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ABSTRACT: 1] Over the first 2.5 years of operation, the FUV instrument on the IMAGE spacecraft observed more than 2400 substorm onsets in the Northern Hemisphere. The observations confirm earlier results of statistical studies in terms of a median substorm onset location at 2300 hours MLT and 66.4 degrees magnetic latitude. The purpose of this report is to publish the list to allow for further investigation. The list can easily be searched for onsets close to certain ground stations or at specific magnetic latitudes or local times. As one example of such use, we demonstrate how the probability of onset observation was determined for the ground-based automatic observatories of the THEMIS (Time History of Events and Macroscale Interactions during Substorms) project.
J. Geophys. Res. 01/2704; 109.
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ABSTRACT: We present the first quantified measure of the rate of energy dissipated per
unit volume by high frequency electromagnetic waves in the transition region of
the Earth's collisionless bow shock using data from the THEMIS spacecraft.
Every THEMIS shock crossing examined with available wave burst data showed both
low frequency (< 10 Hz) magnetosonic-whistler waves and high frequency (> 10
Hz) electromagnetic and electrostatic waves throughout the entire transition
region and into the magnetosheath. The waves in both frequency ranges had large
amplitudes, but the higher frequency waves, which are the focus of this study,
showed larger contributions to both the Poynting flux and the energy
dissipation rates. The higher frequency waves were identified as combinations
of ion-acoustic waves, electron cyclotron drift instability driven waves,
electrostatic solitary waves, and whistler mode waves. These waves were found
to have: (1) amplitudes capable of exceeding dB ~ 10 nT and dE ~ 300 mV/m,
though more typical values were dB ~ 0.1-1.0 nT and dE ~ 10-50 mV/m; (2) energy
fluxes in excess of 2000 x 10^(-6) W m^(-2); (3) resistivities > 9000 Ohm m;
and (4) energy dissipation rates > 3 x 10^(-6) W m^(-3). The dissipation rates
were found to be in excess of four orders of magnitude greater than was
necessary to explain the increase in entropy across the shocks. Thus, the waves
need only be, at times, < 0.01% efficient to balance the nonlinear wave
steepening that produces the shocks. Therefore, these results show for the
first time that high frequency electromagnetic and electrostatic waves have the
capacity to regulate the global structure of collisionless shocks.
05/2013;
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ABSTRACT: Motivated by recent observations of intense electric fields and elevated energetic particle fluxes within flow bursts beyond geosynchronous altitude (Runov et al., 2009, 2011), we apply modeling of particle guiding centers in prescribed but realistic electric fields to improve our understanding of energetic particle acceleration and transport toward the inner magnetosphere through model-data comparisons. Representing the vortical nature of an earthward traveling flow burst, a localized, westward-directed transient electric field flanked on either side by eastward fields related to tailward flow is superimposed on a nominal steady state electric field. We simulate particle spectra observed at multiple THEMIS spacecraft located throughout the magnetotail and fit the modeled spectra to observations, thus constraining properties of the electric field model. We find that a simple potential electric field model is capable of explaining the presence and spectral properties of both geosynchronous altitude and “trans-geosynchronous” injections at higher L-shells (L > 6.6 RE) in a manner self-consistent with the injections' inward penetration. In particular, despite the neglect of the magnetic field changes imparted by dipolarization and the inductive electric field associated with them, such a model can adequately describe the physics of both dispersed injections and depletions (“dips”) in energy flux in terms of convective fields associated with earthward flow channels and their return flow. The transient (impulsive), localized, and vortical nature of the earthward-propagating electric field pulse is what makes this model particularly effective.
