Magnetospheric and solar wind dependences of coupled fast‐mode resonances outside the plasmasphere

Archer, Martin; Hartinger, M.; Walsh, Brian M.; Angelopoulos, V.

doi:10.1002/2016ja023428

Cited by 14 publications

(29 citation statements)

References 79 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This corresponds to a fast-mode wave propagating (assuming low plasma beta) purely in the ± R direction forming a quarter wavelength mode between the magnetopause r mp and an inner boundary at the Alfvén speed local maximum r ib (at r = 3.2 R E ) 40 . From the Alfvén speed profile for this event we calculate this to be 6.3 mHz, clearly much higher than the two remaining signals which were observed.…”

Section: Resultsmentioning

confidence: 99%

Direct observations of a surface eigenmode of the dayside magnetopause

et al. 2019

Self Cite

View full text Add to dashboard Cite

The abrupt boundary between a magnetosphere and the surrounding plasma, the magnetopause, has long been known to support surface waves. It was proposed that impulses acting on the boundary might lead to a trapping of these waves on the dayside by the ionosphere, resulting in a standing wave or eigenmode of the magnetopause surface. No direct observational evidence of this has been found to date and searches for indirect evidence have proved inconclusive, leading to speculation that this mechanism might not occur. By using fortuitous multipoint spacecraft observations during a rare isolated fast plasma jet impinging on the boundary, here we show that the resulting magnetopause motion and magnetospheric ultra-low frequency waves at well-defined frequencies are in agreement with and can only be explained by the magnetopause surface eigenmode. We therefore show through direct observations that this mechanism, which should impact upon the magnetospheric system globally, does in fact occur.

show abstract

Section: Resultsmentioning

confidence: 99%

Direct observations of a surface eigenmode of the dayside magnetopause

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…Future studies could include a more realistic magnetic field and density, informed by observations (e.g., Sandhu et al, ). These will affect the properties of the fast mode (e.g., Archer et al, ) and consequently the details of the FLRs they excite.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Fast Normal Mode Structure and Magnetopause Forcing on FLRs in a 3‐D Waveguide

Elsden

Wright

2019

JGR Space Physics

View full text Add to dashboard Cite

This paper investigates the excitation of waveguide modes in a nonuniform dipole equilibrium and, further, their coupling to field line resonances (FLRs). Waveguide modes are fast compressional ultralow frequency (ULF) waves, whose structure depends upon the magnetospheric equilibrium and the solar wind driving conditions. Using magnetohydrodynamic simulations, we consider how the structure of the excited waveguide mode is affected by various forms of magnetopause driving. We find that the waveguide supports a set of normal modes that are determined by the equilibrium. However, the particular normal modes that are excited are determined by the structure of the magnetopause driver. A full understanding of the spatial structure of the normal modes is required in order to predict where coupling to FLRs will occur. We show that symmetric pressure driving about the noon meridian can excite normal modes which remain around to drive resonances for longer than antisymmetric driving. Further, the critical quantity in terms of efficient coupling is the magnetic pressure gradient aligned with the resonance.

show abstract

“…This is evident by comparing the gradients of the red and blue curves in the top panel of Figure 6 at the FLR locations (vertical black lines). Under different geomagnetic conditions, the shape of the Alfvén speed (and therefore frequency) profile can vary drastically (Archer et al., 2015, 2017). Given it is the local Alfvén frequency gradient which determines the FLR width, we cannot make any generalisations regarding the systematic FLR width variation during storm phases.…”

Section: Discussionmentioning

confidence: 99%

Modeling the Varying Location of Field Line Resonances During Geomagnetic Storms

et al. 2022

View full text Add to dashboard Cite

Previous observational studies have shown that the natural Alfvén frequencies of geomagnetic field lines vary significantly over the course of a geomagnetic storm, decreasing by up to 50% from their quiet time values outside the plasmasphere. This was recently demonstrated statistically using ground magnetometer observations across 132 geomagnetic storm events (Wharton et al., 2020). This then brings into question where field line resonances (FLRs) will form in storm‐time conditions relative to quiet times. With storm‐time radiation belt dynamics depending heavily upon wave‐particle interactions, understanding how FLR locations change over the course of a storm will have important implications for this area. Using 3D magnetohydrodynamic (MHD) simulations, we investigate how changes in the Alfvén frequency continuum of the Earth's dayside magnetosphere over the course of a geomagnetic storm affect the fast‐Alfvén wave coupling. By setting the model Alfvén frequencies consistent with the observations, and permitting a modest change in the plasmapause/magnetopause locations consistent with storm‐time behavior, we show that FLR locations can change substantially during storms. The combined effects of higher fast waveguide frequencies and lower Alfvén frequencies during storm main phases, act together to move the FLR locations radially inwards compared to quiet times. FLRs outside of the plasmasphere are moved radially inward by 1.7 Earth radii for the cases considered.

show abstract

Magnetospheric and solar wind dependences of coupled fast‐mode resonances outside the plasmasphere

Cited by 14 publications

References 79 publications

Direct observations of a surface eigenmode of the dayside magnetopause

Direct observations of a surface eigenmode of the dayside magnetopause

The Effect of Fast Normal Mode Structure and Magnetopause Forcing on FLRs in a 3‐D Waveguide

Modeling the Varying Location of Field Line Resonances During Geomagnetic Storms

Contact Info

Product

Resources

About