Electric field measurements at the magnetopause: 1. Observation of large convective velocities at rotational magnetopause discontinuities

Aggson, T. L.; Gambardella, P. J.; Maynard, N. C.

doi:10.1029/ja088ia12p10000

Cited by 52 publications

(23 citation statements)

References 11 publications

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“…These events occurred primarily near the nose of the magnetopause and had speed increases across them. Recently, Aggson et al (1983a) have confirmed the rotational character of the Sonnerup et al (1981) events using electric and magnetic field data. Using this same technique Agg son et al (1983b) have also reported a rotational magnetopause traversal in which the observed fluid speed decreased; they pointed out that this behavior was permitted for the geometrical circumstances encountered under the MHD description of RD's as outlined, for example, by de Hoffman and Teller (1950) and mentioned by Roederer (1977) .…”

Section: Introductionmentioning

confidence: 82%

Fluid signatures of rotational discontinuities at the Earth's magnetopause

Scudder¹

1984

J. Geophys. Res.

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Fluid signatures in the MHD approximation at rotational discontinuities (RD) of finite width called rotational shear layers (RSL) are examined for general flow and magnetic geometries. Analytical and geometrical arguments illustrate that the fluid speed can either go up or down across an RSL for a fixed normal mass flux. The speed profile may or may not be monotonic with the phase of the magnetic rotation depending on the boundary conditions. The flow velocity may or may not be field aligned or “jetting” as a result of traversing the RSL. In general, significant “convection” is expected in the layer. The observable signatures of (MHD) RSL's depend on seven (boundary condition) parameters: (1) the mass density, (2)–(5) the incident normal and transverse components of the magnetic field and fluid velocity, (6) the angle ε between the incident tangential flow velocity and tangential magnetic field, and (7) the size of the magnetic angular rotation implemented by the layer Δϕ. This general survey illustrates the singular character of the Petschek geometry and that the model predictions of jetting and monotonic speed increases through the layer may not be used as general signatures of RSL's. This is especially true along the Levy, Petschek, and Siscoe curved magnetopause boundary, where the fluid flow, Δϕ, and ε are generally all different from the Petschek regime. Accordingly, the lack of observed speed increases across the magnetopause can no longer be used by itself to infer that the magnetopause is locally closed. Of the spectrum of MHD RSL's that are possible, the “accelerating” ones require special boundary conditions most generally occurring near the nose of the magnetopause; the “decelerating” RSL's become increasingly more probable at magnetopause crossings removed from the subsolar point. Documented RSL's have been located within the spectrum of possible signatures; the number of RSL's reported to date implies only a lower bound for their frequency of occurrence, since surveys conducted to date have excluded the decelerating ones.

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Section: Introductionmentioning

confidence: 82%

Fluid signatures of rotational discontinuities at the Earth's magnetopause

Scudder¹

1984

J. Geophys. Res.

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“…Convincing evidence can be found in the in-situ observations at the magnetopause: from the ISEE and AMPTE satellites (e.g. Paschmann et al, 1979Paschmann et al, , 1986Sonnerup et al, 1981Sonnerup et al, , 1987Sonnerup et al, , 1990Gosling et al, 1982Gosling et al, , 1986Gosling et al, , 1990cGosling et al, , 1991Aggson et al, 1983), recently by IMAGE (e.g. Fuselier et al, 2000), POLAR (e.g.…”

Section: Introductionmentioning

confidence: 99%

Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp

Zheng

Le²,

Slavin³

et al. 2005

Ann. Geophys.