Journal of Geophysical Research 10/2012; 117(A10). · 3.02 Impact Factor
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ABSTRACT: To address the mechanism and factors controlling the injection of energetic particles to the geostationary orbit (GEO), we analyzed the appearance of injections at the GEO drift shell as observed by LANL spacecraft in the cases where the flow bursts and associated transient dipolarization were detected at the entry to the inner magnetosphere, in the high beta plasma sheet region on the nightside between 8 and 13 Re. We analyzed two different data sets, one including Geotail observations in 1995–2005 and another including a set of Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations in 2008–2009. We found that only a small portion of all flow bursts at 8–13 Re were associated with particle injection at GEO but that those injection-associated flows had smaller values of plasma tube entropy parameter (PV5/3) as well as larger change of magnetic field north-south component (dBz). This confirms a scenario that the bursty flows at the entry of the inner magnetosphere (8–13 Re) penetrate into GEO and produce there the energetic particles flux increase. According to the bubble theory of magnetotail plasma flows, the probability of the deep plasma penetration critically depends on how stretched the magnetospheric configuration is, and this dependence is statistically confirmed in a large database to be the major factor controlling the occurrence of GEO injections. We suggest using the background plasma tube entropy value in the nightside part of the GEO drift shell as a suitable parameter to predict the probability of particle injection to GEO. One more outcome of this study is that the energetic particle injections cannot reliably serve as a tool to identify the substorm onset times, as has been done in many past studies.
Journal of Geophysical Research 10/2012; 117(A10207):12 PP. · 3.02 Impact Factor
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J. S. Halekas, V. Angelopoulos,
D. G. Sibeck,
K. K. Khurana,
C. T. Russell,
G. T. Delory,
W. M. Farrell,
J. P. McFadden,
J. W. Bonnell,
D. Larson,
R. E. Ergun,
F. Plaschke,
K. H. Glassmeier
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ABSTRACT: We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration,
Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun), a new lunar mission that re-tasks two
of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at ∼3.5 lunar
radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan,
and Chang’E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake
along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar
models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary
magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements
of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of
electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with
counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations
demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science
from this unique two spacecraft constellation.
KeywordsMoon–Lunar wake–Counter-streaming distributions
Space Science Reviews 04/2012; 165(1):93-107. · 3.61 Impact Factor
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D. G. Sibeck, V. Angelopoulos,
D. A. Brain,
G. T. Delory,
J. P. Eastwood,
W. M. Farrell,
R. E. Grimm,
J. S. Halekas,
H. Hasegawa,
P. Hellinger,
K. K. Khurana,
R. J. Lillis,
M. Øieroset,
T.-D. Phan,
J. Raeder,
C. T. Russell,
D. Schriver,
J. A. Slavin,
P. M. Travnicek,
J. M. Weygand
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ABSTRACT: NASA’s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit
about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of
the Earth’s magnetotail; reconnection, particle acceleration, and turbulence in the Earth’s magnetosphere, at the bow shock,
and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and
its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal
structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to
these baseline scientific objectives.
KeywordsARTEMIS–Moon–Reconnection–Particle acceleration–Turbulence–Wake–Lunar surface–Lunar core–Dust–Electric fields–Crustal anomalies
Space Science Reviews 04/2012; 165(1):59-91. · 3.61 Impact Factor
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XiangNing Chu,
ZuYin Pu,
Xin Cao,
Jue Wang,
V. Mishin, V. Angelopoulos,
Jiang Liu,
Yong Wei,
K. H. Glassmeier,
J. Mcfadden, [......],
I. Mann,
D. Sibeck,
QiuGang Zong,
SuiYan Fu,
Lun Xie,
T. I. Saifudinova,
M. V. Tolochko,
L. A. Sapronova,
H. Reme,
E. Lucek
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ABSTRACT: Two substorms occurred at ∼04:05 and ∼04:55 UT on February 26, 2008 are studied with the in-situ observations of THEMIS satellites and ground-based aurora and magnetic field measurements. Angelopoulos et al. have made
a comprehensive study of the 04:55 UT event. We showed detailed features of the two substorms with much attention to the first
event and to the relationship between mid-tail magnetic reconnection (MR) and substorm activities. It was found that in the
earlier stage of each substorm, a first auroral intensification occurred 2–3 min soon after the start of mid-tail MR, followed
by a slow and very limited expansion. The auroral arcs were weak, short-lived, and localized, characterizing all features
of a pseudobreakup. We regarded the first auroral brightening as the initial onset of the substorms. A few minutes later,
a second stronger auroral intensification appeared, followed by quick and extensive expansions. It was interesting to note
that the second brightening and related poleward expansion happened almost simultaneously (within a couple of minutes) with
the onset of earthward flow and dipolarization in the near-Earth tail and other phenomenon of the substorm expansion phase.
