The Effect of IMF Fluctuations on the Subsolar Magnetopause Position: A Study Using a Global MHD Model

다국어 초록 (Multilingual Abstract)

During southward interplanetary magnetic field (IMF) conditions, the subsolar magnetopause moves inward even under steady solar wind pressure. This is generally referred to as “erosion.” Empirical and computational studies have been conducted to quantify the effect of magnetopause erosion; however, they generally use steady state IMF conditions. Solar wind conditions are not usually constant for very long, especially during such conditions as are present in high‐speed streams, which typically have large fluctuations in the IMF. These IMF fluctuations can occur on a range of times scales and amplitudes, resulting in a series of northward and southward IMF intervals imposed on the magnetosphere. We have simulated the effect of such IMF variations on the magnetopause position using a global magnetohydrodynamic model. We find that there are both time lag and hysteresis‐like effects on the motion of the magnetopause due to the variation in the magnitude of the southward IMF and that the instantaneous position of the magnetopause can be significantly different from what one would expect from steady state conditions.
The boundary between the magnetosphere and the solar wind is known as the magnetopause. The magnetopause location is determined by a balance of pressure from Earth's magnetosphere and the pressure from the solar wind. The interplanetary magnetic field (IMF) can affect this balance by modulating the magnitudes of magnetospheric current systems, thus affecting the magnetospheric magnetic pressure. For southward IMF, this causes the magnetopause to move earthward, which is known as magnetopause erosion. The goal of this study is to see how the magnetopause location changes in a global magnetohydrodynamic simulation if the IMF is fluctuating. A numerical experiment was conducted with sinusoidal IMF inputs for southward IMF. The results indicate that the resulting magnetopause motion exhibits time lag and hysteresis‐like effects in response to solar wind IMF variations and that the instantaneous position of the magnetopause can be significantly different from what one would expect from steady state conditions.


Magnetopause motion exhibits time lag and hysteresis‐like effects in response to solar wind IMF variations in a global MHD simulation
In a global MHD simulations, the magnetopause position is dependent on the solar wind time history and may not match steady state values