  We present an analysis of a Suzaku observation taken during the geomagnetic
storm of 2005 August 23-24. We found time variation of diffuse soft X-ray
emission when a coronal mass ejection hit Earth and caused a geomagnetic storm.
The diffuse emission consists of fluorescent scattering of solar X-rays and
exospheric solarwind charge exchange. The former is characterized by a neutral
oxygen emission line due to strong heating of the upper atmosphere during the
storm time, while the latter is dominated by a sum of C V, C VI, N VI, N VII, O
VII, and O VIII emission lines due to the enhanced solar wind flux in the
vicinity of the exosphere. Using the solar wind data taken with the ACE and
WIND satellites,a time correlation between the solar wind and the strong O VII
line flux were investigated. We estimated necessary column densities for the
solar X-ray scattering and exospheric SWCX. From these results, we argue that a
part of the solar wind ions enter inside the magnetosphere and cause the SWCX
reaction.