We thus regarded the second auroral brightening as the major onset of the substorms. Furthermore, it was seen that during
the growth phase of the two substorms, the polar cap open flux Ψ kept increasing, while it quickly reduced during the substorm expansion and recovery phase. These variations of Ψ implied that the evolution of the two substorm expansion phases were closely related to MR of tail lobe open field lines.
Analysis of substorm activities revealed that the two events studied were small substorms; while estimate of MR rate indicated
that the MR processes in the two substorms were weak. The aforementioned observations suggested that mid-tail MR initiated
the pseudobreakup first; the earthward flow generated by MR transported magnetic flux and energy to the near-Earth tail to
cause the formation of SCW and CD, which induced near-Earth dipolarization and major auroral brightening, and eventually led
to the onset of the substorm expansion phase. These results were clearly consistent with the picture of NENL and RCS models
and supported the two step initiation scenario of substorms.
Keywordsubstorm-auroral intensification/brightening-auroral expansion-dipolarization-magnetic reconnection
Science China Technological Sciences 04/2012; 53(5):1328-1337. · 0.75 Impact Factor
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ABSTRACT: The NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS) project is intended to investigate magnetospheric
substorm phenomena, which are the manifestations of a basic instability of the magnetosphere and a dominant mechanism of plasma
transport and explosive energy release. The major controversy in substorm science is the uncertainty as to whether the instability
is initiated near the Earth, or in the more distant >20 Re magnetic tail. THEMIS will discriminate between the two possibilities
by using five in-situ satellites and ground-based all-sky imagers and magnetometers, and inferring the propagation direction
by timing the observation of the substorm initiation at multiple locations in the magnetosphere. An array of stations, consisting
of 20 all-sky imagers (ASIs) and 30-plus magnetometers, has been developed and deployed in the North American continent, from
Alaska to Labrador, for the broad coverage of the nightside magnetosphere. Each ground-based observatory (GBO) contains a
white light imager that takes auroral images at a 3-second repetition rate (“cadence”) and a magnetometer that records the
3 axis variation of the magnetic field at 2Hz frequency. The stations return compressed images, “thumbnails,” to two central
databases: one located at UC Berkeley and the other at the University of Calgary, Canada. The full images are recorded at
each station on hard drives, and these devices are physically returned to the two data centers for data copying. All data
are made available for public use by scientists in “browse products,” accessible by using internet browsers or in the form
of downloadable CDF data files (the “browse products” are described in detail in a later section). Twenty all-sky imager stations
are installed and running at the time of this publication. An example of a substorm was observed on the 23rd of December 2006,
and from the THEMIS GBO data, we found that the substorm onset brightening of the equatorward arc was a gradual process (>27seconds),
with minimal morphology changes until the arc breaks up. The breakup was timed to the nearest frame (<3s) and located to
the nearest latitude degree at about ±3oE in longitude. The data also showed that a similar breakup occurred in Alaska ∼10 minutes later, highlighting the need for
an array to distinguish prime onset.
Space Science Reviews 04/2012; 141(1):357-387. · 3.61 Impact Factor
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ABSTRACT: Early observations by the THEMIS ESA plasma instrument have revealed new details of the dayside magnetosphere. As an introduction
to THEMIS plasma data, this paper presents observations of plasmaspheric plumes, ionospheric ion outflows, field line resonances,
structure at the low latitude boundary layer, flux transfer events at the magnetopause, and wave and particle interactions
at the bow shock. These observations demonstrate the capabilities of the plasma sensors and the synergy of its measurements
with the other THEMIS experiments. In addition, the paper includes discussions of various performance issues with the ESA
instrument such as sources of sensor background, measurement limitations, and data formatting problems. These initial results
demonstrate successful achievement of all measurement objectives for the plasma instrument.
