A magnetic boundary signature within flux transfer events

Abstract. Flux transfer events (FTEs) are signatures of transient reconnection at the dayside magnetopause, transporting flux from the dayside of the magnetosphere into the magnetotail lobes. They have previously been observed to contain a combination of magnetosheath and magnetospheric plasma. On 12 February 2007, the four Cluster spacecraft were widely separated across the magnetopause and observed a crater-like FTE as they crossed the Earth's dayside magnetopause through its low-latitude boundary layer. The particle instruments on the Cluster spacecraft were in burst mode and returning data providing 3-D velocity distribution functions (VDFs) at 4 s resolution during the observation of this FTE. Moreover, the magnetic field observed during the event remained closely aligned with the spacecraft spin axis and thus we have been able to use these 3-D data to reconstruct nearly full pitch angle distributions of electrons and ions at high time resolution (up to 32 times faster than available from the normal mode data stream). These observations within the boundary layer and inside the core of the FTE show that both the interior and the surrounding structure of the FTE consist of multiple individual layers of plasma, in greater number than previously identified. Our observations show a cold plasma inside the core, a thin layer of antiparallel-moving electrons at the edge of FTE itself, and field-aligned ions with Alfvénic speeds at the trailing edge of the FTE. We discuss the plasma characteristics in these FTE layers, their possible relevance to the magnetopause reconnection processes and attempt to distinguish which of the various different FTE models may be relevant in this case. These data are particularly relevant given the impending launch of NASA's MMS mission, for which similar observations are expected to be more routine.

Section: Discussionmentioning

confidence: 68%

Section: A Varsani Et Al: Analysis Of High-time-resolution Observatmentioning

confidence: 99%

Cluster observations of the substructure of a flux transfer event: analysis of high-time-resolution particle data

Varsani¹,

Owen²,

Fazakerley³

et al. 2014

“…An important feature of FTEs is that they are not equilibrium structures, i.e. there is a total pressure excess (particle plus field) in the event core Rijnbeek et al, 1987;Lockwood and Hapgood, 1998).…”

Section: The Llbl and Flux Transfer Eventsmentioning

confidence: 99%

Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

Lockwood

Fazakerley²,

Opgenoorth

et al. 2001

Abstract. We study a series of transient entries into the lowlatitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ([X GSM , Y GSM , Z GSM ] ≈ [2, 7, 9] R E ). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is well-defined by two separate studies: (1) the magnetospheric variations prior to the northward turning , this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R E in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.

“…Observations in the vicinity of the dayside magnetopause during periods of southward IMF orientation indicate that events marked by bipolar magnetic field signatures normal to the nominal magnetopause and enhanced (Russell and Elphic, 1978) or crater-like (Rijnbeek et al, 1987) magnetic field strength variations are common. Features with these characteristics are called flux transfer events (FTEs).…”

Section: Introductionmentioning

confidence: 99%

Geotail observations of FTE velocities

Korotova

Sibeck

Rosenberg³

2009

Abstract. We discuss the plasma velocity signatures expected in association with flux transfer events (FTEs). Events moving faster than or opposite the ambient media should generate bipolar inward/outward (outward/inward) flow perturbations normal to the nominal magnetopause in the magnetosphere (magnetosheath). Flow perturbations directly upstream and downstream from the events should be in the direction of event motion. Flows on the flanks should be in the direction opposite the motion of events moving at subsonic and subAlfvénic speeds relative to the ambient plasma. Events moving with the ambient flow should generate no flow perturbations in the ambient plasma. Alfvén waves propagating parallel (antiparallel) to the axial magnetic field of FTEs may generate anticorrelated (correlated) magnetic field and flow perturbations within the core region of FTEs. We present case studies illustrating many of these signatures. In the examples considered, Alfvén waves propagate along event axes away from the inferred reconnection site. A statistical study of FTEs observed by Geotail over a 3.5-year period reveals that FTEs within the magnetosphere invariably move faster than the ambient flow, while those in the magnetosheath move both faster and slower than the ambient flow.