Increases in plasma sheet temperature with solar wind driving during substorm growth phases

Forsyth, C.; Watt, Clare E. J.; Rae, I. J.; Fazakerley, A. N.; Kalmoni, N. M. E.; Freeman, M. P.; Boakes, Peter; Nakamura, R.; Dandouras, I.; Kistler, L. M.; Jackman, C. M.; Coxon, J. C.; Carr, C.

doi:10.1002/2014gl062400

Cited by 23 publications

(35 citation statements)

References 55 publications

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“…They have revealed that although ~ 59.0% of our events correspond to a P eqend increase, there are still events with P eqend almost unchanged (~ 28.0%) or even decreasing (~ 13.0%) as compared to P eq0 . We believe that these results may provide an explanation for the previous conflicting results concerning plasma sheet pressure variations, that is, some showing plasma sheet pressure increase during the substorm growth phase (e.g., Forsyth et al, ; Kistler et al, ; Nagai et al, ; Wang et al, ), while others found little or no change (e.g., Kistler et al, ; Snekvik et al, ). We have found that the P eq increase percentage at the end of growth phase is the highest in the premidnight MLT bin (22:00 to 00:00).…”

Section: Conclusion and Discussionmentioning

confidence: 68%

“…The transmission of enhanced electric fields associated with dayside magnetopause reconnection across the open field lines of the magnetotail has been extensively studied (e.g., McPherron et al, ; Russell & McPherron, ). The enhanced electric field due to solar wind convection transports reconnected (i.e., “open”) magnetic flux from the dayside into lobes and has been believed to be responsible for an increase in total pressure in the plasma sheet (e.g., Forsyth et al, ; Kistler et al, ; Wang et al, ; Yue et al, ). However, it has also been suggested that this enhanced electric field will be reflected in the closed field line region of the near tail through compression and rarefaction waves (Coroniti & Kennel, ; Kan, ).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…In many previous studies, the contribution of P e to the total pressure was neglected (e.g., Forsyth et al, ; Kistler et al, ) or assumed to be only a small portion (14%) of the P i (e.g., Petrukovich et al, ; Snekvik et al, ) during substorm growth phase in the tail plasma sheet. However, the cases in Figures and showed that P ezz or P bxy displayed large variations in the growth phase.…”

Section: Electron Pressure Contributionmentioning

confidence: 99%

“…The subsequent flaring of magnetotail as the lobes expand to accommodate the added flux increases the solar wind ram pressure on the magnetopause, which must be balanced by the increase of lobe magnetic pressure (e.g., McPherron et al, ; Russell & McPherron, ). And, in turn, the plasma sheet pressure is expected to increase to balance the enhanced lobe pressure (Forsyth et al, ; Kistler et al, ; Nagai et al, ; Wang et al, ). Substorm growth phase is thus accompanied by many distinct features, such as the thinning of plasma sheet, increasing of the cross‐tail current density, and enhanced convection in the equatorial magnetosphere.…”

Section: Introductionmentioning

confidence: 99%

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Plasma Sheet Pressure Variations in the Near‐Earth Magnetotail During Substorm Growth Phase: THEMIS Observations

Sun

Wei

et al. 2017

JGR Space Physics

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We investigate the plasma sheet pressure variations in the near‐Earth magnetotail (radius distance, R, from 7.5 RE to 12 RE and magnetic local time, MLT, from 18:00 to 06:00) during substorm growth phase with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. It is found that, during the substorm growth phase, about 39.4% (76/193) of the selected events display a phenomenon of equatorial plasma pressure (Peq) decrease. The occurrence rates of Peq decrease cases are higher in the dawn (04:00 to 06:00) and dusk (18:00 to 20:00) flanks (> 50%) than in the midnight region (20:00 to 04:00, < 40%). The mean values of the maximum percentages of Peq decrease during the substorm growth phases are larger in the dawn and dusk flanks (~ −20%) than in the midnight region (~ > −16%). The mean value of Peq increase percentages at the end of substorm growth phase is the highest (~ 40%) in the premidnight MLT bin (22:00 to 00:00) and is almost unchanged in the dawn and dusk flanks. Further investigations show that 13.0% of the events have more than 10% of Peq decrease at the end of substorm growth phase comparing to the value before the growth phase, and ~ 28.0% of the events have small changes (< 10%), and ~ 59.0% events have a more than 10% increase. This study also reveals the importance of electron pressure (Pe) in the variation of Peq in the substorm growth phase. The Pe variations often account for more than 50% of the Peq changes, and the ratios of Pe to ion pressure often display large variations (~ 50%). Among the investigated events, during the growth phase, an enhanced equatorial plasma convection flow is observed, which diverges in the midnight tail region and propagates azimuthally toward the dayside magnetosphere with velocity of ~ 20 km/s. It is proposed that the Peq decreases in the near‐Earth plasma sheet during the substorm growth phase may be due to the transport of closed magnetic flux toward the dayside magnetosphere driven by dayside magnetopause reconnection. Both solar wind and ionospheric conductivity effects may influence the distributions of occurrence rates for Peq decrease events and the Peq increase percentages in the investigated region.

