Science.gov

Sample records for magnetospheric substorms occurring

  1. Observations of magnetospheric substorms occurring with no apparent solar wind/IMF trigger

    SciTech Connect

    Henderson, M.G.; Reeves, G.D.; Belian, R.D.; Murphree, J.S.

    1996-03-01

    An outstanding topic in magnetospheric physics is whether substorms are always externally triggered by disturbances in either the interplanetary magnetic field or solar wind, or whether they can also occur solely as the result of an internal magnetospheric instability. Over the past decade, arguments have been made on both sides of this issue. Horwitz and McPherron have shown examples of substorm onsets which they claimed were not externally triggered. However, as pointed out by Lyons, there are several problems associated with these studies that make their results somewhat inconclusive. In particular, in the McPherron et al. study, fluctuations in the B{sub y} component were not considered as possible triggers. Furthermore, Lyons suggests that the sharp decreases in the AL index during intervals of steady IMF/solar wind, are not substorms at all but rather that they are just enhancements of the convection driven DP2 current system that are often observed to occur during steady magnetospheric convection events. In the present study, we utilize a much more comprehensive dataset (consisting of particle data from the Los Alamos energetic particle detectors at geosynchronous orbit, IMP 8 magnetometer and plasma data, Viking UV auroral imager data, mid-latitude Pi2 pulsation data, ground magnetometer data and ISEE1 magnetic field and energetic particle data) to show as unambiguously as possible that typical substorms can indeed occur in the absence of an identifiable trigger in the solar wind/IMF.

  2. Observations of magnetospheric substorms occurring with no apparent solar wind/IMF trigger

    NASA Astrophysics Data System (ADS)

    Henderson, M. G.; Reeves, G. D.; Belian, R. D.; Murphree, J. S.

    1996-05-01

    An outstanding topic in magnetospheric physics is whether substorms are always externally triggered by disturbances in either the interplanetary magnetic field (IMF) or solar wind, or whether they can also occur solely as the result of an internal magnetospheric instability. Over the past decade, arguments have been made on the both sides of this issue. Horwitz [1985] and McPherron et al. [1986] have shown examples of substorm onsets which they claimed were not externally triggered. However, as pointed out by Lyons [1995, 1996], there are several problems associated with these studies that make their results somewhat inconclusive. In particular, in the McPherron et al. study, fluctuations in the By component were not considered as possible triggers. Furthermore, Lyons suggests that the sharp decreases in the AL index during intervals of steady IMF/solar wind are not substorms at all but rather that they are just enhancements of the convection driven DP 2 current system that are often observed to occur during steady magnetospheric convection events. In the present study, we utilize a much more comprehensive data set (consisting of particle data from the Los Alamos energetic particle detectors at geosynchronous orbit, IMP 8 magnetometer and plasma data, Viking UV auroral imager data, midlatitude Pi 2 pulsation data, ground magnetometer data, and ISEE 1 magnetic field and energetic particle data) to show as unambiguously as possible that typical substorms can indeed occur in the absence of an identifiable trigger in the solar wind/IMF.

  3. Onset of magnetospheric substorms.

    NASA Technical Reports Server (NTRS)

    Tsurutani, B.; Bogott, F.

    1972-01-01

    An examination of the onset of magnetospheric substorms is made by using ATS 5 energetic particles, conjugate balloon X rays and electric fields, all-sky camera photographs, and auroral-zone magnetograms. It is shown that plasma injection to ATS distances, conjugate 1- to 10-keV auroral particle precipitation, energetic electron precipitation, and enhancements of westward magnetospheric electric-field component all occur with the star of slowly developing negative magnetic bays. No trapped or precipitating energetic-particle features are seen at ATS 5 when later sharp negative magnetic-bay onsets occur at Churchill or Great Whale River.

  4. Magnetospheric Substorm Electrodynamics

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.

    1998-01-01

    It was proposed that the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a greater than or equal to 30 min growth phase due to an enhancement in this electric field. The reduction in the electric field is assumed to propagate anti-sunward within the magnetosphere. Triggering by a reduction in the electric field is suggested by the observation that substorms are often triggered by northward turning of the interplanetary magnetic field (IMF). However, under the theory presented here, substorms may be triggered by anything that causes an electric field reduction such as a reduction in the magnitude of the y-component of the IMF. A reduction in the large-scale electric field disrupts both the inward motion and energization of plasma sheet particles that occurs during the growth phase. It is suggested here that this can lead to formation of the expansion-phase current wedge and active aurora. The current wedge results from the magnetic drift of ions, which has a speed proportional to particle energy, and a large azimuthal gradient in mean particle energy that is expected to develop in the vicinity of magnetic midnight during the growth phase. Current wedge formation will most likely be initiated near the radial distance (approx. 6- 10 R(sub E)) of the peak in the growth-phase plasma pressure distribution, and then propagate tailward from that region. Order-of-magnitude calculations show that the above proposal can account for the rapid development of the expansion phase relative to the growth phase, the magnitude of the reduction in the cross-tail current within the current wedge, the speeds of tailward and westward expansion of the current reduction region, the speeds of poleward and westward motion of active aurora in the ionosphere, and the magnitude of wedge field-aligned currents that connect the ionospheric region of active auroral to the divergent cross

  5. A mechanism for magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Erickson, G. M.; Heinemann, M.

    1994-01-01

    Energy-principle analysis performed on two-dimensional, self-consistent solutions for magnetospheric convection indicates that the magnetosphere is unstable to isobaric (yet still frozen-in) fluctuations of plasma-sheet flux tubes. Normally, pdV work associated with compression maintains stability of the inward/outward oscillating normal mode. However, if Earth's ionosphere can provide sufficient mass flux, isobaric expansion of flux tubes can occur. The growth of a field-aligned potential drop in the near-Earth, midnight portion of the plasma sheet, associated with upward field-aligned currents responsible for the Harang discontinuity, redistributes plasma along field lines in a manner that destabilizes the normal mode. The growth of this unstable mode results in an out-of-equilibrium situation near the inner edge. When this occurs over a downtail extent comparable to the half-thickness of the plasma sheet, collapse ensues and forces thinning of the plasma sheet whereby conditions favorable to reconnection occur. This scenario for substorm onset is consistent with observed upward fluxes of ions, parallel potential drops, and observations of substorm onset. These observations include near Earth onset, pseudobreakups, the substorm current wedge, and local variations of plasma-sheet thickness.

  6. Substorms and magnetospheric energy transfer processes

    NASA Technical Reports Server (NTRS)

    Swift, D. W.

    1980-01-01

    Evidence is presented which suggests a direct process for the conversion of solar wind energy into the various manifestations of the auroral substorm. This is in contrast to the widely accepted premise that solar wind energy is accumulated in the magnetosphere and then released by an instability process occurring in the magnetotail. It is shown that much of the plasma sheet behavior associated with auroral substorms can be interpreted in terms of single-particle models and simple variations of the cross-tail electric field intensity which does not invoke release of stored magnetic energy. It is also pointed out that the major entry of substorm energy into the magnetosphere occurs through the boundaries of the lobes of the magnetotail. This paper is not intended to be a complete theory of the magnetospheric substorm - rather the intention of this paper is to point out directions of research deserving of more attention.

  7. Are steady magnetospheric convection events prolonged substorms?

    NASA Astrophysics Data System (ADS)

    Walach, M.-T.; Milan, S. E.

    2015-03-01

    Magnetospheric modes, including substorms, sawtooth events, and steady magnetospheric convection events, have in the past been described as different responses of the magnetosphere to coupling with the solar wind. Using previously determined event lists for sawtooth events, steady magnetospheric convection events, and substorms, we produce a statistical study of these event types to examine their similarities and behavior in terms of solar wind parameters, auroral brightness, open magnetospheric flux, and geomagnetic indices. A superposed epoch analysis shows that individual sawteeth show the same signatures as substorms but occur during more extreme cases of solar wind driving as well as geomagnetic activity. We also explore the limitations of current methods of identifying steady magnetospheric convection events and explain why some of those events are flagged inappropriately. We show that 58% of the steady magnetospheric convection events considered, as identified by criteria defined in previous studies are part of a prolonged version of substorms due to continued dayside driving during expansion phase. The remaining 42% are episodes of enhanced magnetospheric convection, occurring after extended periods of dayside driving.

  8. Postmidnight chorus - A substorm phenomenon. [outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Tsurutani, B. T.; Smith, E. J.

    1974-01-01

    The ELF emissions were detected in the midnight sector of the magnetosphere in conjunction with magnetospheric substorms. The emissions were observed at local midnight and early morning hours and are accordingly called 'post-midnight chorus.' The characteristics of these emissions such as their frequency time structure, emission frequency with respect to the local equatorial electron gyrofrequency, intensity-time variation, and the average intensity were investigated. The occurrence of the chorus in the nightside magnetosphere was investigated as a function of local time, L shell, magnetic latitude, and substorm activity, and the results of this analysis are presented. Specific features of postmidnight chorus are discussed in the context of possible wave-particle interactions occurring during magnetospheric substorms.

  9. Organization of the magnetosphere during substorms

    NASA Astrophysics Data System (ADS)

    Živković, T.; Rypdal, K.

    2012-05-01

    The change in degree of organization of the magnetosphere during substorms is investigated by analyzing various geomagnetic indices, as well as interplanetary magnetic field z-component and solar wind velocity x-component. We conclude that the magnetosphere self-organizes globally during substorms, but neither the magnetosphere nor the solar wind become more predictable in the course of a substorm. This conclusion is based on analysis of substorms in the period from 2000 to 2002. A minimal dynamic-stochastic model of the driven magnetosphere that reproduces many statistical features of substorm indices is discussed.

  10. Magnetospheric Substorms and Tail Dynamics

    NASA Technical Reports Server (NTRS)

    Hughes, W. Jeffrey

    1998-01-01

    This grant funded several studies of magnetospheric substorms and their effect on the dynamics of the earth's geomagnetic tail. We completed an extensive study of plasmoids, plasma/magnetic field structures that travel rapidly down the tail, using data from the ISEE 3 and IMP 8 spacecraft. This study formed the PhD thesis of Mark Moldwin. We found that magnetically plasmoids are better described as flux-ropes (twisted magnetic flux tubes) rather than plasma bubbles, as had been generally regarded up to that point (Moldwin and Hughes, 1990; 1991). We published several examples of plasmoids observed first in the near tail by IMP 8 and later in the distant tail by ISEE 3, confirming their velocities down tail. We showed how the passage of plasmoids distorts the plasma sheet. We completed the first extensive statistical survey of plasmoids that showed how plasmoids evolve as they move down tail from their formation around 30 RE to ISEE 3 apogee at 240 RE. We established a one-to-one correspondence between the observation of plasmoids in the distant tail and substorm onsets at earth or in the near tail. And we showed that there is a class of plasmoid-like structures that move slowly earthward, especially following weak substorms during northward IMF. Collectively this work constituted the most extensive study of plasmoids prior to the work that has now been done with the GEOTAIL spacecraft. Following our work on plasmoids, we turned our attention to signatures of substorm onset observed in the inner magnetosphere near geosynchronous orbit, especially signatures observed by the CRRES satellite. Using data from the magnetometer, electric field probe, plasma wave instrument, and low energy plasma instrument on CRRES we were able to better document substorm onsets in the inner magnetosphere than had been possible previously. Detailed calculation of the Poynting flux showed energy exchange between the magnetosphere and ionosphere, and a short burst of tailward convective

  11. Satellite studies of magnetospheric substorms on August 15, 1968. I - State of the magnetosphere.

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.

    1973-01-01

    The state of the magnetosphere on August 15, 1968, as defined by magnetic indices and ground magnetograms, is described. Onset times of various phases of two magnetospheric substorms are determined. These substorms occurred while the OGO 5 satellite was inbound on the midnight meridian through the cusp region of the geomagnetic tail. It is concluded that at least two worldwide substorm expansions were preceded by growth phases.

  12. Magnetospheric substorms - A newly emerging model

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1981-01-01

    A surge of progress in magnetospheric substorm studies is expected by the following three recent developments: (1) the finding of the solar wind-magnetosphere energy coupling function epsilon, (2) the determination of the Pedersen current distribution over the entire polar region, and (3) a new understanding of the auroral potential structure. In this paper, the significance of the three developments and the newly emerging model of magnetospheric substorms is described.

  13. Magnetospheric substorms - A newly emerging model

    NASA Astrophysics Data System (ADS)

    Akasofu, S.-I.

    1981-10-01

    A surge of progress in magnetospheric substorm studies is expected by the following three recent developments: (1) the finding of the solar wind-magnetosphere energy coupling function epsilon, (2) the determination of the Pedersen current distribution over the entire polar region, and (3) a new understanding of the auroral potential structure. In this paper, the significance of the three developments and the newly emerging model of magnetospheric substorms is described.

  14. Substorms - Future of magnetospheric substorm-storm research

    SciTech Connect

    Akasofu, S.I. )

    1989-04-01

    Seven approaches and/or areas of magnetospheric substorm and storm science which should be emphasized in future research are briefly discussed. They are: the combining of groups of researchers who study magnetic storms and substorms in terms of magnetic reconnection with those that do not, the possible use of a magnetosphere-ionosphere coupling model to merge the groups, the development of improved input-output relationships, the complementing of satellite and ground-based observations, the need for global imaging of the magnetosphere, the complementing of observations with computer simulations, and the need to study the causes of changes in the north-south component of the IMF. 36 refs.

  15. A new theory for magnetospheric substorms

    SciTech Connect

    Lyons, L.R.

    1995-10-01

    It is proposed here that the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a {ge} 30-min growth phase due to an enhancement in this electric field. The reduction in the electric field is assumed to propagate antisunward within the magnetosphere. Triggering by a reduction in the electric field is suggested by the observation that substorms are often triggered by northward turnings of the interplanetary magnetic field (IMF). However, under the theory presented here, substorms may be triggered by anything that causes an electric field reduction such as a reduction in the magnitude of the y component of the IMF. A reduction in the large-scale electric field disrupts both the inward motion and energization of plasma sheet particles that occurs during the growth phase. It is suggested here that this can lead to formation of the expansion phase current wedge and active aurora. The current wedge results from the magnetic drift of ions, which has a speed proportional to particle energy, and a large azimuthal gradient in mean particle energy that is expected to develop in the vicinity of magnetic midnight during the growth phase. Current wedge formation will most likely be initiated near the radial distance ({approximately}6-10 R{sub E}) of the peak in the growth phase plasma pressure distribution, and then propagate tailward from that region. Order-of-magnitude calculations show that the above proposal can account for the rapid development of the expansion phase relative to the growth phase, the magnitude of the reduction in the cross-tail current with the current wedge, the speeds of poleward and westward motion of active aurora in the ionosphere, and the magnitude of wedge field-aligned currents that connect the ionospheric region of active auroral to the divergent cross-tail current within the magnetosphere. 77 refs., 9 figs.

  16. Energy flux in the Earth's magnetosphere: Storm substorm relationship

    NASA Astrophysics Data System (ADS)

    Alexeev, Igor I.

    2003-04-01

    Three ways of the energy transfer in the Earth's magnetosphere are studied. The solar wind MHD generator is an unique energy source for all magnetospheric processes. Field-aligned currents directly transport the energy and momentum of the solar wind plasma to the Earth's ionosphere. The magnetospheric lobe and plasma sheet convection generated by the solar wind is another magnetospheric energy source. Plasma sheet particles and cold ionospheric polar wind ions are accelerated by convection electric field. After energetic particle precipitation into the upper atmosphere the solar wind energy is transferred into the ionosphere and atmosphere. This way of the energy transfer can include the tail lobe magnetic field energy storage connected with the increase of the tail current during the southward IMF. After that the magnetospheric substorm occurs. The model calculations of the magnetospheric energy give possibility to determine the ground state of the magnetosphere, and to calculate relative contributions of the tail current, ring current and field-aligned currents to the magnetospheric energy. The magnetospheric substorms and storms manifest that the permanent solar wind energy transfer ways are not enough for the covering of the solar wind energy input into the magnetosphere. Nonlinear explosive processes are necessary for the energy transmission into the ionosphere and atmosphere. For understanding a relation between substorm and storm it is necessary to take into account that they are the concurrent energy transferring ways.

  17. Extremely Intense Magnetospheric Substorms : External Triggering? Preconditioning?

    NASA Astrophysics Data System (ADS)

    Tsurutani, Bruce; Echer, Ezequiel; Hajra, Rajkumar

    2016-07-01

    We study particularly intense substorms using a variety of near-Earth spacecraft data and ground observations. We will relate the solar cycle dependences of events, determine whether the supersubstorms are externally or internally triggered, and their relationship to other factors such as magnetospheric preconditioning. If time permits, we will explore the details of the events and whether they are similar to regular (Akasofu, 1964) substorms or not. These intense substorms are an important feature of space weather since they may be responsible for power outages.

  18. Explosive magnetic reconnection - Puzzle to be solved as the energy supply process for magnetospheric substorms?

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1985-01-01

    It is pointed out that magnetospheric substorms are perhaps the most basic type of disturbances which occur throughout the magnetosphere. There is little doubt that the energy for magnetospheric substorms is delivered from the sun to the magnetosphere by the solar wind, and theoretical and observational studies have been conducted to uncover the processes associated with the energy transfer from the solar wind to the magnetosphere, and the subsequent processes leading to various magnetospheric substorm phenomena. It has been widely accepted that explosive magnetic reconnection supplies the energy for magnetospheric substorm processes. It is indicated that the auroral phenomena must be various manifestations of a large-scale electrical discharge process which is powered by the solar wind-magnetosphere dynamo. Certain problems regarding explosive magnetic reconnection are discussed.

  19. A magnetospheric substorm observed at Sanae, Antarctica

    SciTech Connect

    Gledhill, J.A.; Dore, I.S.; Haggard, R. ); Goertz, C.K. ); Hughes, W.J. ); Scourfield, M.W.J.; Wakerley, P.A.; Walker, A.D.M. ); Smits, D.P.; Sutcliffe, P.R. ); Stoker, P.H. )

    1987-03-01

    A magnetospheric substorm that occurred at Sanae, Antarctica, on July 27, 1979, was observed by a variety of techniques. A synthesis of the observations is presented, and an attempt made to deduce details of the behavior of the magnetosphere-ionosphere system during the event. While there was some evidence of a growth phase, it was inconclusive. At the onset there was a rapid change in the tail field, which assumed a more dipolar form, accompanied by Pi 2 oscillations and the precipitation of 6-keV electrons, with brightening of the auroral arc, auroral-type sporadic E ionization, and riometer absorption. A positive spike was observed in the D magnetic component, instead of the expected negative one. There was no evidence of the usual westward traveling surge at the beginning of the expansion phase during which the precipitation region, auroral arc, and electrojet moved rapidly poleward, though it may have occurred outside the field of view from Sanae. The H{beta} emission increased by a factor of less than 2, whereas the oxygen and nitrogen emissions monitored increased by 3-4. During the recovery phase, phenomena were consistent with a return of the tail field to an elongated form; a very high ratio of 557.7-nm/630-nm emissions, exceeding 10, was observed; and the electrojet lagged noticeably behind the photon emission regions.

  20. Midday auroras and magnetospheric substorms.

    NASA Technical Reports Server (NTRS)

    Akasofu, S. I.

    1972-01-01

    Auroral activity in the midday sector is examined in some detail on the basis of all-sky photographs taken from Pyramida, Spitzbergen. The equatorward motion of the midday auroras observed during substorms and the subsequent poleward shift during the recovery phase are discussed.

  1. Factors influencing the intensity of magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Baker, D. N.

    1993-01-01

    A definition of the substorm is presented, and it is shown that the typical isolated substorm is produced by the superposition of effects of processes directly driven by the solar wind through dayside reconnection and those driven by unloading through nighttime reconnection. The single factor that determines whether a substorm will occur or not is the clock angle of the interplanetary magnetic field (IMF) around the earth-sun line. Only when this field points south of the GSM equatorial plane do the auroral electrojet indices depart from their quiet values. For a given clock angle, the level of activity increases with the IMF strength and solar wind velocity.

  2. A boundary layer model for magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Rostoker, Gordon; Eastman, Tim

    1987-01-01

    An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.

  3. Dynamics of the inner magnetosphere near times of substorm onsets

    NASA Astrophysics Data System (ADS)

    Maynard, N. C.; Burke, W. J.; Basinska, E. M.; Erickson, G. M.; Hughes, W. J.; Singer, H. J.; Yahnin, A. G.; Hardy, D. A.; Mozer, F. S.

    1996-04-01

    The electrodynamics of the inner magnetosphere near times of substorm onsets have been investigated using CRRES measurements of magnetic and electric fields, energetic electron fluxes, in conjunction with ground-based observations. Six events were studied in detail, spanning the 2100 to 0000 MLT sector and L values from 5 to 7. In each case the dawn-dusk electric field was enhanced over typical background electric fields, and significant, low-frequency pulsation activity was observed. The amplitudes of the pulsations were larger than the background electric fields. Dusk-dawn excursions of the cross-tail electric field often correlated with changes in currents and particle energies at CRRES and with ULF wave activity observed on the ground. Variations of the electric field and Poynting vectors with periods in the Pi 2 range are consistent with bouncing Alfvén waves that provide electromagnetic communication between the ionosphere and plasma sheet. Magnetic signatures of field-aligned current filaments directed away from the ionosphere, presumably associated with the substorm current wedge, were observed during three orbits. In all cases, ground signatures of substorm expansion were observed at least 5 min before the injection of electrons at CRRES. Field-aligned fluxes of counter-streaming, low-energy electrons were detected after three of the injections. We develop an empirical scenario for substorm onset. The process grows from ripples at the inner edge of the plasma sheet associated with dusk-dawn excursions of the electric field, prior to the beginning of dipolarization. Energy derived from the braking of the inward plasma convection flows into the ionosphere in the form of Poynting flux. Subsequently reflected Poynting flux plays a crucial role in the magnetosphere-ionosphere coupling. Substorms develop when significant energy (positive feedback?) flows in both directions, with the second cycle stronger than the initial. Pseudobreakups occur when energy flow

  4. Equatorward shift of the cleft during magnetospheric substorms as observed by Isis 1

    NASA Technical Reports Server (NTRS)

    Yasuhara, F.; Akasofu, S.-I.; Winningham, J. D.; Heikkila , W. J.

    1973-01-01

    Isis 1 satellite observations of the cleft position during magnetospheric substorms show that the cleft shifts equatorward as the interplanetary B sub z component turns southward and substorm activity increases and that it shifts back toward higher latitudes as substorm activity subsides and B sub z returns northward. Also, unusually low latitudes for the cleft (less than 70 deg invariant latitude) were found during geomagnetic storms with significant Dst values and large negative B sub z values. Significant shifts occur in the cleft location with no accompanying effect seen in the AE index; however, B sub z is observed to be southward during these periods.

  5. Boundary layer dynamics in the description of magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Rostoker, G.; Frank, L. A.; Huang, C. Y.; Mitchell, D. G.

    1988-01-01

    This paper presents an analysis of eleven magnetospheric substorm events for which good-quality ground-based magnetometer data and ISEE satellite data were both available. It is shown that the magnetotail particle and field observations associated with a substorm expansive phase can be explained through the spatial movement of the boundary layers and central plasma sheet in the magnetotail. The sweeping of these regions past the satellite, even in the absence of temporal variations within the various regions, can lead to a set of plasma flow observations typical of what is observed in the magnetotail during substorm activity.

  6. The physics of plasma injection events. [during magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Kivelson, M. G.; Kaye, S. M.; Southwood, D. J.

    1980-01-01

    In this paper, plasma injection is defined as an increase of particle flux in a detector of finite bandwidth. Injection can result from dynamic processes or from spacecraft penetration of a quasi-static spatial structure produced by a steady magnetospheric convection pattern. ATS-5 particle spectrograms are found to provide examples of plasma injection events of both sorts. Dynamic injection occurs both with and without local magnetic signatures. For events not associated with clear local magnetic signatures, convection theory with a steady or a time-varying uniform electric field can account for the energy dispersion of injected particles with energy less than 50 keV. The paper concludes with a discussion of the way in which the convection boundaries are related to the substorm injection boundary of Mauk and McIlwain. Several alternative expressions for the local time and K(p) dependence of the injection boundary are given.

  7. Phase transition-like behavior of the magnetosphere during substorms

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Sharma, A. S.; Papadopoulos, K.; Vassiliadis, D.; Valdivia, J. A.; Klimas, A. J.; Baker, D. N.

    2000-06-01

    The behavior of substorms as sudden transitions of the magnetosphere is studied using the Bargatze et al. [1985] data set of the solar wind induced electric field vBs and the auroral electrojet index AL. The data set is divided into three subsets representing different levels of activity, and they are studied using the singular spectrum analysis. The points representing the evolution of the magnetosphere in the subspace of the eigenvectors corresponding to the three largest eigenvalues can be approximated by two-dimensional manifolds with a relative deviation of 10-20%. For the first two subsets corresponding to small and medium activity levels the manifolds have a pleated structure typical of the cusp catastrophe. The dynamics of the magnetosphere near these pleated structures resembles the hysteresis phenomenon typical of first-order phase transitions. The reconstructed manifold is similar to the ``temperature-pressure-density'' diagrams of equilibrium phase transitions. The singular spectra of vBs, AL, and combined data have the power law dependence typical of second-order phase transitions and self-organized criticality. The magnetosphere thus exhibits the signatures of both self-organization and self-organized criticality. It is concluded that the magnetospheric substorm is neither a pure catastrophe of the low-dimensional system nor a random set of avalanches of different scales described by the simple sandpile models. The substorms behave like nonequilibrium phase transitions, with features of both first- and second-order phase transitions.

  8. Variations of the polar cap potential measured during magnetospheric substorms

    SciTech Connect

    Weimer, D.R.; Kan, J.R.; Akasofu, S.I. )

    1992-04-01

    Measurements of the polar cap potential drop and size have been obtained during magnetospheric substorms. Using double-prove electric field measurements on the DE 2 satellite, 148 measurements have been obtained at random times preceding, during, and after 64 substorms. The polar cap potentials are graphed as a function of the difference between the time of the polar cap measurement and the time of the expansion onset of the corresponding substorm. The ratios of the auroral electrojet (AE) indices and the potential are also determined. The results show that on the average the polar cap potential starts to increase at 1.5 hours before onset. However, on a case-by-case basis there are substantial variations from the average, as polar cap potentials over 1,200 kV were measured as early as 1 hour before substorm onset and values as low as 40 kV were observed during the expansion phase. The size of the polar cap ranged from 23{degree} to 38{degree} invariant latitude at the time of onset, and had an average value of 31{degree}. The AE/{Phi}{sub PC} ratio is nearly constant before and after substorms, but decreases slightly during the substorm growth phase and increases greatly during the expansion phase. This increase is most likely due to a higher conductivity and westward electric field within the electrojet during expansion, which causes AE to increase without a corresponding change in the polar cap potential.

  9. Magnetospheric substorms in the distant magnetotail observed by Imp 3.

    NASA Technical Reports Server (NTRS)

    Meng, C. I.; Akasofu, S.; Kawasaki, K.; Hones, E. W., Jr.

    1971-01-01

    Study of variations of the magnetic field and plasma sheet in the distant magnetotail (20 to 40 earth radii) during magnetospheric substorms on the basis of the Imp 3 magnetic-field and particle data. Depending on the locations of the satellite with respect to the boundary of the plasma sheet, the variations differ greatly. However, the present results and the results of other workers give a clear indication of an increase of the magnitude of the field outside the plasma sheet and of the simultaneous ?thinning' of the plasma sheet during an early phase of substorms. At about the maximum epoch or during the recovery phase of substorms, the plasma sheet expands and appears to be inflated to at least the presubstorm level. Furthermore, a large excessive flux of the magnetic (approximately equal to Z component) field, as compared with the flux of the original dipole field, appears across the neutral sheet.

  10. Energy Coupling Between the Ionosphere and Inner Magnetosphere Related to Substorm Onset

    NASA Technical Reports Server (NTRS)

    Maynard, Nelson C.

    1999-01-01

    The investigation of substorm effects in the inner magnetosphere with CRRES data looked in detail at over 50 substorms relative to signatures of onset and early expansion phases. The accomplishments of the project are: Determined perpendicular Poynting flux at CRRES in the inner magnetosphere at substorm onset, including primary direction is azimuthal, not radial, indicating a local source, no obvious signal from the magnetotail to trigger onset, strongly supports substorm onset location near the inner edge of the plasma sheet and process is local and a strong function of Magnetosphere-ionosphere (MI) coupling. We also developed near geosynchronous onset (NGO) model for substorm onset and expansion.

  11. Association of Energetic Neutral Atom Bursts and Magnetospheric Substorms

    NASA Technical Reports Server (NTRS)

    Jorgensen, A. M.; Kepko, L.; Henderson, M. G.; Spence, H. E.; Reeves, G. D.; Sigwarth, J. B.; Frank, L. A.

    2000-01-01

    In this paper we present evidence that short-lived bursts of energetic neutral atoms (ENAs) observed with the Comprehensive Energetic Particle and Pitch Angle Distribution/Imaging Proton Spectrometer (CEPPAD/IPS) instrument on the Polar spacecraft are signatures of substorms. The IPS was designed primarily to measure ions in situ, with energies between 17.5 and 1500 keV. However, it has also proven to be a very capable ENA imager in the range 17.5 keV to a couple hundred keV. It was expected that some ENA signatures of the storm time ring current would be observed. Interestingly, IPS also routinely measures weaker, shorter-lived, and more spatially confined bursts of ENAs with duration from a few tens of minutes to a few hours and appearing once or twice a day. One of these bursts was quickly associated with magnetospheric and auroral substorm activity and has been reported in the literature [Henderson et al., 19971. In this paper we characterize ENA bursts observed from Polar and establish statistically their association with classic substorm signatures (global auroral onsets, electron and ion injections, AL drops, and Pi2 onsets). We conclude that -90% of the observed ENA bursts are associated with classic substorms and thus represent a new type of substorm signature.

  12. Pseudobreakup and substorm growth phase in the ionosphere and magnetosphere

    NASA Technical Reports Server (NTRS)

    Koskinen, H. E. J.; Lopez, R. E.; Pellinen, R. J.; Pulkkinen, T. I.; Baker, D. N.; Bosinger, T.

    1993-01-01

    Observations made during the growth phase and the onset of a substorm on August 31, 1986 are presented. About 20 min after the epsilon parameter at the magnetopause had exceeded 10 exp 11 W, magnetic field dipolarization with an increase of energetic particle fluxes was observed by the AMPTE Charge Composition Explorer (CCE) spacecraft at the geocentric distance of 8.7 R(E) close to magnetic midnight. The event exhibited local signatures of a substorm onset at AMPTE CCE and a weak wedgelike current system in the midnight sector ionosphere, but did not lead to a full-scale substorm expansion; neither did it produce large particle injections at GEO. Only after another 20 min of continued growth phase could the entire magnetosphere-ionosphere system allow the onset of a regular substorm expansion. The initial activation is interpreted as a 'pseudobreakup'. We examine the physical conditions in the near-Earth plasma sheet and analyze the development in the ionosphere using ground-based magnetometers and electric field observations from the STARE radar.

  13. Behavior of outer radiation zone and a new model of magnetospheric substorm.

    NASA Technical Reports Server (NTRS)

    Parks, G. K.; Laval, G.; Pellat, R.

    1972-01-01

    This paper presents particle data obtained from synchronous altitudes and attempts to evaluate the origin and nature of particle flux variations observed during substorms. The correlated particle intensities, time variations, and energy spectrums are compared between the equatorial and auroral zones. The correlated particle and field observations during substorms are tied together and a model of magnetospheric substorms is derived. Among the features predicted by the model is the poleward expansion of visual auroras observed at the onset of magnetospheric substorms. The model also explains how substorms are triggered in a few minutes time scale during sudden commencements.

  14. Theoretical magnetograms based on quantitative simulation of a magnetospheric substorm

    SciTech Connect

    Chen, C.; Wolf, R.A.; Harel, M.; Karty, J.L.

    1982-08-01

    Using substorm currents derived from the Rice computer simulation of the substorm event of September 19, 1976, we have computed theoretical magnetograms as a function of universal time for various stations. A theoretical Dst has also been computed. Our computed magnetograms were obtained by integrating the Biot-Savart law over a maze of approximately 2700 wires and bands that carry the ring currents, the Birkeland currents, and the horizontal ionospheric currents. Ground currents and dynamo currents were neglected. Computed contributions to the magnetic field perturbation from eleven different kinds of currents are displayed (e.g., ring currents, northern hemisphere Birkeland currents). First, overall agreement of theory and data is generally satisfactory, especially for stations at high and mid-magnetic latitudes. Second, model results suggest that the ground magnetic field perturbations arise from very complicated combinations of different kinds of currents and that the magnetic field disturbances due to different but related currents often cancel each other, despite the fact that complicated inhomogeneous conductivities in our model prevent rigorous application of Fukushima's theorem. Third, both the theoretical and observed Dst decrease during the expansion phase of the substorm, but data indicate that Dst relaxes back toward its initial value within about an hour after the peak of the substorm. Fourth, the dawn-dusk asymmetry in the horizontal component of magnetic field disturbance at low latitudes in a substorm is essentially due to a net downward Birkeland current at noon, net upward current at midnight, and generally antisunward flowing electrojets; it is not due to a physical partial ring current injected into the duskside of the inner magnetosphere.

  15. The reason for magnetospheric substorms and solar flares

    NASA Technical Reports Server (NTRS)

    Heikkila, W. J.

    1983-01-01

    It has been proposed that magnetospheric substorms and solar flares are a result of the same mechanism. It is suggested that this mechanism is connected with the escape, or attempted escape, of energized plasma from a region of closed magnetic field lines bounded by a magnetic bottle. In the case of the earth, it must be plasma that is able to maintain a discrete auroral arc, and it is proposed that the cross-tail current connected to the arc is filamentary in nature to provide the field-aligned current sheet above the arc.

  16. A modeling of magnetic field variations during magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.; Corrick, G. K.

    1980-01-01

    Magnetic field variations in the noon-midnight plane during the magnetospheric substorm are studied in terms of changes of three current systems: the dynamo-driven current on the magnetopause, the cross-tail current and the field-aligned current-auroral electrojet system. The field-aligned current is assumed to be generated as a result of interruption and subsequent diversion of the cross-tail current to the ionosphere. It is concluded that the available observations are consistent with a large increase of the three currents.

  17. Problems with mapping the auroral oval and magnetospheric substorms

    NASA Astrophysics Data System (ADS)

    Antonova, E. E.; Vorobjev, V. G.; Kirpichev, I. P.; Yagodkina, O. I.; Stepanova, M. V.

    2015-10-01

    Accurate mapping of the auroral oval into the equatorial plane is critical for the analysis of aurora and substorm dynamics. Comparison of ion pressure values measured at low altitudes by Defense Meteorological Satellite Program (DMSP) satellites during their crossings of the auroral oval, with plasma pressure values obtained at the equatorial plane from Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite measurements, indicates that the main part of the auroral oval maps into the equatorial plane at distances between 6 and 12 Earth radii. On the nightside, this region is generally considered to be a part of the plasma sheet. However, our studies suggest that this region could form part of the plasma ring surrounding the Earth. We discuss the possibility of using the results found here to explain the ring-like shape of the auroral oval, the location of the injection boundary inside the magnetosphere near the geostationary orbit, presence of quiet auroral arcs in the auroral oval despite the constantly high level of turbulence observed in the plasma sheet, and some features of the onset of substorm expansion.

  18. Variation of The Magnetotail Electric Fields During Magnetospheric Substorms

    NASA Astrophysics Data System (ADS)

    Pudovkin, M.; Zaitseva, S.; Nakamura, R.

    The behaviour of the midtail electric fields during two magnetospheric substorms on November, 22, 1995, is investigated. The magnetospheric electric field is supposed to consist of two components: a potential electric field penetrating into the magneto- sphere from the solar wind, and an inductive electric field associated with variation of the geomagnetic field. The first component is supposed to be proportional (with some time delay) to the Y -component of the solar wind electric field, and the second one is estimated from the time derivative of the tail lobe magnetic flux. The latter is obtained by converting total pressure to lobe magnetic field by assuming pressure balance be- tween lobe and plasma sheet (Nakamura et al., 1999). The Y -component of the total electric field is calculated from GEOTAIL spacecraft data as Ey = -[v × B]y. Analysis of experimental data shows that the inductive electric field (Ec) is "switched on" in the magnetotail practically simultaneously with the intensification of the IMF southern component. At the preliminary phase of the substorm, the Ec field within the plasmasheet is directed from dusk to dawn compensating the potential field Ep, so that the total field Ey is rather small there (Semenov and Sergeev, 1981). With the beginning of the active phase, the Ec changes its sign, and adding to the Ep, provides a rapid increase of the dawn­dusk Ey field. As the intensity of Ep during the active phase of the substorm is less than the intensity of the induced field, Ey is determined during this period by the latter mainly and does not correlate with the Esw field. However, the intensity of the potential electric field at this time may be obtained from the data on the velocity of the auroral arc motion (Pudovkin et al., 1992). So, judging by the dynamics of aurorae at the Poker Flat (Alaska) station, Ep field in the inner magnetosphere (X -10 RE) amounts the value of 0.7 mV/m, and it varies in proportion to Esw with the time delay of

  19. Sources and Transport of Plasma Sheet Ions During Magnetospheric Substorms

    NASA Technical Reports Server (NTRS)

    Ashour-Abdalla, M.; El-Alaoui, M.; Peroomian, V.; Raeder, J.; Walker, R. J.; Frank, L. A.; Paterson, W. R.

    1998-01-01

    This study investigates the sources and transport of ions observed in the near-Earth plasma sheet during the growth and expansion phases of a magnetospheric substorm that took place on November 24, 1996. The sources and acceleration mechanisms of ions observed at Geotail were determined by calculating the trajectories of thousands of ions backward in time. We found that during the growth phase of the substorm, most of the ions reaching Geotail had origins in the low latitude boundary layer (LLBL) and were already in the magnetosphere when the growth phase began. Late in the growth phase and in the expansion phase more plasma mantle ions reached the Geotail location. Indeed, during the expansion phase more than 90% of the ions were from the mantle. The ions were accelerated enroute to the spacecraft; however, most of the energy gained was achieved by non-adiabatic acceleration during the ions' crossing of the equatorial current sheet just prior to the detection of the ions.

  20. Substorms

    NASA Astrophysics Data System (ADS)

    Haerendel, Gerhard

    2015-01-01

    This chapter deals with the essence of the magnetospheric substorm, the return of magnetic flux into the magnetosphere after disconnection from the solar wind magnetic field. There are three fundamental transport processes involved: (1) thinning of the tail plasma sheet and accompanying recession of the outer boundary of the dipolar magnetosphere during the growth phase, (2) flux transport along the tail toward that boundary after onset of tail reconnection, and (3) penetration of plasma and magnetic flux into the dipolar magnetosphere. The chapter then looks at corresponding processes in the Jupiter and Saturn magnetospheres and tails, which are strongly dominated by the fast planetary rotations. It elucidates some key aspects of the entry problem, albeit from a personal vantage point, and addresses the still open questions. Finally, the chapter addresses the correlation between solar wind ram pressure and auroral activity and brightness on Jupiter and Saturn.

  1. Quantitative simulation of a magnetospheric substorm. II - Comparison with observations

    NASA Technical Reports Server (NTRS)

    Harel, M.; Wolf, R. A.; Spiro, R. W.; Reiff, P. H.; Chen, C.-K.; Burke, W. J.; Rich, F. J.; Smiddy, M.

    1981-01-01

    Results of the computer simulation of the behavior of the inner magnetosphere during the substorm-type event of September 19, 1976, are discussed. The computed electric fields are found to compare satisfactorily with electric fields measured from S3-2, although there are detailed differences. The three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high-latitude electric field, (2) the degree to which the low-latitude ionosphere is shielded from the high-latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. Simple formulas are presented that give rough estimates of global Joule heating rates from observable parameters.

  2. Coordinated observations of the magnetosphere - The development of a substorm.

    NASA Technical Reports Server (NTRS)

    Mende, S. B.; Sharp, R. D.; Shelley, E. G.; Haerendel, G.; Hones, E. W.

    1972-01-01

    Coordinated observations of a substorm are reported by using data from all-sky camera (ASCA) stations near the northern conjugate of the ATS 5 geostationary satellite, plasma and magnetic-field experiments on the ATS 5 satellite, Vela 5B at 18 earth radii in the magnetotail, the Heos 1 interplanetary probe, and ground-based magnetograms. The substorm event occurred after a very quiet day and was preceded by a development period during which the interplanetary field turned southward and the plasma energy density increased near the earth on the nightside. This period was also evidenced by a depression of the midlatitude H component of the geomagnetic field at the earth's surface. The auroral breakup was preceded by the appearance of quiet arcs, the leveling off of the plasma energy density increase at ATS, and the disappearance of the tail plasma at 18 earth radii.

  3. Linking Space-Borne and Ground-Based Observations Observed Around Substorm Onset to Magnetospheric Processes

    NASA Technical Reports Server (NTRS)

    Kepko, Larry; Spanswick, Emma; Angelopoulos, Vassilis; Donovan, Eric

    2011-01-01

    The combined THEMIS five spacecraft in-situ and ground magnetic and camera arrays have advanced considerably our understanding of the causal relationship between midtail plasma flows, transient ionospheric features, and ground magnetic signatures. In particular, recent work has shown a connection between equatorward moving visible ionospheric transients and substorm onset, in both 6300 nm and white-light emissions. Although both observations detail pre-onset auroral features the interpretations differ substantially. We first provide a brief summary of these observations, highlighting in particular areas where the two observations differ, and suggest reasons for the differences. We then detail how these observations relate to dynamical magnetospheric processes, and show how they constrain models of transient convection. Next, we pull together observations and models of Pi2 generation, substorm current wedge (SCW) initiation and dipolarization to present a self-consistent description of the dynamical processes and communicative pathways that occur just prior to and during substorm expansion onset. Finally, we present a summary of open questions and suggest a roadmap for future work.

  4. New perspectives on substorm injections

    SciTech Connect

    Reeves, G.D.

    1998-12-01

    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.

  5. Energetic Electron Transport in the Inner Magnetosphere During Geomagnetic Storms and Substorms

    NASA Technical Reports Server (NTRS)

    McKenzie, D. L.; Anderson, P. C.

    2005-01-01

    We propose to examine the relationship of geomagnetic storms and substorms and the transport of energetic particles in the inner magnetosphere using measurements of the auroral X-ray emissions by PIXIE. PIXIE provides a global view of the auroral oval for the extended periods of time required to study stormtime phenomena. Its unique energy response and global view allow separation of stormtime particle transport driven by strong magnetospheric electric fields from substorm particle transport driven by magnetic-field dipolarization and subsequent particle injection. The relative importance of substorms in releasing stored magnetospheric energy during storms and injecting particles into the inner magnetosphere and the ring current is currently hotly debated. The distribution of particles in the inner magnetosphere is often inferred from measurements of the precipitating auroral particles. Thus, the global distributions of the characteristics of energetic precipitating particles during storms and substorms are extremely important inputs to any description or model of the geospace environment and the Sun-Earth connection. We propose to use PIXIE observations and modeling of the transport of energetic electrons to examine the relationship between storms and substorms.

  6. Energy supply processes for magnetospheric substorms and solar flares - Tippy bucket model or pitcher model?

    NASA Astrophysics Data System (ADS)

    Akasofu, S.-I.

    1985-01-01

    In the past, both magnetospheric substorms and solar flares have almost exclusively been discussed in terms of explosive magnetic reconnection. Such a model may conceptually be illustrated by the so-called 'tippy-bucket model', which causes sudden unloading processes, namely a sudden (catastrophic, stochastic, and unpredictable) conversion of stored magnetic energy. However, recent observations indicate that magnetospheric substorms can be understood as a result of a directly driven process which can conceptually be illustrated by the 'pitcher model' in which the output rate varies in harmony with the input rate. It is also possible that solar flare phenomena are directly driven by a photospheric dynamo. Thus, explosive magnetic reconnection may simply be an unworkable hypothesis and may not be a puzzle to be solved as the primary energy supply process for magnetospheric substorms and solar flares.

  7. Changes in Magnetosphere-Ionosphere Coupling and FACs Associated with Substorm Onset (Invited)

    NASA Astrophysics Data System (ADS)

    Murphy, K. R.; Mann, I. R.; Rae, I. J.; Waters, C. L.; Anderson, B. J.; Korth, H.; Milling, D. K.; Singer, H. J.; Frey, H. U.

    2013-12-01

    Field aligned currents (FACs) are crucial for the communication of information between the ionosphere and magnetosphere. Utilising in-situ observations from the Iridium constellation and Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) we provide detailed observations of the FAC topology through the substorm growth and expansion phases. In particular, for an isolated substorm on 16 February 2010 we demonstrate a clear and localized reduction in the FACs at least 6 minutes prior to auroral onset. A new auroral arc forms in the region of reduced FAC on closed field lines and initially expands azimuthally in wave like fashion. This newly formed arc continues to brighten and expands poleward signifying the start of the substorm expansion phase. We argue that the change in FACs observed prior to onset is the result of a change in the magnetosphere-ionosphere (M-I) coupling in a region local to the subsequent auroral onset. Such a change implies an important role for M-I coupling in destabilising the near-Earth tail during magnetospheric substorms and perhaps more importantly in selecting the location in the ionosphere where auroral onset begins. Further, we provide, a comprehensive in-situ two-dimensional view of the FAC topology associated with the substorm current wedge and westward traveling surge during the substorm expansion phase. We demonstrate that these current structures, when integrated with latitude to produce a net FAC as a function of MLT, have the same structure as the equivalent line current system comprising the SCW. Moreover, regions of upward FAC are associated with discrete auroral forms during the substorm expansion phase.

  8. Satellite studies of magnetospheric substorms on August 15, 1968. IX - Phenomenological model for substorms.

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Russell, C. T.; Aubry, M. P.

    1973-01-01

    Observations made during three substorms on August 15, 1968, are shown to be consistent with current theoretical ideas about the cause of substorms. The phenomenological model described in several preceding papers is further expanded. This model follows closely the theoretical ideas presented more quantitatively in recent papers by Coronti and Kennel (1972 and 1973).

  9. What Might We Learn About Magnetospheric Substorms at the Earth from the MESSENGER Measurements at Mercury?

    NASA Technical Reports Server (NTRS)

    Slavin, James A.

