Faux Magnetopause Crossings and How to Recognize Them

Yi Qi, University of California, Los Angeles, Earth, Planetary, and Space Sciences, Los Angeles, CA, United States, Cong Zhao, Univ. of Sci. & Tech. of China, Hefei, China, Una Schneck, UCLA, Earth Planetary And Space Sciences, Los Angeles, CA, United States, Hairong Lai, University of California Los Angeles, Department of Earth Planetary and Space Sciences, Los Angeles, CA, United States and Christopher T Russell, University of California Los Angeles, Los Angeles, CA, United States
Abstract:
The magnetopause is the boundary between the shocked solar wind plasma of the magnetosheath and the magnetospheric plasma. One might feel that it is easy to identify the magnetopause as the space where the plasma changes from flowing to stationary. However, it is often difficult to distinguish the two regimes of magnetosheath and magnetosphere. In this presentation, we demonstrate different types of magnetopause crossing events, and introduce their observational properties along with the physical processes behind the observations. Usually when the magnetopause is crossed, the sum of the magnetic and thermal pressure is constant. However, if the magnetopause is crossed through a flux transfer event (FTE), then a flux rope is present in which a region of force-free field exists, and the sum of the magnetic and thermal pressure is not constant. Occasionally we see a structure at the magnetopause in which the sum of the pressures shows a “triangular” peak and there is no flux rope, but rather a thin strong current sheet. We interpret this structure as a third class (but rare) event that we have termed magnetosheath field enhancement (MFE). We investigate the complicated plasma and field structure of these events, illustrated with several examples from MMS data.
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