Abstract
Abstract. The paper analyses one long-term pass (26 August 2007) of the THEMIS spacecraft across the dayside low-latitude magnetopause. THEMIS B, serving partly as a magnetosheath monitor, observed several changes of the magnetic field that were accompanied by dynamic changes of the magnetopause location and/or the structure of magnetopause layers observed by THEMIS C, D, and E, whereas THEMIS A scanned the inner magnetosphere. We discuss the plasma and the magnetic field data with motivation to identify sources of observed quasiperiodic plasma transients. Such events at the magnetopause are usually attributed to pressure pulses coming from the solar wind, foreshock fluctuations, flux transfer events or surface waves. The presented transient events differ in nature (the magnetopause surface deformation, the low-latitude boundary layer thickening, the crossing of the reconnection site), but we found that all of them are associated with changes of the magnetosheath magnetic field orientation and with enhancements or depressions of the plasma density. Since these features are not observed in the data of upstream monitors, the study emphasizes the role of magnetosheath fluctuations in the solar wind-magnetosphere coupling.
Highlights
Quasiperiodic fluctuations of magnetic field and plasma parameters at the magnetopause are often attributed to flux transfer events (FTEs), surface waves or recurrent pressure pulses coming from the solar wind or from the foreshock
The careful analysis revealed that all of them are associated with the change of the magnetosheath magnetic field BZ component
The mutual connection of magnetosheath pressure enhancements and magnetic field rotations can be determined by hybrid simulations that are in under preparation
Summary
Quasiperiodic fluctuations of magnetic field and plasma parameters at the magnetopause are often attributed to flux transfer events (FTEs), surface waves or recurrent pressure pulses coming from the solar wind or from the foreshock. Whereas during the first event all spacecraft entered the magnetosheath, a blow-up of the second event in Fig. 9 shows a low and variable BZ component at THB and almost northward pointing magnetic fields at THC, THD and THE. We applied an indirect evidence for the estimated increase of the magnetosheath pressure (magnetosheath observations were not available in this time interval) that started the inward magnetopause motion This inward displacement was probably further enhanced by the magnetopause erosion caused by southward oriented magnetosheath magnetic field within the core of the event. It observed the southward magnetic field that changed to the slightly northward orientation for about one minute (07:05–07:06 UT) This rotation is associated with the appearance of the magnetosheath-like plasma on magnetospheric field lines that was observed by THC, THD and THE. Fig. 3), the event again demonstrates the importance of magnetosheath fluctuations for the magnetopause processes
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