Highly charged solar wind ions such as O7+ generate soft X-rays via charge exchange with neutral materials in the Earth's exosphere or geocorona. This phenomenon is called geocoronal solar wind charge exchange (SWCX). All the soft X-ray observations from Earth-orbiting satellites must contend with a time-variable foreground emission from geocoronal SWCX. However, it remains difficult to predict some observational properties such as time series and overall flux levels for arbitrary spacecraft look directions. 

Suzaku is one of the suitable satellites for geocoronal SWCX observations thanks to its instrumental and orbital advantages. First, we analyzed five Suzaku detections of bright geocoronal SWCX events and extracted OVII and OVIII emission lines. Then, combining a simplified formula of the Hodges exosphere model, charge exchange cross section values of the Bodewits model, WIND and ACE solar wind data, and Earth’s magnetic field models, we built an empirical model to predict OVII and OVIII line intensities. 

The modeled intensities of OVII emission lines were consistent with the observed ones within a factor of three, except for an intense geomagnetic storm event, while those of OVIII emission lines were underestimated by a factor of three or more. Further uncertainties concerning highly stripped ion states such as O8+ might exist in solar wind data and/or cross section values. The modeled OVII and OVIII light curves were consistent with the observed ones including short-term variations due to line-of-sight directions passing through cusp regions. 

Our model can provide a new estimation of geocoronal SWCX emission including light curves for future X-ray astronomy missions and X-ray imaging missions of the Earth’s magnetosphere.