Princeton Center for Heliophysics Seminar

This presentation numerically examines electromagnetic ion cyclotron (EMIC) wave propagation in the magnetosphere using the full-wave simulation tool, Petra-M. The Petra-M code is a state-of-the-art generic electromagnetic simulation tool for modeling RF wave propagation based on MFEM [http://mfem.org](link is external) and successfully examined wave properties by adopting realistic antenna geometry in tokamaks. This presentation adopts Earth’s dipole magnetic field geometry with a realistic density profile into the Petra-M and examines EMIC wave properties when waves have various wave normal angles (WNAs) and background heavy-ion densities.

The EMIC waves are low-frequency waves typically in the Pc 1-2 frequency range that are excited below the proton gyrofrequency. The existing instability theories and ray tracing suggest that only left-hand polarized EMIC waves are generated near the magnetic equator and propagate along the field line toward the Earth. EMIC waves are predicted to reflect at the Buchsbaum resonance in the higher magnetic field region and not reach the ground. However, these results are inconsistent with observations. A1D full-wave analysis found that EMIC waves can tunnel through the evanescent region between cutoff and ion cyclotron resonance locations and reach the ground, but 1D modeling cannot include 2D magnetic curvature effects. 2D full-wave simulations enable us to overcome these shortcomings of ray tracing or 1D full-wave simulations using an approach that describes wave propagation, mode conversion, tunneling with 2D magnetic curvature effect for arbitrary plasma and magnetic field configurations. Previous 2D simulations using FW2D wave code showed excellent agreement with previous calculations, such as wave cutoff at the Buchsbaum resonance, polarization reversal, and mode conversion at the crossover locations. They also showed that equatorially generated EMIC waves could propagate into the inner or outer magnetosphere depending on the WNA, and thus suggested that WNAs could be one of the critical parameters to control EMIC wave propagation to the ground. However, since the previous work only focuses on wave properties near the ion cyclotron frequency, they did not provide a global picture of wave propagation.

Here, we provide a global structure of the EMIC wave propagation from the source to the ground along the WNAs in various heavy ion compositions and densities. He-mode EMIC waves with small WNA cannot penetrate through the critical frequencies near the He gyrofrequencies; however, obliquely propagate He-mode EMIC waves can reach lower altitude and lower L-shell having right-handed polarization. Interestingly, the secondary mode conversion from the right-handed polarization EMIC waves to the linearly polarized Alfvenic wave occurs in the inner magnetosphere, and these waves can finally reach the ground.