    2008-01-01

    Satellite observations at the Earth, supported by theory and modeling, have established a close connection between the episodes of intense magnetospheric convection termed substorms and the occurrence of magnetic reconnection. Magnetic reconnection at the dayside magnetopause results in strong energy input to the magnetosphere. This energy can either be stored or used immediately to power the magnetospheric convection that produces the phenomena that collectively define the 'substorm.' However, many aspects of magnetic reconnection and the dynamic response of the coupled solar wind - magnetosphere - ionosphere system at the Earth during substorms remain poorly understood. For example, the rate of magnetic reconnection is thought to be proportional to the local Alfven speed, but the limited range of changes in this solar wind parameter at 1 AU have made it difficult to detect its influence over energy input to the Earth's magnetosphere. In addition, the electrical conductance of the ionosphere and how it changes in response to auroral charged particle precipitation are hypothesized to play a critical role in the development of substorms, but the nature of this electrodynamic interaction remain difficult to deduce from Earth observations alone. The amount of energy the terrestrial magnetosphere can store in its tail, the duration of the storage, and the trigger(s) for its dissipation are all thought to be determined by not only the microphysics of the cross-tail current layer, but also the properties of the coupled magnetosphere - ionosphere system. Again, the separation of microphysics effects from system response has proved very difficult using measurements taken only at the Earth. If MESSENGER'S charged particle and magnetic field measurements confirm the occurrence of terrestrial-style substorms in Mercury's miniature magnetosphere, then it may be possible to determine how magnetospheric convection, field-aligned currents, charged particle acceleration

  10. Event study combining magnetospheric and ionospheric perspectives of the substorm current wedge modeling

    NASA Astrophysics Data System (ADS)

    Sergeev, V. A.; Nikolaev, A. V.; Kubyshkina, M. V.; Tsyganenko, N. A.; Singer, H. J.; Rodriguez, J. V.; Angelopoulos, V.; Nakamura, R.; Milan, S. E.; Coxon, J. C.; Anderson, B. J.; Korth, H.

    2014-12-01

    Unprecedented spacecraft and instrumental coverage and the isolated nature and distinct step-like development of a substorm on 17 March 2010 has allowed validation of the two-loop substorm current wedge model (SCW2L). We find a close spatiotemporal relationship of the SCW with many other essential signatures of substorm activity in the magnetotail and demonstrate its azimuthally localized structure and stepwise expansion in the magnetotail. We confirm that ground SCW diagnostics makes it possible to reconstruct and organize the azimuthal spatiotemporal substorm development pattern with accuracy better than 1 h magnetic local time (MLT) in the case of medium-scale substorm. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE)-based study of global field-aligned current distribution indicates that (a) the SCW-related field-aligned current system consists of simultaneously activated R1- and R2-type currents, (b) their net currents have a R1-sense, and (c) locations of net current peaks are consistent with the SCW edge locations inferred from midlatitude variations. Thanks to good azimuthal coverage of four GOES and three Time History of Events and Macroscale Interactions during Substorms spacecraft, we evaluated the intensities of the SCW R1- and R2-like current loops (using the SCW2L model) obtained from combined magnetospheric and ground midlatitude magnetic observations and found the net currents consistent (within a factor of 2) with the AMPERE-based estimate. We also ran an adaptive magnetospheric model and show that SCW2L model outperforms it in predicting the magnetic configuration changes during substorm dipolarizations.

  11. Correlation between convection electric fields in the nightside magnetosphere and several wave and particle phenomena during two isolated substorms.

    NASA Technical Reports Server (NTRS)

    Carpenter, D. L.; Fraser-Smith, A. C.; Unwin, R. S.; Hones, E. W., Jr.; Heacock, R. R.

    1971-01-01

    Correlation of several magnetoionospheric wave and particle phenomena previously linked observationally to magnetospheric substorms and inferred to involve convection electric fields with whistler measurements of convection activity during two relatively isolated substorms. The events occurred at about 0600 UT on July 15, 1965, and about 0500 UT on Oct. 13, 1965. The correlated phenomena include cross-L inward plasma drifts near midnight within the plasmaphere, diffuse auroral radar echoes observed near the dusk meridian, IPDP micropulsations (intervals of pulsations of diminishing period) in the premidnight sector, apparent contractions and expansions of the plasma sheet at about 20 earth radii in the magnetotail, and Pc 1/Pi 1 micropulsation events near or before midnight. Two new vlf phenomena occurred during the October 13 event - a noise band within the plasmasphere associated with a convecting whistler path, and ?hisslers,' falling-tone auroral-hiss forms repeated at intervals of about 2 sec.

  12. Dynamics of the AMPERE Region 1 Birkeland current oval during storms, substorms and steady magnetospheric convection

    NASA Astrophysics Data System (ADS)

    Baker, J. B.; Clausen, L.; Ruohoniemi, J. M.; Milan, S. E.; Kissinger, J.; Anderson, B. J.; Wing, S.

    2012-12-01

    Using radial current densities provided by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) we employ a fitting scheme to identify the location of the maximum Region 1 field-aligned (Birkeland) current at all magnetic local times. We call this parameter the "R1 oval" and we investigate its behavior during various modes of magnetospheric activity such as storms, substorms and steady magnetospheric convection (SMCs). Results show the following: (1) during substorms the radius of the R1 oval undergoes a cyclic inflation and contraction which matches the standard paradigm for substorm growth (loading) and expansion (unloading); (2) during SMCs the R1 oval is relatively steady consistent with balanced dayside and nightside reconnection during these events; and (3) during magnetic storms the size of the R1 oval is strongly correlated with the strength of the ring current specified by the Sym-H index. We also examine the behavior of the R1 oval in the northern and southern hemispheres simultaneously as a function of season in an effort to understand the role that internal magnetosphere-ionosphere coupling influences may play in modulating the response of the magnetosphere during these various types of events.

  13. Pseudobreakup and substorm growth phase in the ionosphere and magnetosphere

    SciTech Connect

    Koskinin, H.E.J.; Pellinen, R.J.; Pulkkinen, T.I. ); Lopez, R.E. ); Baker, D.N. ); Boesinger, T. )

    1993-04-01

    The authors present space and ground based observations made during the growth phase and the onset of a substorm on August 31, 1986. Roughly 20 minutes after the [var epsilon] parameter at the magnetopause had exceeded 10[sup 11] W, the AMPTE Charge Composition Explorer spacecraft observed an increase in energetic particle fluxes consistent with magnetic field depolarization. The craft was close to magnetic midnight at a geocentric distance of 8.7R[sub E]. The event had the initial signature of a substorm onset, but it did not lead to a full-scale substorm expansion based on several ground based observations. There were no large particle injection events at geostationary orbit. After another 20 minutes the event did enter a normal substorm expansion phase. The authors interpret the initial activation as a [open quotes]pseudobreakup[close quotes]. They correlate observations made by spacecraft in the near-Earth plasma sheet, with ground based observations of the ionospheric development from magnetometer and electric field measurements from the STARE radar. The strength and the consequences are concluded to be the main differences of pseudobreakups and ordinary breakups.

  14. Distinct Magnetospheric Responses to Southward IMF in Two Substorms

    NASA Technical Reports Server (NTRS)

    El-Alaoui, Mostafa; Ashour-Abdalla, M.; Richard, R. L.; Frank, L. A.; Paterson, W. R.; Sigwarth, J. B.

    2003-01-01

    Solar wind plasma parameters and the Interplanetary Magnetic Field (IMF) observed by the WIND spacecraft upstream of the bow shock were used as input to magnetohydrodynamic (MHD) simulations of two substorm events. The power deposited into the ionosphere due to electron precipitation was calculated both from VIS observations and from the simulations.

  15. A Modeling substorm Dynamics of the Magnetosphere Using Self-Organized Criticality Approach

    NASA Astrophysics Data System (ADS)

    Bolzan, Mauricio; Rosa, Reinaldo

    2016-07-01

    Responses of Earth magnetic field during substorms exhibits a number of characteristics features such as the power-law spectra of fluctuations on different scales and signatures of low effective dimensions. Due the magnetosphere are constantly out-equilibrium their behavior is similar to real sandpiles during substorms, features of self-organized criticality (SOC) systems. Thus, in this work we presented a simple mathematical model to AE-index based on self-organizing sandpile mentioned by Uritsky and Pudovkin (1998), but we input the dissipation process inside the model. The statistical and multifractal tools to characterization of dynamical processes was used.

  16. Theoretical magnetograms based on quantitative simulation of a magnetospheric substorm

    NASA Technical Reports Server (NTRS)

    Chen, C.-K.; Wolf, R. A.; Karty, J. L.; Harel, M.

    1982-01-01

    Substorm currents derived from the Rice University computer simulation of the September 19, 1976 substorm event are used to compute theoretical magnetograms as a function of universal time for various stations, integrating the Biot-Savart law over a maze of about 2700 wires and bands that carry the ring, Birkeland and horizontal ionospheric currents. A comparison of theoretical results with corresponding observations leads to a claim of general agreement, especially for stations at high and middle magnetic latitudes. Model results suggest that the ground magnetic field perturbations arise from complicated combinations of different kinds of currents, and that magnetic field disturbances due to different but related currents cancel each other out despite the inapplicability of Fukushima's (1973) theorem. It is also found that the dawn-dusk asymmetry in the horizontal magnetic field disturbance component at low latitudes is due to a net downward Birkeland current at noon, a net upward current at midnight, and, generally, antisunward-flowing electrojets.

  17. Magnetosphere-Ionosphere Coupling Processes in the Ionospheric Trough Region During Substorms

    NASA Astrophysics Data System (ADS)

    Zou, S.; Moldwin, M.; Nicolls, M. J.; Ridley, A. J.; Coster, A. J.; Yizengaw, E.; Lyons, L. R.; Donovan, E.

    2013-12-01

    The ionospheric troughs are regions of remarkable electron density depression at the subauroral and auroral latitudes, and are categorized into the mid-latitude trough or high-latitude trough, depending on their relative location to the auroral oval. Substorms are one fundamental element of geomagnetic activity, during which structured field-aligned currents (FACs) and convection flows develop in the subauroral and auroral ionosphere. The auroral/trough region is expected to experience severe electron density variations during substorms. Accurate specification of the trough dynamics during substorms and understanding its relationship with the structured FACs and convection flows are of important practical purpose, including providing observational foundations for assessing the attendant impact on navigation and communication. In addition, troughs are important since they map to magnetospheric boundaries allowing the remote sensing of magnetosphere-ionosphere coupling processes. In this talk, we discuss the dynamics of the mid-latitude and high-latitude troughs during substorms based on multi-instrument observations. Using GPS total electron content (TEC) data, we characterize the location and width of the mid-latitude trough through the substorm lifecycle and compare them with existing trough empirical models. Using a combination of incoherent scattering radar (ISR), GPS TEC, auroral imager and a data assimilative model, we investigate the relationship between the high-latitude trough and FACs as well as convection flows. The high-latitude trough is found to be collocated with a counter-clockwise convection flow vortex east of the Harang reversal region, and downward FACs as part of the substorm current system are suggested to be responsible for the high-latitude trough formation. In addition, complex ionospheric electron temperature within the high-latitude trough is found, i.e., increase in the E region while decrease in the F region. We discuss possible

  18. Phase transition-like behavior of magnetospheric substorms: Global MHD simulation results

    NASA Astrophysics Data System (ADS)

    Shao, X.; Sitnov, M. I.; Sharma, S. A.; Papadopoulos, K.; Goodrich, C. C.; Guzdar, P. N.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.

    2003-01-01

    Using nonlinear dynamical techniques, we statistically investigate whether the simulated substorms from global magnetohydrodynamic (MHD) models have a combination of global and multiscale features, revealed in substorm dynamics by [2000] and featured the phase transition-like behavior. We simulate seven intervals of total duration of 280 hours from the data set used in the above works [, 1985]. We analyze the input-output (vBs-pseudo AL index) system obtained from the global MHD model and compare the results to those inferred from the original set (vBs-observed AL index). The analysis of the coupled vBs-pseudo AL index system shows the first-order phase transition map, which is consistent with the map obtained for the vBs-observed AL index system. Although the comparison between observations and global MHD simulations for individual events may vary, the overall global transition pattern during the substorm cycle revealed by singular spectrum analysis (SSA) is statistically consistent between simulations and observations. The coupled vBs-pseudo AL index system also shows multiscale behavior (scale-invariant power law dependence) in SSA power spectrum. Besides, we find the critical exponent of the nonequilibrium transitions in the magnetosphere, which reflects the multiscale aspect of the substorm activity, different from power law frequency of autonomous systems. The exponent relates input and output parameters of the magnetosphere. We also discuss the limitations of the global MHD model in reproducing the multiscale behavior when compared to the real system.

  19. Recovery phase of magnetospheric substorms and its association with morning-sector aurora

    SciTech Connect

    Opgenoorth, H.J.; Persson, M.A.L.; Pulkkinen, T.I.; Pellinen, R.J.

    1994-03-01

    The authors report on conclusions drawn from an extensive study of ground based measurements of the recovery phase of magnetospheric substorms. Much previous work has considered this phase to simply consist of decay processes of growth phase phenomena as the magnetosphere relaxes to its quiescent state. From their studies of observational data the authors conclude that there is evidence of distinct processes within the recovery phase which are related to it alone. These include intense electrojet activity, high-energy particle precipitation, distinct large scale auroral phenomena, and possibly even expanded auroral activity.

  20. Computer simulation of a geomagnetic substorm

    NASA Technical Reports Server (NTRS)

    Lyon, J. G.; Brecht, S. H.; Huba, J. D.; Fedder, J. A.; Palmadesso, P. J.

    1981-01-01

    A global two-dimensional simulation of a substormlike process occurring in earth's magnetosphere is presented. The results are consistent with an empirical substorm model - the neutral-line model. Specifically, the introduction of a southward interplanetary magnetic field forms an open magnetosphere. Subsequently, a substorm neutral line forms at about 15 earth radii or closer in the magnetotail, and plasma sheet thinning and plasma acceleration occur. Eventually the substorm neutral line moves tailward toward its presubstorm position.

  1. Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event

    SciTech Connect

    Gkioulidou, Matina; Ohtani, S.; Mitchell, D. G.; Ukhorskiy, A. Y.; Reeves, G. D.; Turner, D. L.; Gjerloev, J. W.; Nosé, M.; Koga, K.; Rodriguez, J. V.; Lanzerotti, L. J.

    2015-03-20

    Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ –40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within 10 min, with different dipolarization signatures and duration. The first one is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales.

  2. Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event

    DOE PAGESBeta

    Gkioulidou, Matina; Ohtani, S.; Mitchell, D. G.; Ukhorskiy, A. Y.; Reeves, G. D.; Turner, D. L.; Gjerloev, J. W.; Nosé, M.; Koga, K.; Rodriguez, J. V.; et al

    2015-03-20

    Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ –40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within 10 min, with different dipolarization signatures and duration. The first onemore » is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales.« less

  3. Phase Transition-like Behavior of Magnetospheric Substorms: Global MHD Simulation Results

    NASA Astrophysics Data System (ADS)

    Shao, X.; Sitnov, M.; Sharma, A. S.; Papadopoulos, K.; Guzdar, P. N.; Goodrich, C. C.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.

    2001-12-01

    Because of their relevance to massive global energy loading and unloading, lots of observations and studies have been made for magnetic substorm events. Using nonlinear dynamical techniques, we investigate whether the simulated substorms from global MHD models have the non-equilibrium phase transition-like features revealed by \\markcite{Sitnov et al. [2000]}. We simulated 6 intervals of total duration of 240 hours from the same data set used in Sitnov et al. [2000]. We analyzed the input-output (vBs--pseudo-AL index) system obtained from the global MHD model and compared the results to those in \\markcite{Sitnov et al. [2000, 2001]}. The analysis of the coupled vBs--pseudo-AL index system shows the first-order phase transition map, which is consistent with the map obtained for the vBs--observed-AL index system from Sitnov et al. [2000]. The explanation lies in the cusp catastrophe model proposed by Lewis [1991]. Although, the comparison between observation and individual global MHD simulations may vary, the overall global transition pattern during the substorm cycle revealed by Singular Spectrum Analysis (SSA) is consistent between simulations and observations. This is an important validation of the global MHD simulations of the magnetosphere. The coupled vBs--pseudo-AL index system shows multi-scale behavior (scale-invarianet power-law dependence) in singular power spectrum. We found critical exponents of the non-equilibrium transitions in the magnetosphere, which reflect the multi-scale aspect of the substorm activity, different from power-law frequency of autonomous systems. The exponents relate input and output parameters of the magnetosphere and distinguish the second order phase transition model from the self-organized criticality model. We also discuss the limitations of the global MHD model in reproducing the multi-scale behavior when compared to the real system.

  4. Phase Transition like Behavior of Magnetospheric Substorms: Global and Multiscale Features from MHD Simulations

    NASA Astrophysics Data System (ADS)

    Shao, X.; Sitnov, M. I.; Sharma, A. S.; Papadopoulos, K.; Goodrich, C. C.; Guzdar, P. N.; Milikh, G. M.; Wiltberger, M. J.; Lyon, J. G.

    2002-05-01

    Studies of the magnetosphere during substorms based on the observational data of the solar wind and the geomagnetic indices have shown clear features of phase transition-like behavior [Sitnov et al., 2000]. The global MHD simulations of the events in the Bargatze et al. [1985] database are used to study the non-equilibrium phase transition-like features of substorms. We simulated 7 intervals of total duration of 280 hours from the same data set used in Sitnov et al. [2000]. From the simulations the AL index is computed from the maximum of the westward Hall current and is referred to as the pseudo-AL index. We analyzed the input-output (vBs-pseudo-AL index) system obtained from the global MHD model and compare the results to those in Sitnov et al. [2000, 2001]. The analysis of the coupled vBs-pseudo-AL index system shows the first-order phase transition characterizing global beahavior, similar to the case of vBs-observed-AL index [Sitnov et al., 2000]. Although, the comparison between observations and global MHD simulations for individual events may vary, the overall global transition pattern during the substorm cycle revealed by singular spectrum snalysis is statistically consistent between simulations and observations. The coupled vBs-pseudo-AL index system shows multi-scale behavior (scale-invariant power-law dependence) in singular power spectrum. We find critical exponents of the non-equilibrium transitions in the magnetosphere, which reflect the multi-scale aspect of the substorm activity, different from power-law frequency of autonomous systems. The exponents relate input and output parameters of the magnetosphere.

  5. Electromagnetic and electrostatic emissions at the cusp-magnetosphere interface during substorms

    NASA Technical Reports Server (NTRS)

    Curtis, S. A.; Fairfield, D. H.; Wu, C. S.

    1979-01-01

    Strongly peaked electrostatic emissions near 10.0 kHz and electromagnetic emissions near 0.56 kHz have been observed by the VLF wave detector on board Imp 6 on crossings from the earth's magnetosphere into the polar cusp during the occurrence of large magnetospheric substorms. The electrostatic emissions were observed to be closely confined to the cusp-magnetosphere interface. The electromagnetic emissions were of somewhat broader spatial extent and were seen on higher-latitude field lines within the cusp. Using these plasma wave observations and additional information provided by plasma, magnetometer and particle measurements made simultaneously on Imp 6, theories are constructed to explain each of the two classes of emission. The electromagnetic waves are modeled as whistlers, and the electrostatic waves as electron-cyclotron harmonics. The resulting growth rates predict power spectra similar to those observed for both emission classes. The electrostatic waves may play a significant role via enhanced diffusion in the relaxation of the sharp substorm time cusp-magnetosphere boundary to a more diffuse quiet time boundary.

  6. Energetic Electron Populations in the Magnetosphere During Geomagnetic Storms and Substorms

    NASA Technical Reports Server (NTRS)

    McKenzie, David L.; Anderson, Phillip C.

    2002-01-01

    This report summarizes the scientific work performed by the Aerospace Corporation under NASA Grant NAG5-10278, 'Energetic Electron Populations in the Magnetosphere during Geomagnetic Storms and Subsisting.' The period of performance for the Grant was March 1, 2001 to February 28, 2002. The following is a summary of the Statement of Work for this Grant. Use data from the PIXIE instrument on the Polar spacecraft from September 1998 onward to derive the statistical relationship between particle precipitation patterns and various geomagnetic activity indices. We are particularly interested in the occurrence of substorms during storm main phase and the efficacy of storms and substorms in injecting ring-current particles. We will compare stormtime simulations of the diffuse aurora using the models of Chen and Schulz with stormtime PIXIE measurements.

  7. PC index as a proxy of the solar wind energy that entered into the magnetosphere: Development of magnetic substorms

    NASA Astrophysics Data System (ADS)

    Troshichev, O. A.; Podorozhkina, N. A.; Sormakov, D. A.; Janzhura, A. S.

    2014-08-01

    The Polar Cap (PC) index has been approved by the International Association of Geomagnetism and Aeronomy (IAGA XXII Assembly, Merida, Mexico, 2013) as a new index of magnetic activity. The PC index can be considered to be a proxy of the solar wind energy that enters the magnetosphere. This distinguishes PC from AL and Dst indices that are more related to the dissipation of energy through auroral currents or storage of energy in the ring current during magnetic substorms or storms. The association of the PC index with the direct coupling of the solar wind energy into the magnetosphere is based upon analysis of the relationship of PC with parameters in the solar wind, on the one hand, and correlation between the time series of PC and the AL index (substorm development), on the other hand. This paper (the first of a series) provides the results of statistical investigations that demonstrate a strong correlation between the behavior of PC and the development of magnetic substorms. Substorms are classified as isolated and expanded. We found that (1) substorms are preceded by growth in the RS index, (2) sudden substorm expansion onsets are related to "leap" or "reverse" signatures in the PC index which are indicative of a sharp increase in the PC growth rate, (3) substorms start to develop when PC exceeds a threshold level 1.5 ± 0.5 mV/m irrespective of the length of the substorm growth phase, and (4) there is a linear relation between the intensity of substorms and PC for all substorm events.

  8. Substorms on Mercury?

    NASA Technical Reports Server (NTRS)

    Siscoe, G. L.; Ness, N. F.; Yeates, C. M.

    1974-01-01

    Qualitative similarities between some of the variations in the Mercury encounter data and variations in the corresponding regions of the earth's magnetosphere during substorms are pointed out. The Mariner 10 data on Mercury show a strong interaction between the solar wind and the plant similar to a scaled down version of that for the earth's magnetosphere. Some of the features observed in the night side Mercury magnetosphere suggest time dependent processes occurring there.

  9. Rapid enhancement of energetic oxygen ions in the inner magnetosphere during substorms

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Ebihara, Y.; Tanaka, T.

    2014-12-01

    Satellite observations show that energetic (>100 keV) O+ ions are rapidly increased in the inner magnetosphere during substorms. The ultimate source of O+ ions is the Earth's ionosphere, so that O+ ions must be accelerated from ~eV to 100s keV somewhere in the magnetosphere. A fundamental question still arise regarding why O+ ions are accelerated and transported to the inner magnetosphere. We simulated substorms under two different solar wind conditions by using the global MHD simulation developed by Tanaka et al. (2010, JGR). The solar wind speed is set to be 372 km/s for Case I, and 500 km/s for Case II. In both cases, the MHD simulation result shows that the dawn to dusk electric field is enhanced in the night side tail region at >7 Re just after the substorm onset. In particular, the electric field in the inner region (~7 Re) is highly enhanced by the tension force because of relatively strong magnetic field together with curved field lines. The strongest electric field takes place near the region where the plasma pressure is high. We performed test particle simulation under the electric and magnetic fields for Cases I and II. O+ ions are released from two planes located at ±2 Re in the Z direction in the tail region. O+ ions released at the two planes represent outflowing stream of O+ ions escaping from the Earth. The distribution function at the planes is assumed to be drifting Kappa distribution with temperature of 10 eV, the density of 105 m-3, and the parallel velocity given by the MHD simulation. In total, around a billion of particles are traced. Each test particle carries the real number of particles in accordance with the Liouville theorem. After tracing particles, we reconstructed 6-dimensional phase space density of O+ ions. We obtained the following results. (1) Just after substorm onset, the differential flux of O+ ions is almost simultaneously enhanced in the region where the electric field is strong. (2) The kinetic energy increases rapidly to

  10. Quantitative simulation of a magnetospheric substorm. I - Model logic and overview

    NASA Technical Reports Server (NTRS)

    Harel, M.; Wolf, R. A.; Reiff, P. H.; Spiro, R. W.; Burke, W. J.; Rich, F. J.; Smiddy, M.

    1981-01-01

    Results of a comprehensive computer simulation of the behavior of the earth's inner magnetosphere during a substorm-type event are reported. It is pointed out that the computer model self-consistently computes electric fields, currents, and plasma distributions and velocities in the inner-magnetosphere/ionosphere system; parallel electric fields and ionospheric neutral winds, however, are not included. The basic equations of the model are derived, and the inputs are described. An overview of the results is also given. The first appendix contains derivations of general, useful laws of bounce-averaged gradient, curvature, and E x B drifts in a plasma with isotropic pitch angle distribution. The second appendix gives a description of the numerical method used in the simulation.

  11. An example of using the Virtual Heliospheric and Magnetospheric Observatories for a substorm study

    NASA Astrophysics Data System (ADS)

    Merka, J.; Szabo, A.; Narock, T. W.; Walker, R. J.; King, T.; Slavin, J. A.; Imber, S.; Karimabadi, H.; Faden, J.

    2009-04-01

    Finding and retrieving space physics data is a rather daunting task even when the data are publicly available on the Internet because there are thousands of relatively small and many large data sets stored in various formats and accompanied often only by terse documentation. Virtual Heliospheric and Magnetospheric Observatories (VHO and VMO) are being developed to help researches by creating a single point of uniform discovery, access, and use of heliospheric (VHO) and magnetospheric (VMO) data. Available data can be searched based on various criteria as, for example, spatial location, time of observation, measurement type, parameter values, etc. The VHO and VMO also utilize event lists to quickly narrow down searches by specific events, e.g. bow shock crossings,flux transfer events (FTEs) or CMEs/ICMEs. We will demonstrate the utility of VHO/VMO for geospace studies by reprising a multi-spacecraft, multi-instrument analysis from the literature. In particular, simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms were identified by visual inspection of several years of ISTP measurements by Slavin et al. [2002]. Using the VHO/VMO we show how studies such as these can be carried out with substantial time savings and often with the added value of accessing additional relevant data sets that would not have been available to scientist performing the analysis. References: http://vho.nasa.gov http://vmo.nasa.gov Slavin et al., Simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms, J. of Geophysical Research, 107 (A7), 10.1029/2000JA003501, 2002

  12. Substorm-like magnetospheric response to a discontinuity in the Bx component of interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Nowada, M.; Lin, C.-H.; Pu, Z.-Y.; Fu, S.-Y.; Angelopoulos, V.; Carlson, C. W.; Auster, H.-U.

    2012-04-01

    We examined the magnetospheric magnetic field and plasma responses to an encounter of a discontinuity in the Bx component of interplanetary magnetic field (IMF). The striking variations of simultaneous solar wind dynamic pressure and IMF-Bz were not observed. Furthermore, we found that this IMF-Bx discontinuity was a heliospheric current sheet, separating two high-speed solar wind streams with different velocity and magnetic polarity. In this study, the magnetic field and plasma data were obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS), Cluster, and GOES to investigate the magnetospheric responses, and those were taken from ACE and Geotail to monitor the solar wind conditions. Simultaneous geomagnetic field variations from the ground observatories and aurora activity from Polar were also examined. When the discontinuity encountered the magnetosphere, THEMIS-D, -E, and THEMIS-A observed abrupt and transient magnetic field and plasma variations in the dawnside near-Earth magnetotail and tail-flank magnetopause. Significant magnetic field perturbations were not observed by Cluster as located in the duskside magnetotail at this time interval. Although simultaneous dipolarization and negative bay variations with Pi2 waves were observed by GOES and the ground observatories, global auroral activities were not found. Around the dawnside tail-flank magnetopause, THEMIS-C and -A experienced the magnetopause crossings due to the magnetopause surface waves induced by Kelvin-Helmholtz instability. These results suggest that the magnetic field and plasma variations in the near-Earth magnetotail and tail-flank magnetopause were caused by moderate substorm-like phenomena and magnetopause surface waves. They also indicate that clear magnetospheric disturbances can be brought even without significant variations in the solar wind.

  13. Combining magnetospheric and ionospheric perspectives on the substorm current wedge modeling and dynamics.

    NASA Astrophysics Data System (ADS)

    Sergeev, Viktor

    Unprecedent spacecraft and instrumental coverage, isolated nature and distinct step-like development of the studied event on March 17, 2010 allowed us to investigate and demonstrate close spatio-temportal relationship of the substorm current wedge development with many other essential signatures of substorm activity in the magnetotail, including tailward flux transport in the more distant tail, flow bursts and disruptions of the thin current sheet in the near tail, and the dipolarizations and particle injections at geosynchronous orbit. This case study provides a clear illustration of sectorial organization of the activity in the magnetotail, with activity being confined to azimuthally localized sectors and expanding in step-like way to the new sectors of the magnetotail, presumably reflecting the step-like cross-tail evolution of the reconnection process. We confirm that ground SCW diagnostics allows to reconstruct the azimuthal spatio-temporal substorm development pattern with accuracy better than 1h MLT. Thanks to good azimuthal coverage of four GOES and three THEMIS spacecraft we evaluated the intensities of total SCW R1- and R2-like current loops (using SCW2L model) from combined magetospheric and ground midlatitude magnetic observations and compare it to the field-aligned current estimates provided by AMPERE project. As one more test of SCW2L model we predicted the amplitude of the poleward shift of the ionospheric footpoints due to addition of so-obtained SCW2L currents and found a reasonable agreement with observed poleward expansion of polar auroras and westward electrojet. Finally we run the adapted magnetospheric model and show that previous versions ofadaptive models can not substitite SCW2L to correctly predict the magnetic configuration changes during substorms, which require future efforts.

  14. Electric fields, electron precipitation, and VLF radiation during a simultaneous magnetospheric substorm and atmospheric thunderstorm

    SciTech Connect

    Bering, E.A.; Rosenberg, T.J.; Benbrook, J.R.; Detrick, D.; Matthews, D.L.; Rycroft, M.J.; Saunders, M.A.; Sheldon, W.R.

    1980-01-01

    A balloon payload instrumented with a double-probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L=4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ..delta..B of approx.500 nT at approx.0930 UT. A single-cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from approx.1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one-half the fair weather value prior to 1000 UT; decreased to about one-quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation. Third, the data show a high probability that half-hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from the magnetosphere.

  15. Mass dependent energization of ions in the inner magnetosphere during a substorm

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Ebihara, Y.; Tanaka, T.

    2012-12-01

    Rapid enhancements of energetic ions during a substorm are one of the unsolved issues in the magnetospheric research. Previously, two distinct processes have been suggested to explain the enhancements. The first one is transport from the near-earth plasma sheet, and the other one is local acceleration. To test the latter process, we traced oxygen and hydrogen ions under the electric and magnetic fields that are self-consistently obtained by the global MHD simulation developed by Tanaka et al. (2010, JGR). During the simulated substorm, highly oscillating, large-amplitude electric fields are induced by force imbalance between the JxB force and grad-P force (Ebihara and Tanaka, 2012, submitted to JGR). Low-energy oxygen ions with initial energy less than ~keV only appear to be significantly accelerated by the oscillating electric field on a timescale of gyroperiod. We will discuss in detail the pitch angle and energy distributions of the accelerated ions as a function of time.

  16. A Mechanism for the Loading-Unloading Substorm Cycle Missing in MHD Global Magnetospheric Simulation Models

    NASA Technical Reports Server (NTRS)

    Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.

    2005-01-01

    Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

  17. Old tail lobes effect on the solar-wind - Magnetosphere energy transport for the 27 August 2001 substorm

    NASA Astrophysics Data System (ADS)

    Mishin, V. V.; Mishin, V. M.; Pu, Z.; Lunyushkin, S. B.; Sapronova, L. A.; Sukhbaatar, U.; Baishev, D. G.

    2014-12-01

    The magnetic flux of tail lobes Ψ is divided in two parts of comparable values Ψ1 and Ψ02, with the first that appears during substorm and the second, observed before substorm start. The first was named “new magnetic flux”, the second - “old magnetic flux”. The first, Ψ1, is known to play a definitive role in the energy transport from the solar wind into the magnetosphere-ionosphere-atmosphere system, but the role of Ψ02 in this transport is not well known. From the 27 August 2001 substorm data we study the involvement in the above transport process of the old flux Ψ02. This involvement is observed in the polar cap (PC) area, which existed prior to the substorm and is called respectively “the old PC”. In this study, as distinct from earlier works, we use the balance equation of the energy stored in magnetosphere and energy consumed. Activation of the old PC magnetic flux Ψ02 was found to increase the energy input by ∼85% in the event under consideration.

  18. Statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events

    NASA Astrophysics Data System (ADS)

    Huang, Chao-Song

    2012-02-01

    Substorms cause significant disturbances in the ionosphere. However, it has not been well understood how the electric field and electrojet in the dayside equatorial ionosphere respond to substorm onset. Previous studies found that the equatorial electric field, after substorm onset, could be eastward or westward. Because the onset of isolated substorms is often related to a northward turning of the interplanetary magnetic field (IMF), the measured total electric field is determined by contributions from both IMF northward turning and substorm onset and is not necessarily the signature of the onset. In order to exclude the effect of IMF northward turning, we analyze the variations of ionospheric electric field and electrojet during storm time substorms when the IMF remains stable. Thus, the ionospheric variations can be identified to be caused solely by substorms. The electric field data are measured by the Jicamarca radar, and the electrojet is derived from magnetometers at Jicamarca and Piura. It is found that substorm onset induces an eastward electric field and electrojet in the dayside equatorial ionosphere when the IMF remains continuously southward across the onset. The equatorial electrojet starts to increase at the onset, reaches a maximum value ˜30 min after the onset, and then decreases to the pre-onset value ˜60 min after the onset. Westward electric field and counter-electrojet occur only if the substorm onset is associated with a northward turning of the IMF. It is concluded that the effect of substorm onset on the dayside equatorial ionosphere, without involvement of IMF reorientations, is an enhanced eastward electric field.

  19. Space-borne and ground-based observations of transient processes occurring around substorm onset

    NASA Astrophysics Data System (ADS)

    Kepko, E. L.; Spanswick, E. L.; Angelopoulos, V.; Donovan, E. F.

    2010-12-01

    The combined THEMIS five spacecraft in-situ and ground magnetic and visible camera arrays have advanced considerably our understanding of the causal relationship between midtail plasma flows, transient ionospheric features, and ground magnetic signatures. In particular, recent work has shown a connection between equatorward moving visible ionospheric transients and substorm onset, in both white-light (Nishimura et al., [2010]) and 630 nm (Kepko et al., [2010]) emissions. These observations, together with THEMIS in-situ measurements of bulk flows, provides strict constraints on the sequence of events leading to substorm auroral onset. We first provide a brief summary of these observations, highlighting in particular areas where the two observations differ, and suggest reasons for the differences. Next, by combining the observed correlation of flow and Pi2 waveform with a unified model of global Pi2 generation and substorm current wedge initiation, we present a self-consistent description of the dynamical processes and communicative pathways that occur just prior to and during substorm expansion onset.

  20. Magnetospheric substorm: Loss of the magnetoplasma equilibrium as a nonlinear dynamical bifurcation

    NASA Astrophysics Data System (ADS)

    Kropotkin, A. P.

    2012-04-01

    The fast onset of a substorm—a substorm "explosion"—is usually associated with the moment of stability loss of the magnetoplasma equilibrium in the geomagnetic tail. The origination of such a process either from the near-Earth part of the plasma sheet or from its remote part, which is highly stretched into the tail, is now being studied theoretically and verified experimentally (at the present time, in the THEMIS project). In the first case, the resulting disturbance must have the form of a ballooning mode; in the second case, of tearing perturbation. However, in both cases, this stability loss, i.e., a quick breakdown in the balance, replacing the slow quasi-static evolution of configuration, can only occur as a nonlinear process. Taking into account the specific properties of the configuration and possible disturbances in it, we indicate why such a process cannot be the previously proposed "substorm detonation." It is shown that a suitable mathematical model is a nonlinear dynamical bifurcation occurring on a small time scale, with a delay relative to the moment of passing the marginally stable state.

  1. Near-earth substorm onset: A coordinated study

    SciTech Connect

    Persson, M.A.L.; Opgenoorth, H.J.; Eriksson, A.I.; Dovner, P.O.; Pulkkinen, T.I.; Reeves, G.D.; Belian, R.D.; Andre, M.; Blomberg, L.G.; Erlandson, R.E.

    1994-08-15

    The authors present simultaneous satellite and ground-based measurements of a substorm. Throughout the initial substorm expansion, southward drifting arcs are observed poleward of the expanding substorm aurora, indicating two independent systems of particle precipitation. Freja passes the brightening onset arc in the topside ionosphere near the moment of the substorm onset, observing an Alfven wave, field aligned current and oxygen ion outflow. The substorm onset occurs at low magnetospheric L-shells, near the poleward edge of the region of trapped particles. The location and time for the substorm injection are confirmed by geostationary spacecraft together with magnetometers, all-sky cameras and radar on the ground. The authors believe that the substorm onset may be triggered by modification of the oxygen content of the inner magnetosphere during the growth-phase caused by ionospheric ion outflow. 15 refs., 7 figs.

  2. Multiple-satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral-zone activity

    NASA Technical Reports Server (NTRS)

    Pytte, T.; Mcpherron, R. L.; Kivelson, M. G.; West, H. I., Jr.; Hones, E. W., Jr.

    1977-01-01

    Particle observations from pairs of satellites (Ogo 5, Vela 4A and 5B, Imp 3) during the recovery of plasma sheet thickness late in substorms were examined. Six of the nine events occurred within about 5 min in locations near the estimated position of the neutral sheet, but over wide ranges of east-west and radial separations. The time of occurrence and spatial extent of the recovery were related to the onset (defined by ground Pi 2 pulsations) and approximate location (estimated from ground mid-latitude magnetic signatures) of substorm expansions. It was found that the plasma sheet recovery occurred 10 - 30 min after the last in a series of Pi bursts, which were interpreted to indicate that the recovery was not due directly to a late, high latitude substorm expansion. The recovery was also observed to occur after the substorm current wedge had moved into the evening sector and to extend far to the east of the center of the last preceding substorm expansion.

  3. The problem of the acceleration of electrons of the outer radiation belt and magnetospheric substorms

    NASA Astrophysics Data System (ADS)

    Antonova, E. E.; Stepanova, M. V.

    2015-09-01

    Predicting of the location of the maximum in high-energy electron fluxes filling a new radiation belt is an endeavor being carried out by physicists studying the magnetosphere. We analyzed the data from the Defense Meteorological Satellite Program (DMSP) satellites and ground-based magnetometers obtained during geomagnetic storm on 8-9 October 2012. The minimum value of the disturbance storm time (Dst) was -111 nT, and the maximum in high-energy electron fluxes that appeared during the recovery phase was observed at L = 4 Re. At the same time, we analyzed the motion of the auroral oval toward lower latitudes and related substorm activity using the data of the low-orbiting DMSP satellites and the IMAGE magnetic meridian network. It was found from the DMSP satellites' measurements that the maximum of the energy density of precipitating ions, the maximum of the plasma pressure, and the most equatorial part of the westward auroral electrojet are all located at the 60° geomagnetic latitude. This value corresponds to L = 4 Re, i.e., it coincides with the location of the maximum in high-energy electron fluxes. This L-value also agrees with the predictions of the Tverskaya relation between the minimum in Dst variation and the location of the maximum of the energetic electron fluxes, filling a new radiation belt. The obtained results show that the location of this maximum could be predicted solely from the data of the auroral particle precipitations and/or ground-based magnetic observations.

  4. Active experiments, magnetospheric modification, and a naturally occurring analogue

    NASA Technical Reports Server (NTRS)

    Kivelson, M. G.; Russell, C. T.

    1973-01-01

    Recently, a scheme has been proposed which would modify the magnetosphere by injecting plasma near the equator beyond the plasmapause and initiating wave-particle instabilities. The expected effects have been examined theoretically. Injection of plasma into this region is also a naturally occurring phenomenon produced by the cross-tail electric fields which are associated with geomagnetic activity. For further investigation of magnetospheric instabilities, the advantages of examining artificially injected plasma (control of time and location of injection and of the volume of plasma injected) contrast with the advantages of studying natural enhancements (no extra payload, frequent occurrence). Thus, the two types of experiments are complementary. In preliminary studies of natural plasma enhancements both ULF and ELF emissions have been observed. The ELF noise is consistent with generation by the electron cyclotron instability.

  5. A quantitative study of magnetospheric magnetic field line deformation by a two-loop substorm current wedge

    NASA Astrophysics Data System (ADS)

    Nikolaev, A. V.; Sergeev, V. A.; Tsyganenko, N. A.; Kubyshkina, M. V.; Opgenoorth, H.; Singer, H.; Angelopoulos, V.

    2015-04-01

    Substorm current wedge (SCW) formation is associated with global magnetic field reconfiguration during substorm expansion. We combine a two-loop model SCW (SCW2L) with a background magnetic field model to investigate distortion of the ionospheric footpoint pattern in response to changes of different SCW2L parameters. The SCW-related plasma sheet footprint shift results in formation of a pattern resembling an auroral bulge, the poleward expansion of which is controlled primarily by the total current in the region 1 sense current loop (I1). The magnitude of the footprint latitudinal shift may reach ∼ 10° corrected geomagnetic latitude (CGLat) during strong substorms (I1= 2 MA). A strong helical magnetic field around the field-aligned current generates a surge-like region with embedded spiral structures, associated with a westward traveling surge (WTS) at the western end of the SCW. The helical field may also contribute to rotation of the ionospheric projection of narrow plasma streams (auroral streamers). Other parameters, including the total current in the second (region 2 sense) loop, were found to be of secondary importance. Analyzing two consecutive dipolarizations on 17 March 2010, we used magnetic variation data obtained from a dense midlatitude ground network and several magnetospheric spacecraft, as well as the adaptive AM03 model, to specify SCW2L parameters, which allowed us to predict the magnitude of poleward auroral expansion. Auroral observations made during the two substorm activations demonstrate that the SCW2L combined with the AM03 model nicely describes the azimuthal progression and the observed magnitude of the auroral expansion. This finding indicates that the SCW-related distortions are responsible for much of the observed global development of bright auroras.

  6. Estimation of electric fields and currents from International Magnetospheric Study magnetometer data for the CDAW 6 intervals: Implications for substorm dynamics

    SciTech Connect

    Kamide, Y.; Baumjohann, W.

    1985-02-01

    Using a recently developed numerical scheme combined with International Magnetospheric Study magnetometer data and the Rice University Ionospheric conductivity model as input, the global distribution of the key ionospheric parameters is estimated for the Coordinated Data Analysis Workshop (CDAW) 6 intervals. These outputs include ionospheric electric fields and currents, field-aligned currents and Joule heat production rate at high latitudes, and are compiled in the form of a color movie film, which demonstrates dynamics of substorm changes of the three-dimensional current system as well as of the associated potential pattern. The present paper gives, on the basis of the space-time distribution of the key parameters, the substorm time frame that can be referenced to in terms of the substorm phases when discussing some other magnetospheric and ionospheric records. The distinction between ''substorm expansion'' and ''enhanced convection'' current systems is presented on the basis of the conventional equivalent current and potential patterns and ''true'' ionospheric currents. Although the auroral electrojets flow rather contiguously throughout the dark sector, there are several separate source regions of Joule heating from the electrojet currents. This indicates that the relative importance of the ionospheric conductivity and the electric field in the ionospheric currents varies considerably depending upon latitude and local time. A possible difference in the generation mechanisms of isolated and continuous substorm activity is also discussed to some extent in the light of the two CDAW 6 intervals.

  7. PC index as a proxy of the solar wind energy that entered into the magnetosphere: 2. Relation to the interplanetary electric field E KL before substorm onset

    NASA Astrophysics Data System (ADS)

    Troshichev, OA; Sormakov, DA

    2015-10-01

    This paper (the second of a series) presents the results of statistical investigation of relationship between the interplanetary electric field E KL and the Polar Cap (PC) index in case of magnetic substorms (1998-2001), which have been analyzed in Troshichev et al. (J. Geophys. Res. Space Physics, 119, 2014). The PC index is directly related to the E KL field variations on interval preceding the substorm sudden onset (SO): correlation R > 0.5 is typical of more than 90 % of isolated substorms, 80 % of expanded substorms, and 99 % of events with coordinated E KL and PC jumps. The low or negative correlation observing in ~10 % of examined substorms suggests that the solar wind flow measured by the Advanced Composition Explorer (ACE) spacecraft in the Lagrange point L1 did not encounter the magnetosphere in these cases. Examination of the delay times Δ T in the response of PC index to E KL variations provides the following results: (1) delay times do not depend on separate solar wind parameters, such as solar wind speed V X and interplanetary magnetic field (IMF) B Z component, contrary to general conviction, (2) the Δ T value is best controlled by the E KL field growth rate (d E KL/dt), (3) the lower Δ T limit (5-7 min is attained under conditions of the higher E KL growth rate, and (4) the PC index provides the possibility to verify the solar wind flow transportation time from ACE position (where the solar wind speed is estimated) to magnetosphere. These results, in combination with data testifying that the substorm onsets are related to the PC precursors, demonstrate that the PC index is an adequate ground-based indicator of the solar wind energy incoming into the magnetosphere.

  8. Crossover behavior of multiscale fluctuations in Big Data: Langevin model and substorm time-scales in Earth's magnetosphere

    NASA Astrophysics Data System (ADS)

    Sharma, A. S.; Setty, V. A.

    2015-12-01

    Multiscale fluctuations in large and complex data are usually characterized by a power law with a scaling exponent but many systems require more than one exponent and thus exhibit crossover behavior. The scaling exponents, such as Hurst exponents, represent the nature of correlation in the system and the crossover shows the presence of more than one type of correlation. An accurate characterization of the crossover behavior is thus needed for a better understanding of the inherent correlations in the system, and is an important method of Big Data analysis. A multi-step process is developed for accurate computation of the crossover behavior. First the detrended fluctuation analysis is used to remove the trends in the data and the scaling exponents are computed. The crossover point is then computed by a Hyperbolic regression technique, with no prior assumptions. The time series data of the magnetic field variations during substorms in the Earth's magnetosphere is analyzed with these techniques and yields a crossover behavior with a time scale of ~4 hrs. A Langevin model derived from the data provides an excellent fit to the crossover in the scaling exponents and a good model of magnetospheric dynamics. The combination of fluctuation analysis and mathematical modeling thus yields a comprehensive approach in the analysis of Big Data.

  9. Substorm aurorae and their connection to the inner magnetosphere. Technical report

    SciTech Connect

    Lopez, R.E.; Meng, C.I.; Spence, H.E.

    1994-04-15

    In this report the authors present evidence from the low-altitude DMSP F7 satellite that the poleward edge of auroral luminosity in the nightside auroral zone does not necessarily correspond to the boundary between plasma-filled flux tubes and flux tubes devoid of plasma. Assuming that the low-altitude boundary corresponds to the boundary between the lobe and the plasma sheet, this implies that the boundary between open and closed field lines may lie poleward of the most poleward auroral luminosity. Thus the assumption that the poleward boundary of auroral luminosity is a good indicator of the open-closed boundary may not always be correct. Furthermore, they show clear evidence that an auroral surge may also be located equatorward of the open-closed boundary. Therefore, tailward of the region of the plasma sheet to which the surge is connected there may exist undisturbed plasma sheet that has not yet been disconnected from the ionosphere. This means that substorm-associated reconnection does not necessarily begin to reconnect lobe field lines at the onset of a substorm. Moreover, available evidence strongly suggests that the arc that brightens at the onset of a substorm and that develops into a surge maps to the inner magnetotail, to that region at the inner edge of the plasma sheet where the magnetic field changes from a dipolar to a tail-like configuration. This would be consistent with recent studies that connect auroral breakup to the near-Earth (

  10. Micro- and meso-scale simulations of magnetospheric processes related to the aurora and substorm morphology. Final technical report, June 1989-November 1991

    SciTech Connect

    Swift, D.W.