Space Science Reviews 04/2012; 141(1):477-508. · 3.61 Impact Factor
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I. R. Mann,
D. K. Milling,
I. J. Rae,
L. G. Ozeke,
A. Kale,
Z. C. Kale,
K. R. Murphy,
A. Parent,
M. Usanova,
D. M. Pahud,
E.-A. Lee,
V. Amalraj,
D. D. Wallis, V. Angelopoulos,
K.-H. Glassmeier,
C. T. Russell,
H.-U. Auster,
H. J. Singer
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ABSTRACT: This review describes the infrastructure and capabilities of the expanded and upgraded Canadian Array for Realtime InvestigationS
of Magnetic Activity (CARISMA) magnetometer array in the era of the THEMIS mission. Formerly operated as the Canadian Auroral
Network for the OPEN Program Unified Study (CANOPUS) magnetometer array until 2003, CARISMA capabilities have been extended
with the deployment of additional fluxgate magnetometer stations (to a total of 28), the upgrading of the fluxgate magnetometer
cadence to a standard data product of 1 sample/s (raw sampled 8 samples/s data stream available on request), and the deployment
of a new network of 8 pairs of induction coils (100 samples per second). CARISMA data, GPS-timed and backed up at remote field
stations, is collected using Very Small Aperture Terminal (VSAT) satellite internet in real-time providing a real-time monitor
for magnetic activity on a continent-wide scale. Operating under the magnetic footprint of the THEMIS probes, data from 5
CARISMA stations at 29–30 samples/s also forms part of the formal THEMIS ground-based observatory (GBO) data-stream. In addition
to technical details, in this review we also outline some of the scientific capabilities of the CARISMA array for addressing
all three of the scientific objectives of the THEMIS mission, namely: 1.Onset and evolution of the macroscale substorm instability, 2.Production of storm-time MeV electrons, and 3.Control of the solar wind-magnetosphere coupling by the bow shock, magnetosheath,
and magnetopause. We further discuss some of the compelling questions related to these three THEMIS mission science objectives
which can be addressed with CARISMA.
Space Science Reviews 04/2012; 141(1):413-451. · 3.61 Impact Factor
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ABSTRACT: Stimulated by a recent study of a kinetic ballooning/interchange instability by Pritchett and Coroniti (2010), we present THEMIS events that confirm the predictions of this mechanism. In these events the probes were situated in the plasma sheet at 11 Re, near the presumed location of a B minimum. Prior to substorm onset, they observed strong magnetic oscillations with periods 20-100 s and delta B-X about 10-20 nT. Associated with these were oscillations of the electric field delta E-Y similar to 1 mV/m and the field-aligned electron velocity of several hundreds of km/s. No comparable perturbations in the ion velocity were observed. For two cases cross-correlation analyses proved duskward propagation of the elongated spatial structures with a cross-tail width of a few ion gyroradii and a propagation velocity of about the ion drift velocity. In one case THEMIS probes confirmed a sausage-like geometry of the structures. Citation: Panov, E. V., V. A. Sergeev, P. L. Pritchett, F. V. Coroniti, R. Nakamura, W. Baumjohann, V. Angelopoulos, H. U. Auster, and J. P. McFadden (2012), Observations of kinetic ballooning/interchange instability signatures in the magnetotail, Geophys. Res. Lett., 39, L08110, doi:10.1029/2012GL051668.
Geophysical Research Letters 01/2012; 39. · 3.79 Impact Factor
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J B Tao,
R E Ergun,
D L Newman,
J S Halekas,
L Andersson, V Angelopoulos,
J W Bonnell,
J P McFadden,
C M Cully,
H U Auster,
K H Glassmeier,
D E Larson,
W Baumjohann,
M V Goldman
[show abstract]
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ABSTRACT: The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two-probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high-resolution electric field instrument data with cross-spectrum analysis and cross-correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s(-1). In addition, we perform 1-D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.
