Investigating Potential Causes for the Prediction of Spurious
Magnetopause Crossings at Geosynchronous Orbit in MHD Simulations
Abstract
During intense geomagnetic storms, the magnetopause can move in as far
as geosynchronous orbit, leaving the satellites in that orbit out in the
magnetosheath. Spacecraft operators turn to numerical models to predict
the response of the magnetopause to solar wind conditions, but the
predictions of the models are not always accurate. This study
investigates four storms with a magnetopause crossing by at least one
GOES satellite, using four magnetohydrodynamic models at NASA’s
Community Coordinated Modeling Center (CCMC) to simulate the events, and
analyzes the results to investigate the reasons for errors in the
predictions. Two main reasons can explain most of the erroneous
predictions. Firstly, the solar wind input to the simulations often
contains features measured near the L1 point that did not eventually
arrive at Earth; incorrect predictions during such periods are not the
fault of the models. Secondly, while the models do well when the primary
driver of magnetopause motion is a variation in the solar wind density,
they tend to overpredict or underpredict the Birkeland currents during
times of strong negative IMF Bz, leading to poorer prediction
capability. Coupling the MHD codes to a ring current model, when such a
coupling is available, generally will improve the predictions but will
not always entirely correct them. More work is needed to fully
characterize the response of each code under strong southward IMF
conditions as it relates to prediction of magnetopause location.