    1991-01-01

    The primary methodology during the grant period has been the use of micro or meso-scale simulations to address specific questions concerning magnetospheric processes related to the aurora and substorm morphology. This approach, while useful in providing some answers, has its limitations. Many of the problems relating to the magnetosphere are inherently global and kinetic. Effort during the last year of the grant period has increasingly focused on development of a global-scale hybrid code to model the entire, coupled magnetosheath - magnetosphere - ionosphere system. In particular, numerical procedures for curvilinear coordinate generation and exactly conservative differencing schemes for hybrid codes in curvilinear coordinates have been developed. The new computer algorithms and the massively parallel computer architectures now make this global code a feasible proposition. Support provided by this project has played an important role in laying the groundwork for the eventual development or a global-scale code to model and forecast magnetospheric weather.

  11. Relationship between the growth of the ring current and the interplanetary quantity. [solar wind energy-magnetospheric coupling parameter correlation with substorm AE index

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1979-01-01

    Akasofu (1979) has reported that the interplanetary parameter epsilon correlates reasonably well with the magnetospheric substorm index AE; in the first approximation, epsilon represents the solar wind coupled to the magnetosphere. The correlation between the interplanetary parameter, the auroral electrojet index and the ring current index is examined for three magnetic storms. It is shown that when the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, producing an abnormal growth of the ring current index.

  12. Field-aligned fluxes of energetic electrons related to the onset of magnetospheric substorms

    NASA Astrophysics Data System (ADS)

    Kremser, G.; Korth, A.; Ullaland, S. L.; Roux, A.; Perraut, S.; Pedersen, A.; Schmidt, R.; Tanskanen, P.

    1987-08-01

    Observations of bidirectional field-aligned fluxes of energetic electrons (16 to 80 keV) at magnetic substorm onset are discussed. The electron fluxes appear 4 min after the onset of the expansion phase, last 1.5 min, and are associated with strong spatial gradients of the ion intensity. The observations are interpreted in terms of a model in which a surface wave develops at the transition from dipolelike to taillike geomagnetic fieldlines. The surface wave couples into kinetic Alfven waves that propagate along the fieldlines, are reflected at the ionosphere, and interact with mirrored electrons on their way back towards the equatorial plane.

  13. Solar Wind-Magnetosphere Coupling During an Isolated Substorm Event: A Multispacecraft ISTP Study

    NASA Technical Reports Server (NTRS)

    Pulkkinen, T. I.; Baker, D. N.; Turner, N. E.; Singer, H. J.; Frank, L. A.; Sigwarth, J. B.; Scudder, J.; Anderson, R.; Kokubun, S.; Mukai, T.; Nakamura, R.; Blake, J. B.; Russell, C. T.; Kawano, H.; Mozer, F.; Slavin, J. A.

    1997-01-01

    Multispacecraft data from the upstream solar wind, polar cusp, and inner magnetotail are used to show that the polar ionosphere responds within a few minutes to a southward IMF turning, whereas the inner tail signatures are visible within ten min from the southward turning. Comparison of two subsequent substorm onsets, one during southward and the other during northward IMF, demonstrates the dependence of the expansion phase characteristics on the external driving conditions. Both onsets are shown to have initiated in the midtail, with signatures in the inner tail and auroral oval following a few minutes later.

  14. The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Meredith, Nigel P.; Horne, Richard B.; Johnstone, Alan D.; Anderson, Roger R.

    2000-06-01

    The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere are investigated using data from the CRRES satellite. Equatorial electron distributions and concomitant wave spectra outside the plasmapause on the nightside of the Earth are studied as a function of time since injection determined from the auroral-electrojet index (AE). The electron cyclotron harmonic (ECH) wave amplitudes are shown to be very sensitive to small modeling errors in the location of the magnetic equator. They are best understood at the ECH equator, defined by the local maximum in the ECH wave activity in the vicinity of the nominal magnetic equator, suggesting that the ECH equator is a better measure of the location of the true equator. Strong ECH and whistler mode wave amplitudes are associated with the injected distributions and at the ECH equator, in the region 6.0<=L<7.0, exponential fits reveal wave amplitude decay time constants of 6.3+/-1.2 and 4.6+/-0.7 hours, respectively. Pancake electron distributions are seen to develop from injected distributions that are nearly isotropic in velocity space and, in this region, are seen to form on a similar timescale of approximately 4 hours suggesting that both wave types are involved in their production. The timescale for pancake production and wave decay is comparable with the average time interval between substorm events so that the wave-particle interactions are almost continually present in this region leading to a continual supply of electrons to power the diffuse aurora. In the region 3.8<=L<6.0 the timescale for wave decay at the ECH equator is 2.3+/-0.6 and 1.1+/-0.2 hours for ECH waves and whistler mode waves respectively, although the pancakes in this region show no clear evolution as a function of time.

  15. Hemispheric Asymmetries in Substorm Recovery Time Scales

    NASA Technical Reports Server (NTRS)

    Fillingim, M. O.; Chua, D H.; Germany, G. A.; Spann, James F.

    2009-01-01

    Previous statistical observations have shown that the recovery time scales of substorms occurring in the winter and near equinox (when the nighttime auroral zone was in darkness) are roughly twice as long as the recovery time scales for substorms occurring in the summer (when the nighttime auroral region was sunlit). This suggests that auroral substorms in the northern and southern hemispheres develop asymmetrically during solstice conditions with substorms lasting longer in the winter (dark) hemisphere than in the summer (sunlit) hemisphere. Additionally, this implies that more energy is deposited by electron precipitation in the winter hemisphere than in the summer one during substorms. This result, coupled with previous observations that have shown that auroral activity is more common when the ionosphere is in darkness and is suppressed when the ionosphere is in daylight, strongly suggests that the ionospheric conductivity plays an important role governing how magnetospheric energy is transferred to the ionosphere during substorms. Therefore, the ionosphere itself may dictate how much energy it will accept from the magnetosphere during substorms rather than this being an externally imposed quantity. Here, we extend our earlier work by statistically analyzing the recovery time scales for a large number of substorms observed in the conjugate hemispheres simultaneously by two orbiting global auroral imagers: Polar UVI and IMAGE FUV. Our current results are consistent with previous observations. The recovery time scales are observed to be longer in the winter (dark) hemisphere while the auroral activity has a shorter duration in the summer (sunlit) hemisphere. This leads to an asymmetric energy input from the magnetosphere to the ionosphere with more energy being deposited in the winter hemisphere than in the summer hemisphere.

  16. Three-Dimensional MHD Simulation of Current Sheet Evolution During the Growth Phase of Magnetospheric Substorms

    NASA Astrophysics Data System (ADS)

    Hall, F.; Otto, A.

    2004-12-01

    Current sheet thinning in the near-Earth magnetotail is an important element of growth phase dynamics since it determines the conditions for substorm onset. The growth phase is initiated by the erosion of closed dayside magnetic flux. This flux is replenished by convection of closed magnetic flux from the near-Earth tail region to the dayside. However, this process of magnetic flux replenishment is subject to the entropy and mass conservation constraints imposed on the slow quasi-static convection of magnetic flux tubes from the mid- and far-tail regions, first identified by Erickson and Wolf (1980). We examine whether the depletion of flux from a finite reservoir in the near-Earth tail region leads to the observed current sheet thinning. This hypothesis is tested using a self-consistent three-dimensional MHD code which is coupled to a semi-empirical magnetic field model. The resulting system was relaxed to an equilibrium state using a modification of a `ballistic relaxation' method. We discuss the structure of the equilibrium near-Earth magnetotail. A plasma outflow is prescribed in the near-Earth magnetotail to model the depletion of the `flux reservoir' described above. The resulting evolution of the current sheet is discussed.

  17. Ion Heating in the Earth's Magnetosphere During Substorm and Storm-time

    NASA Astrophysics Data System (ADS)

    Keesee, A. M.; Scime, E. E.; Pollock, C. J.

    2001-12-01

    In this study, energetic neutral atom (ENA) images from the Medium Energy Neutral Atom (MENA) imager on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) observatory are analyzed. In the MENA imager, incident ENAs create secondary electrons at a carbon foil and then strike a detector that records their position and time of impact. The electrons are used to determine the trajectory and time-of-flight of the ENA. Trajectory information and the spacecraft spin enable two-dimensional ENA images to be constructed. The time between the electron and ENA pulses provides an energy measurement if the ENAs are assumed to be hydrogen. Using the energy spectrum of the MENA neutral flux data, images of the plasma ion temperature are created based on estimates of the peak line-of-sight ion temperature. The geomagnetic activity of the magnetosphere in the images ranges from mildly active to stormy. The spatial distribution of ion heating in the magnetosphere during storm activity will be discussed.

  18. Ion Heating in the Earth's Magnetosphere during Substorm and Storm-time

    NASA Astrophysics Data System (ADS)

    Keesee, Amy; Scime, Earl; Pollock, Craig

    2001-10-01

    In this study, energetic neutral atom (ENA) images from the Medium Energy Neutral Atom (MENA) imager on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) observatory are analyzed. In the MENA imager, incident ENAs create secondary electrons at a carbon foil and then strike a detector that records their position and time of impact. The electrons are used to determine the trajectory and time-of-flight of the ENA. Trajectory information and the spacecraft spin enable two-dimensional ENA images to be constructed. The time between the electron and ENA pulses provides an energy measurement if the ENAs are assumed to be hydrogen. Using the energy spectrum of the MENA neutral flux data, images of the plasma ion temperature are created based on estimates of the peak line-of-sight ion temperature. The geomagnetic activity of the magnetosphere in the images ranges from mildly active to stormy. The spatial distribution of ion heating in the magnetosphere during storm activity will be discussed.

  19. The solar wind and magnetospheric dynamics

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1974-01-01

    The dynamic processes involved in the interaction between the solar wind and the earth's magnetosphere are reviewed. The evolution of models of the magnetosphere is first surveyed. The existence of the auroral substorm and the cyclical polar magnetic substorm is evidence that the magnetosphere is a dynamic system. The dynamic changes occurring in the magnetosphere, including erosion of the magnetopause, changes in the size of the polar cap, variations in the flaring angle of the tail, neutral point formation, plasma sheet motions, and the inward collapse of the midnight magnetosphere, are discussed. The cyclical variations of geomagnetic activity are explained in terms of the control of the solar wind-magnetosphere interaction by the north-south component of the interplanetary magnetic field. Present phenomenological models allow prediction of geomagnetic activity from interplanetary measurements, but modeling of detailed magnetospheric processes is still in its infancy.

  20. Magnetic field fluctuations during substorms

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.

    1971-01-01

    Before a magnetospheric substorm and during its early phases the magnetic field magnitude in the geomagnetic tail increases and field lines in the nighttime hemisphere assume a more tail-like configuration. Before the substorm onset a minimum amount of magnetic flux is observed to cross the neutral sheet which means that the neutral sheet currents attain their most earthward locations and their greatest current densities. This configuration apparently results from an increased transport of magnetic flux to the tail caused by a southward interplanetary magnetic field. The field begins relaxing toward a more dipolar configuration at the time of a substorm onset with the recovery probably occurring first between 6 and 10 R sub E. This recovery must be associated with magnetospheric convection which restores magnetic flux to the dayside hemisphere. Field aligned currents appear to be required to connect magnetospheric currents to the auroral electrojets, implying that a net current flows in a limited range of longitudes. Space measurements supporting current systems are limited. More evidence exists for the occurrence of double current sheets which do not involve net current at a given longitude.

  1. PC index and magnetic substorms

    NASA Astrophysics Data System (ADS)

    Troshichev, Oleg; Janzhura, Alexander; Sormakov, Dmitry; Podorozhkina, Nataly

    PC index is regarded as a proxy of the solar wind energy that entered into the magnetosphere as distinct from the AL and Dst indices, which are regarded as characteristics of the energy that realize in the magnetosphere in form of substorm and magnetic storms. This conclusion is based on results of analysis of relationships between the polar cap magnetic activity (PC-index) and parameters of the solar wind, on the one hand, relationships between changes of PC and development of magnetospheric substorms (AL-index) and magnetic storms (Dst-index), on the other hand. This paper describes in detail the following main results which demonstrate a strong connection between the behavior of PC and development of magnetic disturbances in the auroral zone: (1) magnetic substorms are preceded by the РС index growth (isolated and extended substorms) or long period of stationary PC (postponed substorms), (2) the substorm sudden onsets are definitely related to such PC signatures as leap and reverse, which are indicative of sharp increase of the PC growth rate, (3) substorms generally start to develop when the PC index exceeds the threshold level ~ 1.5±0.5 mV/m, irrespective of the substorm growth phase duration and type of substorm, (4) linear dependency of AL values on PC is typical of all substorm events irrespective of type and intensity of substorm.

  2. Substorm recurrence during steady and variable solar wind driving: Evidence for a normal mode in the unloading dynamics of the magnetosphere

    NASA Technical Reports Server (NTRS)

    Klimas, A. J.; Baker, D. N.; Vassiliadis, D.; Roberts, D. A.

    1994-01-01

    Farrugia et al (1993) have recently studied substorm activity driven by the passage of an interplanetary magnetic cloud during which the interplanetary magnetic field turned southward for approximately 18 hours. It was shown that both the epsilon and the VB(sub s) parameters varied slowly on the timescale of a substorm but changed considerably over the interval as a whole. The substorm occurrence rate did not reflect the variation in magnetospheric energy loading rate as measured by these parameters but, rather, remained roughly constant with a 50-min average period. Klimas et al. (1992) showed that the Faraday loop analog model of geomagnetic activity predicts this single unloading rate under various constant loading rates. However, various model parameters were adjusted to yield a 1-hour unloading period in agreement with the Bargatze et al. (1985) linear prediction filters and in approximate agreement with the Farrugia et al. (1993) results. It has since been found necessary to add a slow relaxation mechanism to the Faraday loop model to allow for its approach to a ground state during long periods of inactivity. It is proposed that the relaxation mechanism is provided by slow convection of magnetic flux out of the magnetotail to the dayside magnetosphere. In addition, a rudimentary representation of magnetotail-ionosphere coupling has been added to enable comparison of model output to measured AL. The present study is of the modified Faraday loop model response to solar wind input from the Bargatze et al. data set with comparison of its output to concurrent AL. This study has removed the degree of freedom in parameter choice that had earlier allowed adjustments toward the 1-hour unloading period and has, instead, yielded the 1-hour unloading period under various constant loading rates. It is demonstrated that the second peak of the bimodal Bargatze et al. linear prediction filters at approximately equal 1-hour lag and the approximately constant substorm

  3. Role of heavy ionospheric ions in the localization of substorm disturbances on March 22, 1979: CDAW 6

    SciTech Connect

    Baker, D.N.; Fritz, T.A.; Lennartsson, W.; Wilken, B.; Kroehl, H.W.; Birn, J.

    1985-02-01

    Extensive ground-based arrays of magnetometers and numerous satellite platforms in the outer magnetosphere have established that two separate substorm expansion onsets occurred on March 22, 1979. The first of these occurred at 1055 UT and is demonstrated to be localized in the 0200--0300 LT sector. Concurrent plasma sheet ion composition measurements are used to show that the growth and expansion phase of this substorm occurred while the outer magnetosphere was composed dominantly of solar wind (H/sup +/ and He/sup + +/) plasmas. The 1055 UT substorm greatly perturbed and altered the ion composition of the plasma in the outer magnetosphere such that the second substorm expansion onset (1436 UT) occurred while the outer magnetospheric plasmas were dominantly of ionospheric (O/sup +/) origin. The 1436 UT substorm is shown to have a component of the westward electrojet localized further westward in local time relative to the first substorm. These results are a consistent, well-documented example of the possible important role of heavy ions in the localization and initiation of plasma sheet instabilities during substorms.

  4. Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Wild, J. A.; Milan, S. E.; Yeoman, T. K.

    2008-12-01

    Using data from the Super Dual Auroral Radar Network (SuperDARN) we investigate the ionospheric convection response to magnetospheric substorms. Substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, and were then grouped according to the magnetic latitude of their onset. A superposed epoch analysis of the ionospheric convection patterns for each latitude group was then performed using radar data for the interval 60 minutes before onset to 90 minutes after. It is found that lower latitude onset substorms are associated with generally more enhanced convection than the higher latitude substorms, although they suffer from the most significant localised suppression of the flow in the midnight sector during the expansion phase. On the other hand, the higher-latitude events are associated with a significant and rapid increase in the nightside convection following substorm onset. These results suggest differences in the electrodynamics associated with substorms occurring at different latitudes.

  5. The earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1976-01-01

    The following aspects of the earth's magnetosphere were discussed: general structure, magnetic field merging and magnetospheric convection, time-varying convection and magnetospheric substorms, magnetic storms, and comparative magnetospheres. Solar flares and the magnetospheres of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus were also described.

  6. Does a "substorm precursor" exist in the polar cap?

    NASA Astrophysics Data System (ADS)

    Nosikova, Nataliya; Lorentzen, Dag; Yagova, Nadezda; Baddeley, Lisa; Pilipenko, Vyacheslav; Kozyreva, Olga

    2015-04-01

    An isolated auroral substorm, which occurs without external triggering, can develop as a result of inner instabilities in the geomagnetic tail. The comparative analysis of presubstorm variations of the geomagnetic field and particle flux in the geomagnetic tail along with geomagnetic and auroral disturbances in the polar caps is of key importance for the discrimination between direct triggering and intra-magnetospheric processes in a substorm onset. In the present study we compare the auroral disturbances and geomagnetic pulsations in the frequency range 1-5 mHz (Pc5/Pi3) at nighttime high latitudes during both quiet geomagnetic intervals preceding isolated substorms and non-substorm intervals. Superposed epoch analysis is applied to reveal pre-substorm variations ("substorm precursors"). The data from IMAGE magnetometer network, the Meridian Scanning photometer (Svalbard), and particle flux measured by GEOTAIL, has been used. The effect of presubstorm activation (Yagova, 2000) is reproduced during the solar minimum conditions. References Yagova N., V. Pilipenko, A. Rodger, V. Papitashvili, J. Watermann, Long period ULF activity at the polar cap preceding substorm, in: Proc. 5th International Conference on Substorms, St. Peterburg, Russia (ESA SP-443), 603-606, 2000.

  7. Electrodynamics of solar wind-magnetosphere-ionosphere interactions

    NASA Technical Reports Server (NTRS)

    Kan, Joseph R.; Akasofu, Syun-Ichi

    1989-01-01

    The paper presents a coherent picture of fundamental physical processes in three basic elements of the solar-wind/magnetosphere/ionosphere coupling system: (1) the field-aligned potential structure which leads to the formation of auroral arcs, (2) the magnetosphere-ionosphere coupling which leads to the onset of magnetospheric substorms, and (3) the solar-wind/magnetosphere dynamo which supplies the power driving various magnetospheric processes. Process (1) is forced into existence by the loss-cone constriction effect when the upward field-aligned current density exceeds the loss-cone thermal flux limit. Substorm onset occurs when the ionosphere responds fully to the enhanced magnetospheric convection driven by the solar wind. Energy is transferred from the solar wind to the magnetosphere by a dynamo process, primarily on open field lines.

  8. Comparison of Two Substorms Observed on August 1, 1998

    NASA Astrophysics Data System (ADS)

    Borodkova, Natalia; Parkhomov, Vladimir; Zastenker, Georgy

    Magnetospheric response to the onset and development of two successive substorms, caused by different reasons is investigated. The choice of these events was due to the successful location of satellites in different areas of near-Earth space and the presence of numerous satellite and ground based observations. First substorm initiated at 17.20 UT on August 1, 1998 was caused by spontaneous release of exceeded energy stored in the tail. The second substorm occurred at the same day at 18.30 UT, was triggered by large and sharp solar wind dynamic pressure enhancement, accompanied by fluctuations of the interplanetary magnetic field. This pres-sure enhancement, consisted of a sequence of several fast fluctuations in solar wind dynamic pressure, led to the corresponding variations of magnetic field and energetic particle fluxes at geosynchronous orbit and ground stations and auroral disturbances. It was found that corre-lation coefficients calculated between the solar wind pressure fluctuations and magnetospheric responding parameters are significantly high. It was shown that first substorm was localized in the midnight sector of the aurora, westward auroral bulge was formed during the growth phase and typical recovery phase was observed. In contrast to that the second substorm, caused by an external trigger, was characterized by dayside auroral intensification propagating to down and dusk and nightside auroral activity localized in the premidnight sector.The global modulation of magnetospheric currents by the solar wind dynamic pressure was shown for the second event.

  9. Classification of Initial conditions required for Substorm prediction.

    NASA Astrophysics Data System (ADS)

    Patra, S.; Spencer, E. A.

    2014-12-01

    We investigate different classes of substorms that occur as a result of various drivers such as the conditions in the solar wind and the internal state of the magnetosphere ionosphere system during the geomagnetic activity. In performing our study, we develop and use our low order physics based nonlinear model of the magnetosphere called WINDMI to establish the global energy exchange between the solar wind, magnetosphere and ionosphere by constraining the model results to satellite and ground measurements. On the other hand, we make quantitative and qualitative comparisons between our low order model with available MHD, multi-fluid and ring current simulations in terms of the energy transfer between the geomagnetic tail, plasma sheet, field aligned currents, ionospheric currents and ring current, during isolated substorms, storm time substorms, and sawtooth events. We use high resolution solar wind data from the ACE satellite, measurements from the CLUSTER and THEMIS missions satellites, and ground based magnetometer measurements from SUPERMAG and WDC Kyoto, to further develop our low order physics based model. Finally, we attempt to answer the following questions: 1) What conditions in the solar wind influence the type of substorm event. This includes the IMF strength and orientation, the particle densities, velocities and temperatures, and the timing of changes such as shocks, southward turnings or northward turnings of the IMF. 2) What is the state of the magnetosphere ionosphere system before an event begins. These are the steady state conditions prior to an event, if they exist, which produce the satellite and ground based measurements matched to the WINDMI model. 3) How does the prior state of the magnetosphere influence the transition into a particular mode of behavior under solar wind forcing. 4) Is it possible to classify the states of the magnetosphere into distinct categories depending on pre-conditioning, and solar wind forcing conditions? 5) Can we

  10. Role of sudden commencements in triggering magnetospheric substorms. M.S. Thesis; [based on ATS 1 data

    NASA Technical Reports Server (NTRS)

    Newell, R. E.

    1974-01-01

    Sudden commencement events are examined in terms of available auroral-zone and low-latitude magnetic field, data, interplanetary plasma and magnetic field data, and magnetospheric electron flux and magnetic field data from the geostationary satellite ATS 1.

  11. Space weather and the safety of ground infrastructures. Numerical simulation and prediction of electromagnetic effects induced by real magnetospheric substorms in the Earth's models with real three-dimensional distribution of electrical conductivity

    NASA Astrophysics Data System (ADS)

    Kuvshinov, Alexey; Filippov, Sergey; Kalegaev, Vladimir; Sidorova, Larisa; Mukhametdinova, Ludmila; Pankratov, Oleg; Alexeev, Dmitry

    Strong eruptions at Sun’s surface produce large release of matter (plasma), which, with a speed of 800-1000 km/s (the solar wind), flows into interplanetary space. If the Earth appears to be on the way of the solar wind the interaction of the wind with the Earth's magnetosphere and the ionosphere leads to abnormal disturbance of fluctuating geomagnetic field. In the middle latitudes, the disturbances (geomagnetic storms) last a few days and have amplitudes up to 400 nT. At high latitudes, these perturbations (magnetospheric substorms) last a few hours and have amplitudes up to 3000 nT. According to Faraday’s law of induction, the fluctuating magnetic field in turn generates a electric field. The electric field for intense substorms can reach hundreds of volts/km in the polar region and generate very high, the so-called geomagnetic induced currents in the ground-based systems, such as power grids and pipelines. These currents are one of the most dangerous factors affecting the operation of the above systems. Thus extremely topical task in the field of "space weather" is the quantification and prediction of spatio-temporal distribution of the electric field during substorm activity. Despite the abundance of works carried out in this direction, the problem is still far from a satisfactory solution. In the field of modeling, researchers are still working with highly simplified models of both the source and the conducting Earth. As for prediction the situation is even worse. In this presentation we discuss a general formalism which allows for simulating the electric fields induced by real magnetospheric substorms in the spherical model of the Earth with real three-dimensional distribution of conductivity. We show the first results of such simulations. We also discuss a concept to predict substorm spatio-temporal pattern of the electric field.

  12. Tail reconnection triggering substorm onset.

    PubMed

    Angelopoulos, Vassilis; McFadden, James P; Larson, Davin; Carlson, Charles W; Mende, Stephen B; Frey, Harald; Phan, Tai; Sibeck, David G; Glassmeier, Karl-Heinz; Auster, Uli; Donovan, Eric; Mann, Ian R; Rae, I Jonathan; Russell, Christopher T; Runov, Andrei; Zhou, Xu-Zhi; Kepko, Larry

    2008-08-15

    Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at approximately 10 R(E) (R(E): Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at approximately 20 to 30 R(E). We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 R(E), at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection. PMID:18653845

  13. Steady Magnetospheric Convection: A Review

    NASA Astrophysics Data System (ADS)

    Fairfield, D. H.

    2004-12-01

    On occasion, solar wind energy enters Earth's magnetosphere yet the common discrete energy-dissipation events known as magnetospheric substorms fail to occur. During these times, the magnetotail assumes a configuration where earthward of about 12 Re the tail remains in a stretched tail-like state with a thin current sheet similar to the substorm growth phase. At the same time the more distant tail attains a more relaxed configuration with a thick plasma sheet, weak lobe field and enhanced northward Bz, similar to the substorm recovery phase. Simultaneously, (1) auroral zone currents remain strong and assume a two cell DP 2 convection pattern; (2) the auroral oval is wide and optically active, particularly at its poleward and equatorward edges; (3) polar cap area remains constant and energetic particle boundaries are stable, (4) earthward plasma flow persists near the center of the tail as implied by the name steady magnetospheric convection (SMC) except that it occurs on a time scale of minutes and the flow remains bursty. These small scale flows in the tail correspond to auroral streamers that form near the poleward boundary of the oval and propagate equatorward in a few minutes time. Although SMC events have some substorm-like characteristics, such as Pi2's, particle injections and region 1-type field aligned currents with their associated westward ionospheric currents, such phenomena occur on much shorter time and spatial scales and with much smaller amplitudes than actual substorms. Modeling the global magnetic field for several specific SMC events suggest that a minimum in the equatorial tail field Bz magnitude exists near 12 Re which may correspond to the one known equilibrium field configuration that can avoid the pressure catastrophe that may correspond to substorms. This unique field configuration may permit the return of magnetic flux to the dayside that allows the persistence of the steady state field configuration.

  14. Numerical modeling of the ionospheric effects of substorms

    NASA Astrophysics Data System (ADS)

    Klimenko, M. V.; Klimenko, V. V.

    2008-12-01

    The investigations of the substorm are carried out already many years. In spite of that, the single-valued answers on many questions which arise at the researchers of the substorm till now are not given. To such questions it is possible to concern the questions about the mechanism of occurrence of the substorm and on the influence of the substorm on the Earth's ionosphere. At modeling of the ionospheric effects of substorms it is important to know the following. How does the potential drop through polar caps change at initial stages of the substorm development - stepwise or smoothly? What is the duration of these changes? What and how does occur with the potential drop in the further during development of the substorm down to its termination? How does the time course of intensity of the field aligned currents of the first zone change before the substorm beginning, during substorm and after its termination? Is there a time delay of changes of the field aligned currents of the second zone relative to changes of the field aligned currents of the first zone or potential drop through polar caps? If the delay exists, what is it? How does the high-energy particle precipitation in the auroral zones and polar caps change during the substorm? Is it necessary to set at the modeling of the substorm effects the Substorm Current Wedge? If it is necessary, how make it correctly? On these questions we do not have the single-valued answers. But we shall like very strongly for them to have. We have carried out the modeling researches of the substorm influence on the ionosphere in various statements of the problem. The investigations were spent on the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere, added by the new block of calculation of electric fields in the Earth's ionosphere. In our investigations we have given the particular attention: to electrodynamics of the ionosphere; to changes of the global distributions of foF2, TEC and ion composition of

  15. Turbulence vs Self-organized criticality: A hybrid approach, with implications for substorm dynamics of the magnetosphere

    NASA Astrophysics Data System (ADS)

    Milovanov, Alexander

    Plasmas in astrophysics, cosmical geophysics, and laboratory plasmas are often found in far-from-equilibrium dynamical state usually described as ``turbulence". It has been argued and discussed in the literature that the typical signatures of turbulent systems including power-law power spectral density and the scale-free statistics of fluctuating observable quantities can more or less successfully be reproduced by complex systems in the state of self-organized criticality (SOC). An obvious distinction between the theoretical concepts of turbulence and SOC has not been obtained, though (for the challenges that lie ahead, and current scientific debate, see the recently announced book on ``Self-Organized Criticality Systems" - available in open access from Open Academic Press, http://www.openacademicpress.de/). Here we discuss these issues further and show that the behavior crucially depends on the type of boundary conditions, feedback mechanisms, and the role of nonlinearity. We then apply this approach to the dynamics of Earth's geomagnetic tail and propose a hybrid model of ``turbulent" current sheet, which explicitly takes into account the self-organization processes taking place. The model yields the slope of magnetic fluctuation spectra in the near-Earth stretched magnetotail prior to the substorm below the characteristic frequency turnover scales posed by convection. A comparison between the model theoretical predictions and the available data of in situ satellite observations is given.

  16. Thermospheric density perturbations in response to substorms

    NASA Astrophysics Data System (ADS)

    Clausen, L. B. N.; Milan, S. E.; Grocott, A.

    2014-06-01

    We use 5 years (2001-2005) of CHAMP (Challenging Minisatellite Payload) satellite data to study average spatial and temporal mass density perturbations caused by magnetospheric substorms in the thermosphere. Using statistics from 2306 substorms to construct superposed epoch time series, we find that the largest average increase in mass density of about 6% occurs about 90 min after substorm expansion phase onset about 3 h of magnetic local time east of the onset region. Averaged over the entire polar auroral region, a mass density increase of about 4% is observed. Using a simple model to estimate the mass density increase at the satellite altitude, we find that an energy deposition rate of 30 GW applied for half an hour predominantly at an altitude of 110 km is able to produce mass density enhancements of the same magnitude. When taking into account previous work that has shown that 80% of the total energy input is due to Joule heating, i.e., enhanced electric fields, whereas 20% is due to precipitation of mainly electrons, our results suggest that the average substorm deposits about 6 GW in the polar thermosphere through particle precipitation. Our result is in good agreement with simultaneous measurements of the NOAA Polar-orbiting Operational Environmental Satellite (POES) Hemispheric Power Index; however, it is about 1 order of magnitude less than reported previously.

  17. Substorm current wedge composition by wedgelets

    NASA Astrophysics Data System (ADS)

    Liu, Jiang; Angelopoulos, V.; Chu, Xiangning; Zhou, Xu-Zhi; Yue, Chao

    2015-03-01

    Understanding how a substorm current wedge (SCW) is formed is crucial to comprehending the substorm phenomenon. One SCW formation scenario suggests that the substorm time magnetosphere is coupled to the ionosphere via "wedgelets," small building blocks of an SCW. Wedgelets are field-aligned currents (FACs) carried by elemental flux transport units known as dipolarizing flux bundles (DFBs). A DFB is a magnetotail flux tube with magnetic field stronger than that of the ambient plasma. Its leading edge, known as a "dipolarization front" or "reconnection front," is a product of near-Earth reconnection. Dipolarizing flux bundles, and thus wedgelets, are localized—each is only <3 RE wide. How these localized wedgelets combine to become large-scale (several hours of magnetic local time) region-1-sense SCW FACs is unclear. To determine how this occurs, we investigated wedgelets statistically using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. The results show wedgelet asymmetries: in the dawn (dusk) sector of the magnetotail, a wedgelet has more FAC toward (away from) the Earth than away from (toward) the Earth, so the net FAC is toward (away from) the Earth. The combined effect of many wedgelets is therefore the same as that of large-scale region-1-sense SCW, supporting the idea that they comprise the SCW.

  18. The Role of Self-Organized Criticality in the Substorm Phenomenon and its Relation to Localized Reconnection in the Magnetospheric Plasma Sheet

    NASA Technical Reports Server (NTRS)

    Klimas, Alex J.; Valdivia, J. A.; Vassiliadis, D.; Baker, D. N.; Hesse, M.; Takalo, J.

    1999-01-01

    Evidence is presented that suggests there is a significant self-organized criticality (SOC) component in the dynamics of substorms in the magnetosphere. Observations of BBFs, fast flows, localized dipolarizations, plasma turbulence, etc. are taken to show that multiple localized reconnection sites provide the basic avalanche phenomenon in the establishment of SOC in the plasma sheet. First results are presented from a continuing plasma physical study of this avalanche process. A one-dimensional resistive MHD model of a magnetic field reversal is discussed. Resistivity, in this model, is self-consistently generated in response to the excitation of an idealized current-driven instability. When forced by convection of magnetic flux into the field reversal region, the model yields rapid magnetic field annihilation through a dynamic behavior that is shown to exhibit many of the characteristics of SOC. Over a large range of forcing strengths, the annihilation rate is shown to self-adjust to balance the rate at which flux is convected into the reversal region. Several analogies to magnetotail dynamics are discussed: (1) It is shown that the presence of a localized criticality in the model produces a remarkable stability in the global configuration of the field reversal while simultaneously exciting extraordinarily dynamic internal evolution. (2) Under steady forcing, it is shown that a loading-unloading cycle may arise that, as a consequence of the global stability, is quasi-periodic and, therefore, predictable despite the presence of internal turbulence in the field distribution. Indeed, it is shown that the global loading-unloading cycle is a consequence of the internal turbulence. (3) It is shown that, under steady, strong forcing the loading-unloading cycle vanishes. Instead, a recovery from a single unloading persists indefinitely. The field reversal is globally very steady while internally it is very dynamic as field annihilation goes on at the rate necessary to

  19. Convection dynamics and driving mechanism of a small substorm during dominantly IMF By+, Bz+ conditions

    NASA Astrophysics Data System (ADS)

    Liang, Jun; Sofko, G. J.; Donovan, E. F.; Watanabe, M.; Greenwald, R. A.

    2004-04-01

    Ground-based optical, magnetic and radar measurements detected a small substorm on October 9, 2000. Solar wind observations on GEOTAIL revealed a prolonged dominant Bz+ and steady By+ interplanetary magnetic field (IMF) prior to the substorm onset, except for a southward excursion at 0645-0655 UT, and a ``square-wave'' IMF Bx-By structure at 0727-0735 UT. We find that the IMF southward excursion led to the dayside convection enhancement and energy transport into the magnetosphere. When the dayside convection decreased, two pseudobreakups occurred as the consequence of the release of magnetospheric energy into the ionosphere. The substorm onset was associated with the IMF Bx-By structure in ``directly driven'' fashion. There was also a Stage-2 expansion which was internally driven within the magnetotail.

  20. Planetary magnetospheres

    NASA Technical Reports Server (NTRS)

    Stern, D. P.; Ness, N. F.

    1981-01-01

    A concise overview is presented of our understanding of planetary magnetospheres (and in particular, of that of the Earth), as of the end of 1981. Emphasis is placed on processes of astrophysical interest, e.g., on particle acceleration, collision-free shocks, particle motion, parallel electric fields, magnetic merging, substorms, and large scale plasma flows. The general morphology and topology of the Earth's magnetosphere are discussed, and important results are given about the magnetospheres of Jupiter, Saturn and Mercury, including those derived from the Voyager 1 and 2 missions and those related to Jupiter's satellite Io. About 160 references are cited, including many reviews from which additional details can be obtained.

  1. Substorm statistics: Occurrences and amplitudes

    SciTech Connect

    Borovsky, J.E.; Nemzek, R.J.

    1994-05-01

    The occurrences and amplitudes of substorms are statistically investigated with the use of three data sets: the AL index, the Los Alamos 3-satellite geosynchronous energetic-electron measurements, and the GOES-5 and -6 geosynchronous magnetic-field measurements. The investigation utilizes {approximately} 13,800 substorms in AL, {approximately} 1400 substorms in the energetic-electron flux, and {approximately} 100 substorms in the magnetic field. The rate of occurrence of substorms is determined as a function of the time of day, the time of year, the amount of magnetotail bending, the orientation of the geomagnetic dipole, the toward/away configuration of the IMF, and the parameters of the solar wind. The relative roles of dayside reconnection and viscous coupling in the production of substorms are assessed. Three amplitudes are defined for a substorms: the jump in the AL index, the peak of the >30-keV integral electron flux at geosynchronous orbit near midnight, and the angle of rotation of the geosynchronous magnetic field near midnight. The substorm amplitudes are statistically analyzed, the amplitude measurements are cross correlated with each other, and the substorm amplitudes are determined as functions of the solar-wind parameters. Periodically occurring and randomly occurring substorms are analyzed separately. The energetic-particle-flux amplitudes are consistent with unloading and the AL amplitudes are consistent with direct driving plus unloading.

  2. The Disruption Zone Model of Magnetospheric Substorms: Reconnection at the Very-near-Earth Neutral Line and the Shape of the Resulting Plasmoid

    NASA Astrophysics Data System (ADS)

    Sofko, G. J.; McWilliams, K. A.; Bryant, C. R.

    2011-12-01

    In the near-Earth magnetotail, the neutral sheet (NSh) is bounded by closed stretched field line regions, which we call Disruption Zones (DZs). There, the magnetic field lines have both outward curvature and an outward gradient, away from the deep minimum in the NSh near about 8 - 12 RE. As a result, there is eastward ion drift and current in the DZs, in contrast to the westward ion drift and current in the NSh. This eastward current interrupts the normal westward plasmasheet current from the dawn to dusk LLBL regions, and is the current disruption that causes the Substorm Current Wedge. A double solenoidal current system develops in which eastward current in the DZs closes to westward current in the NSh. This system supplies more closed magnetic flux to the inner DZs and exerts more magnetic pressure on the NSh, causing it to thin further and move earthward. The DZ eastward ion drifts and currents are strongest where the curvature and the outward gradient of the magnetic field are most intense, namely at the earthward end of the NSh. As a result, that is where reconnection occurs near substorm onset. This location is not the usual near-Earth neutral line (NENL), but is a very near-Earth neutral line (VNENL) in the ~ X = 7 - 11 RE range. Once the reconnection occurs between two antiparallel magnetic field lines in the thin earthward part of the NSh, the tailward line of the reconnection pair becomes the "plasmoid". It has a very distinct shape, namely that of a bottle. The bottle has a long neck which is simply the thinned NSh extending from about 7 to 20 RE. Beyond that is the body of the bottle. When reconnection occurs at the VNENL, sealing the neck of the bottle, the NSh plasma in the neck moves tailward at ~ 200 - 300 km/s and spills into the body of the bottle. In the meantime, the next closed field line moves in to replace the previously reconnected line, plasma from the DZs refills the NSh, and the reconnection continues at the VNENL. When the plasma from

  3. Correlative comparison of geomagnetic storms and auroral substorms using geomagnetic indeces. Master's thesis

    SciTech Connect

    Cade, W.B.

    1993-06-01

    Partial contents include the following: (1) Geomagnetic storm and substorm processes; (2) Magnetospheric structure; (3) Substorm processes; (4) Data description; (5) Geomagnetic indices; and (6) Data period and data sets.

  4. Network analysis of geomagnetic substorms using the SuperMAG database of ground-based magnetometer stations

    NASA Astrophysics Data System (ADS)

    Dods, J.; Chapman, S. C.; Gjerloev, J. W.

    2015-09-01

    The overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground-based magnetometers. This paper focuses on the quantitative characterization of substorm dynamics captured by ground-based magnetometer stations. We present the first analysis of substorms using dynamical networks obtained from the full available set of ground-based magnetometer observations in the Northern Hemisphere. The stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold. Dimensionless parameters can then be obtained that characterize the network and by extension, the spatiotemporal dynamics of the substorm under observation. We analyze four isolated substorm test cases as well as a steady magnetic convection (SMC) event and a day in which no substorms occur. These test case substorms are found to give a consistent characteristic network response at onset in terms of their spatial correlation. Such responses are differentiable from responses to the SMC event and nonsubstorm times. We present a method to optimize network parametrization with respect to the different individual station responses, the spatial inhomogeneity of stations in the Northern Hemisphere, and the choice of correlation window sizes. Our results suggest that dynamical network analysis has potential to quantitatively categorize substorms.

  5. Substorm electrodynamics

    NASA Technical Reports Server (NTRS)

    Stern, David P.

    1990-01-01

    The present one-dimensional model analysis of substorm electrodynamics proceeds from the standard scenario in which the plasma sheet collapses into a neutral sheet, and magnetic merging occurs between the two tail lobes; plasma flows into the neutral sheet from the lobes and the sides, undergoing acceleration in the dawn-dusk direction. The process is modified by the tendency of the accelerated plasma to unbalance charge neutrality, leading to an exchange of electrons with the ionosphere in order to maintain neutrality. The cross-tail current is weakened by the diversion: this reduces the adjacent lobe-field intensity, but without notable effects apart from a slight expansion of the tail boundary.

  6. Superposed epoch analysis of the ionospheric convection evolution during substorms: IMF BY dependence

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Milan, S. E.; Yeoman, T. K.; Sato, N.; Yukimatu, A. S.; Wild, J. A.

    2010-10-01

    We present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field (IMF). Observations of the ionospheric convection were provided by the Super Dual Auroral Radar Network (SuperDARN) and substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. We find that during the substorm growth phase the expected IMF BY-dependent dawn-dusk asymmetry is observed over the entire convection pattern, but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone. In the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk-dawn asymmetry being more closely related to the magnetic local time of substorm onset, itself only weakly governed by IMF BY. Owing to the preponderance of substorms occurring just prior to magnetic midnight, the substorm-asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector, a manifestation of the so-called “Harang discontinuity.” This results in the northern (southern) hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative (positive) IMF BY. When the preexisting convection pattern in the northern (southern) hemisphere is driven by positive (negative) IMF BY, the nightside auroral convection changes markedly over the course of the substorm to establish this same “Harang” configuration.

  7. Fluctuating magnetic fields in the magnetosphere. II - ULF waves.

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Russell, C. T.; Coleman, P. J., Jr.

    1972-01-01

    At the present time the existing satellite observations of ULF waves suggest that the level of geomagnetic activity controls the types of waves which occur within the magnetosphere. Consequently, we consider separately quiet times, times of magnetospheric substorms, and times of magnetic storms. Within each of these categories, there are distinctly different wave modes distinguished by their polarization: either transverse or parallel to the ambient field. In addition, these wave phenomena occur in distinct frequency bands. In terms of the standard nomenclature of ground micropulsation studies ULF wave types observed in the magnetosphere include quiet time transverse - Pc 1, Pc 3, Pc 4, Pc 5; quiet time compressional - Pc 1 and Pi 1; substorm compressional Pi 1 and Pi 2; storm transverse - Pc 1; storm compressional Pc 4, 5.

  8. The roles of direct input of energy from the solar wind and unloading of stored magnetotail energy in driving magnetospheric substorms

    NASA Technical Reports Server (NTRS)

    Rostoker, G.; Akasofu, S. I.; Baumjohann, W.; Kamide, Y.; Mcpherron, R. L.

    1987-01-01

    The contributions to the substorm expansive phase of direct energy input from the solar wind and from energy stored in the magnetotail which is released in an unpredictable manner are considered. Two physical processes for the dispensation of the energy input from the solar wind are identified: (1) a driven process in which energy supplied from the solar wind is directly dissipated in the ionosphere; and (2) a loading-unloading process in which energy from the solar wind is first stored in the magnetotail and then is suddenly released to be deposited in the ionosphere. The pattern of substorm development in response to changes in the interplanetary medium has been elucidated for a canonical isolated substorm.

  9. Proton aurora and substorm intensifications

    NASA Technical Reports Server (NTRS)

    Samson, J. C.; Xu, B.; Lyons, L. R.; Newell, P. T.; Creutzberg, F.

    1993-01-01

    Ground based measurements from the CANOPUS array of meridian scanning photometers and precipitating ion and electron data from the DMSP F9 satellite show that the electron arc which brightens to initiate substorm intensifications is formed within a region of intense proton precipitation that is well equatorward (approximately four to six degrees) of the nightside open-closed field line boundary. The precipitating protons are from a population that is energized via earthward convection from the magnetotail into the dipolar region of the magnetosphere and may play an important role in the formation of the electron arcs leading to substorm intensifications on dipole-like field lines.

  10. Substorm theories: United they stand, divided they fall

    NASA Technical Reports Server (NTRS)

    Erickson, Gary M.

    1995-01-01

    Consensus on the timing and mapping of substorm features has permitted a synthesis of substorm models. Within the synthesis model the mechanism for onset of substorm expansion is still unknown. Possible mechanisms are: growth of an ion tearing mode, current disruption by a cross-field current instability, and magnetosphere-ionosphere coupling. While the synthesis model is consistent with overall substorm morphology, including near-Earth onset, none of the onset theories, taken individually, appear to account for substorm expansion onset. A grand synthesis with unification of the underlying onset theories appears necessary.

  11. Observations of the Ionospheric Response to a Weak Substorm Onset

    NASA Astrophysics Data System (ADS)

    Chartier, A.; Gjerloev, J. W.; Ohtani, S.; Nikoukar, R.; Forte, B.

    2015-12-01

    We present observations of substorm onset at Tromsø, Norway. This event was unusually well observed by ground magnetometers, incoherent scatter radar, satellites, an allsky camera and a scintillation monitor in the vicinity of the onset location. At onset, ground magnetometer observations indicate the formation of a westward electrojet above Tromsø and, at the same location, allsky camera images show an arc brightening and moving poleward. Satellite observations are consistent with an onset location at Tromsø, followed by a westward surge of dipolarization. Two features of the ionospheric response are observed by the incoherent scatter radar at Tromsø: 1) At onset, ion drift velocities reduce sharply from 100-400 m/s to roughly zero, consistent with a field-aligned potential drop shielding the ionosphere from magnetospheric convection. 2) There is a two-stage enhancement of the westward electrojet, with each stage directly preceded by an increase of ionization. Both these features are consistent with the theory that the inner magnetosphere acts neither as a current nor a voltage generator during substorm onset. Figure shows EISCAT observations of line-of-sight ion drifts, electron and ion temperatures. There is a transition from ExB drift, indicated by a decrease in ion velocity in panel (a), to electron precipitation indicated by increased electron temperatures in panel (b). Substorm onset occurs at the transition time, around 20:02:30 UT.