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Section: Conclusion and Discussionmentioning

confidence: 68%

Section: Conclusion and Discussionmentioning

confidence: 99%

Section: Electron Pressure Contributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Plasma Sheet Pressure Variations in the Near‐Earth Magnetotail During Substorm Growth Phase: THEMIS Observations

Sun

Wei

et al. 2017

JGR Space Physics

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“…During the growth phase, low-latitude dayside reconnection with the IMF (interplanetary magnetic field) dominates over the nightside reconnection rate, resulting in an accumulation of open field lines in a highly stretched magnetotail (Kokubun & McPherron, 1981;McPherron, 1970McPherron, , 1972Milan et al, 2007). The dipolarization of the magnetic field and the destabilization of the near-Earth tail act to energize particles and drive intense electric currents (e.g., Forsyth et al, 2014;McPherron et al, 1973). The dipolarization of the magnetic field and the destabilization of the near-Earth tail act to energize particles and drive intense electric currents (e.g., Forsyth et al, 2014;McPherron et al, 1973).…”

Section: Introductionmentioning

confidence: 99%

Substorm‐Ring Current Coupling: A Comparison of Isolated and Compound Substorms

et al. 2019

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Substorms are a highly variable process, which can occur as an isolated event or as part of a sequence of multiple substorms (compound substorms). In this study we identify how the low‐energy population of the ring current and subsequent energization varies for isolated substorms compared to the first substorm of a compound event. Using observations of H+ and O+ ions (1 eV to 50 keV) from the Helium Oxygen Proton Electron instrument onboard Van Allen Probe A, we determine the energy content of the ring current in L‐MLT space. We observe that the ring current energy content is significantly enhanced during compound substorms as compared to isolated substorms by ∼20–30%. Furthermore, we observe a significantly larger magnitude of energization (by ∼40–50%) following the onset of compound substorms relative to isolated substorms. Analysis suggests that the differences predominantly arise due to a sustained enhancement in dayside driving associated with compound substorms compared to isolated substorms. The strong solar wind driving prior to onset results in important differences in the time history of the magnetosphere, generating significantly different ring current conditions and responses to substorms. The observations reveal information about the substorm injected population and the transport of the plasma in the inner magnetosphere.

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Three‐dimensional current systems and ionospheric effects associated with small dipolarization fronts

et al. 2015

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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts), associated with small individual BZGSM increases on 31 March 2009 (0200–0900 UT), observed by the Time History of Events and Macroscale Interactions During Substorms mission. This series of events happens during very quiet solar wind conditions, over a period of 7 h preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low‐amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh>2 mV/m), whereas the large‐amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW)‐like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (>5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW‐like current system and particle injections at geosynchronous orbit. This exceptional data set highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat up.

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Increases in plasma sheet temperature with solar wind driving during substorm growth phases

Cited by 23 publications

References 55 publications

Plasma Sheet Pressure Variations in the Near‐Earth Magnetotail During Substorm Growth Phase: THEMIS Observations

Plasma Sheet Pressure Variations in the Near‐Earth Magnetotail During Substorm Growth Phase: THEMIS Observations

Substorm‐Ring Current Coupling: A Comparison of Isolated and Compound Substorms

Three‐dimensional current systems and ionospheric effects associated with small dipolarization fronts

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