Extreme magnetopause locations and their sources

Comparison of observed magnetopause locations with model predictions can serve as a proof of our understanding of the interaction between solar wind and Earth magnetic field. Since the corresponding upstream conditions are usually derived from observation at L1, our knowledge on solar wind propagation and evolution on short scales are tested as well. We have collected about 40 000 of magnetopause crossings observed by THEMIS spacecraft in course of 2007–2019 years and compared the observed magnetopause position with prediction of several empirical magnetopause models using OMNI upstream parameters (mostly derived from ACE observations) and Wind magnetic field and plasma measurements propagated by our two-step propagation routine. The difference between observed and predicted magnetopause radial distance, Robs – Rmod was used for quantification of the model-observation agreement. We have found that the distribution of Robs – Rmod can be well fitted by the Gaussian distribution with FWHM ≈1.2 Re for all models and both upstream monitors. Nevertheless, the tails of the distributions are enhanced for all models and Robs – Rmod larger than 2 Re are rather frequent. A detailed analysis of such events leads to suggestions for improvement of investigated models or for a building of a new empirical model of the equatorial magnetopause.