  12. Electron precipitation patterns and substorm morphology.

    NASA Technical Reports Server (NTRS)

    Hoffman, R. A.; Burch, J. L.

    1973-01-01

    Statistical analysis of data from the auroral particles experiment aboard OGO 4, performed in a statistical framework interpretable in terms of magnetospheric substorm morphology, both spatial and temporal. Patterns of low-energy electron precipitation observed by polar satellites are examined as functions of substorm phase. The implications of the precipitation boundaries identifiable at the low-latitude edge of polar cusp electron precipitation and at the poleward edge of precipitation in the premidnight sector are discussed.

  13. Path of the solar wind energy into the Earth s magnetosphere

    NASA Astrophysics Data System (ADS)

    Alexeev, I.

    The solar wind MHD generator is an unique energy source for all magnetospheric processes. The field-aligned currents directly transport the energy and momentum of the solar wind plasma to the Earth's ionosphere. The magnetospheric lobe and plasma sheet convection generated by the solar wind is another magnetospheric energy source. Plasma sheet particles and cold ionospheric polar wind ions are accelerated by convection electric field in the nightside magnetosphere. After energetic particle precipitation into upper atmosphere the premier solar wind energy transfer into ionosphere and atmosphere. This way of energy transfer can include the tail lobe magnetic field energy storage connected with the increasing of the tail current during southward IMF. After that the magnetospheric substorm occurs. The model calculations of the magnetospheric energy give possibility to determine the ground state of the magnetosphere, and to calculate relative contributions of tail currents, ring currents and field--aligned currents to the magnetospheric energy as well as the contributions to onground magnetic disturbances. The magnetospheric substorms and storms manifest that the permanent solar wind energy transfer ways are not enough for covering of solar wind energy input into the magnetosphere. Nonlinear explosive processes are necessary for energy transmission into ionosphere and atmosphere. Main conclusion tell us that the field--aligned currents are important contributors to magnetospheric energy transformations. For understanding a relation between substorms and storm it is necessary to take into account that both of them are the concurrent energy transferring ways. To test of the model' results a magnetospheric response to the CME-driven shocks that impinged on the Earth's magnetopause on 10 January 1997 and 28 September 1998 are studied.

  14. Magnetospheric observation of large sub-auroral electric fields

    NASA Technical Reports Server (NTRS)

    Maynard, N. C.; Aggson, T. L.; Heppner, J. P.

    1980-01-01

    An example of large subauroral poleward electric fields similar to those observed on OGO-6, S3-2 and AE-C (SAID) has been found in the magnetosphere near L = 4 and 2300 MLT using ISEE-1 electric field data. The event is located adjacent to and outside the plasmapause and occurs 1 1/2 hours into a substorm. The event is accompaned by a significant penetration of the convection electric field inside the plasmasphere. Data from similar regions on the next orbit occurring near the beginning of a substorm did not exhibit these effects. Recent theoretical models predict SAID to occur in the trough regions, where substorm dynamics force currents to flow in regions of low conductivity. These models provide a first-order interpretation of this phenomena; however, the overal picture is more complex.

  15. The earth's magnetosphere. [as astrophysical plasma laboratory

    NASA Technical Reports Server (NTRS)

    Roederer, J. G.

    1974-01-01

    A qualitative description of the general magnetospheric configuration is given, with emphasis on some of the physical processes governing the magnetosphere that are the main targets of current research. The magnetosphere behaves like a huge 'bag' of plasma and radiation that swells and contracts under the influence of the solar wind. The electric field, the magnetospheric plasma, the magnetospheric substorm, and the radiation belt and wave particle interactions are discussed. During the past 15 years, the study of the earth's magnetosphere man's immediate plasma and radiation environment - has undergone a successful stage of discovery and exploration. Investigators have obtained a morphological description of the magnetospheric field, the particle population embedded in it, and its interface with the solar wind, and have identified and are beginning to understand many of the physical processes involved. Quite generally, the magnetosphere reveals itself as a region where it is possible to observe some of the fundamental plasma processes at work that are known to occur elsewhere in the universe.

  16. Current understanding of magnetic storms: Storm-substorm relationships

    SciTech Connect

    Kamide, Y.; Gonzalez, W.D.; Baumjohann, W.; Daglis, I.A.; Grande, M.; Joselyn, J.A.; Singer, H.J.; McPherron, R.L.; Phillips, J.L.; Reeves, E.G.; Rostoker, G.; Sharma, A.S.; Tsurutani, B.T.

    1998-08-01

    the storm-time ring current. An apparently new controversy regarding the relative importance of the two processes is thus created. It is important to identify the role of substorm occurrence in the large-scale enhancement of magnetospheric convection driven by solar wind electric fields. (3) Numerical schemes for predicting geomagnetic activity indices on the basis of solar/solar wind/interplanetary magnetic field parameters continue to be upgraded, ensuring reliable techniques for forecasting magnetic storms under real-time conditions. There is a need to evaluate the prediction capability of geomagnetic indices on the basis of physical processes that occur during storm time substorms. (4) It is crucial to differentiate between storms and nonstorm time substorms in terms of energy transfer/conversion processes, i.e., mechanical energy from the solar wind, electromagnetic energy in the magnetotail, and again, mechanical energy of particles in the plasma sheet, ring current, and aurora. To help answer the question of the role of substorms in energizing ring current particles, it is crucial to find efficient magnetospheric processes that heat ions up to some minimal energies so that they can have an effect on the strength of the storm time ring current. (5) The question of whether the {ital Dst} index is an accurate and effective measure of the storm time ring-current is also controversial. In particular, it is demonstrated that the dipolarization effect associated with substorm expansion acts to reduce the {ital Dst} magnitude, even though the ring current may still be growing. {copyright} 1998 American Geophysical Union

  17. Generation of BBFs and DFs, Formation of Substorm Auroras and Triggers of Substorm Onset

    NASA Astrophysics Data System (ADS)

    Song, Y.; Lysak, R. L.

    2014-12-01

    Substorm onset is a dynamical response of the MI coupling system to external solar wind driving conditions and to internal dynamical processes. During the growth phase, the solar wind energy and momentum are transferred into the magnetosphere via MHD mesoscale Alfvenic interactions throughout the magnetopause current sheet. A decrease in momentum transfer from the solar wind into the magnetosphere starts a preconditioning stage, and produces a strong earthward body force acting on the whole magnetotail within a short time period. The strong earthward force will cause localized transients in the tail, such as multiple BBFs, DFs, plasma bubbles, and excited MHD waves. On auroral flux tubes, FACs carried by Alfven waves are generated by Alfvenic interactions between tail earthward flows associated with BBFs/DFs/Bubbles and the ionospheric drag. Nonlinear Alfvenic interaction between the incident and reflected Alfven wave packets in the auroral acceleration region can produce localized parallel electric fields and substorm auroral arcs. During the preconditioning stage prior to substorm onset, the generation of parallel electric fields and auroral arcs can redistribute perpendicular mechanical and magnetic stresses, "decoupling" the magnetosphere from the ionosphere drag. This will enhance the tail earthward flows and rapidly build up stronger parallel electric fields in the auroral acceleration region, leading to a sudden and violent tail energy release and substorm auroral poleward expansion. We suggest that in preconditioning stage, the decrease in the solar wind momentum transfer is a necessary condition of the substorm onset. Additionally, "decoupling" the magnetosphere from ionosphere drag can trigger substorm expansion onset.

  18. Aspects of global coherence of magnetospheric behavior

    NASA Astrophysics Data System (ADS)

    Siscoe, George

    2011-03-01

    This paper reviews ways in which the magnetosphere manifests coherent behavior on a global scale. Because the magnetosphere is a magnetic object, and is thus deformable under the constraint of total magnetic flux conservation, it can and does exhibit coordinated changes across its whole volume. As a trivial example, the early model of the magnetosphere, envisioned as a magnetically closed vacuum cavity, is compressible as a whole, obeying certain scaling laws. The operative dynamics is simply magnetic compression responding to variable solar wind dynamic pressure. Magnetospheric behavior gets more interesting and its global coherence less obvious when one adds the magnetosphere's response to a variable interplanetary magnetic field (IMF). Then, in addition to changes associated with magnetic compression, there are changes associated with magnetic tension. Aspects of global coherence that then emerge include the following (to a degree that depends on the strength of the coupling to the IMF): one-way transfer of magnetic flux from the dayside to the nightside (magnetotail) associated with a buildup of the region 1 current system and erosion of the dayside magnetosphere, and, under very strong coupling, saturation of erosion and of the cross polar cap potential; two-way transfer of magnetic flux known as the Dungey cycle associated with substorms and, for very strong coupling, sawtooth substorms; a change in shape of the magnetopause as coupling strength increases that includes the development of a dimple at the nose and Alfvén wings along the flanks; involvement of the magnetosheath and bow shock in global dynamics to such an extent that the boundary of the magnetosphere can be said to be the bow shock. One intention of this review is to demonstrate that these aspects are not separate phenomena but occur together as an integral mode of global magnetospheric behavior.

  19. Dynamics of the outer radiation belts in relation to polar substorms and hot plasma injections at geostationary altitude

    NASA Technical Reports Server (NTRS)

    Sauvaud, J. A.; Winckler, J. R.

    1981-01-01

    Geostationary satellite and ground measurements of dynamic variations of the outer radiation belts and their relations with the development of auroral structures during magnetospheric substorms are analyzed. A comparison of measurements of the H or X geomagnetic field components made by seven auroral stations with ATS-6 low-energy and high-energy particle measurements during the multiple-onset substorm of Aug. 16, 1974 is presented which demonstrates that while the decrease in energetic particle fluxed ends only at the time of a strong substorm onset, rapid motions of the outer radiation belts may occur during the flux decrease. All-sky photographs of auroral phenomena taken at Fort Yukon and College, Alaska are then compared with ATS-1 energetic particle flux measurements in order to demonstrate the relation between flux decreases and increases and distinct substorm phases. Results support the hypothesis of a magnetospheric substorm precursor which appears to be an instability growing at the inner boundary of the plasma layer and approaching the earth, and underline the importance of current and magnetic field variations in charged particle dynamics.

  20. A Perfect Substorm: ICME-driven Magnetic Activity Catches Galaxy 15 in the Wrong Place at the Wrong Time

    NASA Astrophysics Data System (ADS)

    Connors, M. G.; Russell, C. T.; Angelopoulos, V.; Singer, H. J.; Glassmeier, K.

    2010-12-01

    At approximately 0825 UT on April 5, 2010, an ICME-driven shock encountered Earth's magnetosphere. The IMF, slightly southward since 0805 UT, turned more so, to an average value close to -15 nT, which was maintained for nearly an hour under high dynamic pressure conditions. Following a substorm growth phase, dipolarizations were observed at 0847 and 0903 UT by GOES West (11) in the midnight sector, at 0903 UT by three THEMIS spacecraft near X=-11, Y=-2 RE, and at about 0900 by GOES 14 near 2 MLT. Electron injections began at 0903 UT at the THEMIS spacecraft, while GOES 11 detected an increase in flux of energetic protons. A major dipolarization event at 0909 UT was observed at all of these spacecraft, and transferred magnetic flux from the vicinity of THEMIS to the inner magnetosphere, resulting in "overdipolarization" in the midnight sector. Extreme currents, more than 3 MA crossing the midnight sector, are inferred from ground magnetic perturbations of over 2000 nT, indicating this was an unusually strong substorm. Flux transfer associated with large electric fields observed at THEMIS (EY of 80 mV/m) is consistent with this increase in inner magnetospheric magnetic field. A second increase in ca. 1 MeV proton flux at this time led to a factor of over 10000 overall increase of this flux in the event. When the effects of this substorm reached synchronous orbit, the Galaxy 15 satellite was in eclipse when photoemission is not available to counter charging by the potentially high fluxes of energetic magnetospheric electrons that can occur during substorms. Galaxy 15 experienced a severe operational anomaly shortly after leaving eclipse and appears to have simply been at the wrong place at the wrong time when the “perfect” substorm occurred.

  1. Nature's Grand Experiment: Linkage between magnetospheric convection and the radiation belts

    NASA Astrophysics Data System (ADS)

    Rodger, Craig J.; Cresswell-Moorcock, Kathy; Clilverd, Mark A.

    2016-01-01

    The solar minimum of 2007-2010 was unusually deep and long lived. In the later stages of this period the electron fluxes in the radiation belts dropped to extremely low levels. The flux of relativistic electrons (>1 MeV) was significantly diminished and at times was below instrument thresholds both for spacecraft located in geostationary orbits and also those in low-Earth orbit. This period has been described as a natural "Grand Experiment" allowing us to test our understanding of basic radiation belt physics and in particular the acceleration mechanisms which lead to enhancements in outer belt relativistic electron fluxes. Here we test the hypothesis that processes which initiate repetitive substorm onsets drive magnetospheric convection, which in turn triggers enhancement in whistler mode chorus that accelerates radiation belt electrons to relativistic energies. Conversely, individual substorms would not be associated with radiation belt acceleration. Contrasting observations from multiple satellites of energetic and relativistic electrons with substorm event lists, as well as chorus measurements, show that the data are consistent with the hypothesis. We show that repetitive substorms are associated with enhancements in the flux of energetic and relativistic electrons and enhanced whistler mode wave intensities. The enhancement in chorus wave power starts slightly before the repetitive substorm epoch onset. During the 2009/2010 period the only relativistic electron flux enhancements that occurred were preceded by repeated substorm onsets, consistent with enhanced magnetospheric convection as a trigger.

  2. Longitudinal structure of substorm injections at synchronous orbit

    SciTech Connect

    Arnoldy, R.L.; Moore, T.E.

    1983-08-01

    From multiple-spacecraft measurements it is shown that the synchronous orbit manifestation of a substorm, i.e., plasma injection and magnetic field reconfiguration to dipolar, has an onset which expands both eastward and westward from a relatively narrow sector near midnight. For low-to-moderate geomagnetic activity the earliest onset sector at synchronous orbit is about 3 hours wide, skewed toward the evening side of midnight. Using the extensive International Magnetospheric Study ground magnetometer network beneath the satellites, it is found that simultaneous westward motion of electrojet intensification is seen in the ground data over a large longitudinal range than the magnetospheric signatures. This might be explained in terms of distortion of the nightside magnetic field at synchronous orbit. Plasma that might be explained in terms of distortion of the nightside magnetic field at synchronous orbit. Plasma that has already been injected near midnight at synchronous altitude undergoes no further change as a result of the westward and eastward motion of the borders of the plasma. This suggest that the expansion does not represent new substorm activation. One can intepret these results in terms of an injection front wedge which makes hot plasma accessible to the inner magnetosphere and which spatially expands or propagates with time. The origin of plasma behind the front is not addressed. Detailed pitch angle data do, however, show that strong precipitation would be expected from the front for about the first 10 min after the front passes over an observer. Finally, as a result of longitudinal expansion of plasma injections from midnight toward evening or morning and the continuation or even enhancement of field inflation in the evening or morning sectors, growth and expansive phase substorm signatures can occur simultaneously.

  3. Substorm related CNA near equatorward boundary of the auroral oval in relation to interplanetary conditions

    NASA Astrophysics Data System (ADS)

    Behera, Jayanta K.; Sinha, Ashwini K.; Singh, Anand K.; Vichare, Geeta; Dhar, Ajay; Labde, Sachin; Jeeva, K.

    2015-07-01

    Cosmic noise absorption (CNA) at high latitudes is a typical manifestation of enhanced precipitation of energetic charged particles during the course of a magnetospheric substorm. Present analysis demonstrates the energetic particles precipitate to the high latitude ionosphere during substorms, affecting upper and lower regions of the ionosphere simultaneously. Previous studies have reported that intense and short-lived CNA events associated with substorms are mostly observed in the midnight sector of the auroral oval. In the current study, we have examined such type of CNA events predominantly occurring during 0000-0600 UT (2300-0500 MLT) at an Indian Antarctic station Maitri (corrected geomagnetic (CGM) coordinates 62.59°S, 53.59°E), which is located at the equatorward edge of the auroral oval. Absorption events related to isolated substorm and storm-time substorms exhibit distinct features in terms of their intensity and extent in latitude and longitude. Our study suggests that the maximum intensity of CNAs depends on the interplanetary conditions, such as, the solar wind speed, southward component of IMF Bz, and duskward component of IEF Ey. Moreover, the role of duskward component of IEF Ey is more noteworthy than other interplanetary parameters.

  4. An Analysis of Conjugate Ground-based and Space-based Measurements of Energetic Electrons during Substorms

    NASA Astrophysics Data System (ADS)

    Sivadas, N.; Semeter, J. L.

    2015-12-01

    Substorms within the Earth's magnetosphere release energy in the form of energetic charged particles and several kinds of waves within the plasma. Depending on their strength, satellite-based navigation and communication systems are adversely affected by the energetic charged particles. Like many other natural phenomena, substorms can have a severe economic impact on a technology-driven society such as ours. Though energization of charged particles is known to occur in the magnetosphere during substorms, the source of this population and its relation to traditional acceleration region dynamics, are not completely understood. Combining measurements of energetic charged particles within the plasmasheet and that of charged particles precipitated in to the ionosphere will provide a better understanding of the role of processes that accelerate these charged particles. In the current work, we present energetic electron flux measured indirectly using data from ground-based Incoherent Scatter Radar and that measured directly at the plasmasheet by the THEMIS spacecraft. Instances of low-altitude-precipitation observed from ground suggest electrons of energy greater than 300 keV, possibly arising from particle injection events during substorms at the magnetically conjugate locations in the plasmasheet. The differences and similarities in the measurements at the plasmasheet and the ionosphere indicate the role different processes play in influencing the journey of these energetic particles form the magnetosphere to the ionosphere. Our observations suggest that there is a lot more to be understood of the link between magnetotail dynamics and energetic electron precipitation during substorms. Understanding this may open up novel and potentially invaluable ways of diagnosing the magnetosphere from the ground.

  5. Theory for substorms triggered by sudden reductions in convection

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.

    1996-01-01

    Many substorm expansions are triggered by interplanetary magnetic field changes that reduce magnetospheric convection. This suggests that expansion onsets are a result of a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind. Such a reduction disrupts the inward motion and energization of plasma sheet particles that occur during the growth phase. It is proposed that the resulting magnetic drift of particles and a large dawn to dusk gradient in the ion energies leads to a longitudinally localized reduction in the plasma pressure, and thus, to the current wedge formation. This theory accounts for the rapid development of the expansion phase relative to growth phase, the magnitude of the wedge currents, the speeds of tailward and westward expansion of the current reduction region in the equatorial plane, and the speeds of the poleward and westward motion of active aurora in the ionosphere.

  6. Observations in the vicinity of substorm onset: Implications for the substrom process

    NASA Technical Reports Server (NTRS)

    Elphinstone, R. D.; Hearn, D. J.; Cogger, L. L.; Murphree, J. S.; Singer, H.; Sergeev, V.; Mursula, K.; Klumpar, D. M.; Reeves, G. D.; Johnson, M.

    1995-01-01

    Multi-instrument data sets from the ground and satellites at both low and high altitude have provided new results concerning substorm onset and its source region in the magnetosphere. Twenty-six out of 37 substorm onset events showed evidence of azimuthally spaced auroral forms (AAFs) prior to the explosive poleward motion associated with optical substorm onset. AAFs can span 8 hours of local time prior to onset and generally propagate eastward in the morning sector. Onset itself is, however, more localized spanning only about 1 hour local time. AAF onset occur during time periods when the solar wind pressure is relatively high. AAFs brighten in conjunction with substorm onset leading to the conclusion that they are a growth phase activity casually related to substorm onset. Precursor activity associated with these AAFs is also seen near geosynchronous orbit altitude and examples show the relationship between the various instrumental definitions of substorm onset. The implied mode number (30 to 135) derived from this work is inconsistent with cavity mode resonances but is consistent with a modified flute/ballooning instability which requires azimuthal pressure gradients. The extended source region and the distance to the open-closed field line region constrain reconnection theory and local mechanisms for substorm onset. It is demonstrated that multiple onset substorms can exist for which localized dipolarizations and the Pi 2 occur simultaneously with tail stretching existing elsewhere. These pseudobreakups can be initiated by auroral streamers which originate at the most poleward set of arc systems and drift to the more equatorward main UV oval. Observations are presented of these AAFs in conjunction with low- and high-altitutde particle and magnetic field data. These place the activations at the interface between dipolar and taillike field lines probably near the peak in the cross-tail current. These onsets are put in the context of a new scenario for substorm

  7. Response of the Earth's Magnetosphere to Changes in the Solar Wind

    NASA Technical Reports Server (NTRS)

    McPherron, Robert L.; Weygand, James M.; Hsu, Tung-Shin

    2007-01-01

    The solar wind couples to the magnetosphere via dynamic pressure and electric field. Pressure establishes the size and shape of the system, while the electric field transfers energy, mass, and momentum to the magnetosphere. When the interplanetary magnetic field (IMF) is antiparallel to the dayside magnetic field, magnetic reconnection connects the IMF to the dipole field. Solar wind transport of the newly opened field lines to the nightside creates an internal convection system. These open field lines must ultimately be closed by reconnection on the nightside. For many decades, it was thought that a magnetospheric substorm was the process for accomplishing this and that all magnetic activity was a consequence of substorms. It is now recognized that there are a variety of modes of response of the magnetosphere to the solar wind. In this paper, we briefly describe these modes and the conditions under which they occur. They include substorms, pseudo-breakups, poleward boundary intensifications (PBI), steady magnetospheric convection (SMC), sawtooth injection events, magnetic storms, high-intensity long-duration continuous AE activities (HILDCAAs), and storm-time activations. There are numerous explanations for these different phenomena, some of which do not involve magnetic reconnection. However, we speculate that it is possible to interpret each mode in terms of differences in the way magnetic reconnection occurs on the nightside.

  8. Magnetospheric ULF waves with increasing amplitude related to solar wind dynamic pressure changes: The Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations

    NASA Astrophysics Data System (ADS)

    Shen, X. C.; Zong, Q.-G.; Shi, Q. Q.; Tian, A. M.; Sun, W. J.; Wang, Y. F.; Zhou, X. Z.; Fu, S. Y.; Hartinger, M. D.; Angelopoulos, V.

    2015-09-01

    Ultralow frequency (ULF) waves play an important role in transferring energy by buffeting the magnetosphere with solar wind pressure impulses. The amplitudes of magnetospheric ULF waves, which are induced by solar wind dynamic pressure enhancements or shocks, are thought to damp in one half a wave cycle or an entire wave cycle. We report in situ observations of solar wind dynamic pressure impulse-induced magnetospheric ULF waves with increasing amplitudes. We found six ULF wave events induced by solar wind dynamic pressure enhancements with slow but clear wave amplitude increase. During three or four wave cycles, the amplitudes of ion velocities and electric field of these waves increased continuously by 1.3-4.4 times. Two significant events were selected to further study the characteristics of these ULF waves. We found that the wave amplitude growth is mainly contributed by the toroidal mode wave. Three possible mechanisms of causing the wave amplitude increase are discussed. First, solar wind dynamic pressure perturbations, which are observed in a duration of 20-30 min, might transfer energy to the magnetospheric ULF waves continually. Second, the wave amplitude increase in the radial electric field may be caused by superposition of two wave modes, a standing wave excited by the solar wind dynamic impulse and a propagating compressional wave directly induced by solar wind oscillations. When superposed, the two wave modes fit observations as does a calculation that superposes electric fields from two wave sources. Third, the normal of the solar wind discontinuity is at an angle to the Sun-Earth line. Thus, the discontinuity will affect the dayside magnetopause continuously for a long time.

  9. Energetic particles of the outer regions of planetary magnetospheres

    NASA Technical Reports Server (NTRS)

    Tsurutani, B. T.; Goldstein, B. E.; Bratenahl, A.

    1976-01-01

    High energy particles, with energies above those attainable by adiabatic or steady-state electric field acceleration, have been observed in and around the outer regions of planetary magnetospheres. Acceleration by large amplitude sporadic cross-tail electric fields over an order of magnitude greater than steady-state convection fields is proposed as a source of these particles. It is suggested that such explosive electric fields will occur intermittently in the vicinity of the tail neutral line in the expansive phase of substorms. Laboratory and satellite evidence are used to estimate this electric potential for substorms at earth; values of 500 kilovolts to 2 megavolts are calculated, in agreement with particle observations. It is further suggested that these particles, which have been accelerated in the night side magnetosphere, drift to the dayside on closed field lines, and under certain interplanetary conditions can escape to regions upstream of the bow shock.

  10. Quasi-static MHD processes in earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Voigt, Gerd-Hannes

    1988-01-01

    An attempt is made to use the MHD equilibrium theory to describe the global magnetic field configuration of earth's magnetosphere and its time evolution under the influence of magnetospheric convection. To circumvent the difficulties inherent in today's MHD codes, use is made of a restriction to slowly time-dependent convection processes with convective velocities well below the typical Alfven speed. This restriction leads to a quasi-static MHD theory. The two-dimensional theory is outlined, and it is shown how sequences of two-dimensional equilibria evolve into a steady state configuration that is likely to become tearing mode unstable. It is then concluded that magnetospheric substorms occur periodically in earth's magnetosphere, thus being an integral part of the entire convection cycle.

  11. Substorm evolution of auroral structures

    NASA Astrophysics Data System (ADS)

    Partamies, N.; Juusola, L.; Whiter, D.; Kauristie, K.

    2015-07-01

    Auroral arcs are often associated with magnetically quiet time and substorm growth phases. We have studied the evolution of auroral structures during global and local magnetic activity to investigate the occurrence rate of auroral arcs during different levels of magnetic activity. The ground-magnetic and auroral conditions are described by the magnetometer and auroral camera data from five Magnetometers — Ionospheric radars — All-sky cameras Large Experiment stations in Finnish and Swedish Lapland. We identified substorm growth, expansion, and recovery phases from the local electrojet index (IL) in 1996-2007 and analyzed the auroral structures during the different phases. Auroral structures were also analyzed during different global magnetic activity levels, as described by the planetary Kp index. The distribution of auroral structures for all substorm phases and Kp levels is of similar shape. About one third of all detected structures are auroral arcs. This suggests that auroral arcs occur in all conditions as the main element of the aurora. The most arc-dominated substorm phases occur in the premidnight sector, while the least arc-dominated substorm phases take place in the dawn sector. Arc event lifetimes and expectation times calculated for different substorm phases show that the longest arc-dominated periods are found during growth phases, while the longest arc waiting times occur during expansion phases. Most of the arc events end when arcs evolve to more complex structures. This is true for all substorm phases. Based on the number of images of auroral arcs and the durations of substorm phases, we conclude that a randomly selected auroral arc most likely belongs to a substorm expansion phase. A small time delay, of the order of a minute, is observed between the magnetic signature of the substorm onset (i.e., the beginning of the negative bay) and the auroral breakup (i.e., the growth phase arc changing into a dynamic display). The magnetic onset was

  12. Magnetosphere-Regolith/Exosphere Coupling: Differences and Similarities to the Earth Magnetosphere-Ionosphere Coupling

    NASA Technical Reports Server (NTRS)

    Gjerleov, J. W.; Slavin, J. A.

    2001-01-01

    Of the three Mercury passes made by Mariner 10, the first and third went through the Mercury magnetosphere. The third encounter which occurred during northward IMF (interplanetary magnetic field) showed quiet time magnetic fields. In contrast the third encounter observed clear substorm signatures including dipolarization, field-aligned currents (FACs) and injection of energetic electrons at geosynchronous orbit. However, the determined cross-tail potential drop and the assumed height integrated conductance indicate that the FAC should be 2-50 times weaker than observed. We address this inconsistency and the fundamental problem of FAC closure whether this takes place in the regolith or in the exosphere. The current state of knowledge of the magnetosphere-exosphere/regolith coupling is addressed and similarities and differences to the Earth magnetosphere-ionosphere coupling are discussed.

  13. 3D PIC Simulation of the Magnetosphere during IMF Rotation from North to South: Signatures of Substorm Triggering in the Magnetotail

    NASA Technical Reports Server (NTRS)

    Nishikawa, Ken-Ichi; Cao. D/ S/; Lembege, B.

    2008-01-01

    Three dimensional PIC simulations are performed in order to analyse the dynamics of the magnetotail as the interplanetary magnetic field (IMF) rotates from northward to southward direction. This dynamics reveals to be quite different within meridian/equatorial planes over two successive phases of this rotation. First, as IMF rotates from North to Dawn-Dusk direction, the X-Point (magnetic reconnection) evidenced in the magnetotail (meridian plane) is moving earthward (from x=-35 Re to x=-17.5 ) distance at which it stabilizes. This motion is coupled with the formation of "Crosstail-S" patterns (within the plane perpendicular to the Sun-Earth mine) through the neutral sheet in the nearby magnetotail. Second, as IMF rotates from dawn-dusk to South, the minimum B field region is expanding within the equatorial plane and forms a ring. This two-steps dynamics is analyzed in strong association with the cross field magnetotail current Jy, in order to recover the signatures of substorms triggering.

  14. Strong induction effects during the substorm on 27 August 2001

    NASA Astrophysics Data System (ADS)

    Mishin, V. V.; Mishin, V. M.; Lunyushkin, S. B.; Pu, Z.; Wang, C.

    2015-10-01

    We report on strong induction effects notably contributing to the cross polar cap potential drop and the energy balance during the growth and active phases of the substorm on 27 August 2001. The inductance of the magnetosphere is found to be crucial for the energy balance and electrical features of the magnetosphere in the course of the substorm. The inductive response to the switching on and off of the solar wind-magnetosphere generator exceeds the effect of the interplanetary magnetic field (IMF) variation. The induction effects are most apparent during the substorm expansion onset when the rapid growth of the ionospheric conductivity is accompanied by the fast release of the magnetic energy stored in the magnetotail during the growth phase. Using the magnetogram inversion technique, we estimated the magnetospheric inductance and effective ionospheric conductivity during the loading and unloading phases.

  15. Substorm probabilities are best predicted from solar wind speed

    NASA Astrophysics Data System (ADS)

    Newell, P. T.; Liou, K.; Gjerloev, J. W.; Sotirelis, T.; Wing, S.; Mitchell, E. J.

    2016-08-01

    Most measures of magnetospheric activity - including auroral power (AP), magnetotail stretching, and ring current intensity - are best predicted by solar wind-magnetosphere coupling functions which approximate the frontside magnetopause merging rate. However radiation belt fluxes are best predicted by a simpler function, namely the solar wind speed, v. Since most theories of how these high energy electrons arise are associated with repeated rapid dipolarizations such as associated with substorms, this apparent discrepancy could be reconciled under the hypothesis that the frequency of substorms tracks v rather than the merging rate - despite the necessity of magnetotail flux loading prior to substorms. Here we investigate this conjecture about v and substorm probability. Specifically, a continuous list of substorm onsets compiled from SuperMAG covering January 1, 1997 through December 31, 2007 are studied. The continuity of SuperMAG data and near continuity of solar wind measurements minimize selection bias. In fact v is a much better predictor of onset probability than is the overall merging rate, with substorm odds rising sharply with v. Some loading by merging is necessary, and frontside merging does increase substorm probability, but nearly as strongly as does v taken alone. Likewise, the effects of dynamic pressure, p, are smaller than simply v taken by itself. Changes in the solar wind matter, albeit modestly. For a given level of v (or Bz), a change in v (or Bz) will increase the odds of a substorm for at least 2 h following the change. A decrease in driving elevates substorm probabilities to a greater extent than does an increase, partially supporting external triggering. Yet current v is the best single predictor of subsequently observing a substorm. These results explain why geomagnetically quiet years and active years are better characterized by low or high v (respectively) than by the distribution of merging estimators. It appears that the flow of energy

  16. Existential variations of brightness auroral glow on a growth phase of a substorm

    NASA Astrophysics Data System (ADS)

    Borisov, G. V.; Velichko, V. A.

    1997-01-01

    In work the advanced way of processing scanning photometer data (scanogramms) is stated. Data processing of a scanning photometer by the offered (suggested) way, and also the analysis of the data published in the literature, and geomagnetic field data (magnetogramms) Yakut meridional chains and stations of a world (global) network have allowed to reveal new properties diffuse aurora brightness on a growth phase of a substorm. It is shown, that the center magnetospheric substorms with a growth phase is formed long before the moment of explosive clearing energy. By results of the analysis of photometric supervision of a background brightness in Yakutia it is found out regular latitude and longitudinal variations of brightness of a luminescence during a growth phase. To the east and to the west of the center of a substorm at all breadthes auroral zones and on equatorial border diffuse spill on a longitude of the center brightness of a background monotonously grows during all growth phase. In longitudinal sector of the future (expected) center of a substorm in the field of discrete forms of polar lights intensity of a background luminescence raises in the beginning of a growth phase with the subsequent reduction prior to the beginning of an explosive phase. At polar edge (territory) of an oval the beginning of downturn of brightness of a background in the center for ten minutes outstrips the moment of fast movement of discrete forms to equator. Feding in a background luminescence it is simultaneously observed also in a vicinity of an equatorial strip of lights, but duration of reduction of his(its) intensity at these breadthes coincides in due course the moment of the beginning of drift of discrete forms to equator prior to the beginning of an explosive phase. It has led to to a conclusion that formation of the local center of a substorm occurs not during last moment before explosion, during all growth phase. The qualitative circuit explaining found out laws is

  17. Substorm currents in the equatorial magnetotail

    SciTech Connect

    Iijima, T.; Watanabe, M.; Potemra, T.A.; Zanetti, L.J.; Kan, J.R.; Akasofu, S.I.

    1993-10-01

    The authors have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed from these variations, and systems of field-aligned currents were deduced. During the growth phase to the maximum phase of the taillike reconfiguration of the near-Earth magnetic field, a positive divergence (away from the equatorial plane) of the westward equatorial current occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the premidnight to early morning MLT sector. This flow direction pattern is the same as that of the region 2 field-aligned current system. The authors have also determined the presence of a radial current that flows toward the earth in the late evening to premidnight sector and flows away from the Earth in the midnight to morning sector. The intensity of the radial currents increases before the expansion phase. Consequently, the patterns of field-aligned currents associated with various substorm phases are the superposition of currents driven by multiple sources with different temporal variations. They have identified at least three different but related sources of field-aligned currents during the growth and expansion phases. These sources are related to the divergence of the westward flowing equatorial current and to distributions of pressure and magnetic field gradients that evolve in the magnetotail. When combined, these complicated systems support the basic region 1 to region 2 field-aligned current flow pattern. 22 refs., 12 figs., 1 tab.

  18. Observations of large transient magnetospheric electric fields

    NASA Technical Reports Server (NTRS)

    Aggson, T. L.; Heppner, J. P.

    1977-01-01

    Transient electric field events were observed with the long, double probe instrumentation carried by the IMP-6 satellite. Nine, clearly defined, exceptionally large amplitude events are presented here. The events are observed in the midnight sector at geocentric distances 3.5 to .5.5 R sub e at middle latitudes within a magnetic L-shell range of 4.8 to 7.5. They usually have a total duration of one to several minutes, with peak power spectra amplitudes occurring at a frequency of about 0.3 Hz. The events occur under magnetically disturbed conditions, and in most cases they can be associated with negative dH/dt excursions at magnetic observatories located near the foot of the magnetic field line intersecting IMP-6. The magnetospheric motions calculated for these electric fields indicated a quasi-stochastical diffusive process rather than the general inward magnetospheric collapsing motion expected during the expansive phases of auroral substorm activity.

  19. Solar-wind-magnetosphere coupling, including relativistic electron energization, during high-speed streams

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Lee, D.-Y.; Kim, H.-J.; Hwang, J. A.; Thorne, R. M.; Horne, R. B.; Smith, A. J.

    2009-07-01

    High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfvén waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during high-speed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements

  20. Ionospheric irregularities during a substorm event: Observations of ULF pulsations and GPS scintillations

    NASA Astrophysics Data System (ADS)

    Kim, H.; Clauer, C. R.; Deshpande, K.; Lessard, M. R.; Weatherwax, A. T.; Bust, G. S.; Crowley, G.; Humphreys, T. E.

    2014-07-01

    Plasma instability in the ionosphere is often observed as disturbances and distortions of the amplitude and phase of the radio signals, which are known as ionospheric scintillations. High-latitude ionospheric plasma, closely connected to the solar wind and magnetospheric dynamics, produces very dynamic and short-lived Global Positioning System (GPS) scintillations, making it challenging to characterize them. It is observed that scintillations in the high-latitude ionosphere occur frequently during geomagnetic storms and substorms. In addition, it is well known that Ultra Low Frequency (ULF) pulsations (Pi2 and Pi1B) are closely associated with substorm activity. This study reports simultaneous observations of Pi2 and Pi1B pulsations and GPS phase scintillations during a substorm using a newly designed Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) installed at the South Pole. The magnetic field and GPS data from the instruments appear to be associated in terms of their temporal and spectral features. Moreover, the scintillation events were observed near the auroral latitudes where Pi1B pulsations are commonly detected. The temporal, spectral and spatial association between the scintillation and geomagnetic pulsation events suggests that the magnetic field perturbations and enhanced electric fields caused by substorm currents could contribute to the creation of plasma instability in the high-latitude ionosphere, leading to GPS scintillations.

  1. Prescribing the Kp, AE and Dst Response Using the Magnetospheric State Technique

    NASA Astrophysics Data System (ADS)

    Fung, S. F.; Van Artsdalen, K. J.; Shao, X.

    2014-12-01

    The magnetosphere exhibits a variety of geomagnetic activities in response to different solar wind and interplanetary magnetic field (IMF) input. Global-scale geomagnetic activities, such as those due to substorms and storms, are reflected in the Kp, AE and Dst indices, which are constructed from ground-based magnetometer observations. Understanding how and the conditions under which a geomagnetic storm or substorm occurs are outstanding questions in heliophysics and space weather predication. While it is generally accepted that Earth-directed coronal mass ejections from the sun can cause geomagnetic storms and substorms in the magnetosphere, the specific necessary and sufficient conditions, in terms of both the solar wind drivers and pre-existing magnetospheric conditions, for triggering different types of geomagnetic activities are yet to be delineated. For example, while it is generally thought that geomagnetic storms can be triggered by extended intervals of southward IMF Bz, it is still not clear how and at what point during the southward-IMF Bz interval a storm will arise, and how the storm-triggering process may be affected by the pre-existing state of the magnetosphere. To address these specific questions, we have applied the magnetospheric state prescription technique developed by Fung and Shao [2008]. We have used solar wind and geomagnetic indices data taken in 1970-2009 to constructed a magnetospheric state lookup table and applied the table to perform out-of-sample predictions or prescriptions of the Kp, AE and Dst indices during different geomagnetic storm intervals (with minimum Dst ≤ -100 nT) that occurred after 2009. Our presentation will discuss the validity of the magnetospheric state prescription technique and the role of different magnetopsheric state parameters in prescribing geomagnetic storm development. Fung, S. F. and X. Shao, Specification of multiple geomagnetic responses to variable solar wind and IMF input, Ann. Geophys., 26, 639

  2. Ionospheric signature of the tail neutral line during the growth phase of a substorm

    SciTech Connect

    Moses, J.J.; Slavin, J.A.; Heelis, R.A.

    1996-03-01

    An isolated substorm occurred on October 21, 1981 at the end of a large geomagnetic storm. Observations of particles and fields were made during the presumed growth phase of this substorm by the DE 2 satellite. The ionospheric convection velocitie averaging {approximately} 500 m/s in an eastward channel flow in the premidnight sector. Despite the convection signature, geomagnetic conditions were quiet with the AL index >{minus}50 nT and very weak field-aligned current. The authors will present an in-depth study of the nightside gap region within the channel of eastward flow. They will discuss the possible effects of a neutral wind flywheel on the convection. Also, they will present a detailed analysis of the electrodynamic structures within the nightside gap which indicates a magnetospheric source. Possible ionospheric signatures of the tail neutral line are discussed. 19 refs., 8 fig.

  3. The magnetotail and substorms. [magnetic flux transport model

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Mcpherron, R. L.

    1973-01-01

    The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

  4. Magnetic substorms and northward IMF turning

    NASA Astrophysics Data System (ADS)

    Troshichev, Oleg; Podorozhkina, Nataly

    To determine the relation of the northward IMF turnings to substorm sudden onsets, we separated all events with sharp northward IMF turnings observed in years of solar maximum (1999-2002) and solar minimum (2007-2008). The events (N=261) have been classified in 5 groups in accordance with average magnetic activity in auroral zone (low, moderate or high levels of AL index) at unchanged or slightly changed PC index and with dynamics of PC (steady distinct growth or distinct decline) at arbitrary values of AL index. Statistical analysis of relationships between the IMF turning and changes of PC and AL indices has been fulfilled separately for each of 5 classes. Results of the analysis showed that, irrespective of geophysical conditions and solar activity epoch, the magnetic activity in the polar caps and in the auroral zone demonstrate no response to the sudden northward IMF turning, if the moment of northward turning is taken as a key date. Sharp increases of magnetic disturbance in the auroral zone are observed only under conditions of the growing PC index and statistically they are related to moment of the PC index exceeding the threshold level (~1.5 mV/m), not to northward turnings timed, as a rule, after the moment of sudden onset. Magnetic disturbances observed in these cases in the auroral zone (magnetic substorms) are guided by behavior of the PC index, like to ordinary magnetic substorms or substorms developed under conditions of the prolonged northward IMF impact on the magnetosphere. The evident inconsistency between the sharp IMF changes measured outside of the magnetosphere and behavior of the ground-based PC index, the latter determining the substorm development, provides an additional argument in favor of the PC index as a ground-based proxy of the solar wind energy that entered into magnetosphere.

  5. Dynamics of the 1054 UT March 22, 1979, substorm event - CDAW 6. [Coordinated Data Analysis Workshop

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.; Manka, R. H.

    1985-01-01

    The Coordinated Data Analysis Workshop (CDAW 6) has the primary objective to trace the flow of energy from the solar wind through the magnetosphere to its ultimate dissipation in the ionosphere. An essential role in this energy transfer is played by magnetospheric substorms, however, details are not yet completely understood. The International Magnetospheric Study (IMS) has provided an ideal data base for the study conducted by CDAW 6. The present investigation is concerned with the 1054 UT March 22, 1979, substorm event, which had been selected for detailed examination in connection with the studies performed by the CDAW 6. The observations of this substorm are discussed, taking into account solar wind conditions, ground magnetic activity on March 22, 1979, observations at synchronous orbit, observations in the near geomagnetic tail, and the onset of the 1054 UT expansion phase. Substorm development and magnetospheric dynamics are discussed on the basis of a synthesis of the observations.

  6. Solar cycle dependence of substorm occurrence and duration: Implications for onset

    NASA Astrophysics Data System (ADS)

    Chu, Xiangning; McPherron, Robert L.; Hsu, Tung-Shin; Angelopoulos, Vassilis

    2015-04-01

    Magnetospheric substorms represent a major energy release process in Earth's magnetosphere. Their duration and intensity are coupled to solar wind input, but the precise way the solar wind energy is stored and then released is a matter of considerable debate. Part of the observational difficulty has been the gaps in the auroral electrojet index traditionally used to study substorm properties. In this study, we created a midlatitude positive bay (MPB) index to measure the strength of the substorm current wedge. Because this index is based on midlatitude magnetometer data that are available continuously over several decades, we can assemble a database of substorm onsets lasting 31 years (1982-2012). We confirmed that the MPB onsets have a good agreement (±2 min) with auroral onsets as determined by optical means on board the IMAGE mission and that the MPB signature of substorms is robust and independent of the stations' position relative to ionospheric currents. Using the MPB onset, expansion, and recovery as a proxy of the respective substorm quantities, we found that the solar cycle variation of substorm occurrence depends on solar wind conditions and has a most probable value of 80 min. In contrast, the durations of substorm expansion and recovery phases do not change with the solar cycle. This suggests that the frequency of energy unloading in the magnetosphere is controlled by solar wind conditions through dayside reconnection, but the unloading process related to flux pileup in the near-Earth region is controlled by the magnetosphere and independent of external driving.

  7. A case study of lightning, whistlers, and associated ionospheric effects during a substorm particle injection event

    NASA Technical Reports Server (NTRS)

    Rodriguez, J. V.; Inan, U. S.; Li, Y. Q.; Holzworth, R. H.; Smith, A. J.; Orville, R. E.; Rosenberg, T. J.

    1992-01-01

    The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena during this event may represent new evidence of direct coupling of lightning energy to the lower ionosphere, either in conjunction with or in the absence of gyroresonant interactions between whistler mode waves and electrons in the magnetosphere.

  8. Auroral substorms as an electrical discharge phenomenon

    NASA Astrophysics Data System (ADS)

    Akasofu, Syun-Ichi

    2015-12-01

    During the last 50 years, we have made much progress in studying auroral substorms (consisting of the growth phase, the expansion phase, and the recovery phase). In particular, we have quantitatively learned about auroral substorms in terms of the global energy input-output relationship. (i) What powers auroral substorms? (ii) Why is there a long delay (1 h) of auroral activities after the magnetosphere is powered (growth phase)? (iii) How much energy is accumulated and unloaded during substorms? (iv) Why is the lifetime of the expansion phase so short (1h)? (v) How is the total energy input-output relationship? (vi) Where is the magnetic energy accumulated during the growth phase? On the basis of the results obtained in (i)-(vi), we have reached the following crucial question: (vii) how can the unloaded energy produce a secondary dynamo, which powers the expansion phase? Or more specifically, how can the accumulated magnetic energy get unloaded such that it generates the earthward electric fields needed to produce the expansion phase of auroral substorms? It is this dynamo and the resulting current circuit that drive a variety of explosive auroral displays as electrical discharge phenomena during the expansion phase, including the poleward advance of auroral arcs and the electrojet. This chain of processes is summarized in Section 4.2. This is the full version of work published by Akasofu (2015).

  9. Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms

    NASA Astrophysics Data System (ADS)

    Clausen, L. B. N.; Baker, J. B. H.; Ruohoniemi, J. M.; Milan, S. E.; Coxon, J. C.; Wing, S.; Ohtani, S.; Anderson, B. J.

    2013-06-01

    We use current density data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to identify the location of maximum region 1 current at all magnetic local times (MLTs). We term this location the R1 oval. Comparing the R1 oval location with particle precipitation boundaries identified in DMSP data, we find that the R1 oval is located on average within 1° of particle signatures associated with the open/closed field line boundary (OCB) across dayside and nightside MLTs. We hence conclude that the R1 oval can be used as a proxy for the location of the OCB. Studying the amount of magnetic flux enclosed by the R1 oval during the substorm cycle, we find that the R1 oval flux is well organized by it: during the growth phase the R1 oval location moves equatorward as the amount of magnetic flux increases whereas after substorm expansion phase onset significant flux closure occurs as the R1 current location retreats to higher latitudes. For about 15 min after expansion phase onset, the amount of open magnetic flux continues to increase indicating that dayside reconnection dominates over nightside reconnection. In the current density data, we find evidence of the substorm current wedge and also show that the dayside R1 currents are stronger than their nightside counterpart during the substorm growth phase, whereas after expansion phase onset, the nightside R1 currents dominate. Our observations of the current distribution and OCB movement during the substorm cycle are in excellent agreement with the expanding/contracting polar cap paradigm.

