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Cluster measurements of the cusp and high latitude magnetopause boundary on 26 January, 2001 confirm that the cusp is a dynamic region full of energetic charged particles and turbulence. An energetic ion layer at high-latitudes beyond and adjacent to the duskside magnetopause exists when the Interplanetary Magnetic Field (IMF) has a southward orientation. Multiple energetic ion flux bursts were observed in the energetic ion layer. Each energetic ion flux burst was closely related to a magnetic flux rope. The axes of the flux ropes lie in the direction pointing duskward/tailward and somewhat upward. An intense axis-aligned current flows inside the ropes, with the current density reaching~10 )8 A/m 2 . The main components of the energetic ions are protons, helium and CNO ions, which originate from the magnetosphere, flowing out into the magnetosheath along the axis of the flux ropes. The velocity of the magnetosheath thermal plasma relative to the deHoffman-Teller (DHT) frame is found to be basically along the axis of the flux ropes also, but towards the magnetosphere. These flux ropes seem to be produced somewhere away via magnetic reconnection and move at similar DHT velocities passing over the spacecraft. These observations further confirm that the high-latitude magnetopause boundary region plays an important role in the solar wind-magnetopause coupling.

Abstract.In spring 2004 Double Star TC-1 measured a number of reconnection signatures at the dayside low-latitude magnetopause (MP) when there was a notable B y component in the magnetosheath. In a number of events we can show that reconnection was operating nearby TC-1 in the subsolar MP region. In this paper we describe three representative events: (a) event on 21 March 2004 in which the reconnection site can be remotely monitored, the spacecraft was passing by the X-line; (b) event on 12 March 2004 in which TC-1 observed the magnetospheric part of the quadrupolar field, together with a consistent flow reversal; (c) event on 26 March 2004 which occurred for northward IMF, TC-1 observed a reversal of v y across the equatorial MP. In these events the shear angles across the MP were considerably smaller than 180 • ; a noticeable guide field was present. These observations are consistent with near equatorial component merging, suggesting that component reconnection preferably occurs at the dayside low-latitude MP. There is evidence that when a pronounced magnetic shear across the MP exists in the B y component, reconnection may operate at the dayside low-latitude MP for northward IMF B z .

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A systematic comparison is carried out for three methods of current density calculation based on simultaneous magnetic field measurements of four‐spacecraft Cluster mission. It is demonstrated analytically and numerically that within the linear approximation, all these methods lead to exactly the same results. As a case study, the current density of multiple flux rope events at the high‐latitude magnetopause on January 26, 2001 is investigated. The result shows that an intense current flows inside the ropes with the current density reaching as high as about 10−8A/m2. The current inside rope is valuable with small relative errors. It is also found that the current direction is almost parallel to the axis of flux rope obtained through the magnetic minimum variance analysis (BMVA). Finally, it is proposed that the current MVA method (CMVA) has great effectness for study of flux rope geometry, particularly when the BMVA is insufficient to determine the flux rope orientation.