Journal of Geophysical Research-Space Physics. 01/2012; 117.
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ABSTRACT: 1] Observations of the Earth's magnetotail plasma sheet boundary layer (PSBL) have been typically accompanied by field-aligned crescent-shaped ion beams, thought to emanate at distant or mid-tail semi-permanent or impulsive acceleration sites. Typically such observations, and the theoretical and modeling efforts to explain them, have been disjoint from the adjacent plasma sheet properties near the equatorial projection of the observation. Thus the plasma sheet boundary layer has been thought of as a harbinger of remote, rather than local plasma sheet activity, exception of plasma sheet expansions during the recovery phase of substorms. Using case and statistical studies from THEMIS, obtained simultaneously at the near-Earth PSBL and at its adjacent central plasma sheet (CPS), we study the transient and impulsive nature of PSBL beams and their inherent connection with CPS bursty bulk flows and associated dipolarization fronts. We show that PSBL beams typically commence a few minutes before CPS flow bursts, which in turn are seen tens of seconds ahead of the arrival of dipolarization fronts. These timing correlations, the crescent shapes of PSBL ion beams, the CPS ion flux enhancements in the earthward and dawnward directions, and other particle distribution characteristics can all be well reproduced by a simple model of ion reflection and acceleration at earthward-propagating dipolarization fronts associated with CPS flow bursts. The emerging paradigm, therefore, unifies impulsive transport phenomena across latitudes in the near-Earth magnetotail plasma sheet.
Journal of Geophysical Research 01/2012; 117. · 3.02 Impact Factor
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ABSTRACT: 1] Earthward-propagating dipolarization fronts (DFs) are often found to be associated with magnetic reconnection and bursty bulk flows (BBFs) in the magnetotail. Recent THEMIS (Time History of Events and Macroscale Interactions During Substorms) probe observations have shown a DF propagating over 10 R E from the mid-tail region to the near-Earth tail region, and THEMIS All-Sky Imager data show a north-south auroral form and intensification of westward auroral zone currents. In this study, we examine THEMIS in situ observations of DFs in the magnetotail and simultaneous observations of the proton aurora from ground-based CANOPUS (the Canadian Auroral Network for the OPEN Program Unified Study) Meridian Scanning Photometers (MSPs). We find that earthward-moving DFs are often associated with intensification of proton aurora when the THEMIS probes are conjugate to the meridian of the MSP. The proton auroral intensifications are transient and in some cases detached from the background proton precipitation. Just before the DFs, the ion distribution is anisotropic in the field-aligned direction (mostly earthward) and the ion energy increases. These observations suggest that plasma sheet protons can be reflected and energized by earthward-moving DFs as they propagate through the magnetotail. We postulate that this population of ions is the source of the proton auroral intensification observed on the ground. This conjecture is tested using our global MHD simulation results, where the proton precipitation is calculated with the field-line curvature (FLC) model. The MHD simulation results show that proton precipitation enhancement can be caused by compression of plasma by approaching DFs/BBFs, which is consistent with ion reflection at DFs. Thus, using the conjugate observations from THEMIS spacecraft and MSP in this study, we are able to directly link the magnetotail dynamics, i.e., dipolarization fronts, with ground auroral activities. However, understanding of DF-associated ion energization requires detailed test-particle simulations with an analytical magnetotail model, such as those in our companion paper.