  10. The solar wind-magnetosphere energy coupling and magnetospheric disturbances

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1980-01-01

    Energy coupling between the solar wind and the magnetosphere is examined and the influence of this coupling on magnetospheric disturbances is discussed. Following a review of the components of the total energy production rate of the magnetosphere and progress in the study of solar wind-magnetosphere correlations, the derivation of the solar wind-magnetosphere energy coupling function, which has been found to correlate well with the total magnetospheric energy production rate, is presented. Examination of the relations between the energy coupling function and the type of magnetic disturbance with which it is associated indicates that magnetic storms with a large sudden storm commencement and a weak main phase are associated with small energy coupling, while values of the coupling function greater than 5 x 10 to the 18th to 10 to the 19th erg/sec are required for the development of a major geomagnetic storm. The magnetospheric substorm is shown to be a direct result of increased solar wind-magnetosphere energy coupling rather than the sudden conversion of stored magnetic energy. Finally, it is indicated that at energy couplings greater than 10 to the 19th erg/sec, the positive feedback process responsible for substorms breaks down, resulting in the abnormal growth of the ring current.

  11. Reconnection in Planetary Magnetospheres

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    2000-01-01

    Current sheets in planetary magnetospheres that lie between regions of "oppositely-directed" magnetic field are either magnetopause-like, separating plasmas with different properties, or tail-like, separating plasmas of rather similar properties. The magnetopause current sheets generally have a nearly limitless supply of magnetized plasma that can reconnect, possibly setting up steady-state reconnection. In contrast, the plasma on either side of a tail current sheet is stratified so that, as reconnection occurs, the plasma properties, in particular the Alfven velocity, change. If the density drops and the magnetic field increases markedly perpendicular to the sheet, explosive reconnection can occur. Even though steady state reconnection can take place at magnetopause current sheets, the process often appears to be periodic as if a certain low average rate was demanded by the conditions but only a rapid rate was available. Reconnection of sheared fields has been postulated to create magnetic ropes in the solar corona, at the Earth's magnetopause, and in the magnetotail. However, this is not the only way to produce magnetic ropes as the Venus ionosphere shows. The geometry of the reconnecting regions and the plasma conditions both can affect the rate of reconnection. Sorting out the various controlling factors can be assisted through the examination of reconnection in planetary settings. In particular we observe similar small-scale tearing in the magnetopause current layers of the Earth, Saturn. Uranus and Neptune and the magnetodisk current sheet at Jupiter. These sites may be seeds for rapid reconnection if the reconnection site reaches a high Alfven velocity region. In the Jupiter magnetosphere this appears to be achieved with resultant substorm activity. Similar seeds may be present in the Earth's magnetotail with the first one to reach explosive growth dominating the dynamics of the tail.

  12. The Origin of the Near-Earth Plasma Population During a Substorm on November 24, 1996

    NASA Technical Reports Server (NTRS)

    Ashour-Abdalla, M.; El-Alaoui, M.; Peroomian, V.; Walker, R. J.; Raeder, J.; Frank, L. A.; Paterson, W. R.

    1999-01-01

    We investigate the origins and the transport of ions observed in the near-Earth plasma sheet during the growth and expansion phases of a magnetospheric substorm that occurred on November 24, 1996. Ions observed at Geotail were traced backward in time in time-dependent magnetic and electric fields to determine their origins and the acceleration mechanisms responsible for their energization. Results from this investigation indicate that, during the growth phase of the substorm, most of the ions reaching Geotail had origins in the low latitude boundary layer (LLBL) and had already entered the magnetosphere when the growth phase began. Late in the growth phase and in the expansion phase a higher proportion of the ions reaching Geotail had their origin in the plasma mantle. Indeed, during the expansion phase more than 90% of the ions seen by Geotail were from the mantle. The ions were accelerated enroute to the spacecraft; however, most of the ions' energy gain was achieved by non-adiabatic acceleration while crossing the equatorial current sheet just prior to their detection by Geotail. In general, the plasma mantle from both southern and northern hemispheres supplied non-adiabatic ions to Geotail, whereas the LLBL supplied mostly adiabatic ions to the distributions measured by the spacecraft. Distribution functions computed at the ion sources indicate that ionospheric ions reaching Geotail during the expansion phase were significantly heated. Plasma mantle source distributions indicated the presence of a high-latitude reconnection region that allowed ion entry into the magnetosphere when the IMF was northward. These ions reached Geotail during the expansion phase. Ions from the traditional plasma mantle had access to the spacecraft throughout the substorm.

  13. AMPERE observations of the Birkeland currents associated with substorms and comparison with simple electrodynamic modelling

    NASA Astrophysics Data System (ADS)

    Milan, S. E.; Coxon, J. C.; Clausen, L. B. N.; Korth, H.; Anderson, B. J.

    2014-04-01

    We present observations of the global terrestrial Birkeland field-aligned current (FAC) pattern observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) during a sequence of substorms. The observations show that the region 1 and 2 current systems move to lower latitudes during the substorm growth phase and retreat to higher latitudes following substorm expansion phase onset. We interpret these observations within the framework of the expanding/contracting polar cap paradigm. This links expansion of the polar cap and equatorward motion of the auroras and FAC systems to the action of magnetopause reconnection increasing the open magnetic flux content of the magnetosphere.

  14. From discovery to prediction of magnetospheric processes

    NASA Astrophysics Data System (ADS)

    Kamide, Y.

    2000-11-01

    Over the last 50 years magnetospheric research has transferred its focus from geomagnetism to space physics, or from inferring the intensity of extraterrestrial currents, through discoveries of the main plasma regions in the magnetosphere, to predicting the processes occurring in the entire solar wind-magnetosphere-ionosphere system. Relating advances in magnetospheric physics to the framework of substorm research, this review paper demonstrates that the ``recent'' space age since 1960s consisted of /(1) an exploratory//discovery phase in which the magnetotail, the plasma sheet, and the acceleration region of auroral particles were identified, and /(2) a phase of comprehensive understanding in which we have attempted to comprehend the nature and significance of the near-Earth space environment. This progress in solar-terrestrial physics has coincided with a number of new discoveries of solar and interplanetary phenomena such as magnetic clouds, coronal mass ejections and coronal holes. Computer simulation techniques have been developed to the degree that satellite observations from a very limited number of points can be used to trace and reproduce the main energy processes. We are now entering a new phase in which we hope to be able to predict the dynamic processes that take place in the solar-terrestrial environment.

  15. Periodic substorm activity in the geomagnetic tail

    NASA Technical Reports Server (NTRS)

    Huang, C. Y.; Eastman, T. E.; Frank, L. A.; Williams, D. J.

    1983-01-01

    On 19 May 1978 an anusual series of events is observed with the Quadrispherical LEPEDEA on board the ISEE-1 satellite in the Earth's geomagnetic tail. For 13 hours periodic bursts of both ions and electrons are seen in all the particle detectors on the spacecraft. On this day periodic activity is also seen on the ground, where multiple intensifications of the electrojets are observed. At the same time the latitudinal component of the interplanetary magnetic field shows a number of strong southward deflections. It is concluded that an extended period of substorm activity is occurring, which causes repeated thinnings and recoveries of the plasma sheet. These are detected by ISEE, which is situated in the plasma sheet boundary layer, as periodic dropouts and reappearances of the plasma. Comparisons of the observations at ISEE with those at IMP-8, which for a time is engulfed by the plasma sheet, indicate that the activity is relatively localized in spatial extent. For this series of events it is clear that a global approach to magnetospheric dynamics, e.g., reconnection, is inappropriate.

  16. On the dynamical development of the downward field-aligned current in the substorm current wedge

    SciTech Connect

    Pellinen, R.J.; Pulkkinen, T.I.; Huuskonen, A.

    1995-08-01

    We report observations of a substorm event on March 4, 1979, onset at 2236 UT, which confirm the participation of the upward accelerated ionospheric electrons in the substorm current wedge current during the first few minutes after the substorm onset. The slow ions do not contribute much to the downward current immediately after the substorm onset, whereas the precipitating magnetospheric electrons quickly set up the upward current. A scanning photometer was centrally placed at the center of the downward current during the event. The observations suggest that the current was mainly caused by cold ionospheric electrons. 27 refs., 8 figs.

  17. A cross-field current instability for substorm expansions

    SciTech Connect

    Lui, A.T.Y. ); Chang, C.L.; Mankofsky, A. ); Wong, H.K. ); Winske, D. )

    1991-07-01

    The authors investigate a cross-field current instability (CFCI) as a candidate for current disruption during substorm expansions. The numerical solution of the linear dispersion equation indicates that (1) the proposed instability can occur at the inner edge or the midsection of the neutral sheet just prior to the substorm expansion onset although the former environment is found more favorable at the same drift speed scaled to the ion thermal speed, (2) the computed growth time is comparable to the substorm onset time, and (3) the excited waves have a mixed polarization with frequencies near the ion gyrofrequency at the inner edge and near the lower hybrid frequency in the midtail region. On the basis of this analysis, they propose a substorm development scenario in which plasma sheet thinning during the substorm growth phase leads to an enhancement in the relative drift between ions and electrons. This results in the neutral sheet being susceptible to the CHCI and initiates the diversion of the cross-tail current through the ionosphere. Whether or not a substorm current wedge is ultimately formed is regulated by the ionospheric condition. A large number of substorm features can be readily understood with the proposed scheme. These include (1) precursory activities (pseudobreakups) prior to substorm onset, (2) substorm initiation region to be spatially localized, (3) three different solar wind conditions for substorm occurence, (4) skew towards evening local times for substorm onset locations, (5) different acceleration characteristics between ions and electrons, (6) tailward spreading of current disruption region after substorm onset, and (7) local time expansion of substorm current wedge with possible discrete westward jump for the evening expansion.

  18. Relativistic electrons near geostationary orbit: Evidence for internal magnetospheric acceleration

    SciTech Connect

    Baker, D. N.; Blake, J. B.; Callis, L. B.; Belian, R. D.; Cayton, T. E.

    1989-06-01

    At times, relativistic electron fluxes in Earth's outer magnetosphere are not obviously related to an external (Jovian or solar) source. This finding suggests that an internal magnetospheric acceleration mechanism may operate under some circumstances. A possible mechanism identified for Jupiter's magnetosphere could also be considered in the terrestrial case. Such a model requires the substorm- generation of a spectrally-soft electron component with subsequent inward radial diffusion (violating the third adiabatic invariant). A large electron energy gain transverse to the magnetic field occurs in this process. Eventually, deep within the magnetosphere, substantial pitch angle scattering occurs violating all adiabatic invariants. Then, at low L-values, there occurs an energy-preserving outward transport of energetic electrons near the mirror points. This leads to a return of the accelerated population to the outer magnetosphere. Such low-altitude processes should result in ''conic'' or ''butterfly'' pitch angle distributions at very high energies as the electrons execute trans-L diffusion at the mirror altitudes and then are magnetically focussed near the equator. Data collected concurrently at geostationary orbit at three widely-spaced local times during a relativisic electron event show a butterfly pitch angle distribution, while lower energy electrons simultaneously show pancake-like distributions. The butterfly pitch angle distributions appear in /similar to/25% of the examined relativistic electron events, thereby providing support for acceleration by a recirculation process. /copyright/ American Geophysical Union 1989

  19. Solar Wind-Magnetosphere Coupling Influences on Pseudo-Breakup Activity

    NASA Technical Reports Server (NTRS)

    Fillingim, M. O.; Brittnacher, M.; Parks, G. K.; Germany, G. A.; Spann, J. F.

    1998-01-01

    Pseudo-breakups are brief, localized aurora[ arc brightening, which do not lead to a global expansion, are historically observed during the growth phase of substorms. Previous studies have demonstrated that phenomenologically there is very little difference between substorm onsets and pseudo-breakups except for the degree of localization and the absence of a global expansion phase. A key open question is what physical mechanism prevents a pseudo-breakup form expanding globally. Using Polar Ultraviolet Imager (UVI) images, we identify periods of pseudo-breakup activity. Foe the data analyzed we find that most pseudo-breakups occur near local midnight, between magnetic local times of 21 and 03, at magnetic latitudes near 70 degrees, through this value may change by several degrees. While often discussed in the context of substorm growth phase events, pseudo-breakups are also shown to occur during prolonged relatively inactive periods. These quiet time pseudo-breakups can occur over a period of several hours without the development of a significant substorm for at least an hour after pseudo-breakup activity stops. In an attempt to understand the cause of quiet time pseudo-breakups, we compute the epsilon parameter as a measure of the efficiency of solar wind-magnetosphere coupling. It is noted that quiet time pseudo-breakups occur typically when epsilon is low; less than about 50 GW. We suggest that quiet time pseudo-breakups are driven by relatively small amounts of energy transferred to the magnetosphere by the solar wind insufficient to initiate a substorm expansion onset.

  20. MESSENGER Observations of Substorm Activity at Mercury

    NASA Astrophysics Data System (ADS)

    Sun, W. J.; Slavin, J. A.; Fu, S.; Raines, J. M.; Zong, Q. G.; Poh, G.; Jia, X.; Sundberg, T.; Gershman, D. J.; Pu, Z.; Zurbuchen, T.; Shi, Q.

    2015-12-01

    MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during crossings of Mercury's magnetotail from 2011 to 2014 have been investigated for substorms. A number of events with clear Earth-like growth phase and expansion phase signatures were found. The thinning of the plasma sheet and the increase of magnetic field intensity in the lobe were observed during the growth phase and plasma sheet was observed to thicken during the expansion phase, which are similar to the observations at Earth. But the time scale of Mercury's substorm is only several minutes comparing with the several hours at Earth [Sun et al., 2015a]. Detailed analysis of magnetic field fluctuations during the substorm expansion phase have revealed low frequency plasma waves, e.g. Pi2-like pulsations. The By fluctuations accompanying substorm dipolarizations are consistent with pulses of field-aligned currents near the high latitude edge of the plasma sheet. Further study shows that they are near-circularly polarized electromagnetic waves, most likely Alfvén waves. Soon afterwards the plasma sheet thickened and MESSENGER detected a series of compressional waves. We have also discussed their possible sources [Sun et al., 2015b]. Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015a), MESSENGER observations of magnetospheric substorm activity in Mercury's near magnetotail. Geophys. Res. Lett., 42, 3692-3699. doi: 10.1002/2015GL064052.Sun, W.-J., J. A. Slavin, S. Y. Fu, et al. (2015b), MESSENGER observations of Alfvénic and compressional waves during Mercury's substorms. Geophys. Res. Lett., 42, in press. doi: 10.1002/ 2015GL065452.

  1. Inertial magnetic field reconnection and magnetospheric substorms.

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.; Cross, M. A.

    1973-01-01

    We describe and calculate the growth rate of a magnetohydrodynamic neutral-sheet instability due to electron-inertia terms in the infinite-conductivity Ohm's law. The results are compared with an approximate Vlasov-equation calculation, and are shown to be particularly germane to the geomagnetic-tail instability.

  2. SAPS onset timing during substorms and the westward traveling surge

    NASA Astrophysics Data System (ADS)

    Mishin, Evgeny, V.

    2016-07-01

    We present multispacecraft observations in the magnetosphere and conjugate ionosphere of the onset time of subauroral polarization streams (SAPS) and tens of keV ring current injections on the duskside in three individual substorms. This is probably the first unequivocal determination of the substorm SAPS onset timing. The time lag between the SAPS and substorm onsets is much shorter than the gradient-curvature drift time of ˜10 keV ions in the plasmasphere. It seemingly depends on the propagation time of substorm-injected plasma from the dipolarization onset region to the plasmasphere, as well as on the SAPS position. These observations suggest that fast onset SAPS and ring current injections are causally related to the two-loop system of the westward traveling surge.

  3. MESSENGER: Exploring Mercury's Magnetosphere

    NASA Technical Reports Server (NTRS)

    Slavin, James A.

    2008-01-01

    The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature magnetosphere since Mariner 10's brief fly-bys in 1974-5. Mercury's magnetosphere is unique in many respects. The magnetosphere of Mercury is the smallest in the solar system with its magnetic field typically standing off the solar wind only - 1000 to 2000 km above the surface. For this reason there are no closed dri-fi paths for energetic particles and, hence, no radiation belts; the characteristic time scales for wave propagation and convective transport are short possibly coupling kinetic and fluid modes; magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to directly impact the dayside regolith; inductive currents in Mercury's interior should act to modify the solar In addition, Mercury's magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionosphere. This lack of an ionosphere is thought to be the underlying reason for the brevity of the very intense, but short lived, approx. 1-2 min, substorm-like energetic particle events observed by Mariner 10 in Mercury's magnetic tail. In this seminar, we review what we think we know about Mercury's magnetosphere and describe the MESSENGER science team's strategy for obtaining answers to the outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic magnetosphere.

  4. Fast ionospheric feedback instability and substorm onset

    NASA Technical Reports Server (NTRS)

    Lysak, Robert L.; Grieger, John; Song, Yan

    1992-01-01

    A study suggesting that the Alfven resonator can play an important role in modifying the ionosphere on the time and space scales required to play a significant role in substorm formation is presented. Although the effect of magnetosphere-ionosphere coupling on the onset of substorms has been studied, the effects due to gradients of the Alfven speed along auroral field line were neglected. The large increase of the Alfven speed with altitude above the ionosphere creates an effective resonant cavity, which can lead to fluctuations in the electric and magnetic fields as well as in particle fluxes in the range 0.1 to 1 Hz. Such fluctuations can be observed from the ground as PiB pulsations associated with substorm onset. These fluctuations can be excited by a fast feedback instability, which can grow on time scales much less than the Alfven travel time between the ionosphere and the plasma sheet. The instability enhances the value of both the Pedersen and Hall conductivity, and may play a role in preparing the ionosphere for substorm onset.

  5. SuperDARN Observations of Pi2 Electric Field Pulsations during THEMIS Substorms

    NASA Astrophysics Data System (ADS)

    Baker, J. B.; Ruohoniemi, J. M.; Frissell, N. A.; Greenwald, R. A.; Rae, I. J.; Kale, Z. C.; Kepko, L.; Lester, M.; Grocott, A.; Yeoman, T. K.; Milan, S. E.

    2008-12-01

    The NASA THEMIS mission is focused on resolving the time sequence of events that occur in the magnetotail during the onset of the expansion phase of magnetospheric substorms. In support of THEMIS mission goals, the SuperDARN community is using a special camping-beam mode during THEMIS conjunctions over North America to maximize the temporal resolution of measurements of ionospheric convection during THEMIS substorm events. The SuperDARN THEMIS mode provides 8-second resolution on a single camping beam while simultaneously marching through each beam of the normal 2-minute scan. In this paper, we present SuperDARN measurements of ULF waves identified on SuperDARN camping beams during the onsets of several THEMIS substorms. These events clearly demonstrate the gains in temporal resolution that can be achieved using the THEMIS camping-beam mode. The characteristics of the Pi2 oscillations measured by the SuperDARN radars are found to be very similar to those seen by nearby ground-based magnetometers.

  6. Impulse Travel Time from the Magnetotail to the Aurora Region during substorm: OpenGGCM Simulation

    NASA Astrophysics Data System (ADS)

    Ferdousi, Banafsheh; Raeder, Jimmy

    2016-07-01

    The onset of substorms is an unsolved problem in Space Physics although there are many models explaining the substorm process. Studying the processes that occur during first 2 minutes of substorm depends critically on the correct timing between different signals in the plasma sheet and the ionosphere. This has been difficult to accomplish with data alone, since signals are sometimes ambiguous, or they have not been observed in the right locations. To investigate signal propagation paths and signal travel times, we use Magnetohydrodynamic global simulations of the Earth magnetosphere: OpenGGCM. The waves are created at different locations in the magnetotail by perturbing plasma pressure in the plasma sheet. Thus, we can study wave path in the magnetotail and determine its travel time to the ionosphere. Contrary to previous studies, we find that wave travel reach the ionosphere from the midtail around 60 seconds. We also find that waves travel faster through the lobes, and the Tamao path is not generally the preferred path for waves originating in the plasma sheet. Furthermore, we find that the impulses that are generated closer to earth lead to dispersed ionosphere signatures, whereas the impulses originated in midtail region lead to more localized signatures.

  7. Prompt Energization of Relativistic and Highly Relativistic Electrons during a Substorm Interval

    NASA Astrophysics Data System (ADS)

    Foster, J. C.; Baker, D. N.; Erickson, P. J.; Spence, H. E.; Wygant, J. R.; Kletzing, C.; Kurth, W. S.; Shprits, Y.; Claudepierre, S. G.; Reeves, G. D.; Thaller, S. A.

    2014-12-01

    On March 17, 2013, a large magnetic storm significantly depleted the multi-MeV radiation belt. We present multi-instrument observations from the Van Allen Probes spacecraft RBSP-A and RBSP-B at ~6 Re in the midnight sector magnetosphere and from ground based ionospheric sensors during a substorm dipolarization followed by rapid re-energization of multi-MeV electrons. At ~ 5 Re radial distance, a 50% increase in magnetic field magnitude occurred simultaneously with dramatic increases in 100 keV electron fluxes and a 100x increase in VLF wave intensity. The 100 keV electrons and intense VLF waves provide a seed population and energy source for subsequent radiation belt enhancements. During the event, the two Van Allen Probes spacecraft were separated by ~ 1 hr along the same orbital track enabling a <~1-hr temporal specification of the multi-MeV electron re-energization. Assocated with the substorm, highly relativistic (> 2 MeV) electron fluxes increased immediately at L* ~ 4.5, and ultra-relativistic 4.5 MeV electron flux increased >90x at L*=4 in a time interval of 5 hours or less. Although plasmasphere expansion brings the enhanced radiation belt multi-MeV fluxes inside the plasmasphere several hours post-substorm, we localize their prompt re-energization during the event to regions outside the plasmasphere.

  8. From space weather toward space climate time scales: Substorm analysis from 1993 to 2008

    NASA Astrophysics Data System (ADS)

    Tanskanen, E. I.; Pulkkinen, T. I.; Viljanen, A.; Mursula, K.; Partamies, N.; Slavin, J. A.

    2011-05-01

    Magnetic activity in the Northern Hemisphere auroral region was examined during solar cycles 22 and 23 (1993-2008). Substorms were identified from ground-based magnetic field measurements by an automated search engine. On average, 550 substorms were observed per year, which gives in total about 9000 substorms. The interannual, seasonal and solar cycle-to-cycle variations of the substorm number (Rss), substorm duration (Tss), and peak amplitude (Ass) were examined. The declining phases of both solar cycles 22 and 23 were more active than the other solar cycle phases due to the enhanced solar wind speed. The spring substorms during the declining solar cycle phase (∣Ass,decl∣ = 500 nT) were 25% larger than the spring substorms during the ascending solar cycle years (∣Ass,acs∣ = 400 nT). The following seasonal variation was found: the most intense substorms occurred during spring and fall, the largest substorm frequency in the Northern Hemisphere winter, and the longest-duration substorms in summer. Furthermore, we found a winter-summer asymmetry in the substorm number and duration, which is speculated to be due to the variations in the ionospheric conductivity. The solar cycle-to-cycle variation was found in the yearly substorm number and peak amplitude. The decline from the peak substorm activity in 1994 and 2003 to the following minima took 3 years during solar cycle 22, while it took 6 years during solar cycle 23.

  9. 2-D Convection and Electrodynamic Features of Substorms Revealed by Multiple Radar Observations (Invited)

    NASA Astrophysics Data System (ADS)

    Zou, S.

    2010-12-01

    Substorms are one of the fundamental elements of geomagnetic activity, which involve complex magnetosphere-ionosphere coupling processes. In this work, we aim to better understand the evolution of high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasis on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom ISR, have been utilized. Observations from these radars, together with those from complementary instruments, including satellites and other ground-based instruments, have enabled fundamental new understanding of the ionospheric electrodynamic properties associated with substorms. In this presentation, I focus on electrodynamics near the nightside Harang reversal region. Observations from the SuperDARN and the PFISR radars revealed that auroral activity at substorm onset is located near the center of the Harang reversal, which represents a key feature of magnetospheric and ionospheric convection and is part of the Region 2 system. The observations also show nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. By synthesizing these observations, a 2-D comprehensive view of the nightside ionospheric electrodynamical features, including electrical equipotentials, flows and FACs, and their evolution associated with substorms has been constructed, which has revealed a strong coupling between the substorm and the Region 2 current systems. This study sheds new light on substorm-related magnetosphere-ionosphere coupling and

  10. Relationship between wave-like auroral arcs and Pi2 pulsations in plasma sheet during substorms

    NASA Astrophysics Data System (ADS)

    Chang, T. F.; Cheng, C. Z.

    2014-12-01

    The observations of substorm onset phenomena in the magnetosphere and ionosphere are examined to investigate their correlation and to understand the substorm onset mechanism. In particular, we examine the Pi2 wave structure, propagation, frequency in the magnetosphere observed by the THEMIS satellites in the near-Earth plasma sheet and the structure and propagation of the substorm auroral onset arcs. The azimuthal mode number values of the wave-like substorm arcs are found to be in the range of ~ 100 - 260 and decrease with increasing geomagnetic latitude of the substorm auroral arc location. The wave-like arc brightness structures on the substorm auroral arcs tend to move azimuthally westward, but with a few exceptions of eastward movement, during tens of seconds prior to the substorm onset. The movement of the wave-like arc brightness structure is linearly correlated with the phase velocity of the Pi2 δBy pulsations in the near-Earth plasma sheet region. The result suggests that the Pi2 transverse δBy disturbances are related to the intensifying wave-like substorm onset arcs. One plausible explanation of the observations is the kinetic ballooning instability, which has high azimuthal mode number due to the ion gyro-radius effect and finite parallel electric field that accelerates electrons into the ionosphere to produce the wave-like arc structure.

  11. Energy coupling between the solar wind and the magnetosphere

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1981-01-01

    A description is given of the path leading to the first approximation expression for the solar wind-magnetosphere energy coupling function (epsilon), which correlates well with the total energy consumption rate (U sub T) of the magnetosphere. It is shown that epsilon is the primary factor controlling the time development of magnetospheric substorms and storms. The finding of this particular expression epsilon indicates how the solar wind couples its energy to the magnetosphere; the solar wind and the magnetosphere make up a dynamo. In fact, the power generated by the dynamo can be identified as epsilon through the use of a dimensional analysis. In addition, the finding of epsilon suggests that the magnetosphere is closer to a directly driven system than to an unloading system which stores the generated energy before converting it to substorm and storm energies. The finding of epsilon and its implications is considered to have significantly advanced and improved the understanding of magnetospheric processes.

  12. Drift-shell splitting of energetic ions injected at pseudo-substorm onsets

    SciTech Connect

    Takahashi, K. |; Anderson, B.J.; Ohtani, S.; Reeves, G.D.; Takahashi, S.; Sarris, T.E. |; Mursula, K.

    1997-10-01

    One feature of a magnetospheric substorm is the injection of energetic particles into closed drift orbits. Injections are routinely observed by geosynchronous satellites and have been used to identify the occurrence of substorms and the local time of particle energization. In this study we examine pitch angle distributions of ion injections in the 50-to 300-keV energy range observed by the Active Magnetospheric Particle Tracer Explorers Charge Composition Explorer (AMPTE/CCE) satellite, hereinafter CCE. In a dipole field, all pitch angles follow the same drift shell, but the day{endash}night asymmetry of the magnetospheric magnetic field introduces a pitch angle dependence in particle drift orbits, so that particles with different pitch angles disperse radially as they drift. The effect is known as drift-shell splitting. For satellite observations near noon at a fixed geocentric distance, the guiding center orbits of ions detected at small pitch angles intersect the midnight meridian at larger geocentric distances than do ions with near-90{degree} pitch angles. The ion pitch angle distributions detected on the dayside therefore provide information about the radial distance of the nightside acceleration region. We apply this principle to study ion injection events observed on September 17{endash}18, 1984, in association with pseudo-substorm onsets. CCE was at 13 hours local time near its apogee (8.8R{sub E}) and observed a series of ion flux enhancements. Energy dispersion of the timing of the flux increases assures that they are due to injections on the nightside. The flux increases were observed only at pitch angles from 0{degree} to 60{degree}. We calculate drift orbits of protons using the Tsyganenko 89c magnetic field model and find that the drift orbits for 60{degree} pitch angle protons observed at the satellite pass through midnight at 9R{sub E}, well outside of geostationary orbit, indicating that the ion injections occurred tailward of 9R{sub E}. Energetic

  13. Interball substorm observations: Christmas for space scientists

    NASA Technical Reports Server (NTRS)

    Sandahl, Ingrid; Pulkkinen, Tuija; Budnik, Elena Yu.; Dubinin, Edouard M.; Eklund, Ulrik; Hughes, Terence J.; Kokubun, Susumu; Koskinen, Hannu; Kudela, Karel; Lepping, Ronald P.; Lin, Robert P.; Lui, Anthony T. Y.; Lutsenko, Volt; Mostroem, Arne; Nozdrachev, Michail; Pissarenko, Novomir, F.; Prokhorenko, Victoria; Sauvaud, Jean-Andre; Yermolaev, Yuri I.; Zakharov, Alexander V.

    1996-01-01

    Observational results from the Interball Tail Probe spacecraft are presented. One of the main objectives of the Interball project is to study the dynamic processes in the magnetosphere. Three events observed by the spacecraft's instruments are investigated: a pseudobreakup during which earthward streaming ions were observed in the vicinity of a thin current sheet; a substorm in which the magnetic signatures in the lobe and on the ground were preceeded by northward re-orientation of the interplanetary magnetic field Bz component; and a magnetic storm at the beginning of which extreme deformation of the magnetotail was observed.

  14. The signatures of kinetic ballooning instability during substorms

    NASA Astrophysics Data System (ADS)

    Chang, Tzu-Fang; Cheng, Chio-Zong

    2016-04-01

    We use the observations of THEMIS spacecraft, THEMIS Ground-Based Observatories and FORMOSAT-2/ISUAL satellite to investigate the behavior of wave-like brightness structure on the substorm auroral arcs associated with disturbances in the ionosphere and in the near-Earth plasma sheet. The results indicate that the exponential growth of the westward electrojet current is correlated with the exponential growth of the arc intensity which may support the theory of Cowling channel effect. We also find that the azimuthal mode number values of the wave-like substorm arcs are found to decrease with increasing geomagnetic latitude of the substorm auroral arc location. It is suggest that the azimuthal mode number is likely related to the ion gyroradius and azimuthal wave number. We also show that the azimuthal mode number of the substorm onset arc wave-like structure is similar to that of the disturbances in the plasma sheet. We discuss the role of the kinetic ballooning instability as a plausible candidate for substorm mechanism in understanding qualitatively the analysis results of these simultaneous observations of the ionospheric and magnetospheric substorm phenomena.

  15. The aurora and the magnetosphere - The Chapman Memorial Lecture. [dynamo theory development, 1600-present

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1974-01-01

    Review of recent progress in magnetospheric physics, in particular, in understanding the magnetospheric substorm. It is shown that a number of magnetospheric phenomena can now be understood by viewing the solar wind-magnetosphere interaction as an MHD dynamo; auroral phenomena are powered by the dynamo. Also, magnetospheric responses to variations of the north-south and east-west components of the interplanetary magnetic field have been identified. The magnetospheric substorm is entirely different from the responses of the magnetosphere to the southward component of the interplanetary magnetic field. It may be associated with the formation of a neutral line within the plasma sheet and with an enhanced reconnection along the line. A number of substorm-associated phenomena can be understood by noting that the new neutral line formation is caused by a short-circuiting of a part of the magnetotail current.

  16. The February 24, 2010 substorm: a refined view involving a pseudobreakup/expansive phase/poleward boundary intensification sequence

    NASA Astrophysics Data System (ADS)

    Connors, Martin; Russell, Christopher T.; Chu, Xiangning; McPherron, Robert L.

    2015-12-01

    A substorm on February 24, 2010 was chosen for study by Connors et al. (Geophys. Res. Lett. 41:4449-4455, 2014) due to simple symmetric subauroral magnetic perturbations observed in North America. It was shown that a substorm current wedge (SCW) three-dimensional current model could represent these perturbations well, gave a reasonable representation of auroral zone perturbations, and matched field-aligned currents determined in space from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) project. The conclusion was that substorm onset was at approximately 4:30 UT and that the substorm current wedge (SCW) formed in the region 1 (more poleward) current system.

  17. Global and Multi-scale Dynamics of the Magnetosphere

    NASA Astrophysics Data System (ADS)

    Sharma, A. S.; Sitnov, M. I.

    2001-05-01

    Earth's magnetosphere during substorms demonstrates a number of characteristic features such as low effective dimension, hysteresis and power-law spectra of fluctuations on different scales. The dynamics, on the largest scale, associated with substorms, are in reasonable agreement with low-dimensional magnetospheric models and in particular those of inverse bifurcations. However, deviations from the low-dimensional picture are not negligible, making the nonequilibrium phase transition more appropriate as a dynamical analogue of the substorm activity. On the other hand, the multi- scale magnetospheric dynamics cannot be restricted to the self-organized criticality (SOC), which is based on a class of mathematical analogues of sandpiles. Like real sandpiles the magnetosphere demonstrates during substorms the features, which are distinct from SOC and more reminiscent again to conventional phase transitions. While the multi-scale substorm activity resembles second-order phase transitions, the largest substorm avalanches are shown to reveal the features of first-order nonequilibrium transitions including hysteresis phenomenon and global structure of the type of the "temperature-pressure-density" diagram. Moreover, this diagram allows one to compute a critical exponent, consistent with the second-order phase transitions, and reflects the multiscale aspect of the substorm activity, different from power-law frequency and scale spectra of autonomous systems. In contrast to SOC exponents, the exponent relates input and output parameters of the magnetosphere. Using an analogy with the dynamical Ising model in the mean-field approximation we show the connection between this data-derived exponent of nonequilibrium transitions in the magnetosphere and the standard critical exponent β of equilibrium second-order phase transitions. We discuss also further developments of the phase tarnsition approach to modeling magnetospheric activity using the multifractal, mutual information

  18. Relationship between auroral substorms and the occurrence of terrestrial kilometric radiation

    NASA Technical Reports Server (NTRS)

    Kaiser, M. L.; Alexander, J. K.

    1977-01-01

    The correlation between magnetospheric substorms as inferred from the AE(11) index and the occurrence of terrestrial kilometric radiation (TKR) is examined. It is found that AE and TKR are well correlated when observations are made from above the 15-03 hr local time zone and are rather poorly correlated over the 03-15 hr zone. High-resolution dynamic spectra obtained during periods of isolated substorms indicate that low-intensity, high-frequency TKR commences at about the same time as the substorm phase. The substorm expansion phase corresponds to a rapid intensification and bandwidth increase of TKR. When combined with previous results, these new observations imply that many TKR events begin at low altitudes and high frequencies (about 400-500 kHz) and spread to higher altitudes and lower frequencies as the substorm expands.

  19. Substorm associated micropulsations at synchronous orbit

    NASA Technical Reports Server (NTRS)

    Mcpherron, R. L.

    1981-01-01

    The state of the art of observations of substorm associated waves in GEO is reviewed and research directions are indicated. Data were taken from fluxgate magnetometers on board the ATS 1 and 6 spacecraft in GEO. Mixed mode Pc 4 and 5 waves, with the largest amplitude of magnetic pulsations observed at GEO, have been found to display a quasi-sinusoidal waveform with amplitudes from 10-30 gamma and a period of 50-200 sec. The wave spectra confined the excited frequencies to a narrow band, and possible generating mechanisms for the Pc 4 and 5 waves are discussed. Pc 1 and 2 magnetic pulsations are the most common in GEO, with Pc 1 occurring every third day, particularly in the afternoon to dusk sector and during major substorm expansion onset. Pi 2 outbursts are observed in the majority of substorms passing through the midnight sector and have been correlated with changes in field aligned currents.

  20. Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

    NASA Astrophysics Data System (ADS)

    Liu, Jun-Ming; Zhang, Bei-Chen; Kamide, Y.; Wu, Zhen-Sen; Hu, Ze-Jun; Yang, Hui-Gen

    2011-01-01

    An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

  1. Simultaneous observation of the poleward expansion of substorm electrojet activity and the tailward expansion of current sheet disruption in the near-earth magnetotail

    SciTech Connect

    Lopez, R.E. ); Koskinen, H.E.J.; Pulkkinen, T.I. ); Boesinger, T. ); McEntire, R.W.; Potemra, T.A. )

    1993-06-01

    This paper reports on observations of a magnetospheric substorm on June 7, 1985. This event was observed simultaneously by a number of different systems. Particle and magnetic field data were collected by AMPTE/CCE, located near the neutral sheet; magnetic field data was monitored by the EISCAT magnetometer cross; STARE radar data was also collected; and Pi 1 data from Sodankyla. The ground based systems observed the poleward and westward expansion of electrojet activity at the start of the storm. The satellite was able to see the storms onset, and record perturbations in the current sheet at the onset of the substorm, in addition to later perturbations, which the authors argue originates tailward of the satellite. Satellite measurements are shown to occur in conjunction with ground events.

  2. Configuration and Generation of Substorm Current Wedge

    NASA Astrophysics Data System (ADS)

    Chu, Xiangning

    The substorm current wedge (SCW), a core element of substorm dynamics coupling the magnetotail to the ionosphere, is crucial in understanding substorms. It has been suggested that the field-aligned currents (FACs) in the SCW are caused by either pressure gradients or flow vortices, or both. Our understanding of FAC generations is based predominately on numerical simulations, because it has not been possible to organize spacecraft observations in a coordinate system determined by the SCW. This dissertation develops an empirical inversion model of the current wedge and inverts midlatitude magnetometer data to obtain the parameters of the current wedge for three solar cycles. This database enables statistical data analysis of spacecraft plasma and magnetic field observations relative to the SCW coordinate. In chapter 2, a new midlatitude positive bay (MPB) index is developed and calculated for three solar cycles of data. The MPB index is processed to determine the substorm onset time, which is shown to correspond to the auroral breakup onset with at most 1-2 minutes difference. Substorm occurrence rate is found to depend on solar wind speed while substorm duration is rather constant, suggesting that substorm process has an intrinsic pattern independent of external driving. In chapter 3, an SCW inversion technique is developed to determine the strength and locations of the FACs in an SCW. The inversion parameters for FAC strength and location, and ring current strength are validated by comparison with other measurements. In chapter 4, the connection between earthward flows and auroral poleward expansion is examined using improved mapping, obtained from a newly-developed dynamic magnetospheric model by superimposing a standard magnetospheric field model with substorm current wedge obtained from the inversion technique. It is shown that the ionospheric projection of flows observed at a fixed point in the equatorial plane map to the bright aurora as it expands poleward

  3. Evolution of high latitude ionospheric convection associated with substorms: Multiple radar observations

    NASA Astrophysics Data System (ADS)

    Zou, Shasha

    The work presented in this dissertation concerns evolution of the high latitude ionospheric convection and the relevant current systems associated with substorms, with emphasize on these features near the nightside Harang reversal region. Three different types of radars, including the Super Dual Auroral Radar Network (SuperDARN) coherent-scatter radars, the new advanced modular incoherent-scatter radar at Poker Flat (PFISR), and the Sondrestrom incoherent-scatter radar (ISR), have been utilized. Observations from those radars, together with those from complementary instruments, including satellites and other ground-based instruments, have revealed fundamental new understand of the ionospheric electrodynamic properties associated with substorms. By using the SuperDARN and the PFISR radars, we found that the auroral activity at substorm onset is located in the center of the Harang reversal, which represents a key region in the magnetospheric and ionospheric convection and is part of the Region 2 system. We have also shown that nightside convection flows exhibit repeatable, distinct variations at different locations relative to the substorm-related auroral activity. Taking advantage of the simultaneous flow and ionization measurements from PFISR, a current closure relation has been found between the Region 2 and the substorm field-aligned current systems. These observations demonstrate a strong coupling between the Region 2 system and the substorm dynamics. This study sheds new light on the substorm-related magnetosphere-ionosphere coupling and contributes to the building of a holistic picture of the substorm dynamics. The third radar has been used to study the dayside ionospheric convection response to the external soar wind and IMF driving and its role in substorm dynamics. The results have been applied to study substorm triggering and in the future could be used to study the relation between the external driving and the formation of the Harang reversal.

  4. Statistical comparison of inter-substorm timings in global magnetohydrodynamics (MHD) and observations

    NASA Astrophysics Data System (ADS)

    Haiducek, J. D.; Welling, D. T.; Morley, S.; Ozturk, D. S.

    2015-12-01

    Magnetospheric substorms are events in which energy stored in the magnetotail is released into the auroral zone and into the downstream solar wind. Because of the complex, nonlinear, and possibly chaotic nature of the substorm energy release mechanism, it may be extremely difficult to forecast individual substorms in the near term. However, the inter-substorm timing (the amount of time elapsed between substorms) can be reproduced in a statistical sense, as was demonstrated by Freeman and Morley (2004) using their Minimal Substorm Model (MSM), a simple solar-wind driven model with the only free parameter being a recurrence time. The goal of the present work is to reproduce the observed distribution of inter-substorm timings with a global MHD model. The period of 1-31 January 2005 was simulated using the Space Weather Modeling Framework (SWMF), driven by solar wind observations. Substorms were identified in the model output by synthesizing surface magnetometer data and by looking for tailward-moving plasmoids. Substorms identified in the MHD model are then compared with observational data from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, Los Alamos National Laboratory (LANL) geostationary satellite energetic particle data, and surface magnetometer data. For each dataset (MHD model and observations), we calculate the substorm occurrence rate, and for the MHD model we additionally calculate the timing error of the substorm onsets relative to the observed substorms. Finally, we calculate distribution functions for the inter-substorm timings in both the observations and the model. The results of this analysis will guide improvements to the MHD-based substorm model, including the use of Hall MHD and embedded particle in cell (EPIC), leading to a better reproduction of the observed inter-substorm timings and an improved understanding of the underlying physical processes. ReferencesM. P. Freeman and S. K. Morley. A minimal substorm model that

  5. The magnetosphere of Mercury

    NASA Technical Reports Server (NTRS)

    Ness, N. F.

    1976-01-01

    Data on Mercury's magnetosphere and on the plasma, planetomagnetic, and energetic particle environment of the planet obtained in three encounters (Mariner 10 flybys) are compared, and tasks for future research are outlined. The Mercury bow shock and magnetopause are much closer to the planet than the earth counterparts are to the earth. The magnetotail with embedded plasma sheet-field reversal region, global deflection of the solar wind by an intrinsic dipolar magnetic field, variations in solar wind momentum flux, and absence of such features as ionosphere, plasmasphere, and radiation belts, are described. Energetic electrons are accelerated in the magnetotail, however, and the interplanetary magnetic field variations distort Mercury's magnetosphere to produce a southward field associated with substorm-like disturbances.

  6. Two substorm studies of relations between westward electric fields in the outer plasmasphere, auroral activity, and geomagnetic perturbations

    NASA Technical Reports Server (NTRS)

    Carpenter, D. L.; Akasofu, S.

    1972-01-01

    Temporal variations of the westward component of the magnetospheric convection electric field in the outer plasmasphere were compared to auroral activity near L = 7, and to variations in the geomagnetic field at middle and high latitudes. The substorms occurred on July 29, 1965 near 0530 UT and on August 20, 1965 near 0730 UT. The results on westward electric field E(w) were obtained by the whistler method using data from Eights, Antarctica (L is approximately 4). All sky camera records were obtained from Byrd, Antarctica, (L is approximately 7), located within about 1 hour of Eights in magnetic local time. It was found that E(w) within the outer plasmasphere increased rapidly to substorm levels about the time of auroral expansion at nearby longitudes. This behavior is shown to differ from results on E(w) from balloons, which show E(w) reaching enhanced levels prior to the expansion. A close temporal relation was found between the rapid, substorm associated increases in E(w) and a well known type of nightside geomagnetic perturbation. Particularly well defined was the correlation of E(w) rise and a large deviation of the D component at middle latitudes.

  7. Sambo-Geos: on three-dimensional substorm dynamics - a case study for 4 March 1979

    SciTech Connect

    Lazutin, L.L.; Khrushchinskii, A.A.; Glassmeier, K.; Gustafsson, G.; Kangas, J.

    1985-01-01

    Ground-based, balloon, and Geos-2 observations of the magnetospheric substorm of Mar. 4, 1979 are examined. It is shown that the substorm can be described by a four-phase scheme, with the active phase divided into two parts: an active-convective phase and a classical active phase. The breakup is shown to take place at closed rather than tailward stretched magnetic field lines. Radial particle movement is described in terms of the dynamic shell splitting effect; it corresponds to structural changes in the magnetosphere and may explain the northward expansion of the westward traveling surge. 7 references.

  8. Substorm electric fields at nightside low latitude

    NASA Astrophysics Data System (ADS)

    Hashimoto, K. K.; Kikuchi, T.; Tomizawa, I.; Nagatsuma, T.

    2014-12-01

    The convection electric field penetrates from the polar ionosphere to low latitude and drives the DP2 currents in the global ionosphere with an intensified equatorial electrojet (EEJ). The electric field often reverses its direction, that is, the overshielding occurs and causes the equatorial counterelectrojet (CEJ) during storm and substorms. In this paper we report that the overshielding electric field is detected by the HF Doppler sounders at low latitude on the nightside. We analyzed the Doppler frequency of the HF radio signals propagated over 120 km in Japan at frequencies of 5 and 8 MHz and compared with the equatorial EEJ/CEJ during the substorm expansion phase. We found that the overshielding electric field reaches around 2 mV/m during major substorms (AL <-1800 nT). Taking the geometrical attenuation into account, we estimate the equatorial electric field to be about 1.5 mV/m. We also found that the correlation coefficient was 0.94 between the overshielding electric field and eastward equatorial electrojet at YAP on the night side. The electric field drives the eastward electrojets in the equatorial ionosphere on the night side. It is to be noted that the overshielding electric field is observed on the nightside at low latitude during the major substorms, while the convection electric field is dominant during smaller size substorms, as the CEJ flows on the dayside. These results suggest that the overshielding electric field associated with the Region-2 field-aligned currents becomes dominant during substorms at low latitude on the nightside as well as on the dayside.

  9. A statistical relationship between the geosynchronous magnetic field and substorm electrojet magnitude

    NASA Technical Reports Server (NTRS)

    Lopez, Ramon E.; Von Rosenvinge, Tycho

    1993-01-01

    The relationship between the geosynchronous magnetic field variations during substorms measured by GOES 5 and the auroral electroject as measured by AE and Poste de la Baleine is examined. It is found that the more taillike the field prior to the local onset, the greater the dipolarization of the field during the substorm. The greater the deviation of the field from a dipolar configuration, the larger the change in AE during the event. It is inferred that stronger cross-tail currents prior to the substorm are associated with larger substorm-associated westward electrojets and thus more intense substorms. Since the westward electroject is the ionospheric leg of the substorm current wedge, it is inferred that the substorm-associated westward electrojet is drawn from the near-earth region. Most of the current diversion is found to occur in the near-earth magnetotail.

