Ultra-Low Frequency Standing Alfven Waves: Global Magnetospheric Modeling of Resonant Wave-Wave Interactions.

Abstract

Alfven waves are an important energy transport modality in the collisionless plasmas that dominate Earth's magnetosphere. While wave-particle interactions are well understood, the mechanisms that govern wave-wave interactions and their associated phenomenological impacts are still poorly understood and have received little attention. To examine both linear and nonlinear resonant mode coupling, we use the Space Weather Modeling Framework (SWMF) with a resistive, ionospheric inner boundary with ideal MHD governing equations in order to explore the excitation of field line resonances and the stability of standing Alfven waves along the magnetopause by using synthetic upstream solar wind drivers. In reproducing the essential features of broadband FLRs, we found multi-faceted local time FLR asymmetries not exclusively determined by correlated asymmetries in the compressional driver. In examining the stability of transverse magnetopause surface waves, we found evidence of an oblique parametric decay instability exciting large-scale, counterpropagating magnetotail kink modes via ponderomotive forces mediated by transverse magnetic beat waves. The latter is responsible for a backward-propagating compressional wave along the magnetopause. These magnetotail waves bear the signature of slow magnetosonic-shear Alfvenic coupling with associated density holes and soliton-like transverse waves with strong field-aligned currents. Our results have significant implications for magnetotail dynamics and the energization of radiation belts in the dayside magnetospheric cavity and is the first study to examine a) negative energy surface waves, b) parametric decay instability of transverse magnetopause surface waves, c) ponderomotive forces via magnetic beat waves, d) the coupling of MP surface waves to magnetotail kink mode waves, e) counterpropagating kink mode waves, and f) the coupling of slow magnetosonic and transverse wave modes.