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Start-to-end global imaging as a sunward propagating, SAPS-associated giant undulation event

Description: We present high-time resolution global imaging of a sunward propagating giant undulation event from start to finish. The event occurred on November 24, 2001 during a very disturbed storm interval. The giant undulations began to develop at around 13UT and persisted for approximately 2 hours. The sunward propagation speed was on the order of 0.6 km/s (relative to SM coordinate system). The undulations had a wavelength of {approx} 750 km, amplitudes of {approx} 890 km and produced ULF pulsations on the ground with a period of {approx} 1108s. We show that the undulations were associated with SAPs flows that were caused by the proton plasma sheet penetrating substantially farther Earthward than the electron plasma sheet on the duskside. The observations appear to be consistent with the development of a shear flow and/or ballooning type of instability at the plasmapause driven by intense SAPS-associated shear flows.
Date: January 1, 2009
Creator: Henderson, Michael G; Donovan, Eric F; Foster, John C; Mann, Ian R; Immel, Thomas J; Mende, Stephen B et al.
Partner: UNT Libraries Government Documents Department

Plasma in Saturn's nightside magnetosphere and the implications for global circulation

Description: We present a bulk ion flow map from the nightside equatorial region of Saturn's magnetosphere derived from the Cassini CAPS ion mass spectrometer data. The map clearly demonstrates the dominance of corotation flow over radial flow and suggests that the flux tubes sampled are still closed and attached to the planet up to distances of 50 R{sub s}. The plasma characteristics in the near-midnight region are described and indicate a transition between the region of the magnetosphere containing plasma on closed drift paths and that containing flux tubes which may not complete a full rotation around the planet. Data from the electron spectrometer reveal two plasma states of high and low density. These are attributed either to the sampling of mass-loaded and depleted flux tubes, respectively, or to the latitudinal structure of the plasma sheet Depleted, returning flux tubes are not, in general, directly observed in the ions, although the electron observations suggest that such a process must take place in order to produce the low density population. Flux tube content is conserved below a limIt defined by the mass-loading and magnetic field strength and indicates that the flux tubes sampled may survive their passage through the tail. The conditions for mass release are evaluated using measured densities, angular velocities and magnetic field strength, The results suggest that for the relatively dense ion populations detectable by IMS, the condition for flux-tube breakage has not yet been exceeded, However, the low-density regimes observed in the electron data suggest that loaded flux tubes at greater distances do exceed the threshold for mass loss and subsequently return to the inner magnetosphere significantly depleted of plasma.
Date: January 1, 2009
Creator: Mcandrews, Hazel J; Wilson, R J; Henderson, M G; Tokar, R L; Jackman, C M; Khurana, K K et al.
Partner: UNT Libraries Government Documents Department

Hybrid modeling of the formation and structure of thin current sheets in the magnetotail

Description: Hybrid simulations are used to investigate the formation of a thin current sheet inside the plasma sheet of a magnetotail-like configuration. The initial equilibrium is subjected to a driving electric field qualitatively similar to what would be expected from solar wind driving. As a result, we find the formation of a raw current sheet, with a thickness of approximately the ion inertial length. The current density inside the current sheet region is supplied largely by the electrons. Ion acceleration in the cross-tail direction is absent due since the driving electric field fails to penetrate into the equatorial region.
Date: July 1, 1996
Creator: Hesse, M.; Winske, D. & Birn, J.
Partner: UNT Libraries Government Documents Department

New perspectives on substorm injections

Description: There has been significant progress in understanding substorm injections since the Third International Conference on Substorms in 1996. Progress has come from a combination of new theories, quantitative modeling, and observations--particularly multi-satellite observations. There is now mounting evidence that fast convective flows are the mechanism that directly couples substorm processes in the mid tail, where reconnection occurs, with substorm processes the inner magnetosphere where Pi2 pulsations, auroral breakups, and substorm injections occur. This paper presents evidence that those flows combined with an earthward-propagating compressional wave are responsible for substorm injections and discusses how that model can account for various substorm injection signatures.
Date: December 1, 1998
Creator: Reeves, G.D.
Partner: UNT Libraries Government Documents Department

Alfven-wave particle interaction in finite-dimensional self-consistent field model

