Modeling magnetospheric response to synthetic Alfvénic fluctuations in the solar wind: ULF wave fields in the magnetosphere

Abstract

AbstractSeveral observational studies suggest that small fluctuations in the solar wind can drive magnetospheric dynamics, notably ultralow frequency (ULF) waves, especially during high‐speed streams (HSS). ULF fluctuations are believed to be a mechanism for controlling and accelerating radiation belt electrons, and are an important aspect to HSS storms. Previous simulation studies have begun to investigate generation of magnetospheric ULF waves by varying upstream solar wind conditions, such as dynamic pressure or velocity shear. Alfvénic fluctuations, however, which are prevalent within the solar wind, have yet to be incorporated into global MHD simulations of the magnetosphere. To investigate the relationship between Alfvénic fluctuations in the solar wind and magnetospheric ULF waves, we present results from the Lyon‐Fedder‐Mobarry global, three‐dimensional magnetohydrodynamic (MHD) code. These simulations are driven with simulated solar wind plasma parameters from the Wang‐Sheeley‐Arge‐Enlil model with and without Alfvén‐like fluctuations added. We show that solar wind Alfvénic fluctuations enhance Kelvin‐Helmholtz waves along the flanks and drive ULF waves in the dayside magnetosphere. The dayside ULF waves are an enhancement of the compressional component in field‐aligned coordinates, due to the varying x component of the velocity (and therefore dynamic pressure) from the Alfvénic fluctuations.