The Earth’s magnetosheath and cusps are the sources of soft X-rays. In the accompanying paper (Part 1) and this paper, we discuss the methods of finding the magnetopause position by analyzing the X-ray images. We use the software developed for the Soft X-ray Imager (SXI) on board the forthcoming Solar wind - Magnetosphere - Ionosphere Link Explorer (SMILE) mission. We show how to find the maximum SXI count rate in noisy count maps. We verify the assumption that the maximum of the X-ray emissivity integrated along the Line-of-Sight (Ix) is tangent to the magnetopause. We consider two cases using two MHD models and apply different methods of magnetospheric masking. Overall, the magnetopause is located close to the maximum Ix gradient or between the maximum Ix gradient and the maximum Ix depending on the method used. But since the angular distance between the maximum Ix gradient and the maximum Ix is relatively small (about 3{degree sign}), the maximum Ix might be used as an indicator of the outer boundary of a wide magnetopause layer usually obtained in MHD simulations.

The magnetopause standoff distance characterizes global magnetospheric compression and deformation in response to changes in the solar wind dynamic pressure and interplanetary magnetic field orientation. We cannot derive this parameter from in-situ spacecraft measurements. However, time-series of the magnetopause standoff distance can be obtained in the near future using observations by soft X-ray imagers. In two companion papers, we describe methods of finding the standoff distance from X-ray images. In Part 1, we present the results of MHD simulations which we use for the calculation of the X-ray emissivity in the magnetosheath and cusps. Some MHD models predict relatively high density in the magnetosphere, larger than observed in the data. Correcting this, we develop magnetospheric masking methods to separate the magnetosphere from the magnetosheath and cusps. We simulate the X-ray emissivity in the magnetosheath for different solar wind conditions and dipole tilts.

We model an interval of sustained northward interplanetary magnetic field, for which we have a comprehensive set of observational data. This interval is associated with the arrival of an interplanetary coronal mass ejection. The solar wind densities at the time are particularly high and the interplanetary magnetic field is primarily northward. This results in strong auroral emissions within the polar cap in a cusp spot, which we associate with lobe reconnection at the high-latitude magnetopause. We also observe areas of upwards field-aligned current within the summer Northern Hemisphere polar cap that exhibit large current magnitudes. The model is able to reproduce the spatial distribution of the field-aligned currents well, even under changing conditions in the incoming interplanetary magnetic field. Discrepancies exist between the modeled and observed current magnitudes. Notably, the winter Southern Hemisphere exhibits much lower current magnitudes overall. We also model a sharp transition of the location of magnetopause reconnection. This changes rapidly from a subsolar location at the low-latitude magnetopause under southward interplanetary magnetic field conditions, to a high-latitude lobe reconnection location when the field is northward. This occurs during a fast rotation of the IMF at the shock front of a magnetic cloud.