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A method to predict magnetopause expansion in radial IMF events by MHD simulations
Author(s) -
Samsonov A. A.,
Sibeck D. G.,
Šafránková J.,
Němeček Z.,
Shue J.H.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023301
Subject(s) - magnetopause , magnetosheath , foreshock , solar wind , magnetosphere , magnetohydrodynamics , interplanetary magnetic field , physics , inflow , geophysics , dynamic pressure , mechanics , computational physics , geology , magnetic field , seismology , quantum mechanics , aftershock
This paper presents a method for taking into account changes of solar wind parameters in the foreshock using global MHD simulations. We simulate four events with very distant subsolar magnetopause crossings that occurred during quasi‐radial interplanetary magnetic field (IMF) intervals lasting from one to several hours. Using previous statistical results, we suggest that the density and velocity in the foreshock cavity decrease to ∼60% and ∼94% of the ambient solar wind values when the IMF cone angle falls below 50°. This diminishes the solar wind dynamic pressure to 53% and causes a corresponding magnetospheric expansion. We change the upstream solar wind parameters in a global MHD model to take these foreshock effects into account. We demonstrate that the modified model predicts magnetopause distances during radial IMF intervals close to those observed by THEMIS. The strong total pressure decrease in the data seems to be a local, rather than a global, phenomenon. Although the simulations with decreased solar wind pressure generally reproduce the observed total pressure in the magnetosheath well, the total pressure in the magnetosphere often agrees better with results for nonmodified boundary conditions. The last result reveals a limitation of our method: we changed the boundary conditions along the whole inflow boundary, although a more correct approach would be to vary parameters only in the foreshock. A model with the suggested global modification of the boundary conditions better predicts the location of part of the magnetopause behind the foreshock but may fail in predicting the rest of the magnetopause.