Large‐Scale Characteristics of Flux Transfer Events on the Dayside Magnetopause

<p>BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. The BepiColombo mission consists of two spacecraft, which are the Mercury Planetary Orbiter (MPO) and Mercury Magnetospheric Orbiter (Mio). The mission made its first planetary flyby, which is the only Earth flyby, on 10 April 2020, during which several instruments collected measurements. In this study, we analyze MPO magnetometer (MAG) observations of Flux Transfer Events (FTEs) in the magnetosheath and the structure of the subsolar magnetopause near the &#160;flow stagnation point. The magnetosheath plasma beta was high with a value of ~ 8 and the interplanetary magnetic field (IMF) was southward with a clock angle that decreased from ~ 100 degrees to ~ 150 degrees. &#160;As the draped IMF became increasingly southward several of the flux transfer event (FTE)-type flux ropes were observed. These FTEs traveled southward indicating that the magnetopause X-line was located northward of the spacecraft, which is consistent with a dawnward tilt of the IMF. Most of the FTE-type flux ropes were in ion-scale, <10 s duration, suggesting that they were newly formed. Only one large-scale FTE-type flux rope, ~ 20 s, was observed. It was made up of two successive bipolar signatures in the normal magnetic field component, which is evidence of coalescence at a secondary reconnection site. Further analysis demonstrated that the dimensionless reconnection rate of the re-reconnection associated with the coalescence site was ~ 0.14. While this investigation was limited to the MPO MAG observations, it strongly supports a key feature of dayside reconnection discovered in the Magnetospheric Multiscale mission, the growth of FTE-type flux ropes through coalescence at secondary reconnection sites.</p>

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

Annales Geophysicae ◽

10.5194/angeo-27-895-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 895-903 ◽

Cited By ~ 7

Author(s):

D. G. Sibeck

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Magnetic Reconnection ◽

Interplanetary Magnetic Field ◽

Flux Transfer Events ◽

Dayside Magnetopause ◽

Two Factors ◽

Flux Transfer ◽

Occurrence Pattern ◽

The Magnetic Field

Abstract. We present an analytical model for the magnetic field perturbations associated with flux transfer events (FTEs) on the dayside magnetopause as a function of the shear between the magnetosheath and magnetospheric magnetic fields and the ratio of their strengths. We assume that the events are produced by component reconnection along subsolar reconnection lines with tilts that depend upon the orientation of the interplanetary magnetic field (IMF), and show that the amplitudes of the perturbations generated during southward IMF greatly exceed those during northward IMF. As a result, even if the distributions of magnetic reconnection burst durations/event dimensions are identical during periods of northward and southward IMF orientation, events occurring for southward IMF orientations must predominate in surveys of dayside events. Two factors may restore the balance between events occurring for northward and southward IMF orientations on the flanks of the magnetosphere. Events generated on the dayside magnetopause during periods of southward IMF move poleward, while those generated during periods of northward IMF slip dawnward or duskward towards the flanks. Due to differing event and magnetospheric magnetic field orientations, events that produce weak signatures on the dayside magnetopause during intervals of northward IMF orientation may produce strong signatures on the flanks.

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Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection

Annales Geophysicae ◽

10.5194/angeo-34-943-2016 ◽

2016 ◽

Vol 34 (11) ◽

pp. 943-959 ◽

Cited By ~ 13

Author(s):

Yann Pfau-Kempf ◽

Heli Hietala ◽

Steve E. Milan ◽

Liisa Juusola ◽

Sanni Hoilijoki ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interplanetary Magnetic Field ◽