Description: A low-dimensional Hamiltonian model is derived for the acceleration of ions in finite amplitude Alfven waves in a finite pressure plasma sheet. The reduced low-dimensional wave-particle Hamiltonian is useful for describing the reaction of the accelerated ions on the wave amplitudes and phases through the self-consistent fields within the envelope approximation. As an example, the authors show for a single Alfven wave in the central plasma sheet of the Earth`s geotail, modeled by the linear pinch geometry called the Harris sheet, the time variation of the wave amplitude during the acceleration of fast protons.
Date: October 9, 1998
Creator: Padhye, N. & Horton, W.
Partner: UNT Libraries Government Documents Department

New insights on geomagnetic storms from observations and modeling

Description: Understanding the response at Earth of the Sun's varying energy output and forecasting geomagnetic activity is of central interest to space science, since intense geomagnetic storms may cause severe damages on technological systems and affect communications. Episodes of southward (Bz<O) interplanetary magnetic field (IMF) which lead to disturbed geomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We show examples of ring current simulations during two geomagnetic storms representative of each interplanetary condition with our kinetic ring current atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. We find that periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. During the HSS-driven storm the convection potential is highly variable and causes small sporadic injections into the ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ring current injection penetrating to lower L shells and stronger ring current buildup.
Date: January 1, 2009
Creator: Jordanova, Vania K
Partner: UNT Libraries Government Documents Department

Structure and evolution of the current sheet by multi-spacecraft observations

Description: On April 22, 1979, from 0840 to 1018 UT, ISEE 1, ISEE 2 and IMP 8 were all in or near the magnetotail current sheet at 17 Re, 16 Re and 35 Re respectively while ISEE 3 monitored the solar wind 206 Re upstream of the Earth. A global perspective of the four spacecraft observations and of the ground magnetic records is presented in this paper. The hyperbolic tangent current sheet model of Harris has been used to calculate the current sheet thickness and to analyze the plasma distribution in the vertical direction. It is found that during this event the current sheet thickness varied from 2.5 Re to 1.5 Re for northward IMF but thinned abruptly to 0.5 Re when the IMF turned southward.
Date: December 31, 1997
Creator: Zhou, X.Y.; Russell, C.T. & Gosling, J.
Partner: UNT Libraries Government Documents Department

Poleward leaping auroras, the substorm expansive and recovery phases and the recovery of the plasma sheet

Description: The auroral motions and geomagnetic changes the characterize the substorm's expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.
Date: January 1, 1992
Creator: Hones, E.W.
Partner: UNT Libraries Government Documents Department

Association of an auroral surge with plasma sheet recovery and the retreat of the substorm neutral line

Description: One of the periods being studied in the PROMIS CDAW (CDAW-9) workshops is the interval 0000-1200 UT on May 3, 1986, designated Event 9C.'' A well-defined substorm, starting at 0919 UT, was imaged by both DE 1 over the southern hemisphere and Viking over the northern hemisphere. The images from Viking, at 80-second time resolution, showed a surge-like feature forming at about 0952 UT at the poleward edge of the late evening sector of the oval. The feature remained relatively stationary until about 1000 UT when it seemed to start advancing westward. ISEE 1 and 2 were closely conjugate to the surge as mapped from both the DMSP and Viking images. We conclude that the plasma sheet recovery was occasioned by the arrival at ISEE 1,2 of a westward traveling wave of plasma sheet thickening, the wave itself being formed by westward progression of the substorm neutral line's tailward retreat. The westward traveling surge was the auroral manifestation of this nonuniform retreat of the neutral line. We suggest that the upward field aligned current measured by DMSP F7 above the surge head was driven by plasma velocity shear in the plasma sheet at the duskward kink'' in the retreating neutral line. By analogy with this observation we propose that the westward traveling surges and the current wedge field aligned currents that characterize the expanding auroral bulge during substorm expansive phase are manifestations of (and are driven by) velocity shear in the plasma sheet near the ends of the extending substorm neutral line.
Date: January 1, 1990
Creator: Hones, E.W. (Mission Research Corp., Los Alamos, NM (USA)); Elphinstone, R.; Murphree, J.S. (Calgary Univ., AB (Canada). Dept. of Physics); Galvin, A.B. (Maryland Univ., College Park, MD (USA). Dept. of Space Physics); Heinemann, N.C. (Boston Coll., Chestnut Hill, MA (USA). Dept. of Physics); Parks, G.K. (Washington Univ., Seattle, WA (USA)) et al.
Partner: UNT Libraries Government Documents Department

