Solar Cycle Variation of Energetic Neutral Atoms in the Subsolar Magnetosheath based on IBEX Observations

Abstract

The in-ecliptic solar wind influences the boundaries of the Earth’s magnetosphere, e.g., by controlling the distances of the magnetopause and bow shock. The exospheric neutral hydrogen has been measured up to the Moon’s orbit. The charge exchange between the solar wind protons and the neutral geocoronal hydrogen creates an energetic neutral atom (ENA). The field-of-view of the IBEX-Hi instrument onboard the Interstellar Boundary Explorer (IBEX) encompasses various portions of the Earth’s magnetosphere during the year, including the subsolar point. Recently, Sokół et al. 2021 (ApJ 922 250) reported periodic, solar cycle enhancements of the solar wind dynamic pressure. We study the solar cycle evolution of the H ENA flux in the subsolar magnetosheath based on the IBEX measurements. We observed an enhancement of the ENA flux after the maximum of solar activity. We also analyze how the ENA flux varies with the solar wind parameters. We observe positive correlations with the solar wind dynamic pressure in the energy range from 0.7 to 4.3 keV and also opposite variations in correlation coefficients between the ENA flux and the solar wind speed and density.