Ion Beams ◽

Bow Shock ◽

Flux Transfer Events ◽

Dayside Magnetopause ◽

Flux Transfer ◽

Push Out ◽

Magnetopause Reconnection

Abstract. We present a scenario resulting in time-dependent behaviour of the bow shock and transient, local ion reflection under unchanging solar wind conditions. Dayside magnetopause reconnection produces flux transfer events driving fast-mode wave fronts in the magnetosheath. These fronts push out the bow shock surface due to their increased downstream pressure. The resulting bow shock deformations lead to a configuration favourable to localized ion reflection and thus the formation of transient, travelling foreshock-like field-aligned ion beams. This is identified in two-dimensional global magnetospheric hybrid-Vlasov simulations of the Earth's magnetosphere performed using the Vlasiator model (http://vlasiator.fmi.fi). We also present observational data showing the occurrence of dayside reconnection and flux transfer events at the same time as Geotail observations of transient foreshock-like field-aligned ion beams. The spacecraft is located well upstream of the foreshock edge and the bow shock, during a steady southward interplanetary magnetic field and in the absence of any solar wind or interplanetary magnetic field perturbations. This indicates the formation of such localized ion foreshocks.

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Concerning the motion of flux transfer events generated by component reconnection across the dayside magnetopause

Journal of Geophysical Research Atmospheres ◽

10.1029/2009ja014677 ◽

2010 ◽

Vol 115 (A4) ◽

pp. n/a-n/a ◽

Cited By ~ 9

Author(s):

D. G. Sibeck ◽

R.-Q. Lin

Keyword(s):

Flux Transfer Events ◽

Dayside Magnetopause ◽

Flux Transfer

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Flux Transfer Events: 1. generation mechanism for strong southward IMF

Annales Geophysicae ◽

10.5194/angeo-24-381-2006 ◽

2006 ◽

Vol 24 (1) ◽

pp. 381-392 ◽

Cited By ~ 115

Author(s):

J. Raeder

Keyword(s):

Magnetic Field ◽

Generation Process ◽

Numerical Resolution ◽

Flux Transfer Events ◽

Dayside Magnetopause ◽

Semiannual Variation ◽

Flux Transfer ◽

Sequential Generation ◽

The Magnetic Field ◽

Dipole Tilt

Abstract. We use a global numerical model of the interaction of the solar wind and the interplanetary magnetic field with Earth's magnetosphere to study the formation process of Flux Transfer Events (FTEs) during strong southward IMF. We find that: (i) The model produces essentially all observational features expected for FTEs, in particular the bipolar signature of the magnetic field BN component, the correct polarity, duration, and intermittency of that bipolar signature, strong core fields and enhanced core pressure, and flow enhancements; (ii) FTEs only develop for large dipole tilt whereas in the case of no dipole tilt steady magnetic reconnection occurs at the dayside magnetopause; (iii) the basic process by which FTEs are produced is the sequential generation of new X-lines which makes dayside reconnection inherently time dependent and leads to a modified form of dual or multiple X-line reconnection; (iv) the FTE generation process in this model is not dependent on specific assumptions about microscopic processes; (v) the average period of FTEs can be explained by simple geometric arguments involving magnetosheath convection; (vi) FTEs do not develop in the model if the numerical resolution is too coarse leading to too much numerical diffusion; and (vii) FTEs for nearly southward IMF and large dipole tilt, i.e., near solstice, should only develop in the winter hemisphere, which provides a testable prediction of seasonal modulation. The semiannual modulation of intermittent FTE reconnection versus steady reconnection is also expected to modulate magnetospheric and ionospheric convection and may thus contribute to the semiannual variation of geomagnetic activity.

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Ionospheric ion upwelling in the wake of flux transfer events at the dayside magnetopause

Journal of Geophysical Research Atmospheres ◽

10.1029/ja093ia06p05641 ◽

1988 ◽

Vol 93 (A6) ◽

pp. 5641 ◽

Cited By ~ 39

Author(s):

M. Lockwood ◽

M. F. Smith ◽

C. J. Farrugia ◽

G. L. Siscoe

Keyword(s):

Flux Transfer Events ◽

Dayside Magnetopause ◽

Flux Transfer ◽

Ion Upwelling

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The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field

Annales Geophysicae ◽

10.5194/angeo-19-707-2001 ◽

2001 ◽

Vol 19 (7) ◽

pp. 707-721 ◽

Cited By ~ 20

Author(s):