Slow-mode shocks in the earth's magnetosphere

Description: The locations and structure of slow-mode shocks in the earth's magnetosphere are reviewed. To date, such shocks have only been identified along the high latitude portions of the lobe-plasma sheet boundary of the geomagnetic tail. Although their intrinsic thickness is of the order of the upstream ion inertial length, they affect the internal state of a relatively much larger volume of surrounding plasma. In particular, they support a well-developed foreshock very similar to that observed upstream of the earth's bow shock, and a turbulent, strongly convecting downstream flow. They also figure importantly in the energy budget of geomagnetic substorms and produce effects which are closely analogous to much of the phenomenology known from solar observations to be associated with two-ribbon flares. 74 refs., 14 figs.
Date: January 1, 1987
Creator: Feldman, W.C.
Partner: UNT Libraries Government Documents Department

Kinetic Ballooning Instability as a Substorm Onset Mechanism

Description: A new scenario of substorm onset and current disruption and the corresponding physical processes are presented based on the AMPTE/CCE spacecraft observation and a kinetic ballooning instability theory. During the growth phase of substorms the plasma beta is larger than unity (20 greater than or equal to beta greater than or equal to 1). Toward the end of the late growth phase the plasma beta increases from 20 to greater than or equal to 50 in approximately 3 minutes and a low-frequency instability with a wave period of 50 - 75 sec is excited and grows exponentially to a large amplitude at the current disruption onset. At the onset, higher-frequency instabilities are excited so that the plasma and electromagnetic field form a turbulent state. Plasma transport takes place to modify the ambient pressure profile so that the ambient magnetic field recovers from a tail-like geometry to a dipole-like geometry. A kinetic ballooning instability (KBI) theory is proposed to explain the low-frequency instability (frequency and growth rate) and its observed high beta threshold (beta subscript c is greater than or equal to 50). Based on the ideal-MHD theory beta subscript c, superscript MHD approximately equals 1 and the ballooning modes are predicted to be unstable during the growth phase, which is inconsistent with observation that no appreciable magnetic field fluctuation is observed. The enhancement beta subscript c over beta subscript c, superscript MHD is due to the kinetic effects of trapped electrons and finite ion-Larmor radii which provide a large stabilizing effect by producing a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension. As a result, beta subscript c is greatly increased over beta subscript c, superscript MHD by a factor proportional to the ratio of the total electron density ...
Date: October 1, 1999
Creator: C.Z.Cheng
Partner: UNT Libraries Government Documents Department

Electromagnetic ion/ion cyclotron instability

Description: Linear analysis and hybrid simulations are used to investigate the properties of a new electromagnetic ion beam instability. Some applications of the instability in space are also discussed. 7 refs., 1 fig.
Date: January 1, 1991
Creator: Winske, D.; McKean, M.E. (Los Alamos National Lab., NM (USA)); Omidi, N. & Chou, V. (California Univ., San Diego, CA (USA))
Partner: UNT Libraries Government Documents Department

Computer simulations of electromagnetic ion instabilities in the plasma sheet boundary layer

Description: Linear Vlasov dispersion theory and one-dimensional hybrid computer simulations are used to study electromagnetic instabilities driven by hot, anisotropic counterstreaming proton components which model those observed from ISEE in the plasma sheet boundary layer of the near-Earth magnetotail. The proton anisotropies lead to the ion cyclotron anisotropy instability, which saturates at a low level of fluctuating fields and yields only weak proton scattering. Modest increases of the proton/proton relative drift, which might correspond to deeper tail conditions, excite the proton/proton nonresistant instability which attains larger fluctuation levels and more strongly heats the protons. If a relatively dense oxygen ion component is also introduced, the ion/ion right-hand resonant instability is excited; the consequent pitch-angle scattering of the protons resembles that indicated in the ISEE data. 6 refs., 5 figs.
Date: January 1, 1989
Creator: Gary, S.P. & Winske, D.
Partner: UNT Libraries Government Documents Department

Physics of Substorm Growth Phase, Onset, and Dipolarization

Description: A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m{sup 2} as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization.
Date: October 22, 2003
Creator: Cheng, C.Z.
Partner: UNT Libraries Government Documents Department

