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Solar wind controls on Mercury's magnetospheric cusp
Author(s) -
He Maosheng,
Vogt Joachim,
Heyner Daniel,
Zhong Jun
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023687
Subject(s) - solar wind , physics , interplanetary magnetic field , magnetopause , astrophysics , geophysics , magnetosphere , cusp (singularity) , magnetic reconnection , magnetic field , geometry , mathematics , quantum mechanics
This study assesses the response of the cusp to solar wind changes comprehensively, using 2848 orbits of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observation. The assessment entails four steps: (1) propose and validate an approach to estimate the solar wind magnetic field (interplanetary magnetic field (IMF)) for MESSENGER's cusp transit; (2) define an index σ measuring the intensity of the magnetic disturbance which significantly peaks within the cusp and serves as an indicator of the cusp activity level; (3) construct an empirical model of σ as a function of IMF and Mercury's heliocentric distance r sun , through linear regression; and (4) use the model to estimate and compare the polar distribution of the disturbance σ under different conditions for a systematic comparison. The comparison illustrates that the disturbance peak over the cusp is strongest and widest extending in local time for negative IMF B x and negative IMF B z , and when Mercury is around the perihelion. Azimuthal shifts are associated with both IMF B y and r sun : the cusp moves toward dawn when IMF B y or r sun decrease. These dependences are explained in terms of the IMF B x ‐controlled dayside magnetospheric topology, the component reconnection model applied to IMF B y and B z , and the variability of solar wind ram pressure associated with heliocentric distance r sun . The applicability of the component reconnection model on IMF B y indicates that at Mercury reconnection occurs at lower shear angles than at Earth.