Journal of Geophysical Research 01/2012; 117. · 3.02 Impact Factor
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ABSTRACT: 1] We present case studies of THEMIS multipoint observations of ion distributions in the magnetotail plasma sheet at various locations upstream of earthward-propagating dipolarization fronts. Observations made near the neutral sheet show a characteristic signature, enhancements of earthward-moving ion fluxes about 30 s before dipolarization front arrival. In previous studies, this signature has been well explained as front-reflected ions confined to a region characterized by their gyroradii over the background B z field that coexist with the ambient population. However, at higher latitudes near the plasma sheet boundary layer, observations suggest that earthward-moving ions appear a few minutes earlier than at the central plasma sheet, indicating that the ions reflected at the same dipolarization front could access farther toward the Earth at higher latitudes. These observed phenomena, as also stated in our companion paper, are associated with transient intensifications of proton auroral brightness, which suggests a direct connection between magnetospheric and ionospheric signatures during geomagnetic disturbed conditions. We carry out numerical simulations and theoretical analysis of ion dynamics to interpret and reproduce these observations, to improve our understanding of interactions between earthward-propagating fronts and the ambient plasma in the near-Earth magnetotail, and to establish the proton auroral effects of dipolarization fronts.
Journal of Geophysical Research 01/2012; 117. · 3.02 Impact Factor
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ABSTRACT: {This paper is a companion to a paper by Liang et al. (2011) which reports a causal connection between the intensification of electrostatic ECH waves and the postmidnight diffuse auroral activity in the absence of whistler mode chorus waves at L = 11.5 on the basis of simultaneous observations from THEMIS spacecraft and NORSTAR optical instruments during 8-9 UT on February 5, 2009. In this paper, we use the THEMIS particle and wave measurements together with the magnetically conjugate auroral observations for this event to illustrate an example where electrostatic electron cyclotron harmonic (ECH) waves are the main contributor to the diffuse auroral precipitation. We use the wave and particle data to perform a comprehensive theoretical and numerical analysis of ECH wave driven resonant scattering rates. We find that the observed ECH wave activity can cause intense pitch angle scattering of plasma sheet electrons between 100 eV and 5 keV at a rate of gt10$^-4$ s$^-1$ for equatorial pitch angles $alpha$$_eq$ lt 30deg. The scattering approaches the strong diffusion limit in the realistic ambient magnetic field to produce efficient precipitation loss of lttilde}5 keV electrons on a timescale of a few hours or less. Using the electron differential energy flux inside the loss cone estimated based upon the energy-dependent efficiency of ECH wave scattering for an 8-s interval with high resolution wave data available, the auroral electron transport model developed by Lummerzheim (1987) produced an intensity of tilde2.3 kR for the green-line diffuse aurora. Separately, Maxwellian fitting to the electron differential flux spectrum produced a green-line auroral intensity of tilde2.6 kR. This is in good agreement with the tilde2.4 kR green-line auroral intensity observed simultaneously at the magnetic foot point (as inferred using the event-adaptive model of Kubyshkina et al. (2009, 2011)) of the location where the in situ observations were obtained. Our results support the scenario that enhanced ECH emissions in the central plasma sheet (CPS) can be an important or even dominant driver of diffuse auroral precipitation in the outer magnetosphere. This paper is an important compliment to recent work that has shown lower band and upper band chorus to be mainly responsible for the occurrences of diffuse aurora in the inner magnetosphere.
Journal of Geophysical Research (Space Physics). 01/2012; 117:1218.
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ABSTRACT: We investigate the global response of the geospace plasma environment to an interplanetary (IP) shock at ∼02:24 UT on 28 May 2008 from multiple THEMIS space-craft observations in the magnetosheath (THEMIS B and C), the mid-afternoon magnetosphere (THEMIS A), and the dusk magnetosphere (THEMIS D and E). The interaction of the transmitted IP shock with the magnetosphere has global effects. Consequently, it can affect geospace plasma signif-icantly. After interacting with the bow shock, the IP shock transmitted a fast shock and a discontinuity which propa-gated through the magnetosheath toward the Earth at speeds of 301 km s −1 and 137 km s −1 , respectively. THEMIS A ob-servations indicate that the IP shock changed the proper-ties of a plasmaspheric plume significantly. The plasmas-pheric plume density increased rapidly from 10 to 100 cm −3 in 4 min and the ion distribution changed from an isotropic to a strongly anisotropic distribution. Electromagnetic ion cyclotron (EMIC) waves observed by THEMIS A are most likely excited by the anisotropic ion distributions caused by the IP shock impact. THEMIS A, but not D or E, observed a plasmaspheric plume in the dayside magnetosphere. Multi-ple spacecraft observations indicate that the dawn-side edge of the plasmaspheric plume was located between THEMIS A and D (or E).