  10. The average ionospheric electrodynamics for the different substorm phases

    SciTech Connect

    Kamide, Y.; Sun, W.; Akasofu, S.I.

    1996-01-01

    The average patterns of the electrostatic potential, current vectors, and Joule heating in the polar ionosphere, as well as the associated field-aligned currents, are determined for a quiet time, the growth phase, the expansion phase, the peak epoch, and the recovery phase of substorms. For this purpose, the Kamide-Richmond-Matsushita magnetogram-inversion algorithm is applied to a data set (for March 17, 18, and 19, 1978) from the six meridian magnetometer chains (the total number of magnetometer stations being 71) which were operated during the period of the International Magnetospheric Study (IMS). This is the first attempt at obtaining, on the basis of individual substorms, the average pattern of substorm quantitities in the polar ionosphere for the different epochs. The main results are as follows: (1) The substorm-time current patterns over the entire polar region consist of two components. The first one is related to the two-cell convection pattern, and the second one is the westward electrojet in the dark sector which is related to the wedge current. (2) Time variations of the two components for the four substorm epochs are shown to be considerably different. (3) The dependence of these differences on the ionospheric electric field and the conductivities (Hall and Pedersen) is identified. (4) It is shown that the large-scale two-cell pattern in the electric potential is dominant during the growth phase of substorms. (5) The expansion phase is characterized by the appearance of a strong westward electrojet, which is added to the two-cell pattern. (6) The large-scale potential pattern becomes complicated during the recovery phase of substorms, but the two-cell pattern appears to be relatively dominant again during their late recovery as the wedge current subsides. These and many other earlier results are consistent with the present ones, which are more quantitatively and comprehensively demonstrated in this global study. 39 refs., 9 figs., 1 tab.

  11. The effect of magnetic substorms on near-ground atmospheric current

    NASA Astrophysics Data System (ADS)

    Belova, E.; Kirkwood, S.; Tammet, H.

    2000-12-01

    Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between substorm and quiet atmospheric currents decreases. The amplitude of this substorm variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.

  12. Growth-phase thinning of the near-Earth current sheet during the CDAW 6 substorm

    NASA Technical Reports Server (NTRS)

    Sanny, Jeff; Mcpherron, R. L.; Russell, C. T.; Baker, D. N.; Pulkkinen, T. I.; Nishida, A.

    1994-01-01

    The thinning of the near-Earth current sheet during the growth phase of the Coordinated Data Analysis Workshop (CDAW) 6 magnetospheric substorm is studied. The expansion onset of the substorm occurred at 1054 UT, March 22, 1979. During the growth phase, two spacecraft, International Sun Earth Explorer (ISEE) 1 and ISEE 2, were within the current sheet approximately 13 R(sub E) from the Earth and obtained simultaneous high-resolution magnetic data at two points in the current sheet. Plasma data were also provided by the ISEE spacecraft and solar wind data by IMP 8. To facilitate the analysis, the GSM magnetic field data are transformed to a 'neutral sheet coordinate system' in which the new x axis is parallel to the average magnetic field above and below the neutral sheet and the new y axis lies in the GSM equatorial plane. A model based on the assumption that the current sheet is a time-invariant structure fails to predict neutral sheet crossing times. Consequently, the Harris sheet model, which allows one to remove the restriction of time invariancy, is used instead. It is found that during the growth phase, a model parameter corresponding to the thickness of the current sheet decreased exponentially from about 5 R(sub E) to 1 R(sub E) with a time constant of about 14 min. In addition, the ISEE 1 and ISEE 2 neutral sheet crossings after expansion onset indicate that the neutral sheet was moving upward at 7 km/s relative to the spacecraft. Since both crossings occurred in approximately 80 s, the current sheet thickness is estimated to be about 500 km. These results demonstrate that the near-Earth current sheet undergoes dramatic thinning during the substorm growth phase and expansion onset.

  13. Dynamics of energetic particles and neutrals in Saturn's variable magnetosphere: results from the MIMI investigation

    NASA Astrophysics Data System (ADS)

    Krimigis, S. M.; Mitchell, D. G.; Hamilton, D. C.; Krupp, N.; Livi, S.; Roelof, E. C.; Dandouras, J.; Mauk, B. H.; Brandt, P. C.; Paranicas, C. P.; Saur, J.; Armstrong, T. P.; Bolton, S.; Cheng, A. F.; Gloeckler, G.; Hill, M. E.; Hsieh, K. C.; Ip, W. H.; Lagg, A.; Lanzerotti, L. J.; McEntire, R. W.; Williams, D. J.

    2005-08-01

    The Magnetospheric IMaging Instrument (MIMI) comprises three sensors: the Ion and Neutral Camera (INCA) provides images using energetic neutral atoms (ENA) and ions; the Charge-Energy-Mass-Spectrometer (CHEMS) determines the mass and charge state of ions; and the Low Energy Magnetospheric Measurement System (LEMMS) measures ion and electron distributions using a dual field-of-view telescope (Krimigis et al, Space Sci Rev,114, 2333-329, 2004). Measurements by MIMI after Saturn orbit insertion on 1 July 2004 have elucidated several new features of the planet's magnetosphere. These include: (1) A dynamical magnetosphere with an11-hour periodicity. (2) The first remotely-sensed radiation belt inside Saturn's D-ring. (3) Abundant water products in the magnetospheric plasma > or = 10 kev/charge, but little nitrogen (N+/O+<0.05); neutral gas is found to be a major mechanism for particle loss. (4) Injections of plasma in the ˜4-11Rs and also >20Rs corotate with the planet and can last for several days. (5) Activity (possibly analogous to Earth's substorms) occurs in Saturn's magnetotail in the 20-40 Rs region during large magnetospheric disturbances; this has not been observed during quiet times. (6) Field-aligned electron beams occur in the dawn to early morning sector as close as ˜10 Rs, and map to latitudes of observed Saturn aurora. (7) A gas cloud around Titan with dimensions > 1 Rs, with strong high ( 3200 km) altitude ENA emissions forms a continuous, asymmetric ``halo." (8) Titan's emission is centered on moon--hot plasma interaction with the exosphere; changing intensity depends on variable (x10-100) ion population and magnetic field orientation about Titan. (9) Upstream ion events have been measured to large (<50 to > 800 Rs) distances; several are enriched in oxygen ions, suggesting a magnetospheric origin. The observations will be presented and discussed in the context of current models of Saturn's magnetosphere.

  14. Pi2 pulsations and substorm onsets: A review

    NASA Astrophysics Data System (ADS)

    Olson, John V.

    1999-08-01

    Pi2 pulsations have been the subject of continuous study since they were recognized to be an integral part of the magnetospheric substorm. With the advent of arrays of ground instruments the nature of the Pi2 has begun to be understood. As adopted by the 13th General Assembly of the International Union of Geodesy and Geophysics in 1963, Pi2 is a designation that includes impulsive pulsations in the period range from 40 to 150 s. The Pi2 signal encompasses a class of pulsations that represents two fundamental processes. The first process is the sudden generation of field-aligned currents in association with the disruption of cross-tail currents in the plasma sheet and their subsequent effects on the ionosphere. The ionosphere appears to be something more than a passive load for this electrodynamic impulse. It responds, sending currents back into a magnetosphere whose topology is changing and, perhaps producing the feedback necessary to cause the explosive growth of the substorm current system. Oscillations of these currents are detected across the nightside of the Earth at onset as the midlatitude and high-latitude portions of Pi2. The second process is the impulse response of the inner magnetosphere to the compressional waves that are generated at substorm onset. Traveling inward, they stimulate field line resonances and surface waves at the plasmapause and excite global oscillations in the inner magnetosphere. The two processes produce wave modes that couple and cross-couple threading energy into the inner magnetosphere and ultimately to the ground. The purpose of this review is to construct a phenomenological overview of the Pi2.

  15. Substorm-associated radar auroral surges

    SciTech Connect

    Freeman, M.P.; Southwood, D.J. ); Lester, M.; Yeoman, T.K. ); Reeves, G.D. )

    1992-08-01

    The authors report a recurrent convection signature observed in the E region ionosphere within {approximately}2 hours of the dusk meridian by the SABRE radar facility. In a typical event, the irregularity drift speed in the SABRE field of view is seen to increase from about 300 m s{sup {minus}1} to of the order of 1 km s{sup {minus}1} in the space of about 10 min. The speed subsequently remains at the enhanced level for 10 min or longer before declining as rapidly as its onset. The total event duration ranges between 30 min and 1 hour. As the irregularity drift speed increases the direction of the drift velocity changes, rotating poleward. At the same time, the radar backscatter power decreases. The onset of the drift speed enhancement crosses the SABRE field of view as a front moving from east to west. Detailed study of individual events indicates that the events are associated with increases in the {vert bar}AL{vert bar} index and with the injection of energetic particles into geosynchronous orbit. The authors thus suggest that the events are a part of the magnetospheric response to the onset of a geomagnetic substorm. However, while each event appears to be associated with a substorm onset, not every substorm onset is associated with an event, at least not at SABRE. They estimate the speed at which the substorm-initiated ionospheric flow enhancement moves from the nightside to be 1-4 km s{sup {minus}1}, a figure that is consistent with the rate at which the drift velocity front crosses the SABRE field of view. Although the front is associated with a rotation in the drift velocity, they see little evidence of strong vertical vorticity as the front passes. However, shears in the flow do develop subsequently which seem likely to correspond to field-aligned current. Although associated with substorm onset, they argue that these events are distinct from westward traveling surges and appear to differ from the midlatitude phenomenon known as subauroral ion drifts.

  16. Solar Wind Drivers for Steady Magnetospheric Convection

    NASA Technical Reports Server (NTRS)

    McPherron, Robert L.; O'Brien, T. Paul; Thompson, Scott; Lui, A. T. Y. (Editor)

    2005-01-01

    Steady magnetospheric convection (SMC) also known as convection bays, is a particular mode of response of the magnetosphere to solar wind coupling. It is characterized by convection lasting for times longer than a typical substorm recovery during which no substorms expansions can be identified. It is generally believed that the solar wind must be unusually steady for the magnetosphere to enter this state. However, most previous studies have assumed this is true and have used such conditions to identify events. In a preliminary investigation using only the AE and AL indices to select events we have shown that these expectations are generally correct. SMC events seem to be associated with slow speed solar wind and moderate, stable IMF Bz. In this report we extend our previous study including additional parameters and the time variations in various statistical quantities. For the intervals identified as SMCs we perform a detailed statistical analysis of the properties of different solar wind variables. We compare these statistics to those determined from all data, and from intervals in which substorms but not SMCs are present. We also consider the question of whether substorms are required to initiate and terminate an SMC. We conclude that the intervals we have identified as SMC are likely to be examples of the original Dungey concept of balanced reconnection at a pair of x-lines on the day and night side of the Earth.

  17. Global Remote Sensing of Precipitating Electron Energies: A Comparison of Substorms and Pressure Pulse Related Intensifications

    NASA Technical Reports Server (NTRS)

    Chua, D.; Parks, G. K.; Brittnacher, M. J.; Germany, G. A.; Spann, J. F.

    2000-01-01

    The Polar Ultraviolet Imager (UVI) observes aurora responses to incident solar wind pressure pulses and interplanetary shocks such its those associated with coronal mass ejections. Previous observations have demonstrated that the arrival of it pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside aurora precipitations. Our observations show it simultaneous brightening over bread areas of the dayside and nightside auroral in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolate substorm. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated event to those during isolated substorms. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has characteristic energies greater than 10 KeV and is structured both in local time and in magnetic latitude. For auroral intensifications following the arrival of'a pressure pulse or interplanetary shock. Electron precipitation is less spatially structured and has greater flux of lower characteristic energy electrons (Echar less than 7 KeV) than during isolated substorm onsets. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

  18. A Comparison of Ion and Electron Energization and Transport Mechanisms in the Magnetotail During Substorms

    NASA Astrophysics Data System (ADS)

    Pan, Q.; Ashour-Abdalla, M.; Walker, R. J.; El-Alaoui, M.

    2014-12-01

    We report a recent study comparing electron and ion energization and transport mechanisms in the magnetotail during substorms. The simulation scheme combines global magnetohydrodynamic (MHD) modeling of the magnetosphere driven by realistic upstream solar wind conditions, with large-scale kinetics (LSK) simulations in which we calculate the trajectories of millions of test particles in the electric and magnetic fields from the MHD simulation. In particular, during a modest substorm event that occurred on February 7, 2009, we found multiple earthward propagating dipolarizations driven by reconnection outflow jets in the MHD simulation results. Ion trajectories in the ion LSK simulation show that ions that originating near the reconnection site first gained energy non-adiabatically, and then gained energy adiabatically as they "caught up with and then rode on" the earthward propagating dipolarizations. Consequently, the integrated high-energy (>25 keV) ion fluxes were enhanced where and when the dipolarizations intensified. High-speed flows in narrow channels controlled the earthward ion transport in the magnetotail due to the dominance of E×B drift. The mechanisms of non-local energization by dipolarizations and transport controlled by high-speed flows operate similarly for electrons as reported in studies of other events by Ashour-Abdalla et al. [2011] and Pan et al. [2014]. We perform an electron LSK simulation for the same February 7, 2009 event to examine these similarities.

  19. Effects of a “day-time” substorm on the ionosphere and radio propagation

    NASA Astrophysics Data System (ADS)

    Blagoveshchensky, D.; Kalishin, A.; MacDougall, J.

    2009-11-01

    Propagation mechanisms of lateral (non-great-circle) signals on a high-latitude HF radio path during magnetospheric substorms that occurred in the day-time have been considered. The path is equipped with oblique ionospheric sounding (OIS) from Murmansk to St. Petersburg. The OIS method gives the possibility to determine propagation modes, MOF (maximum observed frequency) values, signal delays, etc. Data of the CUTLASS radar, the IMAGE magnetometer system, the Finnish riometer chain, and the Tromso ionosonde were also used for the analysis. The main results are the following: (1) the lateral signal propagation takes place, as a rule, if the path midpoint is located near the irregularity region that moves sharply from high to low latitudes. The lateral signal propagation appearing during day-time is a new effect. (2) Formation of dense field-aligned irregularities during a substorm leads to decreasing F2MOF values on radio paths. These results can be useful for problems of radiolocation, HF communications and navigation.

  20. Magnetospheric electric fields and currents

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.; Zanetti, L. J.

    1987-01-01

    The progress made in the years 1983-1986 in understanding the character and operation of magnetospheric electric fields and electric currents is discussed, with emphasis placed on the connection with the interior regions. Special attention is given to determinations of global electric-field configurations, measurements of the response of magnetospheric particle populations to the electric-field configurations, and observations of the magnetospheric currents at high altitude and during northward IMF. Global simulations of current distributions are discussed, and the sources of global electric fields and currents are examined. The topics discussed in the area of impulsive and small-scale phenomena include substorm current systems, impulsive electric fields and associated currents, and field-aligned electrodynamics. A key finding of these studies is that the electric fields and currents are interrelated and cannot be viewed as separate entities.

  1. Reconnection in substorms and solar flares: analogies and differences

    SciTech Connect

    Birn, Joachim

    2008-01-01

    Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and on energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares.

  2. CDAW-9 analysis of magnetospheric events on 3 May 1986: Event C. Technical report

    SciTech Connect

    Baker, D.N.; Pulkkinen, T.I.; McPherron, R.L.; Craven, J.D.; Frank, L.A.

    1993-10-01

    The ninth Coordinated Data Analysis Workshop (CDAW-9) focussed upon several intervals within the PROMIS period (March-June 1986). Event interval C comprised the period 0000-1200 UT on 3 May 1986 which was a highly disturbed time near the end of a geomagnetic storm interval. A very large substorm early in the period commenced at 0111 UT and had a peak AE index value of approx. 1500 nT. Subsequent activity was lower, but at least three other substorms occurred at 2-3 hour intervals. The substorms on 3 May were well observed by a variety of satellites, including ISEE-1, -2, and IMP-8 in the magnetotail plus SCATHA, GOES, GMS, and LANL spacecraft at or near geostationary orbit. A particularly important feature of the 0111 UT substorm was the simultaneous imaging of the southern auroral oval by DE-1 and of the northern oval by Viking. The excellent constellation of spacecraft near local midnight in the radial range 5-9 RE made it possible to study the strong cross-tail current development during the substorm growth phase and the current disruption and current wedge development during the expansion phase. The authors use a time-evolving magnetic field model to map observed auroral features out into the magnetospheric equatorial plane. There was both a dominant eastward and a weaker westward progression of activity following the expansion phase. A clear latitudinal separation of the initial region of auroral brightening and the region of intense westward electrojet current was identified.

  3. Electrodynamics of convection in the inner magnetosphere

    NASA Technical Reports Server (NTRS)

    Spiro, R. W.; Wolf, R. A.

    1984-01-01

    During the past ten years, substantial progress has been made in the development of quantitative models of convection in the magnetosphere and of the electrodynamic processes that couple that magnetosphere and ionosphere. Using a computational scheme first proposed by Vasyliunas, the convection models under consideration separate the three-dimensional problem of convection in the inner magnetosphere/ionosphere into a pair of two-dimensional problems coupled by Birkeland currents flowing between the two regions. The logic, development, and major results of the inner magnetosphere convection model are reviewed with emphasis on ionospheric and magnetospheric currents. A major theoretical result of the models has been the clarification of the relationship between the region 1/region 2 picture of field-aligned currents and the older partial ring current/tail current interruption picture of substorm dynamics.

  4. Estimates of magnetic flux, and energy balance in the plasma sheet during substorm expansion

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Pulkkinen, Tuija

    1996-01-01

    The energy and magnetic flux budgets of the magnetotail plasma sheet during substorm expansion are investigated. The possible mechanisms that change the energy content of the closed field line region which contains all the major dissipation mechanisms of relevance during substorms, are considered. The compression of the plasma sheet mechanism and the diffusion mechanism are considered and excluded. It is concluded that the magnetic reconnection mechanism can accomplish the required transport. Data-based empirical magnetic field models are used to investigate the magnetic flux transport required to account for the observed magnetic field dipolarizations in the inner magnetosphere. It is found that the magnetic flux permeating the current sheet is typically insufficient to supply the required magnetic flux. It is concluded that no major substorm-type magnetospheric reconfiguration is possible in the absence of magnetic reconnection.

  5. On the correlation between the fast solar wind flow changes and substorm occurrence

    NASA Astrophysics Data System (ADS)

    Semenov, V. S.; Kubyshkina, D. I.; Kubyshkina, M. V.; Kubyshkin, I. V.; Partamies, N.

    2015-07-01

    There is a point of view that solar wind factors, which break the magnetotail symmetry, are more effective in triggering the magnetospheric substorm. To clarify the question we use a database of substorm onsets and found the evident dependence of the substorm probability on the solar wind flow direction jumps (asymmetric factor), while distribution of the substorm occurrence on the solar wind number density jumps (symmetric factor) is homogeneous. The theoretical interpretation is based on the extension of the existing symmetric Kan model for a bent current sheet. Allowing the model tilt angle to vary in time, we found that the induced electric field penetrates to the central region of the bent current sheet. If the solar wind direction jump increases the bending, then induced electric field thins the current sheet and thus stimulates the reconnection. In the opposite case the current sheet thickens. We claim that this effect is sufficient (provides twice or more thinning of the current sheet in 10 min).

  6. Electric currents of a substorm current wedge on 24 February 2010

    NASA Astrophysics Data System (ADS)

    Connors, Martin; McPherron, Robert L.; Anderson, Brian J.; Korth, Haje; Russell, Christopher T.; Chu, Xiangning

    2014-07-01

    The three-dimensional "substorm current wedge" (SCW) was postulated by McPherron et al. (1973) to explain substorm magnetic perturbations. The origin and coherence as a physical system of this important paradigm of modern space physics remained unclear, however, with progress hindered by gross undersampling, and uniqueness problems in data inversion. Complementing AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) space-derived radial electric currents with ground magnetic data allowing us to determine currents from the ionosphere up, we overcome problems of uniqueness identified by Fukushima (1969, 1994). For a substorm on 24 February 2010, we quantify SCW development consistently from ground and space data. Its westward electrojet carries 0.5 MA in the more poleward part of the auroral oval, in Region 1 (R1) sense spanning midnight. The evening sector electrojet also feeds into its upward current. We thus validate the SCW concept and obtain parameters needed for quantitative study of substorms.

  7. Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail during Substorms: Implications for Magnetic Field Models

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Our studies elucidated the relationship between the auroral arcs and magnetotail phenomena. One paper examined particle energization in the source region of the field-aligned currents that intensify at substorm onset when the arc brightens to form the westward electrojet. A second paper examined the relationship between the precipitating particles in the arcs, the location of the westward electrojet, and magnetospheric source regions. Two earlier papers also investigated the roles that field aligned currents and particle acceleration have during substorms.

  8. CDAW 7 revisited - Further evidence for the creation of a near-earth substorm neutral line. [Coordinated Data Analysis Workshop

    NASA Technical Reports Server (NTRS)

    Kettmann, G.; Fritz, T. A.; Hones, E. W., Jr.

    1990-01-01

    Eastman et al. (1988) have interpreted the CDAW 7 substorm of April 24, 1979, previously taken as unambiguously supporting the near-earth neutral line model of magnetospheric substorms, in terms of spatial movements of a preexisting plasma-sheet boundary layer (PSBL) and its associated current sheets across the observing ISEE 1 and 2 spacercraft. It is presently noted that, by contrast, a reinvestigation of ISEE 1 and 2 energetic particle measurements around substorm onset on short time-scales shows the observed flux pattern to require the formation of a particle source eastward of the ISEE spacecraft, well within the plasma sheet, associated with the substorm onset. Strong flows were absent prior to substorm onset, indicating the temporal nature of the event, as opposed to an encounter with a preexisting PSBL containing large flows.

  9. Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Wild, J. A.; Milan, S. E.; Yeoman, T. K.

    2009-02-01

    Using data from the Super Dual Auroral Radar Network (SuperDARN) we investigate the ionospheric convection response to magnetospheric substorms. Substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, and were then binned according to the magnetic latitude of their onset. A superposed epoch analysis of the ionospheric convection patterns for each onset-latitude bin was then performed using radar data for the interval 60 min before onset to 90 min after. It is found that lower onset-latitude substorms are associated with generally more enhanced convection than the higher latitude substorms, although they suffer from a significant localised reduction of the flow in the midnight sector during the expansion phase. Higher-latitude substorms are associated with a significant and rapid increase in the nightside convection following substorm onset, with all onset-latitude bins showing an enhancement over onset values by ~60 min into the expansion phase. A rudimentary inspection of the concurrent auroral evolution suggests that the duration of the flow reduction following substorm onset is dependent on the strength and duration of the expansion phase aurora and its associated conductivity enhancement.

  10. Nuclear burst plasma injection into the magnetosphere and resulting spacecraft charging

    NASA Technical Reports Server (NTRS)

    Pavel, A. L.; Cipolla, J. A.; Silevitch, M. B.; Golden, K. I.

    1977-01-01

    The passage of debris from a high altitude ( 400 km) nuclear burst over the ionospheric plasma is found to be capable of exciting large amplitude whistler waves which can act to structure a collisionless shock. This instability will occur in the loss cone exits of the nuclear debris bubble, and the accelerated ambient ions will freestream along the magnetic field lines into the magnetosphere. Using Starfish-like parameters and accounting for plasma diffusion and thermalization of the propagating plasma mass, it is found that synchronous orbit plasma fluxes of high temperature electrons (near 10 keV) will be significantly greater than those encountered during magnetospheric substorms. These fluxes will last for sufficiently long periods of time so as to charge immersed bodies to high potentials and arc discharges to take place.

  11. From Space Weather Toward Space Climate Time Scales: Substorm Analysis from 1993 to 2008

    NASA Technical Reports Server (NTRS)

    Tanskanen, E. I.; Pulkkinen, T. I.; Viljanen, A.; Partamies, N.; Slavin, J. A.

    2011-01-01

    Magnetic activity in the Northern Hemisphere auroral region was examined during solar cycles 22 and 23 (1993- 2008). Substorms were identified from ground-based magnetic field measurements by an automated search engine. On average, 550 substorms were observed per year, which gives in total about 9000 substorms. The interannual, seasonal and solar cycle-to-cycle variations of the substorm number (R(sub ss)), substorm duration (T(sub ss)), and peak amplitude (A(sub ss)) were examined. The declining phases of both solar cycles 22 and 23 were more active than the other solar cycle phases due to the enhanced solar wind speed. The spring substorms during the declining solar cycle phase (absolute value of A(sub ss,decl)) - 500 nT) were 25% larger than the spring substorms during the ascending solar cycle years ((absolute value of A(sub ss,asc) = 400 nT). The following seasonal variation was found: the most intense substorms occurred during spring and fall, the largest substorm frequency in the Northern Hemisphere winter, and the longest-duration substorms in summer. Furthermore, we found a winter-summer asymmetry in the substorm number and duration. which is speculated to be due to the variations in the ionospheric conductivity. The solar cycle-Io-cycle variation was found in the yearly substorm number and peak amplitude. The decline from the peak substorm activity in 1994 and 2003 to the following minima took 3 years during solar cycle 22, while it took 6 years during solar cycle 23.

  12. M-I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

    NASA Astrophysics Data System (ADS)

    Sandholt, P. E.; Farrugia, C. J.; Denig, W. F.

    2014-04-01

    We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δ Bz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross

  13. Magnetic signatures of precursors to substorm expansive phase onset

    SciTech Connect

    de Groot-Hedlin, C.D.; Rostoker, G. )

    1987-06-01

    The expansive phase of magnetospheric substorms involves the development of auroral loops and surges with particular emphasis on the westward travelling surge which is identified with the western edge of the substorm current wedge. The authors use as a working hypothesis the contention that the wavelike auroral structures associated with the current wedge are a manifestation of the action of a Kelvin-Helmholtz instability at the interface between the central plasma sheet (CPS) and the adjacent boundary layer plasmas in the deep magnetotail. Based on this concept, they used ground-based magnetometer data in an attempt to identify the growth of ionospheric current systems which might be associated with the growth of the Kelvin-Helmholtz instability. They have, in fact, found that the expansive phase is preceded by the growth of a weak substorm current wedge which strengthens explosively at the time of onset. They suggest that field-aligned current flows out of the ionosphere as part of a process damping a growing wave at the CPS/boundary layer interface. When the field-aligned current density exceeds {approximately} 1 {mu}A/m{sup 2}, an acceleration region at altitudes of {approximately} 1 R{sub E} is activated marking the onset of the substorm expansive phase.

  14. A missing variable in the data-based substorm studies

    NASA Astrophysics Data System (ADS)

    Sergeev, Viktor; Angelopoulos, Vassilis; Sormakov, Dmitry

    Nowadays the quantitative characterization of the magnetospheric activity is predominantly based on the amplitude of auroral zone magnetic perturbations (e.g., AL index value). This approach ignores the long-established fact that ground magnetic perturbations are basically formed by the Hall currents (Fukushima theorem), which depend critically on the Hall conductivity and, therefore, are sensitive to the plasma sheet electron parameters (Te and Ne, which also control the production of energetic electrons by their field-aligned acceleration). Observational confirmation of such influence is difficult because of many complicating factors, main of which are the inhomogeneity of Te, Ne parameters in the magnetotail and, especially, the reconnection-induced production of low-density and high-temperature electrons during substorms in the magnetotail. In this study, based on long-term monitoring of plasma sheet electrons by THEMIS spacecraft, we (a) demonstrate a strong variation of auroral zone currents (by an order of magnitude depending on the plasma sheet Te/Ne value) under the conditions of the substorm growth phase (when substorm-related acceleration is weak), (b) compare the average behaviors of Te, Ne during substorms under very large (very small) Te/Ne conditions and (c) briefly discuss a number of ’phantom problems’ which arise due to the ignorance of this dependence (incl. the problem of pseudobreakups, etc).

  15. A superposed epoch analysis of the regions 1 and 2 Birkeland currents observed by AMPERE during substorms

    NASA Astrophysics Data System (ADS)

    Coxon, J. C.; Milan, S. E.; Clausen, L. B. N.; Anderson, B. J.; Korth, H.

    2014-12-01

    We perform a superposed epoch analysis of the evolution of the Birkeland currents (field-aligned currents) observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) during substorms. The study is composed of 2900 substorms provided by the SuperMAG experiment. We find that the current ovals expand and contract over the course of a substorm cycle and that currents increase in magnitude approaching substorm onset and are further enhanced in the expansion phase. Subsequently, we categorize the substorms by their onset latitude, a proxy for the amount of open magnetic flux in the magnetosphere, and find that Birkeland currents are significantly higher throughout the epoch for low-latitude substorms. Our results agree with previous studies which indicate that substorms are more intense and close more open magnetic flux when the amount of open flux is larger at onset. We place these findings in the context of previous work linking dayside and nightside reconnection rate to Birkeland current strengths and locations.

  16. MESSENGER: Exploring Mercury's Magnetosphere

    NASA Technical Reports Server (NTRS)

    Slavin, James A.; Krimigis, Stamatios M.; Acuna, Mario H.; Anderson, Brian J.; Baker, Daniel N.; Koehn, Patrick L.; Korth, Haje; Levi, Stefano; Mauk, Barry H.; Solomon, Sean C.; Zurbuchen, Thomas H.

    2005-01-01

    The MESSENGER mission to Mercury offers our first opportunity to explore this planet s miniature magnetosphere since the brief flybys of Mariner 10. Mercury s magnetosphere is unique in many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands off the solar wind only - 1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic particles and, hence, no radiation belts. The characteristic time scales for wave propagation and convective transport are short and kinetic and fluid modes may be coupled. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury s interior may act to modify the solar wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects may be an important source of information on the state of Mercury s interior. In addition, Mercury s magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived, - 1-2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury s magnetic tail. Because of Mercury s proximity to the sun, 0.3 - 0.5 AU, this magnetosphere experiences the most extreme driving forces in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and re-cycling of neutrals and ions between the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury s magnetosphere are expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection at the magnetopause and in the tail, and the pick-up of planetary ions all

  17. Solar wind-magnetosphere coupling leading to relativistic electron energization during high-speed streams

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Lee, D.-Y.; Thorne, R. M.; Horne, R. B.; Smith, A. J.

    2005-11-01

    Enhancements in relativistic electron fluxes in the outer radiation belt often occur following magnetic storms and have been suggested to result from resonant interactions with enhanced whistler-mode chorus emissions observed on the dawnside. Using observations during a period of persistent high-speed, corotating, solar wind streams, we investigate the aspects of solar wind-magnetosphere coupling that lead to these enhanced chorus emissions. We find that relativistic electron energization occurs in association with large-amplitude Alfvén waves within the high-speed streams. These waves last for multiday periods and cause multiday intervals having intermittent periods of significantly enhanced convection. The enhanced convection periods are followed by repetitive substorm onsets caused by the Alfvén wave related repetitive reductions in convection. We use these substorm onsets, identified using geosynchronous particles and midlatitude H components, as indicators of preceding periods of enhanced convection and of reductions in convection. We use ground-based chorus observations from the Halley station VLF/ELF Logger Experiment (VELOX) instrument to indicate magnetospheric chorus intensities. These data give evidence that the periods of enhanced convection that precede substorm expansions lead to the enhanced dawnside chorus wave. We also see that the enhanced solar wind densities nsw ahead of high-speed streams are associated with significant energetic electron loss at geosynchronous orbit and that the subsequent flux increases appear to not begin until nsw drops below ˜5 cm-3 even if the solar wind speed increases earlier. The sequence of loss during the leading interval of high nsw, followed by energization during high-speed streams, occurs whether or not the high nsw interval leads to a magnetic storm.

  18. The electric field and global electrodynamics of the magnetosphere

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1979-01-01

    The conception of the electrodynamics of the quiet-time magnetosphere obtained during the last four years of magnetospheric study is presented. Current understandings of the open magnetosphere, convective plasma flows in the plasma sheet, the shielding of the inner magnetosphere from the convective magnetospheric electric field, the space charge produced when injected electrons drift towards dawn and injected ions drift towards dusk, the disruption of the flow of the Birkeland current by plasma instabilities and the shielding of the convective electric field by the dayside magnetopause are discussed. Attention is also given to changes of magnetic field line topology magnetic storms and substorms. Unresolved questions and new tools which may play a role in the further understanding of magnetospheric electrodynamics and the role of the magnetospheric electric field are presented.

  19. Time development of high-altitude auroral acceleration region plasma, potentials, and field-aligned current systems observed by Cluster during a substorm

    NASA Astrophysics Data System (ADS)

    Hull, A. J.; Chaston, C. C.; Fillingim, M. O.; Mozer, F.; Frey, H. U.

    2013-12-01

    The auroral acceleration region is an integral link in the chain of events that transpire during substorms, and the currents, plasma and electric fields undergo significant changes driven by complex dynamical processes deep in the magnetotail. These auroral acceleration processes in turn accelerate and heat the plasma that ultimately leads to some of the most intense global substorm auroral displays. The complex interplay between field-aligned current system formation, the development of parallel electric fields, and resultant changes in the plasma constituents that occur during substorms within or just above the auroral acceleration zone remain unclear. We present Cluster multi-point observations within the high-altitude acceleration region (> 3 Re altitude) at key instances during the development of a substorm. Of particular emphasis is on the time-development of the plasma, potentials and currents that occur therein with the aim of ascertaining high-altitude drivers of substorm active auroral acceleration processes and auroral emission consequences. Preliminary results show that the initial onset is dominated by Alfvenic activity as evidenced by the sudden occurrence of relatively intense, short-spatial scale Alfvenic currents and attendant energy dispersed, counterstreaming electrons poleward of the growth-phase arc. The Alfvenic currents are locally planar structures with characteristic thicknesses on the order of a few tens of kilometers. In subsequent passages by the other spacecraft, the plasma sheet region became hotter and thicker via the injection of new hot, dense plasma of magnetospheric origins poleward of the pre-existing growth phase arc. In association with the heating and/or thickening of the plasma sheet, the currents appeared to broaden to larger scales as Alfven dominated activity gave way to either inverted-V dominated or mixed inverted-V and Alfvenic behavior depending on location. The transition from Alfven dominated to inverted-V dominated

  20. Multipoint observations of a small substorm

    NASA Technical Reports Server (NTRS)

    Lopez, R. E.; Anderson, B. J.; Newell, P. T.; Mcentire, R. W.; Luehr, H.

    1990-01-01

    Results are presented of multipoint observations of a small substorm which occurred at about 0110 UT on April 25, 1985, carried out by AMPTE CCE, AMPTE IRM, DMSP F6, and DMSP F7, as well as by ground auroral stations and midlatitude stations. These data yield information on the latitudinal extent of the polar cap and provide visual identification of substorm aurorae, magnetic perturbations produced directly beneath aurorae, and the situ magnetic field. In addition, they provide magnetic-particle observations of the disruption of the cross-tail current sheet and observations concerning the spatial expansion of the current disruption region. Evidence is presented that the current sheet disruption observed by CCE in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at Syowa.

  1. Substorm triggering by poleward boundary intensification and related equatorward propagation

    NASA Astrophysics Data System (ADS)

    Mende, S. B.; Frey, H. U.; Angelopoulos, V.; Nishimura, Y.

    2011-04-01

    Recently, a revised auroral substorm onset sequence has been proposed, in which onset is preceded by a poleward boundary intensification (PBI) and subsequent equatorward propagation of N-S-aligned auroral features to breakup arc latitudes. We reanalyzed 20 randomly selected samples of the Nishimura et al. (2010) 251-event database and show in greater detail to what degree the observed features in this subset of events are consistent with the proposed scenario. To assess the sensitivity of space-based imagers for seeing this scenario, we calibrated the absolute responsivity of the THEMIS ground-based imagers. We also show that although not suitable for studies from apogee, IMAGE/FUV imagers can also observe a consistent scenario from a lower altitude. We conclude that in some cases PBIs and subsequent plasma flows can be effective in providing a trigger if the inner magnetosphere is ready to produce a substorm.

  2. Occurrency frequency of substorm field and plasma signatures observed near-earth by ISEE-1/2

    NASA Technical Reports Server (NTRS)

    Hsu, T. S.; McPherron, R. L.

    1996-01-01

    The onset of the majority of substorms occurs when the tail field stops growing more tail-like and begins to become more dipolar. This corresponds to the onset signatures on the ground and in geosynchronous orbit. The AE indices and the IGS Pi 2 data were used to determine the major substorm onsets of 1978 and 1979. The time delay between successive substorms, the distribution of the substorm growth phase duration and the probability of tailward flows were determined as a function of spacecraft location. About a half of the substorms exhibit a plasma signature including earthward or tailward flows or plasma sheet drop out and recovery. Earthward flows are often seen at substorm onset, and almost always during substorm recovery. Tailward flows are occasionally seen at onset as the spacecraft is close enough to the neutral sheet. The experimental results are compared to predictions based on the neutral line and current sheet disruption models.

  3. Substorm aurora and magnetic tail dynamics during interplanetary shock compression: THEMIS observations

    NASA Astrophysics Data System (ADS)

    Angelopoulos, Vassilis; Zhou, Xiaoyan

    2012-07-01

    Fast and forward interplanetary shocks compress and squeeze the Earth magnetosphere and cause a series of magnetospheric and ionospheric reactions. In addition to the enhancement of chorus, electromagnetic ion cyclotron (EMIC) waves and magnetospheric hiss, the ionospheric convection is enhanced as well. Shock aurora is generated, which is a phenomenon first an auroral brightness onset near local noon right after the shock impingement then followed by a fast anti-sunward auroral propagation along the oval. It has been found that substorm auroral activity can be significantly intensified by the shock compression when the shock upstream magnetic field was in southward in a certain period of time. This paper will present recent results based on the THEMIS spacecraft and ground-based observations. With multiple spacecraft in the magnetotail, the complex dynamics of the compressed tail is identified and analyzed. Correlations between the tail dynamics and substorm auroral variations will be discussed. *On-leave from Jet Propulsion Laboratory

  4. Localized activation of the distant tail neutral line just prior to substorm onsets

    NASA Astrophysics Data System (ADS)

    Watanabe, Masakazu; Pinnock, Michael; Rodger, Alan S.; Sato, Natsuo; Yamagishi, Hisao; Sessai Yukimatu, A.; Greenwald, Raymond A.; Villain, Jean-Paul; Hairston, Marc R.

    1998-08-01

    We have found flow burst features in the nightside ionosphere that are thought to be the ionospheric signature of distant tail reconnection. These are observed to form just prior to substorm onsets. Simultaneous observations by the Goose Bay-Stokkseyri dual HF radars and DMSP satellites provide the data. Our conclusions are based on equatorward flow bursts on the nightside during two isolated substorms that followed a long period of magnetospheric inactivity associated with a northward interplanetary magnetic field. Both flow bursts start ~60 min after the growth phase onset and last ~10-20 min until the expansion phase onset, migrating equatorward with time. Simultaneous DMSP observations of precipitating particles show that the flow burst occurs at the polar cap boundary, suggesting that the equatorward migration corresponds to the expansion of the polar cap during the growth phase. For one event, the reconnection electric field at 400 km altitude was 14 mV/m and its longitudinal scale was 290 km, which is equivalent to a reconnection voltage of 4.1 kV. For the other event, these values were 11 mV/m (reconnection electric field), 380 km (longitudinal scale), and 4.0 kV (reconnection voltage). In addition to the reconnection signatures, we discuss implications for substorm dynamics during the final stage of the substorm growth phase. The morphology indicates that the distant tail neutral line is activated ~1 hour after the growth phase onset and at the same time the nightside separatrix starts to move equatorward much faster than during the preceding early and middle growth phases. The 1-hour time lag would correspond to the timescale on which slow rarefaction waves from both northern and southern tail lobes converge in the equatorial magnetotail. The fast-moving separatrix on the nightside implies a rapid change of magnetotail configuration resulting from nonlinear enhancement and/or earthward movement of the cross-tail current for the last 10-20 min prior to the

  5. Flow Pattern relative to the Substorm Current Wedge

    NASA Astrophysics Data System (ADS)

    Chu, X.; McPherron, R. L.; Hsu, T.

    2013-12-01

    Magnetospheric substorms play a key role in the coupling of the solar wind and the magnetosphere. The Substorm Current Wedge (SCW) is a key element in the present physical model of substorms. It is widely accepted that the SCW is created by earthward busty flows, but the generation mechanism is still unknown. Previous studies suggest pressure gradients and magnetic vortices are possible candidates. Due to the sparse coverage of satellites in space, these studies were strongly dependent on the assumption that the satellites were in the generation region of the field-aligned currents (FAC) forming the SCW. In this work, we take advantage of an inversion technique that determines the parameters describing the SCW and perform a statistical study on the plasma and magnetic field parameters of the flow pattern relative to the SCW. The inversion technique finds the location and the intensity of the SCW from midlatitude magnetic data. The technique has been validated using auroral observations, Equivalent Ionospheric Currents (EIC), SYM-H index from SuperMAG, and magnetic perturbations at geosynchronous orbit by the GOES satellite. A database of substorm events has been created using midlatitude positive bays, which are the ground signature of the SCW at lower latitudes. The inversion technique is applied to each event in the database to determine the location of the origin of the SCW. The inversion results are also used to find conjunction events with space observations from VAP (RBSP), THEMIS and GOES. The plasma and magnetic field parameters such as the pressure gradient and magnetic vorticity are then categorized as a function of their location relative to the origin of the SCW. How the distribution/pattern of the pressure gradient and vorticity are related to the properties of the SCW (locations and intensity of the FAC), and flows (entropy, velocity and density) will be determined.

  6. Magnetospheric plasma regions and boundaries

    NASA Technical Reports Server (NTRS)

    Heikkila, W. J.

    1975-01-01

    The boundaries of the various regions of the magnetospheric plasma are considered, taking into account the bow shock, the magnetopause, the outer boundary of the plasma sheet, the inner boundary of the plasma sheet, and the trapping boundary for energetic particles. Attention is given to the steady state, or quasi-steady state, to substorm effects in which temporal changes are important, and to primary auroral processes. A description is presented of the high latitude lobes of the magnetotail. The characteristics of magnetic field topology associated with interconnected interplanetary and geomagnetic field lines are illustrated with the aid of a graph.

  7. Random and periodic substorms and their origins in the solar wind

    SciTech Connect

    Borovsky, J.E.; Belian, R.D.; Nemzek, R.J.; Smith, C.W.

    1994-05-01

    Substorms occur (recur) in two fashions: periodically with time or randomly in time. A statistical analysis of the time intervals {Delta}t between subsequent substorm onsets clearly shows these two types of substorms. When substorms are recurring periodically, the period is 3.1 {plus_minus} 1.2 hours, and the distribution of periods is gaussian. When substorms are occurring randomly, the time intervals {Delta}t between successive substorm onsets are distributed according to the exponential distribution exp({minus}{delta}t//5 hours), with a 5-hour mean interval between random onsets. With the use of the Los Alamos geosynchronous energetic-particle dam and the OMNI solar-wind data, it is shown that periodic substorms are associated with time intervals when the average value of the IMF is southward for extended periods of time and it is shown that randomly occurring substorms are statistically correlated with randomly occurring northward-to-southward reversals of the 1-hour-averaged values of the IMF B{sub z}.

  8. Response of plasmaspheric configuration to substorms revealed by Chang’e 3

    PubMed Central

    He, Han; Shen, Chao; Wang, Huaning; Zhang, Xiaoxin; Chen, Bo; Yan, Jun; Zou, Yongliao; Jorgensen, Anders M.; He, Fei; Yan, Yan; Zhu, Xiaoshuai; Huang, Ya; Xu, Ronglan

    2016-01-01

    The Moon-based Extreme Ultraviolet Camera (EUVC) of the Chang’e 3 mission provides a global and instantaneous meridian view (side view) of the Earth’s plasmasphere. The plasmasphere is one inner component of the whole magnetosphere, and the configuration of the plasmasphere is sensitive to magnetospheric activity (storms and substorms). However, the response of the plasmaspheric configuration to substorms is only partially understood, and the EUVC observations provide a good opportunity to investigate this issue. By reconstructing the global plasmaspheric configuration based on the EUVC images observed during 20–22 April 2014, we show that in the observing period, the plasmasphere had three bulges which were located at different geomagnetic longitudes. The inferred midnight transit times of the three bulges, using the rotation rate of the Earth, coincide with the expansion phase of three substorms, which implies a causal relationship between the substorms and the formation of the three bulges on the plasmasphere. Instead of leading to plasmaspheric erosion as geomagnetic storms do, substorms initiated on the nightside of the Earth cause local inflation of the plasmasphere in the midnight region. PMID:27576944

  9. Response of plasmaspheric configuration to substorms revealed by Chang'e 3.

    PubMed

    He, Han; Shen, Chao; Wang, Huaning; Zhang, Xiaoxin; Chen, Bo; Yan, Jun; Zou, Yongliao; Jorgensen, Anders M; He, Fei; Yan, Yan; Zhu, Xiaoshuai; Huang, Ya; Xu, Ronglan

    2016-01-01

    The Moon-based Extreme Ultraviolet Camera (EUVC) of the Chang'e 3 mission provides a global and instantaneous meridian view (side view) of the Earth's plasmasphere. The plasmasphere is one inner component of the whole magnetosphere, and the configuration of the plasmasphere is sensitive to magnetospheric activity (storms and substorms). However, the response of the plasmaspheric configuration to substorms is only partially understood, and the EUVC observations provide a good opportunity to investigate this issue. By reconstructing the global plasmaspheric configuration based on the EUVC images observed during 20-22 April 2014, we show that in the observing period, the plasmasphere had three bulges which were located at different geomagnetic longitudes. The inferred midnight transit times of the three bulges, using the rotation rate of the Earth, coincide with the expansion phase of three substorms, which implies a causal relationship between the substorms and the formation of the three bulges on the plasmasphere. Instead of leading to plasmaspheric erosion as geomagnetic storms do, substorms initiated on the nightside of the Earth cause local inflation of the plasmasphere in the midnight region. PMID:27576944

  10. Force Balance and Substorm Effects in the Magnetotail

    NASA Technical Reports Server (NTRS)

    Kaufmann, Richard L.; Larson, Douglas J.; Kontodinas, Ioannis D.; Ball, Bryan M.

