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  • 1
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    Speciation and Mobility of Arsenic in Agricultural Lime (2009)
    Wiley
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    Publication Date: 2009-09-01
    Print ISSN: 0047-2425
    Electronic ISSN: 1537-2537
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 2
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    Empirical modeling of 3D Force-balanced Plasma and Magnetic Field Structures during Substorm Growth Phase (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: Accurate evaluation of the physical processes during the substorm growth phase, including formation of field-aligned currents (FACs), isotropization by current sheet scattering, instabilities, and ionosphere-magnetosphere connection relies on knowing the realistic 3 dimensional (3D) magnetic field configuration, which cannot be reliably provided by current available empirical models. We have established a 3D substorm growth phase magnetic field model, which is uniquely constructed from empirical plasma sheet pressures under the constraint of force balance. We investigated the evolution of model pressure and magnetic field responding to increasing energy loading, and their configurations under different solar wind dynamic pressure (P SW ) and sunspot number. Our model reproduces the typical growth phase evolution signatures: plasma pressure increases, magnetic field lines become more stretched, current sheet becomes thinner, and the Region-2 FACs are enhanced. The model magnetic fields agree quantitatively well with observed fields. The magnetic field is substantially more stretched under higher P SW while the dependence on sunspot number is non-linear and less substantial. By applying our modeling to a substorm event, we found that (1) the equatorward movement of proton aurora during the growth phase is mainly due to continuous stretching of magnetic field lines, (2) the ballooning instability is more favorable during late growth phase around midnight tail where there is a localized plasma beta peak, and (3) the equatorial mapping of the breakup auroral arc is at X ~ –14 R E near midnight, coinciding with the location of the maximum growth rate for the ballooning instability.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    First Satellite Imaging of Auroral Pulsations by the Fast Auroral Imager on e-POP (2015)
    Wiley
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    Publication Date: 2015-08-14
    Description: We report the first satellite imaging of auroral pulsations by the Fast Auroral Imager (FAI) onboard the Enhanced Polar Outflow Probe (e-POP) satellite. The near-infrared camera of FAI is capable of providing up to two auroral images per second, ideal for investigation of pulsating auroras. The auroral pulsations were observed within the auroral bulge formed during a substorm interval on 2014 February 19. This first satellite view of these pulsations from FAI reveals that (1) several pulsating auroral channels (PACs) occur within the auroral bulge, (2) periods of the intensity pulsations span over one decade within the auroral bulge, and (3) there is no apparent trend of longer pulsation periods associated with higher latitudes for these PACs. Although PACs resemble in some respect stable pulsating auroras reported previously but they have several important differences in characteristics.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Temporal evolutions of the solar wind conditions at 1 AU prior to the near-Earth X-lines in the tail: Superposed epoch analysis (2016)
    Wiley
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    Publication Date: 2016-07-20
    Description: Utilizing conjunction observations of the Geotail and ACE satellites from 1998 to 2005, we investigated the temporal evolutions of the solar wind conditions prior to the formation of X-lines in the near-Earth magnetotail. We first show the statistical properties of Bz, By, density, and velocity of the solar wind related to the 374 tail X-line events. A superposed epoch analysis is performed to study the temporal evolutions of the solar wind conditions 5 hours prior to the tail X-lines. The solar wind conditions for tail X-lines during southward IMF (SW-IMF) and northward IMF (NW-IMF) are analyzed. The main results are as follows: 1) For events classified as SW-IMF, near-Earth X-line observations in the magnetosphere are preceded by ~2 hour intervals of southward IMF; 2) For events classified a NW-IMF, the northward IMF orientation preceding near-Earth X-line observations lasts ~ 40 minutes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    Empirical modeling of plasma-sheet pressure and three-dimensional force-balanced magnetospheric magnetic field structure: 1. Observation (2013)
    Wiley
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    Publication Date: 2013-09-25