Three-dimensional computer modeling of dynamic reconnection in the magnetotail

Description: Two- and three-dimensional computer models of the dynamics of the magnetosphere and in particular the magnetotail have shown, that the basic features of the idealized linear or steady state reconnection theory are still found in time dependent and spatially more complicated configurations such as the magnetotail, which basically resembles a plane sheet pinch but in addition has small magnetic field components perpendicular to the sheet, field line flaring and variations along both directions parallel to the current sheet. These basic features are the formation of a magnetic neutral x-line or separator, where two surfaces separating magnetic fluxes of different topology intersect, with the generation of an electric field along the separator and the production of strong plasma flows parallel to the current sheet away from the separator in opposite directions. In addition, the computer models of magnetotail dynamics have produced many large scale features that are directly observed or deduced from observation in relation with magnetospheric substorms. Among those features are: the thinning of the plasma sheet, the formation of a plasmoid, a region of closed magnetic loops detached from Earth, which moves tailward at a speed of several hundreds of km/sec, and the generation of field-aligned currents. In view of the recent discovery of plasmoid signatures in the distant magnetotail at about 200 R/sub E/ from ISEE-3 satellite measurements, we discuss the properties of the plasmoid in the computer simulations, in particular its topology, spatial extent and speed, the current system associated with it and its local appearance at a fixed location in space. Furthermore, we discuss the conversion of the energy flux around the separator, current deviations and the occurrence of field-aligned currents and their generation by shear flows. 10 references, 21 figures, 2 tables.
Date: January 1, 1983
Creator: Birn, J.
Partner: UNT Libraries Government Documents Department

A dc sheet plasma for extraction of H/sup -/ and D/sup -/

Description: We are testing operation and H/sup -/ yield of a sheet plasma source having a narrow primary electron channel (11 cm high, 30 cm long, and <1 cm wide). The design goal was J/sub H/sup -// = 30 mA/cm/sup 2/ at V/sub arc/ = 100V, I/sub arc/ = 200A, B < 200g, and p/sub g/ = 5mT. Conditions outside the sheet are favorable for H/sup -/ production; at p/sub g/ = 10mT (cold fill - 8 sccm), V/sub arc/ = 75V, I/sub arc/ = 125A, and B = 200 G, 1 cm from the sheet edge, J/sup +/ = 380 mA/cm/sup 2/, T/sub e/ = 1.4 eV, and n/sub e/ = 5 . 10/sup 12//cm/sup 3/, determined from Langmuir probe measurements. The movable negative ion extractor has a circular source aperture of area 1 cm/sup 2/. J/sub H/sup -// is measured calorimetrically as well as electrically. Agreement of these two signals confirms the effectiveness of the carbon electron dump. Initial extraction at the above conditions produced J/sub H/sup -// = 7 mA/cm/sup 2/ at 2 cm from the sheet edge. This current density is far below the design goals. We conclude that the sheet geometry is not primarily responsible for the high yield of J/sub H/sup -//. 2 refs., 5 figs., 1 tab.
Date: October 1, 1987
Creator: Lietzke, A.F. & Guethlein, G.
Partner: UNT Libraries Government Documents Department

Bidirectional electron heat flux events in space

Description: In this paper we discuss a number of space plasma phenomena which have been illuminated by a powerful diagnostic tool provided by tracing heat flux carried by the solar wind. Measurements of this flow of heat energy from the sun and other hot plasma regions have been employed to increase our understanding of the solar wind interaction with solar system objects. Similarly, anomalies in the heat flux have helped to explain unusual plasma entities which are sometimes found in the interplanetary solar wind. The heat flux is principally carried by the solar wind electrons, since they are much more mobile than the ions. The electrons conduct heat outward from the hot solar corona and in a sense they constitute test particles that trace out the various plasma structures found in the solar wind and in the vicinities of bodies immersed in the interplanetary plasma flow. In the following sections we begin by discussing the electron heat flux which flows outward from the solar corona. This flux is ordinarily found flowing in one direction, i.e., it is unidirectional. Sometimes it is observed counterstreaming, i.e., it is bidirectional. In later sections we discuss how detection of bidirectional heat fluxes has contributed to a more complete understanding of the Earth's bow shock, the bow wave at Comet Giacobini-Zinner, interplanetary plasma structures injected into the solar wind by solar activity processes, and finally polar rain electrons that are found precipitating over the Earth's poles but are believed to originate in the hot solar corona. 37 refs., 16 figs.
Date: January 1, 1986
Creator: Bame, S.J. & Gosling, J.T.
Partner: UNT Libraries Government Documents Department

MHD Ballooning Instability in the Plasma Sheet

Description: Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.
Date: October 20, 2003
Creator: Cheng, C.Z. & Zaharia, S.
Partner: UNT Libraries Government Documents Department

Plasma sheet behavior during substorms

Description: Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process.
Date: January 1, 1983
Creator: Hones, E.W. Jr.
Partner: UNT Libraries Government Documents Department