Spatial profile of magnetic field in the near‐Earth plasma sheet prior to dipolarization by THEMIS: Feature of minimum B

Saito, Miho; Hau, L.‐N.; Hung, Chi-Hang; Lai, Yi‐Chyi; Chou, Yu-Chen

doi:10.1029/2010gl042813

Cited by 43 publications

(43 citation statements)

References 29 publications

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“…In such a model, steady convection becomes possible. Such a profile has been found to be maintained persistently before the substorm onset [Saito et al, 2010], proving observational support of the idea that B z evolves in a manner that the excess pressure issue is avoided. During the growth phase, intense cross-tail current density is required in the near-Earth tail to account for the observed increasingly stretched field [Kaufmann, 1987].…”

Section: Introductionsupporting

confidence: 48%

“…The interval of interest in this study between 6 and 7 UT has been previously studied by Saito et al [2010]. They analyzed the spatial profile of B z and found the formation of a magnetic field minimum from 0640 UT to 0656 UT.…”

Section: Observation Resultsmentioning

confidence: 99%

“…[11] This analysis uses THEMIS spacecraft data from the substorm event on April 8, 2009 studied by Saito et al [2010]. All five THEMIS probes [Angelopoulos, 2008;Frey et al, 2008] in formation flight with identical instrumentation are used to reveal the latitudinal profile of the current sheet.…”

Section: Resultsmentioning

confidence: 99%

“…[18] The plots of B r and B z versus Z were used for examining the validity of the thin geometry approximation of the model by Saito et al [2010]. Various plasma parameters shown in Figures 3 and 4 also confirm that the spatial profiles in Figures 3 and 4 can be regarded as the latitudinal profiles of the current/plasma sheet at X = −11 R E and Y = −4 R E for the intervals before and during the thinning of the tail, respectively.…”

Section: Observation Resultsmentioning

confidence: 99%

“…The above assumptions are applicable to a thin current sheet geometry observed for the event to be studied here and previously shown by Saito et al [2010], who examined the spatial profiles of the magnetic field. Both radial and z components of the magnetic field are well ordered by the z position of the five spacecraft, while they are not well ordered by r and .…”

Section: Model Assumptionsmentioning

confidence: 99%

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Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Saito

Fairfield

et al. 2011

J. Geophys. Res.

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[1] THEMIS five-point observations on April 8, 2009 were used to study thinning of the current sheet in the near-Earth tail that led to the onset of a small substorm. Taking advantage of a fortuitous alignment of the five spacecraft near 2300 LT and 11 R E and within 1.5 R E of the current sheet center, latitudinal gradients are analyzed. A significant latitudinal pressure gradient is present indicating the necessity of a (J × B) z force to maintain the pre-onset equilibrium state. During thinning the total pressure remained approximately constant at all spacecraft rather than increasing. Within the plasma sheet, magnetic field strength increased while plasma pressure decreased due to decreasing temperature. We present a comprehensive explanation for the relationship between the thinning, the stretched structure, and development of intense current density. Our analysis of this event suggests that (1) the thinning in this event is an MHD force-balanced self-evolving process and is not a forced process due to an increased lobe field; (2) the thinning changes flux tube structure in length and curvature but not significantly in volume; (3) the thinning evolves with a change of the radial plasma pressure profile in the near-Earth tail, which is associated with a locally intensified current sheet. The conclusion is that the increased lobe field strength is not the necessary and the primary cause for cross tail current sheet thinning but rather thinning can occur within the plasma sheet as a result of unknown internal processes.

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Section: Introductionsupporting

confidence: 48%

Section: Observation Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Observation Resultsmentioning

confidence: 99%

Section: Model Assumptionsmentioning

confidence: 99%

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Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Saito

Fairfield

et al. 2011

J. Geophys. Res.

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Empirical modeling of plasma sheet pressure and three‐dimensional force‐balanced magnetospheric magnetic field structure: 2. Modeling

et al. 2013

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[1] The magnetic field configuration is crucial to plasma sheet dynamics and magnetosphere-ionosphere coupling. In this study we established 3-D force-balanced magnetic fields and investigated configuration changes with Kp and solar wind dynamic pressure (P SW ). Pressure distributions from the empirical model developed in Wang et al. (2013) were used for obtaining the force-balanced field. Based on our model results, we found that (1) higher P SW mainly enhances pressure in the tail plasma sheet, while larger convection during higher Kp drives plasma sheet further earthward, resulting in a pressure increase closer to the Earth; (2) comparing with the magnetic field changes due to increasing P SW , the Kp associated pressure enhancement causes the azimuthal current density (J φ ) peak and field-aligned currents (FACs) to move deeper earthward, the magnetic field to decrease further near Earth but increase more in the tail, and field lines to stretch more significantly; (3) as Kp and P SW change, the whole plasma sheet remains stable to interchange instability but may be ballooning unstable in the midnight region at X between À15 and À10 R E ; (4) the force-balanced configurations are characteristically different from the non-force-balanced Tsyganenko 89 (T89) magnetic field. A region of positive dBz/dz in the near-Earth region, which has been observed, is seen in our field but not in T89. On the other hand, a local equatorial Bz minimum is predicted by T89 but not by our model. J ϕ bifurcation appears in the near-Earth region as a result of our J ϕ configuration being approximately aligned with field lines, while the T89 J ϕ everywhere decreases monotonically with increasing Z by construction.Citation: Yue, C., C.-P. Wang, S. G. Zaharia, X. Xing, and L. Lyons (2013), Empirical modeling of plasma sheet pressure and three-dimensional force-balanced magnetospheric magnetic field structure: 2. Modeling,

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Magnetic flux transport by dipolarizing flux bundles

2014

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A dipolarizing flux bundle (DFB) is a small magnetotail flux tube (typically <~3 R E in X GSM and Y GSM ) with a significantly more dipolar magnetic field than its background. Dipolarizing flux bundles typically propagate earthward at a high speed from the near-Earth reconnection region. Knowledge of a DFB's flux transport properties leads to better understanding of near-Earth (X = À6 to À30 R E ) magnetotail flux transport and thus conversion of magnetic energy to kinetic and thermal plasma energy following magnetic reconnection. We explore DFB properties with a statistical study using data from the Time History of Events and Macroscale Interactions during Substorms mission. To establish the importance of DFB flux transport, we compare it with transport by bursty bulk flows (BBFs) that typically envelop DFBs. Because DFBs coexist with flow bursts inside BBFs, they contribute >65% of BBF flux transport, even though they last onlỹ 30% as long as BBFs. The rate of DFB flux transport increases with proximity to Earth and to the premidnight sector, as well as with geomagnetic activity and distance from the neutral sheet. Under the latter two conditions, the total flux transport by a typical DFB also increases. Dipolarizing flux bundles appear more often during increased geomagnetic activity. Since BBFs have been previously shown to be the major flux transporters in the tail, we conclude that DFBs are the dominant drivers of this transport. The occurrence rate of DFBs as a function of location and geomagnetic activity informs us about processes that shape global convection and energy conversion.

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Spatial profile of magnetic field in the near‐Earth plasma sheet prior to dipolarization by THEMIS: Feature of minimum B

Cited by 43 publications

References 29 publications

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Empirical modeling of plasma sheet pressure and three‐dimensional force‐balanced magnetospheric magnetic field structure: 2. Modeling

Magnetic flux transport by dipolarizing flux bundles

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