Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

Abstract

We present evidence of resonant wave‐wave coupling via toroidal field line resonance (FLR) signatures in the Space Weather Modeling Framework's (SWMF) global, terrestrial magnetospheric model in one simulation driven by a synthetic upstream solar wind with embedded broadband dynamic pressure fluctuations. Using in situ, stationary point measurements of the radial electric field along the 1500 LT meridian, we show that SWMF reproduces a multiharmonic, continuous distribution of FLRs exemplified by 180° phase reversals and amplitude peaks across the resonant L shells. By linearly increasing the amplitude of the dynamic pressure fluctuations in time, we observe a commensurate increase in the amplitude of the radial electric and azimuthal magnetic field fluctuations, which is consistent with the solar wind driver being the dominant source of the fast mode energy. While we find no discernible local time changes in the FLR frequencies despite large‐scale, monotonic variations in the dayside equatorial mass density, in selectively sampling resonant points and examining spectral resonance widths, we observe significant radial, harmonic, and time‐dependent local time asymmetries in the radial electric field amplitudes. A weak but persistent local time asymmetry exists in measures of the estimated coupling efficiency between the fast mode and toroidal wave fields, which exhibits a radial dependence consistent with the coupling strength examined by Mann et al. (1999) and Zhu and Kivelson (1988). We discuss internal structural mechanisms and additional external energy sources that may account for these asymmetries as we find that local time variations in the strength of the compressional driver are not the predominant source of the FLR amplitude asymmetries. These include resonant mode coupling of observed Kelvin‐Helmholtz surface wave generated Pc5 band ultralow frequency pulsations, local time differences in local ionospheric dampening rates, and variations in azimuthal mode number, which may impact the partitioning of spectral energy between the toroidal and poloidal wave modes.

The Broadband Excitation of 3‐D Alfvén Resonances in a MHD Waveguide

“…They recently extended this work to consider the inclusion of a plasmasphere in their model, which still resulted in significant, albeit reduced, resonant excitation (Claudepierre et al, 2016). In a similar manner, Ellington et al (2016) also showed significant resonance excitation within a global simulation. Degeling et al (2010) considered a compressed dipole model of the magnetosphere again displaying the prevalence of FLR excitation in 3-D.…”

The story of plumes: the development of a new conceptual framework for understanding magnetosphere and ionosphere coupling

“…What is now clear is that plumes connect the equatorial F region ionosphere to the dayside magnetopause and the nightside magnetotail plasma sheet (e.g., Su et al, 2001a, b;Horvath and Lovell, 2011;Walsh et al, 2014a, b;Foster et al, 2014). Through the formation and evolution of the different plumes, they impact wave generation and wave-particle interactions (e.g., Summers et al, 2008;Chen et al, 2012;Halford et al, 2015), particle precipitation (Spasojević and Fuselier, 2009;Yuan et al, 2011Yuan et al, , 2013, ion outflow (e.g., Zeng and Horowitz, 2008;Tu et al, 2007), local-time asymmetries in ULF wave field-line resonance (FLR) signatures (e.g., Archer et al, 2015;Ellington et al, 2016), satellite communication and navigation systems (Ledvina et al, 2004;Basu et al, 2005;Datta-Barua et al, 2014), and even the coupling efficiency of the solar wind to the magnetosphere (Borovsky and Denton, 2006;Borovsky et al, 2013;Ouellette et al, 2016;Fuselier et al, 2016). Though we now have a new appreciation and understanding of plumes, there are still many unanswered questions on their formation (e.g., Kelley et al, 2004;Horvath and Lovell, 2011;Zou et al, 2013Zou et al, , 2014Borovsky et al, 2014) and impact on global magnetospheric dynamics McFadden et al 2008;Walsh et al, 2014Walsh et al, , 2015.…”

Identifying ULF Wave Eigenfrequencies in SuperDARN Backscatter Using a Lomb‐Scargle Cross‐Phase Analysis

“…The technique requires the presence of a broadband source as described above to excite the field lines at each station at their local eigenfrequency (Menk et al, 2004;Waters et al, 1991). Claudepierre et al (2010), Ellington et al (2016), and Elsden and Wright (2018) have all shown that such a broadband source can be used to excite field lines using simulations. Many studies have utilized the cross-phase technique to study magnetospheric ultralow frequency (ULF) waves (e.g., Clausen et al, 2008;Kawano et al, 2002;Sandhu et al, 2018;Waters et al, 1995).…”