    1997-01-01

    A model of the quiet time middle magnetotail is developed using a consistent orbit tracing technique. The momentum equation is used to calculate geocentric solar magnetospheric components of the particle and electromagnetic forces throughout the current sheet. Ions generate the dominant x and z force components. Electron and ion forces almost cancel in the y direction because the two species drift earthward at comparable speeds. The force viewpoint is applied to a study of some substorm processes. Generation of the rapid flows seen during substorm injection and bursty bulk flow events implies substantial force imbalances. The formation of a substorm diversion loop is one cause of changes in the magnetic field and therefore in the electromagnetic force. It is found that larger forces are produced when the cross-tail current is diverted to the ionosphere than would be produced if the entire tail current system simply decreased. Plasma is accelerated while the forces are unbalanced resulting in field lines within a diversion loop becoming more dipolar. Field lines become more stretched and the plasma sheet becomes thinner outside a diversion loop. Mechanisms that require thin current sheets to produce current disruption then can create additional diversion loops in the newly thinned regions. This process may be important during multiple expansion substorms and in differentiating pseudoexpansions from full substorms. It is found that the tail field model used here can be generated by a variety of particle distribution functions. However, for a given energy distribution the mixture of particle mirror or reflection points is constrained by the consistency requirement. The study of uniqueness also leads to the development of a technique to select guiding center electrons that will produce charge neutrality all along a flux tube containing nonguiding center ions without the imposition of a parallel electric field.

  11. Magnetospheric equilibrium configurations and slow adiabatic convection

    NASA Technical Reports Server (NTRS)

    Voigt, Gerd-Hannes

    1986-01-01

    This review paper demonstrates how the magnetohydrostatic equilibrium (MHE) theory can be used to describe the large-scale magnetic field configuration of the magnetosphere and its time evolution under the influence of magnetospheric convection. The equilibrium problem is reviewed, and levels of B-field modelling are examined for vacuum models, quasi-static equilibrium models, and MHD models. Results from two-dimensional MHE theory as they apply to the Grad-Shafranov equation, linear equilibria, the asymptotic theory, magnetospheric convection and the substorm mechanism, and plasma anisotropies are addressed. Results from three-dimensional MHE theory are considered as they apply to an intermediate analytical magnetospheric model, magnetotail configurations, and magnetopause boundary conditions and the influence of the IMF.

  12. Energy storage and dissipation in the magnetotail during substorms. 1. Particle simulations

    SciTech Connect

    Winglee, R.M. ); Steinolfson, R.S. )

    1993-05-01

    The authors present a simulation study of the particle dynamics in the magnetotail during the development of substorms. They look at how energy flows into the magnetotail under external magnetospheric conditions, and study the energy storage and dissipation in the magnetic field, and the role of particle dynamics in this process. They consider two primary external influences in their model. First is the pressure exerted by the magnetospheric boundary layer, on the nightside magnetopause. This pressure is expected to grow in response to solar wind penetration into the magnetosphere when the interplanetary magnetic field becomes southward in the initial phases of substorm growth. Second is the dawn to dusk electric field. This field is expected to grow as the current sheet thins and energy stored in the magnetic field rises. The authors argue that the simultaneous increase in both the magnetic pressure and electric field can better model magnetotail response. One sees strong earthward flows in conjunction with increased energy storage in the tail, and at substorm onset one sees the ejection of plasmoids in a tailward direction with increased particle heating. The clumping of particles in the current sheet due to the opposing effects of the magnetic pressure and electric field could be responsible for substorm onset, rather than instabilities such as the tearing mode.

  13. Energy Characteristics of Auroral Electron Precipitation: A Comparison of Substorms and Pressure Pulse Related Auroral Activity

    NASA Technical Reports Server (NTRS)

    Chua, D.; Parks, G. K.; Brittnacher, M. J.; Peria, W.; Germany, G. A.; Spann, J. F., Jr.; Carlson, C.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    The Polar Ultraviolet Imager (UVI) observes auroral responses to incident solar wind pressure pulses and interplanetary shocks such as those associated with coronal mass ejections. The arrival of a CME pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside auroral precipitation. Our observations show a simultaneous brightening over broad areas of the dayside and nightside aurora in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolated substorms. We estimate the average energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has average energies greater than 10 keV and is structured both in local time and magnetic latitude. For auroral intensifications following the arrival of a pressure pulse or interplanetary shock, electron precipitation is less spatially structured and has greater ux of lower energy electrons (Eave _ 7 keV) than during isolated substorm, onsets. The average energies of the precipitating electrons inferred from UVI are consistent with those measured in-situ by the FAST spacecraft. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

  14. The Study of Non-Linear Acceleration of Particles during Substorms Using Multi-Scale Simulations

    SciTech Connect

    Ashour-Abdalla, Maha

    2011-01-04

    To understand particle acceleration during magnetospheric substorms we must consider the problem on multple scales ranging from the large scale changes in the entire magnetosphere to the microphysics of wave particle interactions. In this paper we present two examples that demonstrate the complexity of substorm particle acceleration and its multi-scale nature. The first substorm provided us with an excellent example of ion acceleration. On March 1, 2008 four THEMIS spacecraft were in a line extending from 8 R{sub E} to 23 R{sub E} in the magnetotail during a very large substorm during which ions were accelerated to >500 keV. We used a combination of a global magnetohydrodynamic and large scale kinetic simulations to model the ion acceleration and found that the ions gained energy by non-adiabatic trajectories across the substorm electric field in a narrow region extending across the magnetotail between x = -10 R{sub E} and x = -15 R{sub E}. In this strip called the 'wall region' the ions move rapidly in azimuth and gain 100s of keV. In the second example we studied the acceleration of electrons associated with a pair of dipolarization fronts during a substorm on February 15, 2008. During this substorm three THEMIS spacecraft were grouped in the near-Earth magnetotail (x {approx}-10 R{sub E}) and observed electron acceleration of >100 keV accompanied by intense plasma waves. We used the MHD simulations and analytic theory to show that adiabatic motion (betatron and Fermi acceleration) was insufficient to account for the electron acceleration and that kinetic processes associated with the plasma waves were important.

  15. Where and when does reconnection occur in the tail?

    NASA Astrophysics Data System (ADS)

    McPherron, Robert L.

    2016-05-01

    We comment on the question of when and where reconnection begins in the tail and how it is related to the onset of auroral expansion. This question was addressed in a workshop dedicated to Unsolved Problems in Magnetospheric Physics held in Scarborough, UK, in September 2015. The answer is that it typically occurs first in the midtail a little beyond 20 Re somewhat before midnight about 55 min after a southward turning of the solar wind magnetic field. It appears to be a consequence of plasma sheet thinning down to the scale of an ion gyroradius. The onset of the activation and expansion of auroral activity and accompanying magnetic signatures typically occur within 1 or 2 min of the appearance of signatures of midtail reconnection. The unanswered question is which comes first and whether reconnection is the cause of the auroral expansion. We point out that older observations clearly established that plasmoids (flux ropes) are released from near 20 Re within a few minutes of the usual signatures of expansion onset. This is only possible if reconnection occurs close to the Earth. More detailed observations with modern spacecraft have led to the development of new explanations for the cause of the substorm expansion that appear to neglect older observations. We conclude that it is essential to carefully define the various terms used in the study of substorms and to develop quantitative methods that enable statistical studies of the various processes associated with auroral expansion onset.

  16. Equatorial counterelectrojets during geomagnetic storms and their possible dynamos in the magnetosphere

    NASA Astrophysics Data System (ADS)

    Kikuchi, T.; Hashimoto, K. K.; Ebihara, Y.; Tsuji, Y.; Veenadhari, B.; Nishimura, T.; Tanaka, T.; Fujita, S.; Nagatsuma, T.

    2012-12-01

    During the substorm growth phase and storm main phase, the high pressure plasma accumulated in the cusp and mantle regions activates a dynamo for the dawn-to-dusk convection electric field and the Region-1 field-aligned currents (R1 FACs) [Tanaka, 1995]. The electric field and FACs are conveyed by the shear Alfven waves to the polar ionosphere and the electric field extends promptly to low latitude through the Earth-ionosphere waveguide [Kikuchi and Araki, 1979]. The electric field drives the DP2 currents at mid latitudes [Wilson et al., 2001; Tsuji et al., 2012] and intensifies the equatorial electrojet (EEJ) [Kikuchi et al., 1996, 2008]. The convection electric field extends to the inner magnetosphere promptly [Nishimura et al., 2009] and energizes the plasma in the partial ring current region with the help of the gradient and curvature drift [Ebihara and Ejiri, 2000], which in turn works as a dynamo for the dusk-to-dawn electric field and the R2 FACs. The dusk-to-dawn electric field causes the counterelectrojet (CEJ) at the equator when the IMF turns northward [Rastogi, 1975]. The CEJ often appears during substorms [Kobea et al., 2000; Kikuchi et al., 2000]. Both the R1 and R2 FACs are intensified by the substorm expansion, with the R2 FACs strong enough to cause the CEJ [Hashimoto et al., 2011]. The CEJ often occurs during the recovery phase of geomagnetic storms [Kikuchi et al., 2008; Tsuji et al., 2012], while the CEJ also appears during the storm main phase under the relatively stable southward IMF [Fejer et al., 2007; Veenadhari et al., 2010]. In this paper, we analyzed several storm events to identify the dynamo for the stormtime CEJ. The disturbance dynamo is a commonly accepted dynamo for the long lasting stormtime CEJ [Blanc and Richmond, 1980; Fejer and Scherliess 1997]. However, the observed rapid and periodic development of the CEJ should be attributed to the R2 FACs generated in the inner magnetosphere. Based on the magnetometer and radar

  17. Propagating substorm injection fronts

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Arnoldy, R. L.; Feynman, J.; Hardy, D. A.

    1981-01-01

    It is argued that a series of two-satellite observations leads to a clarification of substorm plasma injection, in which boundary motion plays a major role. Emphasis is put on a type of event characterized by abrupt, dispersionless changes in electron intensity and a coincident perturbation that consists of both a field magnitude increase and a small rotation toward more dipolar orientation. Comparing plasma observations at two points, it is found that in active, preinjection conditions the two most important features of the plasma sheet are: (1) the low-energy convection boundary for near-zero energy particles, determined by the magnitude of the large-scale convection electric field; and (2) the precipitation-flow boundary layer between the hot plasma sheet and the atmospherically contaminated inner plasma sheet.

  18. Coupling between pre-onset flows and substorm onset waves

    NASA Astrophysics Data System (ADS)

    Nishimura, T.; Lyons, L. R.; Angelopoulos, V.; Donovan, E.; Mende, S. B.

    2015-12-01

    A critical, long-standing problem in substorm research is identification of the sequence of events leading to substorm expansion phase onset. Recent THEMIS all-sky imager (ASI) array observations have shown a repeatable pre-onset sequence, which is initiated by a poleward boundary intensification (PBI) and is followed by auroral streamers moving equatorward (earthward flow in the plasma sheet) and then by substorm onset. On the other hand, substorm onset is also preceded by azimuthally propagating waves, indicating a possible importance of wave instability for triggering substorm onset. However, it has been difficult to identify the link between fast flows and waves. We have found an isolated substorm event that was well-instrumented with the Poker Flat incoherent scatter radar (PFISR), THEMIS white-light ASI, and multi-spectral ASI, where the auroral onset occurred within the PFISR and ASI fields-of-view. This substorm onset was preceded by a PBI, and ionospheric flows propagated equatorward from the polar cap, crossed the PBI and reached the growth phase arc. This sequence provides evidence that flows from open magnetic field lines propagate across the open-closed boundary and reach the near-Earth plasma sheet prior to the onset. Quasi-stable oscillations in auroral luminosity and ionospheric density are found along the growth phase arc. These pre-onset auroral waves amplified abruptly at the onset time, soon after the equatorward flows reached the onset region. This sequence suggests a coupling process where pre-existing stable waves in the near-Earth plasma sheet interact with flows from further downtail and then evolve to onset instability.

  19. Isolated nighttime substorms and morning geomagnetic Pc5 pulsations from ground-based and satellite (THEMIS) observations

    NASA Astrophysics Data System (ADS)

    Kauristie, K.; Uspensky, M. V.; Kleimenova, N. G.; Kozyreva, O. V.; Dubyagin, S. V.; Vlasov, A. A.

    2013-09-01

    The analysis results of a complex of phenomena that were developing in the evening and morning magnetospheric and ionospheric sectors during two events (January 18 and February 19, 2008) are presented. The analysis is based on the observation data in the magnetotail from the THEMIS satellites and ground-based observations in the morning (MIRACLE network) and nighttime (THEMIS ground-based network) sectors. The events with moderate substorms in the nighttime sector were preceded by strong geomagnetic Pc5 pulsations in the morning sector, the regime of which changed during the development of auroral disturbances. The substorms were accompanied by dipolizations in the magnetotail at distances of ~10 Re and unexpected jump-like fluxes of ˜200-keV electrons. The fluxes appeared within several minutes after a breakup at three central THEMIS satellites simultaneously spaced up to 1.7 Re. According with the ASC data at the NAL observatory (3 frames/min) and with the THEMIS network of ASC data, onset of auroral activations in the night and morning sectors occurred simultaneously. Probable reasons for the sudden suppression or intensification of Pc5 pulsations are discussed.

  20. Energetics of the magnetosphere, revised

    NASA Technical Reports Server (NTRS)

    Stern, D. P.

    1984-01-01

    The approximate magnitudes of power inputs and energies associated with the Earth's magnetosphere were derived. The nearest 40 R sub E of the plasma sheet current receive some 3.10 to the 11th power watt, and much of this goes to the Birkeland currents, which require 1-3 10 to the 11th power watt. Of that energy, about 30% appears as the energy of auroral particles and most of the rest as ionosphere joule heating. The ring current contains about 10 to the 15th power joule at quiet times, several times as much during magnetic storms, and the magnetic energy stored in the tail lobes is comparable. Substorm energy releases may range at 1.5 to 30 10 to the 11th power watt. Compared to these, the local energy release rate by magnetic merging in the magnetosphere is small. Merging is essential for the existence of open field lines, which make such inputs possible. Merging also seems to be implicated in substorms: most of the released energy only becomes evident far from the merging region, though some particles may gain appreciable energy in that region itself, if the plasma sheet is squeezed out completely and the high latitude lobes interact directly.

  1. Observations of the phases of the substorm

    NASA Astrophysics Data System (ADS)

    Voronkov, I. O.; Donovan, E. F.; Samson, J. C.

    2003-02-01

    Following the database of large-scale vortices during pseudo-breakup and breakup registered by the Gillam All-Sky Imager, we selected one event (19 February 1996) for a detailed consideration. This event is a sequence of pseudo-breakup and local substorm, and breakup followed by the large substorm, which is isolated from the previous pseudo-breakup by the second growth phase. Commencement of these elements of auroral activity was clearly seen above the Churchill line of the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS; pseudo-breakup was completely covered by the field of view of the Gillam All-Sky Imager). Geotail was located at ˜19 RE in the equatorial plane of midnight sector, which, along with supporting observations from two geostationary satellites (GOES 8 and 9), allowed for a comparison of ground-based, geostationary orbit and midtail signatures. The pseudo-breakup consisted of two distinct stages: a near-exponential arc intensity growth and a poleward vortex expansion that started simultaneously with dipolarization in the inner magnetosphere. The latter corresponded to explosive onset of short-period (tens of millihertz) pulsations observed at geostationary orbit and on the ground in the vicinity of the arc. No significant disturbances poleward of the vortex were observed. Pseudo-breakup was followed by the second growth phase, which involved a significant thinning of the plasma sheet. Breakup was of a similar two-stage character as the pseudo-breakup. Full onset of the expansive phase that followed breakup was seen simultaneously by all instruments including Geotail, which detected strong perturbations in the midtail. The expansive phase onset launched the second postbreakup package of Pi2 pulsations that were of larger amplitude. Finally, during the substorm recovery phase, the poleward boundary intensifications (PBIs) were observed as long-period, on the order of 10 min, pulses of electron precipitation. PBI commencement

  2. Saturn's outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Schardt, A. W.; Behannon, K. W.; Carbary, J. F.; Eviatar, A.; Lepping, R. P.; Siscoe, G. L.

    1983-01-01

    Similarities between the Saturnian and terrestrial outer magnetosphere are examined. Saturn, like Earth, has a fully developed magnetic tail, 80 to 100 RS in diameter. One major difference between the two outer magnetospheres is the hydrogen and nitrogen torus produced by Titan. This plasma is, in general, convected in the corotation direction at nearly the rigid corotation speed. Energies of magnetospheric particles extend to above 500 keV. In contrast, interplanetary protons and ions above 2 MeV have free access to the outer magnetosphere to distances well below the Stormer cutoff. This access presumably occurs through the magnetotail. In addition to the H+, H2+, and H3+ ions primarily of local origin, energetic He, C, N, and O ions are found with solar composition. Their flux can be substantially enhanced over that of interplanetary ions at energies of 0.2 to 0.4 MeV/nuc.

  3. Modeling Magnetospheric Sources

    NASA Technical Reports Server (NTRS)

    Walker, Raymond J.; Ashour-Abdalla, Maha; Ogino, Tatsuki; Peroomian, Vahe; Richard, Robert L.

    2001-01-01

    We have used global magnetohydrodynamic, simulations of the interaction between the solar wind and magnetosphere together with single particle trajectory calculations to investigate the sources of plasma entering the magnetosphere. In all of our calculations solar wind plasma primarily enters the magnetosphere when the field line on which it is convecting reconnects. When the interplanetary magnetic field has a northward component the reconnection is in the polar cusp region. In the simulations plasma in the low latitude boundary layer (LLBL) can be on either open or closed field lines. Open field lines occur when the high latitude reconnection occurs in only one cusp. In the MHD calculations the ionosphere does not contribute significantly to the LLBL for northward IMF. The particle trajectory calculations show that ions preferentially enter in the cusp region where they can be accelerated by non-adiabatic motion across the high latitude electric field. For southward IMF in the MHD simulations the plasma in the middle and inner magnetosphere comes from the inner (ionospheric) boundary of the simulation. Solar wind plasma on open field lines is confined to high latitudes and exits the tailward boundary of the simulation without reaching the plasma sheet. The LLBL is populated by both ionospheric and solar wind plasma. When the particle trajectories are included solar wind ions can enter the middle magnetosphere. We have used both the MHD simulations and the particle calculations to estimate source rates for the magnetosphere which are consistent with those inferred from observations.

  4. The triggering of local substorm activity by HF SURA heater

    NASA Astrophysics Data System (ADS)

    Ruzhin, Yuri; Parrot, Michel; Kovalev, Victor; Plastinin, Yuri; Kuznetsov, Vladimir; Vladimir Frolov, S.

    The results of analysis of helio-geophisical conditions of experiments 2007-2012 on local modification of ionosphere by powerful HF radio waves of SURA facility are presented. All experiment were conducted at sector of local time of Harang discontinuity for most probable influence of powerful HF pumping during the heater functioning on activation of natural processes at subauroral ionosphere - magnetosphere region. The peculiarity of these experiments was that all of these were executed with use of operative frequency, which was higher than upper hybrid frequency for background plasma of F2-layer maximum. It was obtained that, at least, in two experiments the observed substorm activity in zone northern SURA heater could be stimulated by its functionment.In the present study the ray tracing analysis clearly shows that ionosphere density decreasing (from DEMETER and IONEX data) at higher than SURA latitudes can redirect and refocused transmitter beam power in northward structure away from the beam center by refraction. By this way we have chance to participate by means of radiated SURA HF power in subauroral and auroral processes It is shown that results of groundbased, International Space Station and satellite DEMETER measurements as in vicinity a SURA location and in magnetic conjugated region support the conclusion (output) about reasons and possibility of substorm localization by action of SURA heater. The possible mechanisms of the local substorm activation are discussed.

  5. A proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution

    NASA Technical Reports Server (NTRS)

    Anderson, P. C.; Hanson, W. B.; Heelis, R. A.; Craven, J. D.; Baker, D. N.; Frank, L. A.

    1993-01-01

    The temporal relationship between subauroral ion drifts (SAIDs) and the phases of an auroral substorm is examined on the basis of multisatellite data. The time of expansive phase onset is identified and the time at which recovery begins is estimated. SAIDs are found to typically occur well after substorm onset (more than 30 min), during the substorm recovery phase. Substantial westward ion drifts and field-aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm, but the drifts lack the narrow spike signature associated with SAIDs. A phenomenological model of SAID production that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship is proposed.

  6. Electric and magnetic field observations during a substorm on February 24, 1970

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.; Akasofu, S.-I.

    1974-01-01

    Description of a series of electric field measurements obtained from the Injun 5 satellite and simultaneous magnetic disturbances observed in the interplanetary medium and on the ground during a magnetic substorm. The substorm analyzed took place on Feb. 24, 1970. Prior to the onset of the substorm, a greatly enhanced antisunward plasma flow was observed over the polar cap. The enhanced plasma flow occurred about 30 minutes after a switch in the direction of the interplanetary magnetic field from northward to southward. The electric fields across the polar cap immediately before and during the substorm were essentially unchanged, and it is thus indicated that an enhancement in the ionospheric conductivity rather than the electric field must be responsible for the large increase in the auroral electrojet current during the substorm.

  7. Electric and magnetic field observations during a substorm of 24 February 1970

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.; Akasofu, S. I.

    1974-01-01

    A series of electric field measurements is reported which was obtained from the Injun 5 satellite along with a simultaneous magnetic disturbance observed in the interplanetary medium and on the ground during a magnetic substorm. The substorm analyzed took place on February 24, 1970. Prior to the onset of the substorm a greatly enhanced anti-sunward plasma flow was observed over the polar cap. The enhanced plasma flow occurred about 30 minutes after a switch in the direction of the interplanetary magnetic field from northward to southward. The electric fields across the polar cap immediately before and during the substorm were essentially unchanged indicating that an enhancement in the ionospheric conductivity rather than the electric field must be responsible for the large increase in the auroral electrojet current during the substorm.

  8. A Double-Disruption Substorm Model - The Growth Phase

    NASA Astrophysics Data System (ADS)

    Sofko, G. J.; McWilliams, K. A.; Hussey, G. C.

    2014-12-01

    When the IMF turns from Bz- to Bz+, dayside merging forms open lobe field lines at low latitudes. These lobe lines are populated with shocked solar wind and dayside magnetospheric plasma from the reconnection inflow. As those lobe flux tubes pass tailward over the polar caps, they are also populated with outflow from the north and south polar cap ionospheres. As the lobe lines move tailward, they acquire a convex curvature that blocks the westward-flowing cross-tail current (XTJ). This constitutes the first stage of XTJ disruption, and it begins less than 10 min after the frontside merging.The disrupted XTJ closes dawn-to-dusk in the transition plasmasheet (TPS), where it produces a downward FAC to the ionosphere. This causes the proton arc, which is seen for the period from about 10 - 80 min after frontside merging begins at time t=0. The lobe lines eventually reconnect well downtail at about t=30 minutes. The middle section that closes the lobe lines has concave curvature and is called the Neutral Sheet (NSh). The resulting stretched field lines thus have a central NSh which separates the two convex-curvature regions to the north and south, regions which are called the Disruption Zones (DZs); the overall combination of the NDZ, NSh and SDZ is called the Stretched Plasmasheet (SPS). As the SPS continues to grow and the stretched lines are pulled earthward to relieve the magnetic tension, the filling of the NSh occurs both from the DTNL with the higher energy magnetospheric particle population on the lobe lines, but eventually also at about 25 earth radii when the polar cap ionospheric outflow (PCO) component finally reaches the NSh. A NSh FAC system forms, from which electrons flow down to the auroral ionosphere to create the pre-onset arc, starting at about t=65 min. At the same time, the Lyons-Speiser mechanism is initiated in the inner NSh, causing the PCO ions to become trapped and accelerated in the inner NSh region. Eventually, when the SPS grows earthward

  9. Firehose instability near substorm expansion-phase onset?

    NASA Astrophysics Data System (ADS)

    Ji, S.; Wolf, R. A.

    2003-12-01

    The evolution of plasma ejected earthward from a patch of reconnection at about 25 RE is studied using a double-adiabatic-MHD simulation of a thin filament. Firehose instability occurs in the simulation after a compressional shock reflects from the near-Earth region. The tailward-propagating compressional wave, which brakes the earthward flow in the filament, is thus characterized by strong magnetic fluctuations. Within the context of the Near-Earth-Neutral-Line model of substorms, we suggest that firehose instability might cause the intense magnetic-field fluctuations that are observed in the inner plasma sheet at substorm onset. To assess the accuracy of double-adiabatic MHD, we tested it for a situation that resembles the substorm-generated filament but is simple enough to allow an exact kinetic theory solution. The test confirms that double-adiabatic MHD does a reasonable job of predicting when the firehose criterion is satisfied.

  10. Substorm onset: A switch on the sequence of transport from decreasing entropy to increasing entropy

    NASA Astrophysics Data System (ADS)

    Chen, C. X.

    2016-05-01

    In this study, we propose a scenario about the trigger for substorm onset. In a stable magnetosphere, entropy is an increasing function tailward. However, in the growth phase of a substorm, a later born bubble has lower entropy than earlier born bubbles. When a bubble arrives at its final destination in the near-Earth region, it will spread azimuthally because of its relatively uniform entropy. The magnetic flux tubes of a dying bubble, which cause the most equatorward aurora thin arc, would block the later coming bubble tailward of them, forming an unstable domain. Therefore, an interchange instability develops, which leads to the collapse of the unstable domain, followed by the collapse of the stretched plasma sheet. We regard the substorm onset as a switch on the sequence of transport, i.e., from a decreasing entropy process to an increasing entropy process. We calculated the most unstable growth rates and the wavelengths of instability, and both are in agreement with observations.

  11. The Four-Part Field-Aligned Current System in the Ionosphere at Substorm Onset

    NASA Astrophysics Data System (ADS)

    McWilliams, K. A.; Sofko, G. J.; Bristow, W. A.; Hussey, G. C.

    2015-12-01

    Whereas the plasma circulation in the ionosphere is driven by convective drift which is the same for ions and electrons, the magnetospheric plasma circulation includes curvature and gradient drifts, which are charge-dependent. There is even a region of the Neutral Sheet in which the ions, but not the electrons, are "unmagnetized" and where charge separation can occur even for convective drift, which the electrons execute but the ions do not. Due to the charge separations in the magnetosphere, field-aligned currents are generated. The FACs and the associated electric fields play an important role in producing the convection pattern in the ionosphere. Here we argue that there are two pairs of FACs near substorm onset. One pair involves the auroral zone portion of the convection. There, a downward D FAC occurs in the poleward part of the auroral zone and an upward U FAC occurs in the equatorward part. We show that the D-U auroral FAC pair results from the odd situation in the INSh, where the electrons can convect earthward while the unmagnetized ions do not and so remain further tailward of the electrons. The equatorward edge of the auroral zone is marked by a convection reversal, because the auroral zone flows have an eastward velocity component, whereas subauroral flows have a westward component. At the convection reversal, the flow is strictly southward and the electric field strictly westward. The subauroral zone maps out to the outer radiation belt, where the high-energy electrons precipitate tailward of the energetic electron trapping boundary,and high-energy ions precipitate tailward of the energetic ion trapping boundary, the latter being earthward of the former. As a result, another FAC pair forms on field lines in the ORB/subauroral regions. The U FAC of the latter region is adjacent but earthward of the U FAC of the auroral zone pair. The D-U auroral zone pair is poleward of the U-D subauroral (Radiation Belt) pair. Finally, we note that the electric field

  12. Charged Particle Energization and Transport in the Magnetotail during Substorms

    NASA Astrophysics Data System (ADS)

    Pan, Qingjiang

    This dissertation addresses the problem of energization of particles (both electrons and ions) to tens and hundreds of keV and the associated transport process in the magnetotail during substorms. Particles energized in the magnetotail are further accelerated to even higher energies (hundreds of keV to MeV) in the radiation belts, causing space weather hazards to human activities in space and on ground. We develop an analytical model to quantitatively estimate flux changes caused by betatron and Fermi acceleration when particles are transported along narrow high-speed flow channels from the magnetotail to the inner magnetosphere. The model shows that energetic particle flux can be significantly enhanced by a modest compression of the magnetic field and/or shrinking of the distance between the magnetic mirror points. We use coordinated spacecraft measurements, global magnetohydrodynamic (MHD) simulations driven by measured upstream solar wind conditions, and large-scale kinetic (LSK) simulations to quantify electron local acceleration in the near-Earth reconnection region and nonlocal acceleration during plasma earthward transport. Compared to the analytical model, application of the LSK simulations is much less restrictive because trajectories of millions of test particles are calculated in the realistically determined global MHD fields and the results are statistical. The simulation results validated by the observations show that electrons following a power law distribution at high energies are generated earthward of the reconnection site, and that the majority of the energetic electrons observed in the inner magnetosphere are caused by adiabatic acceleration in association with magnetic dipolarizations and fast flows during earthward transport. We extend the global MHD+LSK simulations to examine ion energization and compare it with electron energization. The simulations demonstrate that ions in the magnetotail are first nonadiabatically accelerated in the weak

  13. Multipoint Measurements of Injection Region Evolution in the Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Spanswick, E.; Gabrielse, C.; Donovan, E.; Angelopoulos, V.; Kabin, K.; Liang, J.; Danskin, D. W.

    2014-12-01

    The Dispersionless Injection (DI) region is the source of substorm associated enhancements in high energy particle flux (10s to 100s of keV). At any given time as it unfolds, DI is occurring across an extended region near the inner edge of the thin current sheet. This region forms around the time of substorm onset and evolves radially inward towards the ring current region. The Earthward edge of the injection region (the injection front) is capable of penetrating deep into the inner magnetosphere, providing a key seed population for the ring current, the radiation belts, and high-energy electron precipitation that affects atmospheric composition and technologies that rely on radio propagation through the upper atmosphere. Typically observed with in situ particle detectors, our knowledge of the injection front and the fate of injected particles is limited by the number and location of spacecraft observations. In this paper, we present multipoint observations of substorm injections in the Canadian sector derived from coordinated THEMIS and ground-based riometer measurements. The combined information of ground and in situ data provides key information about injection region evolution and the loss of injected particles in the inner magnetosphere. Utilizing more than twenty-five riometers operating in Canada and Scandinavia during the THEMIS era, we are able to constrain spacecraft observations in MLT and latitude/radial location, as well as monitor the precipitation from the resulting drifting electron population (the dispersed injections). Focusing on the 1624 dispersionless electron injection events discussed in Gabrielse et al. (2014), we present statistics of injection location and radial evolution as well as parameters such as radial penetration depth, ionospheric energy deposition and the relationship between them. We also present detailed examples of events in which THEMIS and the ground observations provide a complete picture of the injection region evolution

  14. A comprehensive analysis of the geomagnetic storms occurred dur

    NASA Astrophysics Data System (ADS)

    Ghamry, Essam; Lethy, Ahmed; Arafa-Hamed, Tareq; Abd Elaal, Esmat

    2016-06-01

    The Geomagnetic storms are considered as one of the major natural hazards. Egyptian geomagnetic observatories observed multiple geomagnetic storms during 18 February to 2 March 2014. During this period, four interplanetary shocks successively hit the Earth's magnetosphere, leading to four geomagnetic storms. The storm onsets occurred on 18, 20, 23 and 27 February. A non-substorm Pi2 pulsation was observed on 26 February. This Pi2 pulsation was detected in Egyptian observatories (Misallat and Abu Simbel), Kakioka station in Japan and Carson City station in US with nearly identical waveforms. Van Allen Probe missions observed non-compressional Pc4 pulsations on the recovery phase of the third storm. This Pc4 event is may be likely attributed to the decay of the ring current in the recovery phase.

  15. Bursty reconnection modulating the substorm current wedge, a substorm case study re-analysed by ECLAT tools.

    NASA Astrophysics Data System (ADS)

    Opgenoorth, Hermann; Palin, Laurianne; Ågren, Karin; Zivkovic, Tatjana; Facsko, Gabor; Sergeev, Victor; Kubyshkina, Marina; Nikolaev, Alexander; Milan, Steve; Imber, Suzanne; Kauristie, Kirsti; Palmroth, Minna; van de Kamp, Max; Nakamura, Rumi; Boakes, Peter

    2015-04-01

    Multi-instrumental data mining and interpretation can be tedious and complicated. In this context, the ECLAT (European Cluster Assimilation Technology) project was created to « provide a novel and unique data base and tools for space scientists, by providing an upgrade of the European Space Agency's Cluster Active Archive (CAA). » How can this new tool help the space plasma physics community? Here we demonstrate the power of coordinated global and meso-scale ground-based data to put satellite data into the proper context. We re-analyse a well-isolated substorm with a strong growth phase, which starts right overhead the Scandinavian network of instruments on 8 September 2002. This event was previously studied in detail by Sergeev et al (2005), based on a THEMIS-like configuration near-midnight using a unique radial constellation of LANL (~6.6Re), Geotail and Polar (~9Re), and Cluster (~16Re). In this new study we add detailed IMAGE spacecraft and ground-based network data. Magnetospheric models are specially adapted using solar wind conditions and in-situ observations. Simulation results are compared to the in-situ observations and discussed. We show how - both before and after substorm onset - bursty reconnection in the tail modulates the localised field aligned current flow associated with the substorm current wedge.

  16. "Old" tail lobes provide significant additional substorm power

    NASA Astrophysics Data System (ADS)

    Mishin, V.; Mishin, V. V.; Karavaev, Y.

    2012-12-01

    In each polar cap (PC) we mark out "old PC" observed during quiet time before the event under consideration, and "new PC" that emerges during rounding the old one and expanding the PC total area. Old and new PCs correspond in the magnetosphere to the old and new tail lobes, respectively. The new lobe variable magnetic flux Ψ1 is usually assumed to be active, i.e. it provides transport of the electromagnetic energy flux (Poynting flux) ɛ' from solar wind into the magnetosphere. The old lobe magnetic flux Ψ2 is usually supposed to be passive, i.e. it remains constant during the disturbance and does not participate in the transporting process which would mean the old PC electric field absolute screening from the convection electric field created by the magnetopause reconnection. In fact, screening is observed, but it is far from absolute. We suggest a model of screening and determine its quantitative characteristics in the selected superstorm. The coefficient of a screening is the β = Ψ2/Ψ02, where Ψ02 = const is open magnetic flux through the old PC measured prior to the substorm, and Ψ2 is variable magnetic flux during the substorm. We consider three various regimes of disturbance. In each, the coefficient β decreased during the loading phase and increased at the unloading phase, but the rates and amplitudes of variations exhibited a strong dependence on the regime. We interpreted decrease in β as a result of involving the old PC magnetic flux Ψ2, which was considered to be constant earlier, to the ' transport process of the Poynting flux from the solar wind into the magnetosphere. A weakening of the transport process at the subsequent unloading phase creates increase in β. Estimates showed that coefficient β during each regime and the computed Poynting flux varied manifolds. In general, unlike the existing substorm conception, the new scenario describes an unknown earlier tail lobe activation process during a substorm growth phase that effectively

  17. Energy dissipation in substorms

    NASA Technical Reports Server (NTRS)

    Weiss, Loretta A.; Reiff, P. H.; Moses, J. J.; Heelis, R. A.; Moore, B. D.

    1992-01-01

    The energy dissipated by substorms manifested in several ways is discussed: the Joule dissipation in the ionosphere; the energization of the ring current by the injection of plasma sheet particles; auroral election and ion acceleration; plasmoid ejection; and plasma sheet ion heating during the recovery phase. For each of these energy dissipation mechanisms, a 'rule of thumb' formula is given, and a typical dissipation rate and total energy expenditure is estimated. The total energy dissipated as Joule heat (approximately) 2 x 10(exp 15) is found about twice the ring current injection term, and may be even larger if small scale effects are included. The energy expended in auroral electron precipitation, on the other hand, is smaller than the Joule heating by a factor of five. The energy expended in refilling and heating the plasma sheets is estimated to be approximately 5 x 10(exp 14)J, while the energy lost due to plasmoid ejection is between (approximately) (10 exp 13)(exp 14)J.

  18. Pi2 pulsations in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Lin, C. C.; Cahill, L. J., Jr.

    1975-01-01

    Several substorms were observed at Explorer 45 in November and December 1971, and January and February 1972, while the satellite was in the evening quadrant near L = 5. These same substorms were identified in ground level magnetograms from auroral zone and low latitude stations. The satellite vector magnetic field records and rapid run ground magnetograms were examined for evidence of simultaneous occurrence of Pi2 magnetic pulsations. Pulsations which began abruptly were observed at the satellite during 7 of the 13 substorms studied and the pulsations occurred near the estimated time of substorm onset. These 7 pulsation events were also observed on the ground and 6 were identified in station comments as Pi2. All of the events observed were principally compressional waves, that is, pulsations in field magnitude. There were also transverse components elliptically polarized counter-clockwise looking along the field line. Periods observed ranged from 40 to 200 sec with 80 sec often the dominant period.

  19. Observational evidence for an inside-out substorm onset scenario

    SciTech Connect

    Henderson, Michael G

    2008-01-01

    We present observations which provide strong support for a substorm onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The auroral intensification shows an exponential growth with an estimated e-folding time of around 188 seconds (linear growth rate, {gamma} of 5.33 x 10{sup -3} s{sup -1}). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onsel. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called 'inside-out' substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

  20. Calibrating a Magnetotail Model for Storm/Substorm Forecasting

    NASA Astrophysics Data System (ADS)

    Horton, W.; Siebert, S.; Mithaiwala, M.; Doxas, I.

    2003-12-01

    The physics network model called WINDMI for the solar WIND driven Magnetosphere-Ionosphere weather system is calibrated on substorm databases [1] using a genetic algorithm. We report on the use of the network as a digital filter to classify the substorms into three types; a process traditionally performed individual inspection. We then turn to using the filter on the seven Geospace Environmental Modeling (GEM) Storms designated for community wide study. These storms cover periods of days and contain many substorms. First the WINDMI model is run with the 14 parameters set from the study based on the Blanchard-McPherron database of 117 isolated substorms with 80% of the data having the AL below -500nT. In contrast, the GEM storms have long periods with AL in the range of -1000nT. The prediction error measured with the average-relative variance (ARV) is of approximately unity. Reapplying the genetic algorithm the parameters shift such that the one long storm has an ARV=0.59. Physics modifications of the basic WINDMI model including the injection of sheet plasma into the ring current are being evaluated in terms of their impact on the ARV and comparisons with non-physics based signal processing prediction filters. Ensembles of initial conditions are run with 700MHz G3 CPU run times of order 17 sec per orbit per day of real data. The AMD AthlonXP 1700+ processor takes 5sec per orbit per day. The IBM SP-2 speed will be reported. With such speeds it is possible to run balls of initial conditions. Substrom Classification with the WINDMI Model, W. Horton, R.S. Weigel, D. Vassiliadis, and I. Doxas, Nonlinear Processes in Geophysics, 1-9, 2003. This work was supported by the National Science Foundation Grant ATM-0229863.

  1. Special features of a substorm during high solar wind dynamic pressure

    SciTech Connect

    Lui, A.T.Y.; Ohtani, S.; Newell, P.T.

    1995-10-01

    A substorm on July 24, 1986, exhibiting a rather unusual auroral morphology is analyzed with data from spacecraft (Viking; DMSP F6 and F7; GOES 5 and 6; three LANL geosynchronous satellites; CCE; and IMP 8). This substorm occurred during high solar wind dynamic pressure (>5 nPa). Several notable features for this substorm are: (1) the substorm onset activity was preceded by prominent auroral activations in the morning sector with spatial separations between adjacent bright regions ranging from {approximately}160 to 640 km, and their intensity was modulated at {approximately}3.2-min intervals; (2) the initial substorm activity was concentrated in the morning sector, followed by a sudden activation in the dusk sector, leaving the midnight sector relatively undisturbed, in sharp contrast to the traditional substorm development; (3) while a substorm injection was observed at a geocentric distance of {approximately}8.4 R{sub E} by CCE in association with the substorm onset, particle injections (detectable with three LANL geosynchronous satellites) and dipolarization signatures (detectable by the two GOES satellites) were not observed until subsequent intensifications; (4) timing subsequent substorm intensifications from injections at the geosynchronous altitude differed from timing intensifications based on Viking auroral images by as much as {approximately}3 min; (5) the polar cap boundary was at a significantly higher latitude than the poleward boundary delineated by detectable auroral luminosity in the auroral oval. Detailed timing analysis suggests the substorm onset to be associated with southward interplanetary magnetic field (IMF), possibly with the crossing of an IMF sector boundary (interplanetary current sheet). The dimming of auroral luminosity in the midnight region was associated with a sudden northward turning of the IMF during high solar wind dynamic pressure condition. 36 refs., 14 figs.

  2. Solar wind control of magnetospheric pressure (CDAW 6)

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.

    1985-01-01

    The CDAW 6 data base is used to compare solar wind and magnetospheric pressures. The flaring angle of the tail magnetopause is determined by assuming that the component of solar wind pressure normal to the tail boundary is equal to the total pressure within the tail. Results indicate an increase in the tail flaring angle from 18 deg to 32 deg prior to the 1055 substorm onset and a decrease to 25 deg after the onset. This behavior supports the concept of tail energy storage before the substorm and subsequent release after the onset.

  3. Ground-based studies of ionospheric convection associated with substorm expansion

    NASA Technical Reports Server (NTRS)

    Kamide, Y.; Richmond, A. D.; Emery, B. A.; Hutchins, C. F.; Ahn, B.-H.; De La Beaujardiere, O.; Foster, J. C.; Heelis, R. A.; Kroehl, H. W.; Rich, F. J.

    1994-01-01

    The instantaneous patterns of electric fields and currents in the high-latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground-based magnetometer observations for October 25, 1981. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large-scale potential distributions are indeed of general two-cell patterns representing the southward IMF status, but the night-morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively.

  4. Ground-based studies of ionospheric convection associated with substorm expansion

    SciTech Connect

    Kamide, Y. |; Richmond, A.D.; Emery, B.A.; Hutchins, C.F.; Ahn, B.H. |; Beaujardiere, O. de la; Foster, J.C.; Heelis, R.A.; Kroehl, H.W.; Rich, F.J.

    1994-10-01

    The instantaneous patterns of electric fields and currents in the high-latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground-based magnetometer observations for October 25, 1981. For this purpose, an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used. These global patterns are unobtainable from any single data set. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE 2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large-scale potential distributions are indeed of general two-cell patterns representing the southward IMF status, but the night-morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively. 40 refs., 12 figs., 1 tab.

  5. Ground-based studies of ionospheric convection associated with substorm expansion

    SciTech Connect

    Kamide, Y.; Richmond, A.D.; Emery, B.A.; Hutchins, C.F.; Ahn, B.H.

    1994-10-01

    The instantaneous patterns of electric fields and currents in the high-latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground-based magnetometer observations for October 25, 1981. For this purpose, an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used. These global patterns are unobtainable from any single data set. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in genernal, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE 2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the epansion and maximum phases of the substorm show the first clear evidence of the coezistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large-scale potential distributions are indeed of general two-cell patterns representing the southward LMF status, but the night-morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement respectively.

  6. The role of substorms in the formation of the ring current

    SciTech Connect

    Rostoker, G.

    1996-07-01

    It has long been recognized that the formation of the terrestrial ring current is accompanied by strong substorm expansive phase activity in the auroral oval. While large amplitude substorm activity seems to be a prerequisite for ring current formation to take place, it has long been puzzling as to why some large amplitude substorm activity in the auroral oval is not associated with significant ring current development. In this paper I shall outline the basis for the renovated boundary layer dynamics model of magnetospheric substorms showing how the onset of the substorm expansive phase can be associated with a sudden decrease in shielding space charge in the region of the near-Earth plasma sheet threaded by Region 2 field-aligned currents. I shall suggest that an episode of sufficiently large southward IMF lasting over a sufficiently lengthy period of time can lead to a sequence of substorm expansive phases, each one being initiated closer to the Earth than the previous one. Each expansive phase is attributed to a sudden decrease in radially localized cross-tail current (viz. a decrease in shielding space charge) and with each onset the inner edge of the plasma sheet moves inward. The inductive electric field associated with each crosstail current decrease is responsible for the acceleration of already energetic particles to energies of significance for ring current formation. Only when the inner edge of the crosstail current is sufficiently close to the Earth do the acceleration processes associated with substorm onset produce a long lived ring current. {copyright} {ital 1996 American Institute of Physics.}

  7. A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS)

    NASA Astrophysics Data System (ADS)

    Lee, S.; Shiokawa, K.; McFadden, J. P.; Nishimura, Y.

    2011-12-01

    We have statistically investigated the electron density ne,M and temperature Te,M in the near-Earth plasma sheet in terms of the magnetosphere-ionosphere coupling process, as measured by the electrostatic analyzer (ESA) on board the Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) satellite from November 2007 to January 2010. To find out when and where an aurora can occur, either with or without electron acceleration, the thermal current j∥th and the conductivity K along the magnetic field line were also estimated from observations of the magnetospheric electrons with pitch angle information inside 12 RE. The thermal current, j∥th(∝ ne,M Te,M1/2), represents the upper limit of the field-aligned current that can be carried by magnetospheric electrons without a field-aligned potential difference. The conductivity, K(∝ ne,M Te,M-1/2), relates the upward field-aligned current, j∥, to the field-aligned potential difference, V∥, assuming adiabatic electron transport. The thermal current is estimated by two methods: (1) from the relation by using ne,M and Te,M and (2) from the total downward electron number flux. We find that in the dawnside inner magnetosphere, the thermal currents estimated by both methods are sufficient to carry typical region 2 upward field-aligned current. On the other hand, in the duskside outer magnetosphere, a field-aligned potential difference is necessary on the region 1 current since the estimated thermal current is smaller than the typical region 1 current. By using the relationship, j∥ = KV∥, where K is the conductivity estimated from Knight's relation and j∥ is the typical auroral current, we conclude that a field-aligned potential difference of V∥ = 2-5 kV is necessary on the duskside region 1 upward field-aligned current.

  8. Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail During Substorms: Implications for Magnetic Field Models

    NASA Technical Reports Server (NTRS)

    Spence, Harlan E.

    1996-01-01

    discrete features in the context of the global picture. We reported on our initial study at national and international meetings and published the results of our predictions of the low-altitude signatures of the plasma sheet. In addition, the PI was invited to contribute a publication to the so-called 'Great Debate in Space Physics' series that is a feature of EOS. The topic was on the nature of magnetospheric substorms. Specific questions of the when and where a substorm occurs and the connection between the auroral and magnetospheric components were discussed in that paper. This paper therefore was derived exclusively from the research supported by this grant. Attachment: Empirical modeling of the quite time nightside magnetosphere.' 'CRRES observations of particle flux dropout event.' The what, where, when, and why of magnetospheric substorm triggers'. and 'Low altitude signature of the plasma sheet: model prediction of local time dependence'.

  9. Ulf waves in the low-latitude boundary layer and their relationship to magnetospheric pulsations: A multisatellite observation

    SciTech Connect

    Takahashi, K.; Sibeck, D.G.; Newell, P.T.; Spence, H.E.

