Magnetopause Location: Empirical and Computer Models in a Light of New Observations

Abstract:

Our ability to predict the magnetopause location under diverse upstream conditions and various states of the inner magnetosphere can be considered as a test of the understanding of the mechanisms of the Sun-Earth relations. The solar wind dynamic pressure is believed to be a principal factor and its influence is usually considered in a power-law form. However, the power indices vary from -1/4.8 to -1/6.6 in present magnetopause models. The second parameter that is often included into empirical models is a vertical component of the interplanetary magnetic field (IMF) but a number of other factors influencing the magnetopause location like the solar UV flux, solar wind speed, or magnetospheric internal state was suggested in course of years. The development of the empirical models encounters many difficulties connected with a determination of upstream parameters, spacecraft orbits or difficult description of the internal magnetospheric state. On the other hand, present global models of the solar wind- magnetosphere interaction would not suffer with such limitations.

In the paper, we use a set of about 40 000 of dayside magnetopause crossings collected from the Interball, Magion, Geotail, Cluster, THEMIS, and MMS spacecraft in course of two solar cycles. The crossings were observed in a broad range of upstream pressures (0.2–20 nPa) and under various IMF orientations. We discuss two major topics: (1) a relationship between the dynamic pressure and the magnetopause stand-off distance; and (2) the magnetopause flaring angle as a function of the IMF direction and upstream pressure. The results are compared with a similar analysis of the runs of several computer models of the solar wind magnetosphere interaction.