Ann. Geophys. 01/2012; 30:379-387.
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M Øieroset,
T D Phan,
J P Eastwood,
M Fujimoto,
W Daughton,
M A Shay, V Angelopoulos,
F S Mozer,
J P McFadden,
D E Larson,
K-H Glassmeier
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ABSTRACT: We report the direct detection by three THEMIS spacecraft of a magnetic flux rope flanked by two active X lines producing colliding plasma jets near the center of the flux rope. The observed density depletion and open magnetic field topology inside the flux rope reveal important three-dimensional effects. There was also evidence for nonthermal electron energization within the flux rope core where the fluxes of 1-4 keV superthermal electrons were higher than those in the converging reconnection jets. The observed ion and electron energizations differ from current theoretical predictions.
Physical Review Letters 10/2011; 107(16):165007. · 7.37 Impact Factor
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ABSTRACT: Cumulative magnetic flux transport earthward/tailward of the reconnection site in the plasma sheet or equatorward toward the neutral sheet (Φ) has been shown to be one of the most useful quantities for remotely sensing reconnection onset in the magnetotail. We examine the behavior of Φ during substorms near the onset meridian using superposed epoch analysis of Time History of Events and Macroscale Interactions during Substorms (THEMIS) probe observations at different downtail distances. Observational data come from the THEMIS Substorm Database, assembled under the auspices of the Geospace Environment Modeling (GEM) program ( http://www.igpp.ucla.edu/themis/events/). We find that Φ starts to increase a few minutes prior to ground midlatitude Pi2 onset. Although our study cannot monitor regions beyond 30 RE, the apogee of the most distant probe (P1), enhanced transport tends to begin at 20–30 RE and moves progressively inward just prior to ground Pi2 onset. Our results are consistent with recent THEMIS case studies showing that reconnection initiates the substorm expansion phase process.
Journal of Geophysical Research 03/2011; 116(A00I29). · 3.02 Impact Factor
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ABSTRACT: 1] We study current carriers observed within thin current sheets ahead of and during the passage of earthward moving dipolarization fronts in the near‐Earth plasma sheet using Time History of Events and Macroscale Interactions During Substorms (THEMIS) multipoint measurements. The fronts are embedded within flow bursts at the initial stage of bursty bulk flow events. Simultaneous north‐south and radial separations between probes P3, P4, and P5 and the planar current sheet approximation enable estimation of cross‐tail current density in the current sheet ahead of and within the fronts, respectively. The cross‐tail current density increase ahead of the fronts, a substorm growth phase signature, is predominantly due to the ion diamagnetic current; at times, however, the electron pressure gradient may contribute up to 60% of the total current density. Note that in this paper we refer to the horizontal (vertical) current sheet as the cross‐tail current sheet (current sheet associated with dipolarization fronts). At the dipolarization fronts, the horizontal cross‐tail current sheet (with a current density of several nA/m 2) relaxes, and a vertical current sheet (with a current density of several tens of nA/m 2), consistent with the thin interface of the front, appears. Thus, the cross‐tail current at longitudes adjacent to the flow burst feeds into the dipolarization front's current sheet and may be extended to higher latitudes. The vertical current density also decreases after passage of the front. The pressure gradient of 1–10 keV electrons is a dominant contributor to the current in the dipolarization fronts. In the event studied, probes P1 and P2, which were several Earth radii downtail, reveal a tailward expansion of the current reduction process at a propagation velocity ∼50 km/s, even as the bulk flow carrying the magnetic flux remains earthward. This study shows how dipolarization fronts and their current systems are building blocks of the large‐scale substorm current wedge.
Journal of Geophysical Research 01/2011; 116. · 3.02 Impact Factor