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Abstract. In this paper, we present a case study of continuous reconnection at the dayside magnetopause observed by the Cluster spacecraft. On 1 April 2003, the four Cluster spacecraft experienced multiple encounters with the Earth's dayside magnetopause under a fairly stable southwestward interplanetary magnetic field (IMF). Accelerated plasma flows, whose magnitude and direction are consistent with the predictions of the reconnection theory (the Walén relation), were observed at and around the magnetopause current layer for a prolonged interval of ∼3 h at two types of magnetopause crossings, one with small magnetic shears and the other one with large magnetic shears. Reversals in the Y component of ion bulk flow between the magnetosheath and magnetopause current layer and acceleration of magnetosheath electrons were also observed. Kinetic signatures using electron and ion velocity distributions corroborate the interpretation of continuous magnetic reconnection. This event provides strong in-situ evidence that magnetic reconnection at the dayside magnetopause can be continuous for many hours. However, the reconnection process appeared to be very dynamic rather than steady, despite the steady nature of the IMF. Detailed analysis using multi-spacecraft magnetic field and plasma measurements shows that the dynamics and structure of the magnetopause current layer/boundary can be very complex. For example, highly variable magnetic and electric fields were observed in the magnetopause current layer. Minimum variance analysis shows that the magnetopause normal deviates from the model normal. Surface waves resulting from the reconnection process may be involved in the oscillation of the magnetopause.

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“…Dungey [1963] also mentioned the possibility of cusp reconnection for northward interplanetary magnetic field (IMF). There is considerable evidence that reconnection at the dayside magnetopause is the dominant mechanism of the mass, energy, and momentum transfer from the shocked solar wind flow to the magnetosphere, including acceleration of the magnetosheath plasma upon entry onto open field lines [e.g., Paschmann et al, 1979Paschmann et al, , 1984Sonnerup et al, 1981;Gosling et al, 1982Gosling et al, , 1991Aggson et al, 1983], the momentum and energy balance across the magnetopause and reconnection of magnetosheath and magnetospheric fields at one lobe with subsequent reconnection at another lobe, leading to a closed field tube at the dayside magnetopause.…”

Section: Introductionmentioning

confidence: 99%

Different types of low‐latitude boundary layer as observed by Interball Tail probe

Вайсберг¹,

Смирнов²,

Avanov³

et al. 2001

J. Geophys. Res.

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Abstract. Interball Tail probe crossed dayside magnetopause during late winter to middle autumn months. The high-latitude magnetopause was crossed outbound orbit, while the lowlatitude magnetopause was crossed inbound. We analyze 31 low-latitude magnetopause/lowlatitude boundary layer (LLBL) crossings recorded in 1996 in the fast mode of SCA-1 ion spectrometer. Data from the MIF/FM-3 magnetometers and ELECTRON spectrometer are also used. The majority of magnetopause/LLBL crossings fall into two categories: (1) highly structured LLBL (14 cases) and (2) weakly structured LLBL (9 cases). The highly structured LLBL usually consists of short-time (0.5-5 min) transients including fast-moving (of an order of magnetosheath velocity) plasma as well as density transients that are nearly stationary relative to the magnetospheric plasma. The observed ensemble of transients shows evolution of plasma parameters from magnetosheath-like to magnetosphere-like. Fast-moving transients frequently have flux transfer event (FTE) magnetic signatures. This type of LLBL is usually accompanied by various reconnection signatures and is more frequently observed when the interplanetary magnetic field (IMF) and/or magnetosheath magnetic field has a negative Bz component. The weakly structured LLBL shows a significantly smaller variation of number density and hotter plasma temperature. Strong velocity shear is frequently observed at the magnetopause in the weakly structured case. Dispersed ion signatures are often seen within this type of LLBL. The ion and electron temperatures within the weakly structured LLBL are more elevated in respect to the magnetosheath values compared to the highly structured LLBL. The weakly structured LLBL has a tendency to occur at positive IMF and/or magnetosheath magnetic field Bz. The cause of significant differences between the two kinds of LLBL lies, apparently, in the significantly larger distance of the plasma entry site from the observation point, for weakly structured LLBL, as opposed to highly structured LLBL. While the highly structured LLBL originates at low latitudes, the weakly structured LLBL is most probably formed at high latitudes.

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Electric field measurements at the magnetopause: 1. Observation of large convective velocities at rotational magnetopause discontinuities

Cited by 52 publications

References 11 publications

Fluid signatures of rotational discontinuities at the Earth's magnetopause

Fluid signatures of rotational discontinuities at the Earth's magnetopause

Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp

Different types of low‐latitude boundary layer as observed by Interball Tail probe

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