K. A. McWilliams ◽

T. K. Yeoman ◽

J. B. Sigwarth ◽

L. A. Frank ◽

M. Brittnacher

Keyword(s):

Large Scale ◽

Small Region ◽

Radar Data ◽

Hf Radar ◽

Current Response ◽

Plasma Convection ◽

Flux Transfer Events ◽

Field Aligned Current ◽

Flux Transfer ◽

The Imf

Abstract. We examine the large-scale ultraviolet aurora and convection responses to a series of flux transfer events that immediately followed a sharp and isolated southward turning of the IMF. During the interval of interest, SuperDARN was monitoring the plasma convection in the dayside northern ionosphere, while the VIS Earth Camera and the Far Ul-traviolet Imager (UVI) were monitoring the northern hemisphere’s ultraviolet aurora. Reconnection signatures were seen in the SuperDARN HF radar data in the postnoon sector following a sharp southward turning of the IMF. The presence of flux transfer events is supported by measurements of a classic dispersed ion signature in the low-altitude cusp from the DMSP spacecraft. Subsequent to the onset of reconnection, the postnoon convection and ultraviolet aurora expanded in concert, reaching 18 MLT in half an hour. The auroral oval was found to move equatorward at the convection speed in the 16–18 MLT sector, implying that it was related directly to an adiaroic magnetospheric boundary. In the present study, we have estimated the field-aligned current response to magnetic reconnection in terms of the vorticity of the ionospheric plasma convection velocity. The convection velocities were obtained using two methods: (a) direct reconstruction of the full vector velocities from bistatic measurements of the convection by the SuperDARN HF radars in a relatively small region of the auroral zone, and (b) from global-scale spherical harmonic fits to the SuperDARN velocities deduced from the map potential model. Regions of high vorticity, which were predicted to be an estimate of a component of the total field-aligned current, agree extremely well with the images of the dayside UV aurora, indicating that, in this case, the plasma vorticity is an excellent estimator of the morphology of dayside field-aligned currents (FACs). The morphology of the aurora and ionospheric electric field in the postnoon sector supports the existence of a dayside current wedge induced in response to dayside reconnection.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions; solar wind magne-tosphere interactions)

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The azimuthal extent of three flux transfer events

Annales Geophysicae ◽

10.5194/angeo-26-2353-2008 ◽

2008 ◽

Vol 26 (8) ◽

pp. 2353-2369 ◽

Cited By ~ 48

Author(s):

R. C. Fear ◽

S. E. Milan ◽

A. N. Fazakerley ◽

E. A. Lucek ◽

S. W. H. Cowley ◽

...

Keyword(s):

Flux Tube ◽

Time Varying ◽

Magnetic Shear ◽

Simple Interpretation ◽

Flux Transfer Events ◽

Dayside Magnetopause ◽

In Situ Observations ◽

Flux Transfer ◽

Separation Size

Abstract. In early 2006, the Cluster spacecraft crossed the dayside magnetopause twice each orbit with the spacecraft at their largest separation of the entire mission (~10 000 km). In this paper, we present in situ observations at this separation size of flux transfer events (FTEs), which are a signature of transient or time-varying magnetopause reconnection. We study a magnetopause crossing on 27 January 2006; for half an hour, the tetrahedron of Cluster spacecraft straddled the magnetopause and during this time a large number of flux transfer events were observed. Three particular FTEs were observed by all four spacecraft, enabling it to be shown that individual FTEs at the magnetopause can extend azimuthally for at least 10 000 km. By combining the Cluster tetrahedron geometry with the observed velocity of the FTEs, it can be shown that the poleward extent of one FTE is significantly smaller than its azimuthal extent. The location of the Cluster spacecraft when they observed this FTE suggests that it is inconsistent with the simple interpretation of an "elbow-shaped" flux tube. The FTE's azimuthal extent suggests that it was more likely generated at a comparatively long reconnection line or lines, although the magnetic shear across the magnetopause is not high enough to exclude the "elbow-shaped" model entirely.

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