The Impact of Solar Wind Magnetic Field Fluctuations on the Magnetospheric Energetics.

Solar wind drives magnetospheric dynamics through coupling with the geospace system at the magnetopause. While upstream fluctuations correlate with geomagnetic activity, their impact on the magnetopause energy transfer is an open question. In this study, we examine three‐dimensional global magnetospheric simulations using the Geospace configuration of the Space Weather Modeling Framework. We examine the effects of solar wind fluctuations during a substorm event by running the model with four different driving conditions that vary in fluctuation frequency spectrum. We demonstrate that upstream fluctuations intensify the energy exchange at the magnetopause increasing both energy flux into and out of the system. The increased energy input is reflected in ground magnetic indices. Moreover, the fluctuations impact the magnetopause dynamics by regulating the energy exchange between the polar caps and lobes and energy transport within the magnetotail neutral sheet. Plain Language Summary: Earth's magnetic field shields the near‐Earth space plasma environments from the direct influence of solar wind. Solar wind however drives the magnetosphere when physical processes at the magnetopause boundary enable the transfer of energy between the plasmas. The coupling has global consequences in the magnetosphere system and its efficiency is particularly dependent on the orientation of interplanetary magnetic field and its magnitude but also on magnetic field fluctuation power. We capture the impact of upstream fluctuations on magnetopause energy exchange and nightside magnetotail dynamics by analyzing magnetohydrodynamic simulations of the global magnetosphere using various upstream driving conditions. We discover that more energy flows out from and into the system at the magnetopause when the upstream solar wind plasma include magnetic field fluctuations. The upstream fluctuation power is moreover reflected in nightside magnetotail, where flow patterns at the neutral sheet are regulated, as well as to ground indices with fluctuations driving a stronger geomagnetic response. Key Points: Solar wind magnetic field ULF fluctuations (2–8 mHz) increase energy transfer at the magnetopause boundary and into the inner magnetosphereThe upstream fluctuations regulate the lobe dynamics and plasma flows at the magnetotail neutral current sheetThe varying lobe and nightside dynamics are reflected in ground indices with solar wind fluctuations driving a stronger geomagnetic response [ABSTRACT FROM AUTHOR]