    Description: [1]  A three-dimensional (3D) magnetic field configuration in force balance with a realistic plasma pressure distribution can provide more accurate evaluation of the role of magnetic field on plasma sheet dynamics and M-I coupling. We used Geotail and THEMIS data to establish an empirical model for nightside equatorial isotropic plasma pressure to r  = 30 R E for Kp = 0–5 and for solar wind dynamic pressure (P SW ) = 1.5 and 3 nPa. The model pressure is used in the companion paper for modeling a 3D force-balanced pressure and magnetic field equilibrium. Larger convection during higher Kp drives the plasma sheet further earthward, resulting in larger increase of pressure and pressure gradient at smaller radial distance. On the other hand, magnetosphere compression by increasing P SW enhances pressure and pressure gradient mainly in the tail plasma sheet. While both pressure and radial gradients are enhanced with increasing Kp or P SW , there is no significant azimuthal pressure variation statistically under all Kp and P SW conditions. The empirical pressures well reproduce these statistical profiles with very high correlation coefficients. Additionally, comparisons with pressure gradients computed using two simultaneous measurements from two THEMIS spacecraft show reasonable agreement. Furthermore, our model provides more accurate pressure gradients than previous empirical models. The model magnetic field distributions obtained in the companion paper from requiring force balance with these empirical pressure profiles are also found to be consistent with the magnetic field observations, indicating that our equilibria well represent realistic 3D pressure and magnetic field configurations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Time delay of interplanetary magnetic field penetration into Earth's magnetotail (2015)
    Wiley
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    Publication Date: 2015-04-10
    Description: Many previous studies have demonstrated that the interplanetary magnetic field (IMF) can control the magnetospheric dynamics. Immediate magnetospheric responses to the external IMF has been assumed for a long time. The specific processes by which IMF penetrates into magnetosphere, however, is actually unclear. Solving this issue will help to accurately interpret the time sequence of magnetospheric activities (e.g., substorm, tail plasmoids) exerted by IMF. With two carefully selected cases, we found that the penetration of IMF into magnetotail is actually delayed by 1~1.5 hours, which significantly lags behind the magnetotail response to the solar wind dynamic pressure. The delayed time appears to vary with different auroral convection intensity, which may suggest that IMF penetration in the magnetotail is controlled considerably by the dayside reconnection. Several unfavorable cases demonstrates that the penetration lag time is more clearly identified when storm/substorm activities are not involved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Cross-field current instability for auroral bead formation in breakup arcs (2016)
    Wiley
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    Publication Date: 2016-06-17
    Description: The physical process responsible for the onset of substorm expansion is still unresolved in spite of decades of research on the topic. Detailed properties of the spatially periodic auroral beads on prebreakup auroral arcs that initiate substorm expansion onset are now available. These auroral bead properties impose severe observational constraints on the onset process. In this work, theoretical predictions of the cross-field current instability are evaluated in terms of these constraints. The growth rates and wavelengths associated with auroral beads in several previously published events are reproduced by the cross-field current instability, implying that the instability can indeed account for the characteristics of auroral beads that eventually lead to substorm onset. The present results contradict the conclusion reached by a previous analysis that the shear flow ballooning instability can account for the growth and spatial scales of auroral beads better than the cross-field current instability.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Effects of Modeled Ionospheric Conductance and Electron Loss on Self-Consistent Ring Current Simulations during the 5–7 April 2010 Storm (2015)
    Wiley
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    Publication Date: 2015-05-25
