Verifying Ray Tracing Amplitude Methods for Global Magnetospheric Modeling

• Published in: Journal of geophysical research. Space physics 2023-05, Vol.128 (5), p.n/a
• Main Authors: Holmes, Justin C., Delzanno, G. L., Colestock, P. L., Yakymenko, K.
• Format: Article
• Language: English
• Subjects: Amplitudes; ASTRONOMY AND ASTROPHYSICS; Cyclotrons; Data points; Earth magnetosphere; Electromagnetic radiation; Energy conservation; Exact solutions; Finite element method; Magnetosphere; Modelling; Particle interactions; Radiation belt remediation; Ray tracing; Robustness (mathematics); ULF waves; Wave energy; Wave propagation; Wave-particle interactions; Whistler
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2023JA031348

Ray tracing is a commonly used method for modeling the propagation of electromagnetic waves in Earth's magnetosphere. To apply ray tracing results to global models of wave‐particle interaction such as energetic electron scattering, it is useful to map the discrete rays to a volume filling mesh. However, some methods have inherent losses of energy from the wave source, or do not account for the full range of wave properties within a sample volume. We have developed and tested a 3D magnetospheric ray tracing code “MESHRAY” which resolves these issues. MESHRAY uses the conservation of Poynting flux through ray triplets with finite volume to determine the local field amplitudes. Electromagnetic wave energy density from all ray data points is mapped to a mesh and verified against the wave source power for energy conservation varying time step length, number of rays, and total time steps. We find that the method is self‐consistent and numerically robust. We further investigate whether the neglect of phase information and superposition has a significant impact on the accuracy of mapping wave intensity to a mesh. We find excellent agreement between the analytic solution for waves emitted by a line source in a plane‐stratified medium and an equivalent ray tracing solution. When phase information is excluded, ray tracing reproduces an average amplitude spread over regions of coherent constructive and destructive interference. This may be an important consideration for interpolating ray tracing results of longer wavelength waves such as magnetosonic, electromagnetic ion cyclotron, or ULF waves. Key Points Ray tracing amplitude calculations using finite‐volume ray triplets and methods using discrete, constant‐power rays are self‐consistent Integrating electric and magnetic field wave energy density onto a space‐filling mesh is energy conserving for sufficiently small time steps Spatially averaged amplitudes are consistent with superposed waves for regions larger than the scale of interference pattern structure