Modeling and Observations of the Effects of the Alfvén Velocity Profile on the Ionospheric Alfvén Resonator

• Published in: Journal of geophysical research. Space physics 2024-01, Vol.129 (1), p.n/a
• Main Authors: Hodnett, R. M., Yeoman, T. K., Beggan, C. D., Wright, D. M.
• Format: Article
• Language: English
• Subjects: Alfvén velocity; Alfvén waves; Atmospheric models; Boundary conditions; Density distribution; Electric fields; Free electrons; Frequency variation; Ground-based observation; Harmonics; IAR; Ionosphere; Ionospheric Alfvén Resonator; IRI; Magnetic fields; Plasma density; Resonant frequencies; Resonators; Sunlight; Upper atmosphere; Velocity distribution; Wave equations
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2023JA032308

We have modeled the individual harmonic frequencies of the Ionospheric Alfvén Resonator (IAR) at Eskdalemuir by solving a one‐dimensional wave equation and using non‐uniform modeled Alfvén velocity profiles. By comparing the results of the modeling alongside harmonics obtained from the Eskdalemuir, UK, data set from 2013 to 2021, the effects of the non‐uniformity of the Alfvén velocity profile on the IAR are considered. We calculated the offset between the fundamental frequency and the harmonic frequency separation and found that this is not constant. From this parameter, we infer that the lower boundary condition of the electric field of the IAR is closest to a node, which agrees with previous studies. We compare the results of the non‐uniform model with previous uniform models and evaluate their interpretations and the implications for the lower boundary condition. Plain Language Summary The ionosphere is the part of Earth's tenuous upper atmosphere which has been ionized by sunlight, resulting in the separation of heavier ions and free electrons into a state termed a “plasma.” Like on a taut string, waves travel through the ionosphere along magnetic field lines reflecting from near the bottom of the ionosphere and back again at a boundary higher up. These waves can be observed in ground‐based magnetic field data, and their frequencies can tell us about conditions in the ionosphere, including its plasma density distribution along the wave path. We have modeled these frequencies and then compared them with magnetic field measurements at an observatory in the UK. As the amount of plasma along the field line threading through the ionosphere changes, we can detect this as frequency variations and investigate how this affects the behavior of the waves. Key Points Solving a one‐dimensional wave equation results in modeled harmonics of the Ionospheric Alfvén Resonator Non‐uniform Alfvén velocity profiles lead to different separations between the harmonics From the offset of the fundamental frequency and average frequency separation, lower boundary conditions can be inferred