Sources of Transients in the LLBL

The upstream conditions play a significant role in the dayside magnetopause configuration and its motion. Our investigations are focused on the detailed analysis of the magnetopause reformation after sudden changes of the IMF orientation and description of the magnetosheath coupling with magnetopause low-latitude boundary layer under northward and southward IMF Bz components. The paper analyzes data of the Themis spacecraft in the dayside low--latitude magnetopause when Themis B served partly a magnetosheath monitor. During a few passes through the LLBL, many plasma transients are observed. These transients are analyzed, classified and attributed to the different corresponding sources. Among them, the sudden rotation of the magnetosheath magnetic field seems to be very frequent and a very import factor. The study is supported with a large-scale comparison between THEMIS in situ plasma and magnetic field observations and the predictions of a global numerical MHD model.