A Global Magnetohydrodynamic Simulation Study of Ultra-low-frequency Wave Activity in the Inner Magnetosphere: Corotating Interaction Region + Alfvénic Fluctuations

Abstract

Using global magnetohydrodynamic (MHD) simulations, we investigate the role played by a complex solar structure composed of a corotating interaction region (CIR) followed by solar wind Alfvénic fluctuations on the magnetosphere’s nightside, equatorial electric field oscillations in the ultra-low-frequency range. A series of numerical experiments are performed employing synthetic solar wind inputs resembling those of a real CIR+Alfvénic fluctuation event that reached Earth’s magnetosphere on 2003 April 20. The following is found: (i) Radial electric field component fluctuations are excited via magnetopause boundary motions driven either by solar wind density variations characteristic of CIRs or by solar wind Alfvénic fluctuations with a given oscillation period. (ii) Azimuthal electric field component fluctuations nearer to Earth, that is, at radial distances R less than about 5R E ( Earth radius), are apparently not related to either of the two types of sinusoidal solar wind Alfvénic fluctuations used in this study featuring monochromatic frequencies of 0.833 mHz (20-minute period) and 1.666 mHz (10-minute period). Instead, these innermost azimuthal component fluctuations show enhanced activity when inner magnetosphere convection increases as a result of a southward turning of the interplanetary magnetic field component B z . (iii) Lastly, outermost (R ≳ 7 R E) azimuthal electric field oscillations weakly respond to monochromatic solar wind Alfvénic fluctuations by showing power spectral density peaks at both driving frequencies, but only near the flanks of the magnetopause, thus suggesting that such oscillations are being excited also owing to magnetopause boundary motions driven by solar wind Alfvénic fluctuations.

Modos de ondas magnetohidrodinámicas influenciados por la corriente de desplazamiento

“…En la formulación presentada en este manuscrito, las ecuaciones (46) y (60) pueden usarse en cualquier plasma que cumpla con las condiciones (simplificaciones) adoptadas en la ecuación de Ohm (10). Dejamos claro que al incorporar otros términos en la ley de Ohm, no significa que invalide el uso de J d sino que tendremos aumento en la complejidad del sistema, que lleva hacer un estudio numérico del problema, así como también la inclusión de otros fenómenos físicos tales como inestabilidades y algunos tipos de ondas [18].…”

“…donde ρ m la densidad del fluido. Las ondas de Alfvén se pueden encontrar, por ejemplo, en la atmósfera solar, el viento solar, la magnetosfera de la Tierra, plasmas astrofísicos y los producidos en laboratorios [5,[15][16][17][18]. Generalmente, en un fluido magneto-conductor el campo magnético no es uniforme en todo el espacio ocupado por el fluido.…”

Modeling Radiation Belt Electron Dropouts During Moderate Geomagnetic Storms Using Radial Diffusion Coefficients Estimated With Global MHD Simulations

“…It is known that narrowband ULF waves are likely generated by internal sources, that is, resulting from drift-bounce resonances with ring current ions (Sandhu et al [2021] and references therein). According to Jauer et al (2019), solving the drift physics of the bulk flow through the inner magnetosphere, as in our MHD simulations by CIMI, is critical to determining the local power distribution of these high-frequency E ϕ ULF waves.…”

“…nRMSE) between measured and simulated PSD at L* = 4.3 and L* = 4.9. The nRMSE values were calculated as inWelling and Ridley (2010) andJauer et al (2019), where a smaller nRMSE means a better PSD prediction from the model. It is quantitatively proven in this table that the 1D simulations better solve the gradual dropout in Case 2 since the nRMSE values of this case are smaller overall.…”

Dynamic Mechanisms Associated With High‐Energy Electron Flux Dropout in the Earth's Outer Radiation Belt Under the Influence of a Coronal Mass Ejection Sheath Region

“…It is extensively used by the scientific community to study the large-scale interaction between different solar wind structures and Earth's magnetosphere. It also has been widely used to address the low-frequency waves generation (in a few to tens of mHz range) like the ULF waves in the inner magnetosphere, specifically in the radiation belts (e.g., Alves et al, 2016;Claudepierre et al, 2010Claudepierre et al, , 2008Da Silva et al, 2019;Jauer et al, 2019;Komar et al, 2017;Souza et al, 2017). Da Silva et al (2019) and Souza et al (2017) used the SWMF/BATS-R-US model to study the ULF waves in the equatorial and nightside magnetosphere during the influence of the Alfvénic fluctuations associated with HSS.…”