Boundary Detection in Three Dimensions With Application to the SMILE Mission: The Effect of Model‐Fitting Noise

Abstract

The magnetosheath and near-Earth solar wind emit X-rays due to charge-exchange between the extended atmosphere and highly ionized particles in the solar wind. These emissions can be used to remotely sense the dynamic processes in this region. The Solar Wind Magnetosphere Ionosphere Link Explorer mission will carry out these measurements. In a previous paper, we looked at the effect of photon counting statistics on determining the location of the magnetopause and bow shock. In this paper we explore, through simulations, the more challenging question of orbital viewing geometry bias when the model and the emissions do not match each other exactly. Our simulations conclude that while care must be taken to avoid false minima in the fitting, there is very little to no orbital bias in extracting the position and large-scale shape of the magnetopause and bow shocks from 2-D X-ray images from the future Solar Wind Magnetosphere Ionosphere Link Explorer mission.

Deriving the Magnetopause Position from the Soft X‐Ray Image by Using the Tangent Fitting Approach

“…Tangent directions for the set of magnetopause morphologies are numerically calculated and recorded while looping over all the possible values of r 0 , α y , and α z . As the number of variables are limited to 3 in this study, it is feasible to use the algorithm such that every point in the search space is visited, so that the possible false minima caused by an inaccurate initial guess can be successfully avoided (Jorgensen, Sun, Wang, Dai, Sembay, Zheng, et al, 2019). These tangent directions are compared with those derived from the X‐ray image, that is, the black curve in Figure 2a.…”

“…Consequently, the greatly reduced number of free parameters in the TFA makes it feasible to avoid the possible false minima caused by an inaccurate initial guess. Therefore, unlike the BFA indicated by Jorgensen, Sun, Wang, Dai, Sembay, Zheng, et al (2019), applying the TFA does not require simultaneous solar wind observations to provide a carefully evaluated initial guess. Third, as the TFA calculated the tangent directions of the magnetopause, it is not applicable while the satellite is inside the magnetosphere.…”

“…One of the techniques is presented by Jorgensen, Sun, Wang, Dai, Sembay, Wei, et al (2019) and Jorgensen, Sun, Wang, Dai, Sembay, Zheng, et al (2019), and we refer to it here as the boundary fitting approach (BFA). Based on the MHD simulation results, they first assumed some parameterized descriptions of the magnetopause and bow shock locations as well as the X-ray emissivity distribution function in the magnetosheath.…”

“…This technique makes it possible to derive the 3-D magnetopause from a single image, applicable even to events under fast solar wind variations. Nevertheless, Jorgensen, Sun, Wang, Dai, Sembay, Zheng, et al (2019) also mentioned that the initial guess should be carefully chosen to avoid false minima in the fitting procedure. Therefore, the BFA is applicable to situations where simultaneous solar wind observations are available while imaging the magnetopause, which helps in obtaining a reasonable initial guess based on models.…”

A new inversion method for reconstruction of plasmaspheric He⁺ density from EUV images

“…The soft Xrays arise from the charge exchange interaction between solar wind heavy ions and Earth's neutral particles (Cravens, 2000). The measured value of the SXI imager is the line integration of volume emission that is proportional to the ion density (Cravens, 2000;Sun TR et al, 2015;Jorgensen et al, 2019). The imaging process of SXI is the same with as the projection process of CT, so the ART-TV method can be generalized to study SXI images from the SMILE mission.…”