the propagation conditions are constantly changing, nonlinear interaction between waves can occur, all contributing to the wave spectrum variability. Recently, Forbes et al. [2018] demonstrated that the tidal spectrum can be modulated by PWs (3-20 days). The dissipating tides with the imprinted PW oscillation generate PW period fluctuations in the mean state. Focusing on the October 2009 time period, the Thermosphere-Ionosphere-Electrodynamics GCM (TIEGCM) simulation showed good agreement with the PW oscillations in the neutral mass density and plasma density at 325 km derived from CHAMP data. The PW oscillations can account for approximately ±30-40% of the ionospheric variability. The Earth's magnetic field is expected to contribute to ionospheric variability by wave number broadening and hydromagnetic coupling which will change the wave spectrum. It is still not fully understood how much the geomagnetic field contributes to the IT variability.

In this study we build on our results of the October 2009 periods and focus on the contribution of Earth's magnetic field to the PWs and tidal induced variability in the IT system. We will conduct numerical experiments with the TIEGCM with simplified geomagnetic main field configurations, and compare with the simulation using a realistic Earth magnetic field model. We will examine the change in the PW spectrum, and quantify the effects on the IT variability. Possible mechanism of influencing the PW spectrum will be examined by analyzing neutral winds, ExB drifts and plasma distributions.

Forbes, J. M., Zhang, X., Maute, A., & Hagan, M. E. (2018). Zonally symmetric oscillations of the thermosphere at planetary wave periods. Journal of Geophysical Research: Space Physics, 123, 4110-4128. https://doi.org/10.1002/2018JA025258