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Tangent Directions of the Cusp Boundary Derived From the Simulated Soft X‐Ray Image
Author(s) -
Sun Tianran,
Wang Xue,
Wang Chi
Publication year - 2021
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2020ja028314
Subject(s) - physics , cusp (singularity) , solar wind , magnetohydrodynamics , tangent , astrophysics , magnetopause , geometry , magnetic field , mathematics , quantum mechanics
Abstract The magnetospheric cusp plays an essential role in mass and energy transportation from the solar wind to the geo‐space environment. Recent development of the X‐ray imaging technique makes it possible to study the large scale properties of the cusp region from a global view. As the detected X‐ray signals will be integrated along the line‐of‐sight (LOS), it is a challenging task to derive the information about the 3D cusp region from a 2D X‐ray image. Based on global magnetohydrodynamic (MHD) code, this paper simulated and analyzed the X‐ray image of cusp. An approach was developed to present the following aspects related to the morphology of cusp from the X‐ray image: (1) The tangent direction of the cusp boundary is the direction with appreciable increase of local standard deviation in X‐ray intensity, and (2) the direction running through the cusp center is the direction with peak X‐ray intensity. Lack of knowledge on radial distribution of X‐ray signal along the line‐of‐sight, exact position of cusp cannot be further derived without assumptions. Nevertheless, under special solar wind conditions such as zero Interplanetary Magnetic Field (IMF) B y , it is reasonable to assume that the cusp center is in the noon‐midnight meridian plane. Therefore, position of the cusp center can be reconstructed. Based on MHD simulations, the above conclusions have been validated with different viewing geometries and solar wind conditions. With reasonable assumptions, the large‐scale cusp features in response to the solar wind variations can be clearly revealed by analyzing X‐ray images.