The soft X‐ray emissions from the Earth's magnetosheath and cusp regions are simulated under different solar wind conditions, based on the PPMLR‐MHD code. The X‐ray images observed by a hypothetical telescope are presented, and the basic responses of the magnetopause and cusp regions are discernable in these images. From certain viewing geometries, the magnetopause position in the equatorial plane, as well as the latitudinal scales and azimuthal extent of cusp can be directly extracted from the X‐ray images. With these reconstructed positions, the issues we are able to analyze include but are not limited to the compression of magnetopause and widening of the cusp after an enhancement of solar wind flux, as well as the erosion of the magnetopause and equatorward motion of cusp after the southward turning of the interplanetary magnetic field. Hence, the X‐ray imaging is an appropriate technique to study the large‐scale motion of magnetopause and cusps in response to solar wind variations.

The LEXI and SMILE missions will provide soft X‐ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X‐ray and low‐ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X‐rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global‐scale magnetopause reconnection. When dayside imagers are installed with high‐ENA inner‐magnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self‐standing manner without relying upon other observatories. Soft X‐ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather.

Imaging is one of the essential techniques to observe astronomical structures. While analyzing the observed images, it is a challenge in many scientific fields to reconstruct the 3‐D structures from 2‐D image(s). This report discusses this challenge in the context of reconstructing the structure of the Earth's magnetosphere from the X‐ray image and presents a new technique. Specifically, it finds the optimum match of tangent directions derived from the X‐ray image and the parameterized magnetopause function. We name this approach as the tangent fitting approach (TFA). TFA is further validated based on the magnetohydrodynamic (MHD) simulations of the X‐ray images with different viewing geometries. TFA enables the reconstruction of the large‐scale magnetopause from a single X‐ray image, applicable to time‐dependent situations such as cases during magnetic storms. It is also noted that TFA has a potential broader application to remote sensing data, for instance, energetic neutral atom (ENA) observations. Lastly, this new approach is compared with other magnetopause reconstruction approaches.

This paper simulates the Kelvin‐Helmholtz wave (KHW)‐induced X‐ray emissions at the low‐latitude magnetopause based on a global MHD code. A method is proposed to extract the KHW information from the X‐ray intensity measured by a hypothetical X‐ray telescope onboard a satellite assumed with a low Earth orbit. Specifically, the X‐ray intensity at high latitude is subtracted from the intensity map as a background to highlight the role of KHW. Using this method, global features of KHW such as the vortex velocity, perturbation degree, spatial distribution, and temporal evolution could be evaluated from the X‐ray intensity map. The validity of this method during intervals of solar wind disturbances is also verified. According to the simulation results, X‐ray imaging of KHW is suggested as a promising observation technique to essentially “see” the large‐scale configuration and evolution of KHW for the first time.

Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a novel self-standing mission dedicated to observing the solar wind–magnetosphere coupling via simultaneous in situ solar wind/magnetosheath plasma and magnetic field measurements, soft X-ray images of the magnetosheath and polar cusps, and UV images of global auroral distributions. While analyzing the observed images after the launch of SMILE, it will be a challenging task to reconstruct the 3-dimensional surface of the magnetopause from 2-dimensional images. Therefore, one of the most important key issues about SMILE is the reconstruction of magnetopause from X-ray images. This paper will review four main approaches have been developed so far, namely, the boundary fitting approach (BFA), the tangent fitting approach (TFA), the tangential direction approach (TDA), and the computed tomography approach (CTA). We will discuss their scope of application and pros and cons, and hopefully inspire future efforts.

Imaging magnetospheric satellite missions provide information, which is complementary to in situ observations. Imaging is often able to provide an instantaneous picture of large‐scale structures, whereas in situ measurements, even multipoint in situ measurements, can only provide an average view of large‐scale structure. But imaging also presents some challenges. When three‐dimensional structures need to be extracted from two‐dimensional images, it is necessary to either make suitable assumptions or record a large enough number of images from different viewing geometries to allow a reconstruction (e.g., tomography). Imaging data exist over a wide range of sources including visible light, ultraviolet light, extreme ultraviolet, energetic neutral atoms, and X‐rays, each informing different physical mechanisms. In this paper we consider the extraction of the geometry of the magnetopause and the bow shock from single X‐ray images expected from the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission. We examine the effect of photon‐counting noise in determining the boundary geometries. We also consider the effect of different viewing geometries in the form of orbital vantage point and target look direction. Finally, we consider the effect of background noise. We find that our approach is relatively robust to viewing geometry effects and works at low count rates.