The effects of a magnetic B y component on geomagnetic tail equilibria

[1] The strong magnetic field B y component (in GSM coordinates) has been increasingly noticed to play an important role in the dynamics of tail current sheet (CS). The distribution profile of strong B y components in the tail CS (i.e., those with guide field), however, is not well known. In the present work, by using the simultaneous multipoint observations of Cluster satellites, the profile of a strong B y component in tail current sheets is explored, through detailed case studies, as well as in a statistical study. It is discovered that around the midnight meridian, the strength of the strong B y component, i.e., |B y |, is basically enhanced at the center of the CS relative to that in the CS boundaries and lobes and forms a north-south symmetric distribution about the center of CS. Generally, however, for strong guide field cases in the non-midnight meridian, the profile of B y strength basically becomes north-south asymmetric, the strength of the B y component in the northern side of the CS is found to be either stronger or weaker than that in the counterpart southern side. By considering the modulation of the tail flaring magnetic field with magnetic local time, we propose an interpretation to account for the variation of the B y -profile, which is supported by the statistical survey. These results offer an observation basis for further studies.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Profile of strong magnetic field B_y component in magnetotail current sheets

Rong¹,

Wan²,

Shen³

et al. 2012

“…To our knowledge, no analysis of self‐consistent sheet structures with B y ≠ 0 has been presented thus far. Earlier investigations of the shear influence on particle dynamics in current sheets were made with the help of particle tracing for relatively thick current sheet [e.g., Birn and Hesse , 1994; Larson and Kaufmann , 1996; Hilmer and Voigt , 1987] as well as in TCSs [ Kaufmann et al , 1997; Holland et al , 1996; Delcourt and Belmont , 1998; Delcourt et al , 2000]. In the study of Delcourt et al [2000], the particle dynamics was analyzed over a wide range of parameters, from the magnetized regime to the unmagnetized one.…”

Section: Introductionmentioning

confidence: 99%

Thin current sheets in the presence of a guiding magnetic field in Earth's magnetosphere

Malova¹,

Popov²,

Мингалев³

et al. 2012

[1] A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field B y (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field B y are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field B y = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with B y = 0, the character of "particle-current sheet" interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the B y component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant B y . In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed.

“…This guide field in the tail current sheet could arise of the penetration of IMF into the magnetosphere, and statistically the B y in the tail current sheet is found to be linear to IMF B y [ Fairfield , 1979; Lui , 1983; Tsurutani et al , 1984; Nagai , 1987; Hau and Voigt , 1992; Hau and Erickson , 1995]. The most penetration rate of IMF B y appears in the neutral sheet in the near earth and mid tail regions, and the penetration of IMF B y becomes less in the plasma sheet and least in the lobes [ Lui , 1983; Hilmer and Voigt , 1987; Kaymaz et al , 1994]. However, the features of the tail current sheet with guide field, and the instabilities occurring in it, have been stressed less than for that of normal current sheets [ Lui , 1983].…”

Section: Introductionmentioning

confidence: 99%

Flattened current sheet and its evolution in substorms

Shen

Liu

et al. 2008

[1] In this research, the properties of a tail current sheet, which has a flattened geometry, and its evolution during substorm activity have been investigated. The geometrical configuration of the magnetic field and the spatial distribution of the current density in a flattened current sheet have been revealed with certainty for the first time. It is found that such a flattened current sheet has sufficiently strong B y (GSM) within its neutral sheet that the magnetic field lines (MFLs) in the neutral sheet are lie almost in the GSM equatorial plane and that the normal directions are generally northward. Detailed analyses show that, the magnetic field lines are spiral-like, not plane curves, which are left-handed or right-handed spirals for B y > 0 or B y < 0. This magnetic rotation occurs predominantly in the neutral sheet. The flattened current sheet may be very thin, and the thickness of the neutral sheet is much less than the minimum radius of the curvature of the MFLs in the current sheet. The analysis also suggests that the neutral sheet current is field-aligned and lies mainly duskward. The curvature current makes little contribution to the total current in the flattened current sheet. The main current carriers in the neutral sheet of the flattened current sheet are electrons. A statistical survey shows that there is one positive correlation between B y in the flattened current sheet and IMF B y and penetration efficiency is 0.67. Flattened current sheets may occur in both quiet and disturbed periods and may appear at all phases of the substorms. During the growth phase of a substorm event, the neutral sheet of the flattened current sheet is shown to become progressively thinner, while the associated current density is increasing gradually. It is found that the northern turning of the IMF has triggered the explosive growth phase at the end of the growth phase, which lasts several minutes. At the explosive growth phase, the flattened current sheet becomes much thinner and the current density in the neutral sheet then increases considerably and reaches a value larger than 0.017 mAm À2 . Just after the onset of the substorm, the current density in the neutral sheet drops abruptly and varies turbulently.