Extreme magnetopause locations and their sources

Magnetopause is a critical boundary dividing the space controlled by the Earth magnetic field from the solar wind and interplanetary magnetic field. Its position is controlled mainly by the solar wind dynamic pressure and north-south IMF component and these quantities are included in a variety of empirical magnetopause models. 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 dayside magnetopause crossings observed by THEMIS, Cluster and Geotail spacecraft in course of 2007–2019 years and compared the observed magnetopause position with prediction of several empirical magnetopause models using OMNI upstream parameters. 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 median values of R_obs – R_mod are well predicted by the tested models till R_obs≈12 R_e for all models but large positive deviations were found for larger magnetopause distances. A detailed analysis of such events revealed that they are connected with transient magnetopause displacements caused by magnetosheath perturbations of large amplitude and we are searching for their sources.