    Description: We investigate the effects of different ionospheric conductance and electron loss models on ring current dynamics during the large magnetic storm of 5–7 April 2010 using the magnetically and electrically self-consistent Rice Convection Model – Equilibrium (RCM-E). The time-varying RCM-E proton distribution boundary conditions are specified using a combination of TWINS 1 and 2 ion temperature maps and in-situ THEMIS and GOES spectral measurements in the plasma sheet. With strong electron pitch-angle diffusion, the simulated equatorial ring current electron pressure is weak with (1) uniform conductance or (2) conductance based on parameters from the International Reference Ionosphere 2007 and the feedback of simulated precipitating electrons. With the Chen and Schulz electron loss model that includes strong diffusion in the plasma sheet and weak diffusion in the plasmasphere, the stormtime equatorial RCM-E electron pressure is enhanced in the inner magnetosphere from midnight through dawn to the dayside. The enhancement extends to lower geocentric distance with uniform conductance than with the more realistic ionospheric conductance model due to electric field shielding effects. Electron losses affect not only the simulated electron pressures, but through magnetospheric-ionospheric coupling, the redistributed electric and magnetic fields affect the ring current proton transport. The simulations reproduced features observed by in-situ magnetic field and proton flux data, and TWINS global ENA observations. The simulated stormtime ring current energization can vary significantly depending on the ionospheric conductance and electron loss model used. Thus, it is important to incorporate realistic descriptions of ionospheric conductance and electron losses in inner magnetospheric models.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    A 2D empirical plasma sheet pressure model for substorm growth phase using the Support Vector Regression Machine (2015)
    Wiley
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    Publication Date: 2015-02-19
    Description: The plasma sheet pressure and its spatial structure during the substorm growth phase are crucial to understanding the development and initiation of substorms. In this paper, we first statistically analyzed the growth phase pressures using Geotail and THEMIS data, and identified that solar wind dynamic pressure (P SW ), energy loading, and sunspot number as the three primary factors controlling the growth phase pressure change. We then constructed a 2D equatorial empirical pressure model and an error model within r ≤ 20 R E using the Support Vector Regression Machine (SVRM) with the three factors as input. The model predicts the plasma sheet pressure accurately with median errors of 5%, and predicted pressure gradients agree reasonably well with observed gradients obtained from two-probe measurements. The model shows that pressure increases linearly as P SW increases, and the P SW effect is stronger under lower energy loading. However, the pressure responses to energy loading and sunspot number are nonlinear. The pressure increases first with increasing loading or sunspot number, then remains relatively constant after reaching a peak value at ~8000 kV∙min loading or sunspot number of ~80. The loading effect is stronger when P SW is lower and the pressure variations stronger near midnight than away from midnight. The sunspot number effect is clearer at smaller r. The pressure model can also be applied to understand the pressure changes observed during a substorm event by providing evaluations of the effects of energy loading and P SW , as well as the temporal and spatial effects along the spacecraft trajectory.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Tailward leap of multiple expansions of the plasma sheet during a moderately intense substorm: THEMIS observations (2012)
    Wiley
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    Publication Date: 2012-07-26
    Description: A moderately intense substorm on 1 March 2008, from 0830 to 1000 UT, observed by THEMIS probes and the Ground Based Observatory (GBO) is examined to investigate the global evolution of substorm phenomena. During this interval, all five THEMIS probes are closely aligned along the tail axis near midnight covering a radial range from ∼9 Re to ∼18 Re. After the substorm onset, plasma sheet expansions take place successively at multiple locations in the magnetotail as measured by different probes. The positions of the plasma sheet expansions have a tailward leap progression with an average velocity of ∼36 km/s. There are two types of dipolarization detected in this substorm. The first type is the dipolarization front which is associated with the bursty bulk flow (BBF). While the second type, which we call ‘global dipolarization’, is associated with plasma sheet expansions. In the substorm studied, there are four intensifications as shown in the THEMIS AE index. We can detect the effects of localized and short-lived magnetic energy release processes occurring in the magnetotail corresponding to each of the four AE intensifications. Furthermore, the inner four probes can detect the global dipolarization signatures ∼4–15 min earlier than plasma sheet expansions, while the outermost probe (P1) cannot detect this before the plasma sheet expansion. These two phenomena are caused by the same process (magnetic energy release process) but the effects detected by probes locally appear delayed. The observations in this case are not sufficient to distinguish between the two competing substorm models.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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