Initial results of high‐latitude magnetopause and low‐latitude flank flux transfer events from 3 years of Cluster observations

Abstract

[1] We present initial results from a statistical study of Cluster multispacecraft flux transfer event (FTE) observations at the high-latitude magnetopause and low-latitude flanks from February 2001 to June 2003. Cluster FTEs are observed at both the highlatitude magnetopause and low-latitude flanks for both southward and northward IMF. Among the 1222 FTEs, 36%, 20%, 14%, and 30% are seen by one, two, three, and four Cluster satellites, respectively. There are 73% (27%) of the FTEs observed outside (inside) the magnetopause, which might be caused by the motion of FTEs toward the magnetosheath when they propagate from subsolar magnetopause to the midlatitude and high-latitude magnetopause and low-latitude flanks. We obtain an average FTE separation time of 7.09 min, which is at the lower end of the previous results. The mean B N peak-peak magnitude of Cluster FTEs is significantly larger than that from low-latitude FTE studies. FTE B N peak-peak magnitude clearly increases with increasing absolute magnetic latitude (MLAT), it has a weaker dependence on magnetic local time (MLT) with a peak near the magnetic local noon, and it has a complex dependence on Earth dipole tilt with a peak at around zero. FTE periodic behavior is found to be controlled by MLT, with a general increase of FTE separation time with increasing MLT, and by Earth dipole tilt, with a peak FTE separation time at around zero Earth dipole tilt. There is no clear dependence of FTE separation time on MLAT. There is a weak increase of FTE B N peak-peak magnitude with increasing FTE separation time, and we see no clear dependence of it on FTE B N peak-peak time. When no FTE identification thresholds are used, more accurate calculations of some FTE statistical parameters, including the mean B N peak-peak time, can be obtained. Further, comparing results with different thresholds can help obtain useful information about FTEs. Citation: Wang, Y., et al. (2005), Initial results of high-latitude magnetopause and low-latitude flank flux transfer events from 3 years of Cluster observations,

Concerning the occurrence pattern of flux transfer events on the dayside magnetopause

“…during periods of southward IMF orientation. (Wang et al, 2005). The solid curve shows a fit to the distribution.…”

“…To determine the magnitude of this effect and for comparison with prior observations studies, we must identify the fraction of FTEs with amplitudes exceeding a specified detection threshold as a function of the shear angle θ between the magnetosheath and magnetospheric magnetic fields. Figure 4 presents the distribution of FTE magnetic field strength perturbations (peak -surroundings) observed by Cluster on the flank and high-latitude dayside magnetopause as reported by Wang et al (2005) and a fit given by…”

MESSENGER observations of large flux transfer events at Mercury

“…Here we report a comprehensive survey of the MESSENGER magnetic field data for the occurrence of FTEs. From definitions developed for Earth's magnetosphere [e.g., Wang et al, 2005;Fear et al, 2007], six FTEs were identified during the two flybys with all, save one, strongly resembling flux ropes. Unfortunately, MESSENGER does not make the high-time-resolution plasma moment measurements necessary to analyze these FTEs using the Grad-Shafranov (GS) reconstruction technique [Zhang et al, 2008;Eriksson et al, 2009].…”

Motion of flux transfer events: a test of the Cooling model

“…The equatorward motion (one of the possibilities proposed by Kawano and Russell, 1997b) was explained by the Cooling et al (2001) model, which showed that if the component reconnection site was initiated in the Southern Hemisphere and in the super-Alfvénic magnetosheath flow region, the open magnetic field lines which were connected to the Southern Hemisphere ionosphere would be swept across the location of the X-line and could be swept equatorward, matching the observed motion of the FTEs. Wang et al (2005Wang et al ( , 2006 presented a larger survey of 1222 FTEs observed by Cluster, based on two and a half magnetopause crossing seasons (February 2001to June 2003. These authors observed that approximately 30% of events were observed by all four spacecraft, although during this time the inter-spacecraft distance at the magnetopause crossing varied from ∼100 km to ∼1 R E .…”

“…A similar percentage of magnetosheath events was observed if the high latitude (near-noon) and low latitude (flank) regions were examined separately. Wang et al (2005) suggested that this was because FTEs were more likely to extend further out into the magnetosheath than they extend into the magnetosphere; recent analysis of some individual FTEs observed by Cluster has confirmed that this may be the case (Hasegawa et al, 2006). However, a further possible explanation is that the magnetospheric signatures of FTEs at high latitudes, particularly in the vicinity of the cusp, may often be more complicated than low latitude signatures, possibly leading to an underestimate of the number of magnetospheric events (Thompson et al, 2004;Fear et al, 2005a).…”