Temporal variations of geocoronal and heliospheric X‐ray emission associated with the solar wind interaction with neutrals

Abstract

X‐ray emission due to charge transfer collisions between heavy solar wind ions and neutrals has been predicted to exist both in the heliosphere and in the geocorona. The heliospheric X‐ray emission can account for roughly half of the observed soft X‐ray background intensity. It was also suggested that temporal variations in the heliospheric and geocoronal soft X‐ray intensities will result from solar wind variations. In this paper, a simple model of the charge exchange X‐ray emission mechanism is combined with measured solar wind parameters as a function of time and used to generate predictions of the temporal variation of the X‐ray intensity observed at Earth for the time periods 1990–1993 and 1996–1998. Measured solar wind proton fluxes are also directly compared with the “long‐term enhancement” part of the soft X‐ray background measured by the Röntgen Satellite (ROSAT). A significant positive correlation exists, which supports the existence of X‐ray emission associated with the solar wind interaction with either interstellar neutrals and/or with geocoronal neutral hydrogen.