Magnetospheric Cavity Modes Driven by Solar Wind Dynamic Pressure Fluctuations

TL;DR

This study uses 3D MHD simulations to show that fluctuations in solar wind dynamic pressure can generate and energize magnetospheric cavity modes, leading to ULF pulsations on the dayside.

Contribution

It demonstrates through simulations that solar wind pressure fluctuations can excite magnetospheric cavity modes when their frequencies match natural magnetospheric frequencies.

Findings

ULF pulsations can be driven by solar wind dynamic pressure fluctuations.

Cavity modes are energized when driving frequencies match natural frequencies.

Simulations isolate pressure fluctuations as the primary driver.

Abstract

We present results from Lyon-Fedder-Mobarry (LFM) global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere interaction. We use these simulations to investigate the role that solar wind dynamic pressure fluctuations play in the generation of magnetospheric ultra-low frequency (ULF) pulsations. The simulations presented in this study are driven with idealized solar wind input conditions. In four of the simulations, we introduce monochromatic ULF fluctuations in the upstream solar wind dynamic pressure. In the fifth simulation, we introduce a continuum of ULF frequencies in the upstream solar wind dynamic pressure fluctuations. In this numerical experiment, the idealized nature of the solar wind driving conditions allows us to study the magnetospheric response to only a fluctuating upstream dynamic pressure, while holding all other solar wind driving parameters constant. The simulation results suggest that ULF fluctuations in the solar wind dynamic pressure can drive magnetospheric ULF pulsations in the electric and magnetic fields on the dayside. Moreover, the simulation results suggest that when the driving frequency of the solar wind dynamic pressure fluctuations matches one of the natural frequencies of the magnetosphere, magnetospheric cavity modes can be energized.