    1994-01-31

    On April 30 (day 120), 1985, the magnetosphere was compressed at 0923 UT and the subsolar magnetopause remained near 7 RE geocentric for approx. 2 hours, during which the four spacecraft Spacecraft Charging At High Altitude (SCATHA), GOES 5, GOES 6, and Active Magnetospheric Particle Tracer Explorers (AMPTE) CCE were all in the magnetosphere on the morning side. SCATHA was in the low-latitude boundary layer (LLBL) in the second half of this period. The interplanetary magnetic field was inferred to be northward from the characteristics of precipitating particle fluxes as observed by the low-altitude satellite Defense Meteorological Satellite Program (DMSP) F7 and also from absence of substorms. The authors used magnetic field and particle data from this unique interval to study ULF waves in the LLBL and their relationship to magnetic pulsations in the magnetosphere. The LLBL was identified from the properties of particles, including bidirectional field-aligned electron beams at approx. 200 eV. In the boundary layer the magnetic field exhibited both a 5-10 min irregular compressional oscillation and a broadband (Delta(f)/f approx. 1) primarily transverse oscillations with a mean period of approx. 50 s and a left-hand sense of polarization about the mean field. The former can be observed by other satellites and is likely due to pressure variations in the solar wind, while the latter is likely due to a Kelvin-Helmoltz (K.-H.) instability occurring in the LLBL or on the magnetopause.

  10. GEOTAIL and POLAR Observations of Auroral Kilometric Radiation and Terrestrial Low Frequency Bursts and their Relationship to Energetic Particles, Auroras, and Other Substorm Phenomena

    NASA Technical Reports Server (NTRS)

    Anderson, R . R.; Gurnett, D. A.; Frank, L. A.; Thomsen, Michelle F.; Parks, G. K.; Brittnacher, M. J.; Spann, James F., Jr.; Imhoff, W. L.; Mobilia, J. H.

    1999-01-01

    Terrestrial low frequency (LF) bursts are plasma wave phenomena that appear to be a part of the low frequency end of the auroral kilometric radiation (AKR) spectrum and are observed during strong substorms, GEOTAIL and POLAR plasma wave observations from within the magnetosphere show that the AKR increases in intensity and its lower frequency limits decrease when LF bursts are observed. The first is expected as it is shows substorm onset and the latter indicates that the AKR source region is expanding to higher altitudes. Images from the POLAR VIS Earth Camera operating in the far-UV range and the POLAR UVI experiment usually feature an auroral brightening and an expansion of the aurora to higher latitudes at the time of the LF bursts. Enhanced fluxes of X-rays from precipitating electrons have also been observed by POLAR PIXIE. High resolution ground Abstract: magnetometer data from the CANOPUS and IMAGE networks show that the LF bursts occur when the expansive phase onset signatures are most intense. The ground magnetometer data and the CANOPUS meridian scanning photometer data sometimes show that during the LF burst events the expansive phase onset starts at unusually low latitudes and moves poleward. Large injections of energetic protons and electrons have also been detected by the GOES and LANL geosynchronous satellites during LF burst events. While most of the auroral brightenings and energetic particle injections associated with the LF bursts occur near local midnight, several have been observed as early as mid-afternoon. From these various measurements, we are achieving a better understanding of the plasma and particle motions during substorms that are associated with the generation and propagation of terrestrial LF bursts

  11. Energy density of ionospheric and solar wind origin ions in the near-Earth magnetotail during substorms

    NASA Technical Reports Server (NTRS)

    Daglis, Loannis A.; Livi, Stefano; Sarris, Emmanuel T.; Wilken, Berend

    1994-01-01

    Comprehensive energy density studies provide an important measure of the participation of various sources in energization processes and have been relatively rare in the literature. We present a statistical study of the energy density of the near-Earth magnetotail major ions (H(+), O(+), He(++), He(+)) during substorm expansion phase and discuss its implications for the solar wind/magnetosphere/ionosphere coupling. Our aim is to examine the relation between auroral activity and the particle energization during substorms through the correlation between the AE indices and the energy density of the major magnetospheric ions. The data we used here were collected by the charge-energy-mass (CHEM) spectrometer on board the Active Magnetospheric Particle Trace Explorer (AMPTE)/Charge Composition Explorer (CCE) satellite in the near-equatorial nightside magnetosphere, at geocentric distances approximately 7 to 9 R(sub E). CHEM provided the opportunity to conduct the first statistical study of energy density in the near-Earth magnetotail with multispecies particle data extending into the higher energy range (greater than or equal to 20 keV/E). the use of 1-min AE indices in this study should be emphasized, as the use (in previous statistical studies) of the (3-hour) Kp index or of long-time averages of AE indices essentially smoothed out all the information on substorms. Most distinct feature of our study is the excellent correlation of O(+) energy density with the AE index, in contrast with the remarkably poor He(++) energy density - AE index correlation. Furthermore, we examined the relation of the ion energy density to the electrojet activity during substorm growth phase. The O(+) energy density is strongly correlated with the pre-onset AU index, that is the eastward electrojet intensity, which represents the growth phase current system. Our investigation shows that the near-Earth magnetotail is increasingly fed with energetic ionospheric ions during periods of enhanced

  12. Particle acceleration by inductive electric fields in the Earth’s magnetosphere

    NASA Astrophysics Data System (ADS)

    Ilie, Raluca; Daldorff, Lars K. S.; Ganushkina, Natalia; Liemohn, Michael

    2015-04-01

    The terrestrial magnetosphere has the capability to rapidly accelerate charged particles up to very high energies over relatively short times and distances, leading to an increase in the near Earth currents. These energetic particles are injected from the magnetotail into the inner magnetosphere through two primary mechanisms. One transport method is the potential-driven convection. This occurs during periods of southward Interplanetary Magnetic Field (IMF), which allows part of the dawn-to-dusk solar wind electric field to effectively map down to the polar ionosphere. The second transport process, substorm activity, involves a sudden reconfiguration of the magnetic field and the creation of transient induced electric fields. The relative contribution of potential and inductive electric field driven convection resulting in the development of the storm-time ring current has remained an unresolved question in Geospace research.Since the energy of charged particles can be altered only by means of electric fields, knowledge of the relative contribution of potential versus inductive electric fields at intensifying the hot ion population in the inner magnetosphere is required. However, it is not possible to distinguish the two terms by only measuring the electric field. Therefore assessing the importance of induced electric field is possible by thorough examination of the time varying magnetic field and current systems using global modeling of the entire system.The induced electric field is calculated as a 3D integration over the entire magnetosphere domain. However, though computationally challenging, the full volume integration approach removes the need to trace independent field lines and lifts the assumption that the magnetic field lines can be treated as frozen in a stationary ionosphere.In this work, we quantitatively assess the relative contributions on potential and inductive electric fields at driving plasma sheet ions into the inner magnetosphere, as well as

  13. Particle acceleration during substorm growth and onset

    NASA Technical Reports Server (NTRS)

    Williams, D. J.; Mitchell, D. G.; Huang, C. Y.; Frank, L. A.; Russell, C. T.

    1990-01-01

    ISEE-1 observations of ion and electron energization made at 11 RE during a substorm event on April 2, 1978 are presented. An analysis of the dominant cross-tail current systems in this event (Mitchell et al., 1990) has made it possible to uniquely associate particle energization processes with the development and/or disruption of the cross-tail currents. It is found that significant ion acceleration occurs as the ions participate in serpentine cross-tail motion (Speiser, 1965), establishing the dominant plasma sheet current system just prior to onset. As this current disrupts, the magnetic field configuration dipolarizes and further ion energization and the bulk of the electron energization occurs. During dipolarization energization is due primarily to the inductive electric field, including betatron and Fermi acceleration processes.

  14. Is Mercury's Magnetosphere Driven By Flux Transfer Events?

    NASA Astrophysics Data System (ADS)

    Slavin, J. A.

    2014-12-01

    Mercury's magnetosphere closely resembles that of Earth in terms of its topology and structure, but major differences are found when their dynamics are compared. The strong interplanetary magnetic fields at 0.3 to 0.5 AU result in low Alfven Mach numbers, weak bow shocks and low plasma β magnetosheaths at Mercury. These conditions support the development of strong plasma depletion layers adjacent to the magnetopause and intense magnetopause reconnection. MESSENGER observations indicate that reconnection occurs for all non-zero shear angles across the magnetopause with magnetosheat β being the primary factor controlling its rate. Flux transfer events (FTEs) with ~ 1-2 s durations and flux rope topology are observed during nearlly all magnetopause crossings. In contrast with the Earth where FTEs are typically observed every ~ 8 min, FTE ecounters at Mercury are separated on average by only ~ 10 s. At lower altitudes near the cusp MESSENGER observes ~1-2-s-long strong decreases in mgnetic field intensity that are termed cusp plasma filaments. These filaments are beleived to be formed by the inflow of magnetosheath plasma associated with flux transfer events. Mercury's magnetotail exhibits magnetic flux loading/unloading events similar to those observed at Earth during substorms. The Dungey cycle durations and lobe flux loading amplitudes are ~ 2 - 3 min and ~ 30 to 50% at Mercury as compared to ~ 1 - 2 hr and ~ 10 to 25% at Earth. However, FTEs at Earth account for only a few per cent of the magnetic flux carried by the Dungey cycle, while the contribution of FTEs at Mercury is estimated to be ~ 30 to 50%. Mercury also differs from Earth in that it lacks an ionosphere, but possesses a large, highly conducting iron core. The strong IMF and lack of an ionosphere results in a relatively large dawn-to-dusk cross-magnetosphere potential drop of ~ 30 kV at Mercury. Inductive coupling between Mercury's magnetosphere and its large iron core stiffens the dayside

  15. Current sheet thinning, reconnection onset, and auroral morphology during geomagnetic substorms

    NASA Astrophysics Data System (ADS)

    Otto, A.; Hsieh, M. S.

    2015-12-01

    Geomagnetic substorms represent a fundamental energy release mechanism for the terrestrial magnetosphere. Specifically, the evolution of thin currents sheets during the substorm growth phase plays a key role for substorms because such current sheets present a much lower threshold for the onset of tearing modes and magnetic reconnection than the usually thick magnetotail current sheet. Here we examine and compare two basic processes for current sheet thinning in the Earth's magnetotail: Current sheet thinning (1) through closed magnetic flux depletion (MFD) in the near Earth magnetotail caused by divergent flux transport to replace closed flux on the dayside and (2) through accumulation of open flux magnetic flux in the tail lobes also caused by dayside reconnection. Both processes are expected to operate during any period of enhanced dayside reconnection. It is demonstrated that closed magnetic flux depletion (MFD) in the near Earth magnetotail and the increase of open lobe magnetic flux can lead to the evolution of two separate thin current sheets in the near Earth and the mid tail regions of the magnetosphere. While the auroral morphology associated with MFD and near Earth current sheet formation is well consistent with typical substorm growth observation, midtail current sheet formation through lobe flux increase shows only a minor influence on the auroral ionosphere. We discuss the physics of the dual current sheet formation and local and auroral properties of magnetic reconnection in either current sheet. It is suggested that only reconnection onset in the near Earth current sheet may be consistent with substorm expansion because the flux tube entropy depletion of mid tail reconnection appears insufficient to cause geosynchronous particle injection and dipolarization. Therefore reconnection in the mid tail current sheet is more likely associated with bursty bulk flows or dipolarization fronts which stop short of geosynchronous distances.

  16. Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Lester, M.; Parkinson, M. L.; Yeoman, T. K.; Dyson, P. L.; Devlin, J. C.; Frey, H. U.

    2006-12-01

    At 08:35 UT on 21 November 2004, the onset of an interval of substorm activity was captured in the southern hemisphere by the Far UltraViolet (FUV) instrument on board the IMAGE spacecraft. This was accompanied by the onset of Pi2 activity and subsequent magnetic bays, evident in ground magnetic data from both hemispheres. Further intensifications were then observed in both the auroral and ground magnetic data over the following ~3 h. During this interval the fields-of-view of the two southern hemisphere Tasman International Geospace Enviroment Radars (TIGER) moved through the evening sector towards midnight. Whilst initially low, the amount of backscatter from TIGER increased considerably during the early stages of the expansion phase such that by ~09:20 UT an enhanced dusk flow cell was clearly evident. During the expansion phase the equatorward portion of this flow cell developed into a narrow high-speed flow channel, indicative of the auroral and sub-auroral flows identified in previous studies (e.g. Freeman et al., 1992; Parkinson et al., 2003). At the same time, higher latitude transient flow features were observed and as the interval progressed the flow reversal region and Harang discontinuity became very well defined. Overall, this study has enabled the spatial and temporal development of many different elements of the substorm process to be resolved and placed within a simple conceptual framework of magnetospheric convection. Specifically, the detailed observations of ionospheric flows have illustrated the complex interplay between substorm electric fields and associated auroral dynamics. They have helped define the distinct nature of different substorm current systems such as the traditional substorm current wedge and the more equatorward currents associated with polarisation electric fields. Additionally, they have revealed a radar signature of nightside reconnection which provides the promise of quantifying nightside reconnection in a way which has

  17. Electrostatic waves in the magnetosphere.

    NASA Technical Reports Server (NTRS)

    Scarf, F. L.; Fredricks, R. W.

    1972-01-01

    Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves. In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The Ogo 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging.

  18. Magnetic effects of the substorm current wedge in a “spread-out wire” model and their comparison with ground, geosynchronous, and tail lobe data

    NASA Astrophysics Data System (ADS)

    Sergeev, V. A.; Tsyganenko, N. A.; Smirnov, M. V.; Nikolaev, A. V.; Singer, H. J.; Baumjohann, W.

    2011-07-01

    Although the substorm current wedge (SCW) is recognized as a basic 3-D current system of the substorm expansion phase, its existing models still do not extend beyond a cartoon-like sketch, and very little is known of how well they reproduce magnetic variations observed in the magnetosphere during substorms. A lack of a realistic quantitative SCW model hampers testing model predictions against large sets of spacecraft data. This paper (1) presents a computationally efficient and flexible model with a realistic geometry of field-aligned currents, conveniently parameterized by the SCW strength, longitudinal width, and position, all derived from ground-based midlatitude magnetic variations; and (2) tests the model against INTERMAGNET network observations during substorms and compares its predictions with space magnetometer data. The testing demonstrated significant and systematic discrepancies between the observed and predicted magnetic variations, depending on spacecraft location, concurrent magnetotail configuration, and substorm phase. In particular, we found that the net SCW current derived from the midlatitude field variations corresponds to only a relatively small and variable fraction of the distant 3-D substorm current, inferred from spacecraft data in the lobe and at geosynchronous distance. The discrepancy can be partly attributed to additional region 2 polarity field-aligned currents in the same longitudinal sector, associated with azimuthal diversion of the earthward plasma flow when it encounters the region of strong quasi-dipolar field in the inner magnetosphere.

  19. TWINS and IBEX Observations of shock-associated Storms and Substorms

    NASA Astrophysics Data System (ADS)

    Valek, P. W.; McComas, D. J.; Dayeh, M. A.; Goldstein, J.; Ogasawara, K.

    2014-12-01

    The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) and Interstellar Boundary EXplorer (IBEX) missions provide a unique set of Energetic Neutral Atom (ENA) images of the magnetosphere. The TWINS mission has two spacecraft flown in Molniya orbits (inclination of 63.4, apogees of ~ 7.2 Re). Instruments aboard each spacecraft measure ENAs in the energy range from 1 to 100 keV / amu, and provide composition measurements for energies <~ 32 keV. The phasing of the two TWINS spacecraft allows for near continuous observations of the inner magnetosphere with high temporal (~ 1 min) and spatial (~0.1 Re) resolution. The IBEX mission is equipped with two sensitive ENA cameras designed to observe the interactions between our heliosphere and the interstellar medium. However, its vantage point from outside the magnetosphere (apogee ~ 40 Re in the ecliptic plane) also provides a unique 'outside in' view of the magnetosphere. IBEX images ENAs in the energy range of ~0.4 - 6 keV along a broad cut of the magnetosphere along the GSE-Z direction. The complementary ENA observations from TWINS and IBEX provide a global perspective of the dynamics of the magnetosphere. We present these observations of the global magnetospheric ENA response to shock-associated storms and substorms.

  20. Ionospheric loop currents and associated ULF oscillations at geosynchronous altitudes during preonset intervals of substorm aurora

    NASA Astrophysics Data System (ADS)

    Saka, O.; Hayashi, K.; Leonovich, A. S.

    2015-04-01

    A substorm aurora was observed at 04:52 UT on 27 January 1986 by an all-sky imager installed at Shamattawa (66.3°N, 336.0° in corrected geomagnetic coordinates) and a magnetometer on board a conjugate satellite (GOES 6) at geosynchronous altitudes. In the preonset intervals lasting for approximately 50 min prior to the expansion onset, an equatorward drift of the auroras beginning from 71°N to 64°N was observed. Meanwhile, GOES 6 observed ULF oscillations in 25-200 s periods at geosynchronous altitudes after about 10 min following the start of the equatorward drift. During the equatorward drift of the arc, the flow reversal occurred, where the auroral arc propagating eastward was replaced by a westward propagation. Simultaneously, the major axes of the ULF oscillations rotated clockwise by ~90° in the equatorial plane. We conclude that the ULF oscillations are azimuthally small-scale Alfvén waves excited in the magnetosphere by field-aligned currents associated with ionospheric loop currents.

  1. Plasma Circulation in the Magnetosphere

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Fok, Mei-Ching; Delcourt, D. C.; Slinker, S.; Fedder, J. A.; Buenfil, M.

    2006-01-01

    We investigate the global structure and dynamics of plasma circulation produced by prototypical solar wind disturbances of the interplanetary magnetic field and dynamic pressure. We track the global circulation and energization of solar wind, polar wind, and auroral wind plasmas throughout the magnetosphere, until they precipitate or escape into the downstream solar wind. We use the full equations of motion of the plasma ions within fields produced by a global MHD simulation of the dynamic solar wind interaction. We use the dynamic hot plasma density and Poynting energy flux specified at the inner boundary of the MHD simulation as drivers of conjugate ion outflow fluxes using local empirical relations obtained from the FAST and Polar missions. Birkeland currents computed by the MHD code are used to derive a field-parallel potential drop from a Knight-like relation [as modified by Lyons and Evans, 1980]. This potential drop is applied to each ion as an initial bulk energy, added to a thermal heating driven by the locally incident Poynting flux. The solar wind pressure increase case (B(sub Y) = 5; B(sub z) = 0 nT) produces an immediate substorm owing to compression of pre-existing plasmas. The SB(sub z), interval (embedded in NB(sub z)) produces a substorm after about one hour of development. Both disturbances enhance the auroral wind flux and heavy ion pressure of the magnetosphere substantially, with complex dynamic structuring by auroral acceleration vortexes and dynamic reconnection. Comparisons are made with observations during disturbed periods including the Halloween 2003 super-storm and other periods.

  2. Mercury's Magnetosphere

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.

    1999-01-01

    Among the major discoveries made by the Mariner 10 mission to the inner planets was the existence of an intrinsic magnetic field at Mercury with a dipole moment of approx. 300 nT R(sup 3, sub M). This magnetic field is sufficient to stand off the solar wind at an altitude of about 1 R(sub M) (i.e. approx. 2439 km). Hence, Mercury possesses a 'magnetosphere' from which the so]ar wind plasma is largely excluded and within which the motion of charged particles is controlled by the planetary magnetic field. Despite its small size relative to the magnetospheres of the other planets, a Mercury orbiter mission is a high priority for the space physics community. The primary reason for this great interest is that Mercury unlike all the other planets visited thus far, lacks a significant atmosphere; only a vestigial exosphere is present. This results in a unique situation where the magnetosphere interacts directly with the outer layer of the planetary crust (i.e. the regolith). At all of the other planets the topmost regions of their atmospheres become ionized by solar radiation to form ionospheres. These planetary ionospheres then couple to electrodynamically to their magnetospheres or, in the case of the weakly magnetized Venus and Mars, directly to the solar wind. This magnetosphere-ionosphere coupling is mediated largely through field-aligned currents (FACs) flowing along the magnetic field lines linking the magnetosphere and the high-latitude ionosphere. Mercury is unique in that it is expected that FACS will be very short lived due to the low electrical conductivity of the regolith. Furthermore, at the earth it has been shown that the outflow of neutral atmospheric species to great altitudes is an important source of magnetospheric plasma (following ionization) whose composition may influence subsequent magnetotail dynamics. However, the dominant source of plasma for most of the terrestrial magnetosphere is the 'leakage'of solar wind across the magnetopause and more

  3. Energy coupling in the magnetospheres of earth and Mercury

    NASA Technical Reports Server (NTRS)

    Baker, D. N.

    1990-01-01

    The mechanisms involved in the dissipation of solar-wind energy during magnetospheric substorms are considered theoretically, comparing models for earth and Mercury. In the model for terrestrial substorms, IMF lines interconnect with terrestrial field lines near the front of the magnetosphere and are dragged back, carrying plasma and energy, to form tail lobes; a magnetic neutral region is then formed by reconnection of the open lines as the plasma sheet thins, and reconnective heating and acceleration of tail plasma lead to plasma inflow at the poles and formation of a plasmoid flowing down the tail at high velocity. Analogous phenomena on Mercury could produce precipitation of particles carrying 10-1000 GW of power into 'auroral zones' on the dark side of the planet. The feasibility of remote or in situ observations to detect such processes is discussed.

  4. The Relationship Between Magnetotail Dynamics and Substorm Onset Longitudes Determined from Spacecraft Images

    NASA Technical Reports Server (NTRS)

    Ieda, A.; Fairfield, D. H.; Mukai, T.; Saito, Y.

    1999-01-01

    Geotail plasma and magnetic field observations of plasmoids between 25 and 30 Re have been compared to Polar UVI observations of auroral brightenings. Plasmoids almost always corresponded to brightenings but the brightenings were sometimes weak and spatially limited and did not always grow to a global substorm. Even a case where a plasmoid event occurred with fast post-plasmoid flow corresponded to a weak brightening but no substorm. Some brightenings did not correspond to plasmoids, but these events were observed away from the longitude of Geotail. The plasmoids are observed 0-2 min after the brightenings in most cases. It seems likely that formation of a near-Earth neutral line causes each brightening in the polar ionosphere, but these formations do not have a one-to-one relationship with a substorm onset. What causes development of the full, large-scale substorm remains an open question.

  5. Traveling compression region observed in the mid-tail lobes near substorm expansion phase onset

    NASA Technical Reports Server (NTRS)

    Taguchi, S.; Slavin, J. A.; Lepping, R. P.; Nose, M.

    1996-01-01

    The characteristics of traveling compression regions (TCRs) in the midtail lobes are examined. Through the use of the AL index, isolated substorm events with well developed expansion phases are selected. The TCR events which feature a field compression coincident with modified Bz variations are categorized into different types, and the magnetic variations are interpreted in terms of the relative location of the point of observation to the plasmoid at the time of release and the effects of tail flaring. In order to understand the relationship between the plasmoid release time and the substorm onset time, the time difference between the different types of TCR and the substorm onset determined by Pi 2 pulsations at mid-latitude ground stations, is examined. The results suggest that the downtail release of most of the plasmoids created earthwards of -38 earth radii occurs at almost the same distance as the substorm onset.

  6. Substorms observations over Apatity during geomagnetic storms in the period 2012 - 2016

    NASA Astrophysics Data System (ADS)

    Guineva, Veneta; Werner, Rolf; Despirak, Irina; Kozelov, Boris

    2016-07-01

    In this work we studied substorms, generated during enhanced geomagnetic activity in the period 2012 - 2016. Observations of the Multiscale Aurora Imaging Network (MAIN) in Apatity have been used. Solar wind and interplanetary magnetic field parameters were judged by the 1-min sampled OMNI data base. Substorm onset and further development were verified by the 10-s sampled data of IMAGE magnetometers and by data of the all-sky camera at Apatity. Subject of the study were substorms occurred during geomagnetic storms. The so-called "St. Patrick's day 2015 event" (17-21 March 2015), the events on 17-18 March 2013 and 7-17 March 2012 (a chain of events generated four consecutive storms) which were among the events of strongest geomagnetic activity during the current solar cycle 24, were part of the storms under consideration. The behavior of the substorms developed during different phases of the geomagnetic storms was discussed.

  7. Observations of magnetic field dipolarization during auroral substorm onset

    NASA Astrophysics Data System (ADS)

    Frank, L. A.; Paterson, W. R.; Sigwarth, J. B.; Kokubun, S.

    2000-07-01

    The dynamical behavior of plasmas and magnetic fields in the vicinity of the equatorial crossing of magnetic field lines threading the onset auroral arc is examined for two substorms on November 26, 1997. The locations of the initial brightenings of the auroral arcs were determined with the cameras for visible and far-ultraviolet wavelengths on board the Polar spacecraft. The equatorial positions of the field lines were in the range of radial distances of 8-12RE as computed with models of Earth's global magnetic field. The radial distance of the Geotail spacecraft was 14 RE at a position in the premidnight sector that was 2RE below the current sheet. This spacecraft was embedded in a low-β plasma that was located adjacent to the central hot plasma sheet. For the first substorm, with onset at 1310 UT, no substantial effect was observed in the plasmas and magnetic fields, although the Geotail spacecraft was located only about 2 hours in magnetic local time from the field lines threading the onset auroral arc. For the second substorm onset, at 1354 UT, the spacecraft was positioned within tens of minutes in local time of the position of the magnetic field lines threading the onset auroral arc. This fortuitous spacecraft position in the relatively quiescent plasma and magnetic fields adjacent to the central plasma sheet and within several Earth radii of the position of the onset mechanism allowed determination of the beginning time of the dipolarization of the magnetic fields. This time was simultaneous with the onset brightening of the auroral arc within the approximately 1-min time resolution of the auroral images. The simultaneity of the initial brightening of the auroral arc and of the initiation of the dipolarization of the magnetic field, presumably due to diversion of current from the equatorial current sheet to the ionosphere, provides an important guideline for global dynamical MHD models of Earth's magnetosphere.

  8. Pulsars Magnetospheres

    NASA Technical Reports Server (NTRS)

    Timokhin, Andrey

    2012-01-01

    Current density determines the plasma flow regime. Cascades are non-stationary. ALWAYS. All flow regimes look different: multiple components (?) Return current regions should have particle accelerating zones in the outer magnetosphere: y-ray pulsars (?) Plasma oscillations in discharges: direct radio emission (?)

  9. Nuclear magnetohydrodynamic EMP, solar storms, and substorms

    SciTech Connect

    Rabinowitz, M. ); Meliopoulous, A.P.S.; Glytsis, E.N. . School of Electrical Engineering); Cokkinides, G.J. )

    1992-10-20

    In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear burst produces a relatively slow magnetohydrodynamic EMP (MHD EMP), whose effects are like those from solar storm geomagnetically induced currents (SS-GIC). The MHD EMP electric field E [approx lt] 10[sup [minus] 1] V/m and lasts [approx lt] 10[sup 2] sec, whereas for solar storms E [approx gt] 10[sup [minus] 2] V/m and lasts [approx gt] 10[sup 3] sec. Although the solar storm electric field is lower than MHD EMP, the solar storm effects are generally greater due to their much longer duration. Substorms produce much smaller effects than SS-GIC, but occur much more frequently. This paper describes the physics of such geomagnetic disturbances and analyzes their effects.

  10. Evidence for magnetospheric effects on the sodium atmosphere of Mercury

    NASA Astrophysics Data System (ADS)

    Potter, A. E.; Morgan, T. H.

    1990-05-01

    Monochromatic images of Mercury at the sodium D2 emission line showed excess sodium emission in localized regions at high northern and southern latitudes and day-to-day global variations in the distribution of sodium emission. These phenomena support the suggestion that magnetospheric effects could be the cause. Sputtering of surface minerals could produce sodium vapor in polar regions during magnetic substorms, when magnetospheric ions directly impact the surface. Another important process may be the transport of sodium ions along magnetic field lines toward polar regions, where they impact directly on the surface of Mercury and are neutralized to regenerate neutral sodium atoms. Day-to-day variations in planetary sodium distributions could result from changing solar activity, which can change the magnetosphere in time scales of a few hours. Observations of the sodium exosphere may provide a tool for remote monitoring of the magnetosphere of Mercury.

  11. Anthropogenic trigger of substorms and energetic particles precipitations

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. D.; Ruzhin, Yu. Ya.

    2014-12-01

    The high-frequency (HF) emission in near-Earth space from various powerful transmitters (radio communications, radars, broadcasting, universal time and navigation stations, etc.) form an integral part of the modern world that it cannot do without. In particular, special-purpose research facilities equipped with powerful HF transmitters are used successfully for plasma experiments and local modification of the ionosphere. In this work, we are using the results of a complex space-ground experiment to show that exposure of the subauroral region to HF emission can not only cause local changes in the ionosphere, but can also trigger processes in the magnetosphere-ionosphere system that result in intensive substorm activity (precipitations of high-energy particles, aurorae, significant variations in the ionospheric parameters and, as a consequence, in radio propagation conditions).

  12. Substorm warnings - An ISEE-3 real time data system

    NASA Technical Reports Server (NTRS)

    Tsurutani, B.; Baker, D.

    1979-01-01

    The use of solar wind measurements made by ISEE-3 in its halo orbit around the L1 libration point to predict the onsets of magnetospheric substorms and geomagnetic storms is discussed. Consideration is given to the limitations on the predictive ability of the satellite measurements set by the bulk solar wind velocity, the elliptical orbit of the satellite and the correlation lengths of the magnetic field and the solar wind plasma. The ISEE-3 real-time data system is presented, with attention given to the ground receiving stations, the NASCOM communications system, the Multisatellite Operations Control Center and Information Processing Division at the Goddard Space Flight Center, the link between Goddard and the NOAA Space Environmental Services Center, and the NOAA Space Environment Laboratory data acquisition and display data system, which includes displays allowing storm forecasts. It is noted that the entire system should be operational by March, 1980.

  13. Magnetic energy storage and the nightside magnetosphere-ionosphere coupling

    SciTech Connect

    Horton, W.; Pekker, M.; Doxas, I.

    1998-05-01

    The change m in the magnetic energy stored m in the Earth`s magnetotail as a function of the solar wind, BIF conditions are investigated using an empirical magnetic field model. The results are used to calculate the two normal modes contained m in the low-dimensional global model called WINDMI for the solar wind driven magnetosphere-ionosphere system. The coupling of the magnetosphere-ionosphere (MI) through the nightside region 1 current loop transfers power to the ionosphere through two modes: a fast (period of minutes) oscillation and a slow (period of one hour) geotail cavity mode. The solar wind drives both modes m in the substorm dynamics.

  14. The large-scale current system during auroral substorms

    NASA Astrophysics Data System (ADS)

    Gjerloev, J. W.; Hoffman, R. A.

    2014-06-01

    We present an empirical model of the equivalent current system in the ionosphere during the peak of a classical bulge-type auroral substorm. This model is derived from measurements made by ~110 ground magnetometer stations during 116 substorms. The data are temporally and spatially organized using global auroral images obtained by the Polar Visible Imaging System Earth Camera. The empirical equivalent current system displays three key features: a poleward shift of the westward electrojet connecting the postmidnight and premidnight components; a polar cap swirl; and significantly different magnitudes of the postmidnight and premidnight westward electrojets. This leads us to propose a two-wedge current system linking the ionosphere to the magnetosphere. The bulge current wedge is located in the premidnight region just equatorward of the open-closed field line boundary while another three-dimensional current system is located in the postmidnight region well within the auroral oval. We use Biot and Savart calculations and Tsyganenko mapping and show that this new model is a likely solution for the large-scale current system.

  15. Substorm simulation: Formation of westward traveling surge

    NASA Astrophysics Data System (ADS)

    Ebihara, Y.; Tanaka, T.

    2015-12-01

    Auroral substorm expansion is characterized by initial brightening of aurora, followed by a bulge expanding in all directions, and a westward traveling surge (WTS). On the basis of the result obtained by a global magnetohydrodynamic simulation, we propose a scenario for the onset and the subsequent formation of WTS. (1) Near-Earth neutral line releases magnetic tension in the near-Earth plasma sheet to compress plasma and accelerate it earthward. (2) Earthward, perpendicular flow is converted to parallel flow in the near-Earth tail region. (3) Plasma moves earthward parallel to a field line. The plasma pressure is additionally enhanced at off-equator with an expanding slow-mode variation. (4) Flow vorticities coexist near the off-equatorial high-pressure region. Resultant field-aligned current (FAC) is connected to the ionosphere, which may manifest initial brightening. (5) Due to continued earthward flow, the high-plasma pressure region continues to expand to the east and west. (6) The ionospheric conductivity continues to increase in the upward FAC region, and the conductivity gradient becomes steeper. (7) The convergence of the Hall current gives rise to divergent electric field near the steep gradient of the conductivity. (8) Due to the divergent electric field, magnetospheric plasma moves counterclockwise at low altitude (in the Northern Hemisphere). (9) The additional flow vorticity generates a localized upward FAC at low altitudes, which may manifest WTS, and redistributes the ionospheric current and conductivity. Thus, WTS may be maintained in a self-consistent manner, and be a natural consequence of the overflow of the Hall current.

  16. Simulation of the westward traveling surge and Pi 2 pulsations during substorms

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Sun, W.

    1985-01-01

    The westward traveling surge and the Pi2 pulsations are simulated as a consequence of an enhanced magnetospheric convection in a model of magnetosphere coupling. The coupling is characterized by the bouncing of Alfven waves launched by the enhanced convection. The reflection of Alfven waves from the ionosphere is treated in which the height-integrated conductivity is allowed to be highly nonuniform and fully anisotropic. The reflection of Alfven waves from the magnetosphere is characterized by the coefficient Rm, depending on whether the field lines are open or closed. The conductivity in the model is self-consistently enhanced with increasing upward field-aligned current density. The results of the simulation, including the convection pattern, the electrojets, the field-aligned current, the conductivity enhancement, the oscillation of the westward electrojet, and the average speed of the westward surge are in reasonable agreement with the features of the westward traveling surge and the Pi 2 pulsations observed during substorms.

  17. On the relationship between the energetic particle flux morphology and the change in the magnetic field magnitude during substorms

    NASA Technical Reports Server (NTRS)

    Lopez, R. E.; Lui, A. T. Y.; Sibeck, D. G.; Takahashi, K.; Mcentire, R. W.

    1989-01-01

    The relationship between the morphology of energetic particle substorm injections and the change in the magnetic field magnitude over the course of the event is examined. Using the statistical relationships between the magnetic field during the growth phase and the change in the field magnitude during substorms calculated by Lopez et al. (1988), a limited number of dispersionless ion injections observed by AMPTE CCE are selected. It is argued that this limited set is representative of a large set of events and that the conclusions drawn from examining those events are valid for substorms in general in the inner magnetosphere. It is demonstrated that in an event when CCE directly observed the disruption of the current sheet, the particle and field data show that the region of particle acceleration was highly turbulent and was temporally, and perhaps spatially, limited and that the high fluxes of energetic particles are qualitatively associated with intense inductive electric fields.

  18. Quantifying the spatio-temporal correlation during a substorm using dynamical networks formed from the SuperMAG database of ground based magnetometer stations.

    NASA Astrophysics Data System (ADS)

    Dods, J.; Chapman, S. C.; Gjerloev, J. W.; Barnes, R. J.

    2014-12-01

    The overall morphology and dynamics of magnetospheric substorms is well established in terms of observed qualitative auroral features and signatures seen in ground based magnetometers. The detailed evolution of a given substorm is captured by typically ~100 ground based magnetometer observations and this work seeks to synthesise all these observations in a quantitative manner. We present the first analysis of the full available set of ground based magnetometer observations of substorms using dynamical networks. SuperMAG offers a database containing ground station magnetometer data at a cadence of 1min from 100s stations situated across the globe. We use this data to form dynamic networks which capture spatial dynamics on timescales from the fast reconfiguration seen in the aurora, to that of the substorm cycle. Windowed linear cross-correlation between pairs of magnetometer time series along with a threshold is used to determine which stations are correlated and hence connected in the network. Variations in ground conductivity and differences in the response functions of magnetometers at individual stations are overcome by normalizing to long term averages of the cross-correlation. These results are tested against surrogate data in which phases have been randomised. The network is then a collection of connected points (ground stations); the structure of the network and its variation as a function of time quantify the detailed dynamical processes of the substorm. The network properties can be captured quantitatively in time dependent dimensionless network parameters and we will discuss their behaviour for examples of 'typical' substorms and storms. The network parameters provide a detailed benchmark to compare data with models of substorm dynamics, and can provide new insights on the similarities and differences between substorms and how they correlate with external driving and the internal state of the magnetosphere.

  19. Magnetic flux transfer in the 5 April 2010 Galaxy 15 substorm: an unprecedented observation

    NASA Astrophysics Data System (ADS)

    Connors, M.; Russell, C. T.; Angelopoulos, V.

    2011-03-01

    At approximately 08:25 UT on 5 April 2010, a CME-driven shock compressed Earth's magnetosphere and applied about 15 nT of southward IMF for nearly an hour. A substorm growth phase and localized dipolarization at 08:47 UT were followed by large dipolarizations at 09:03 UT and 09:08 UT, observed by GOES West (11) in the midnight sector, and by three THEMIS spacecraft near X=-11, Y=-2 RE. A large electric field at the THEMIS spacecraft indicates so much flux transfer to the inner magnetosphere that "overdipolarization" took place at GOES 11. This transfer is consistent with the ground and space magnetic signature of the substorm current wedge. Significant particle injections were also observed. The ensemble of extreme geophysical conditions, never previously observed, is consistent with the Near-Earth Neutral Line interpretation of substorms, and subjected the Galaxy 15 geosynchronous satellite to space weather conditions which appear to have induced a major operational anomaly.

  20. Global Simulation of Proton Precipitation Due to Field Line Curvature During Substorms

    NASA Technical Reports Server (NTRS)

    Gilson, M. L.; Raeder, J.; Donovan, E.; Ge, Y. S.; Kepko, L.

    2012-01-01

    The low latitude boundary of the proton aurora (known as the Isotropy Boundary or IB) marks an important boundary between empty and full downgoing loss cones. There is significant evidence that the IB maps to a region in the magnetosphere where the ion gyroradius becomes comparable to the local field line curvature. However, the location of the IB in the magnetosphere remains in question. In this paper, we show simulated proton precipitation derived from the Field Line Curvature (FLC) model of proton scattering and a global magnetohydrodynamic simulation during two substorms. The simulated proton precipitation drifts equatorward during the growth phase, intensifies at onset and reproduces the azimuthal splitting published in previous studies. In the simulation, the pre-onset IB maps to 7-8 RE for the substorms presented and the azimuthal splitting is caused by the development of the substorm current wedge. The simulation also demonstrates that the central plasma sheet temperature can significantly influence when and where the azimuthal splitting takes place.

  1. Particle Energization During Magnetic Storms with Steady Magnetospheric Convection

    NASA Astrophysics Data System (ADS)

    Kissinger, J.; Kepko, L.; Baker, D. N.; Kanekal, S. G.; Li, W.; McPherron, R. L.; Angelopoulos, V.

    2013-12-01

    Relativistic electrons pose a space weather hazard to satellites in the radiation belts. Although about half of all geomagnetic storms result in relativistic electron flux enhancements, other storms decrease relativistic electron flux, even under similar solar wind drivers. Radiation belt fluxes depend on a complex balance between transport, loss, and acceleration. A critically important aspect of radiation belt enhancements is the role of the 'seed' population--plasma sheet particles heated and transported Earthward by magnetotail processes--which can become accelerated by wave-particle interactions with chorus waves. While the effect of substorms on seed electron injections has received considerable focus, in this study we explore how quasi-steady convection during steady magnetospheric convection (SMC) events affects the transport and energization of electrons. SMC events are long-duration intervals of enhanced convection without any substorm expansions, and are an important mechanism in coupling magnetotail plasma populations to the inner magnetosphere. We detail the behavior of the seed electron population for stormtime SMC events using the Van Allen Probes in the outer radiation belt and THEMIS in the plasma sheet and inner magnetosphere. Together, the two missions provide the ability to track particle transport and energization from the plasma sheet into the radiation belts. We present SMC events with Van Allen Probes/THEMIS conjunctions and compare plasma sheet fast flows/enhanced transport to radiation belt seed electron enhancements. Finally we utilize statistical analyses to quantify the relative importance of SMC events on radiation belt electron acceleration in comparison to isolated substorms.

  2. Effects of Finite Element Resolution in the Simulation of Magnetospheric Particle Motion

    NASA Technical Reports Server (NTRS)

    Hansen, Richard

    2006-01-01

    This document describes research done in conjunction with a degree program. The purpose of the research was to compare particle trajectories in a specified set of global electric and magnetic fields; to study the effect of mesh spacing, resulting in an evaluation of adequate spacing resolution; and to study time-dependent fields in the context of substorm dipolarizations of the magnetospheric tail.

  3. Stepwise tailward retreat of magnetic reconnection: THEMIS observations of an auroral substorm

    NASA Astrophysics Data System (ADS)

    Ieda, A.; Nishimura, Y.; Miyashita, Y.; Angelopoulos, V.; Runov, A.; Nagai, T.; Frey, H. U.; Fairfield, D. H.; Slavin, J. A.; Vanhamäki, H.; Uchino, H.; Fujii, R.; Miyoshi, Y.; Machida, S.

    2016-05-01

    Auroral stepwise poleward expansions were clarified by investigating a multiple-onset substorm that occurred on 27 February 2009. Five successive auroral brightenings were identified in all-sky images, occurring at approximately 10 min intervals. The first brightening was a faint precursor. The second brightening had a wide longitude; thus, it represented the Akasofu substorm onset. Other brightenings expanded poleward; thus, they were interpreted to be auroral breakups. These breakups occurred stepwise; that is, later breakups were initiated at higher latitudes. Corresponding reconnection signatures were studied using Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations between 8 and 24 RE down the magnetotail. The Akasofu substorm onset was not accompanied by a clear reconnection signature in the tail. In contrast, the three subsequent auroral breakups occurred simultaneously (within a few minutes) with three successive fast flows at 24 RE; thus, these were interpreted to be associated with impulsive reconnection episodes. These three fast flows consisted of a tailward flow and two subsequent earthward flows. The flow reversal at the second breakup indicated that a tailward retreat of the near-Earth reconnection site occurred during the substorm expansion phase. In addition, the earthward flow at the third breakup was consistent with the classic tailward retreat near the end of the expansion phase; therefore, the tailward retreat is likely to have occurred in a stepwise manner. We interpreted the stepwise characteristics of the tailward retreat and poleward expansion to be potentially associated by a stepwise magnetic flux pileup.

  4. Shape-Constrained Sparse and Low-Rank Decomposition for Auroral Substorm Detection.

    PubMed

    Yang, Xi; Gao, Xinbo; Tao, Dacheng; Li, Xuelong; Han, Bing; Li, Jie

    2016-01-01

    An auroral substorm is an important geophysical phenomenon that reflects the interaction between the solar wind and the Earth's magnetosphere. Detecting substorms is of practical significance in order to prevent disruption to communication and global positioning systems. However, existing detection methods can be inaccurate or require time-consuming manual analysis and are therefore impractical for large-scale data sets. In this paper, we propose an automatic auroral substorm detection method based on a shape-constrained sparse and low-rank decomposition (SCSLD) framework. Our method automatically detects real substorm onsets in large-scale aurora sequences, which overcomes the limitations of manual detection. To reduce noise interference inherent in current SLD methods, we introduce a shape constraint to force the noise to be assigned to the low-rank part (stationary background), thus ensuring the accuracy of the sparse part (moving object) and improving the performance. Experiments conducted on aurora sequences in solar cycle 23 (1996-2008) show that the proposed SCSLD method achieves good performance for motion analysis of aurora sequences. Moreover, the obtained results are highly consistent with manual analysis, suggesting that the proposed automatic method is useful and effective in practice. PMID:25826810

  5. Boundary layers of the earth's outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Frank, L. A.

    1984-01-01

    The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.

  6. Transport and acceleration of plasma in the magnetospheres of Earth and Jupiter and expectations for Saturn

    NASA Astrophysics Data System (ADS)

    Kivelson, M. G.

    The first comparative magnetospheres conference was held in Frascati, Italy thirty years ago this summer, less than half a year after the first spacecraft encounter with Jupiter's magnetosphere (Formisano, V. (Ed.), The Magnetospheres of the Earth and Jupiter, Proceedings of the Neil Brice Memorial Symposium held in Frascati, Italy, May 28-June 1, 1974. D. Reidel Publishing Co., Boston, USA, 1975). Disputes highlighted various issues still being investigated, such as how plasma transport at Jupiter deviates from the prototypical form of transport at Earth and the role of substorms in Jupiter's dynamics. Today there is a wealth of data on which to base the analysis, data gathered by seven missions that culminated with Galileo's 8-year orbital tour. We are still debating how magnetic flux is returned to the inner magnetosphere following its outward transport by iogenic plasma. We are still uncertain about the nature of sporadic dynamical disturbances at Jupiter and their relation to terrestrial substorms. At Saturn, the centrifugal stresses are not effective in distorting the magnetic field, so in some ways the magnetosphere appears Earthlike. Yet the presence of plasma sources in the close-in equatorial magnetosphere parallels conditions at Jupiter. This suggests that we need to study both Jupiter and Earth when thinking about what to anticipate from Cassini's exploration of Saturn's magnetosphere. This paper addresses issues relevant to plasma transport and acceleration in all three magnetospheres.

  7. Global numerical simulation of the growth phase and the expansion onset for a substorm observed by Viking

    SciTech Connect

    Fedder, J.A.; Slinker, S.P.; Lyon, J.G.

    1995-10-01

    The authors report the first global magnetohydrodynamic (MHD) simulation of an actual magnetospheric substorm, which was recorded by the Viking spacecraft on October 19, 1986. The simulation is driven by IMP 8 solar wind parameters measured upstream of the Earth`s bow shock. The substorm, which had expansion onset at 1132 UT, was caused by a brief period of southward interplanetary magnetic field (IMF) and two weak solar wind shocks. The simulation model includes a self-consistent auroral ionospheric conductance depending directly on the MHD magnetospheric plasma parameters and magnetic field. Synthetic auroral emissions, derived from simulation results, are compared to the Viking images, which show considerable dayside activity preceding the substorm. The authors also compare model-derived synthetic AU and AL indices to geomagnetic measurements. The simulation results are seen to be in reasonable agreement with the observations throughout the growth phase and expansion onset. Moreover, the results allow the authors to form conclusions concerning which essential processes were responsible for the substorm occurrence. These results are a highly encouraging first step leading toward development of a space weather forecasting methodology based on the directly measured solar input. 19 refs., 5 figs.

  8. Multipoint observations of a small substorm

    SciTech Connect

    Lopez, R.E. Applied Research Corp., Landover, MD ); Luehr, H. ); Anderson, B.J.; Newell, P.T.; McEntire, R.W. )

    1990-11-01

    In this paper the authors present multipoint observations of a small substorm which occurred just after 0110 UT on April 25, 1985. The observations were made by spacecraft (AMPTE CCE, AMPTE IRM, DMSP F6, and DMSP F7), ground auroral stations (EISCAT magnetometer cross, Syowa, Narssarssuaq, Great Whale River, and Fort Churchill), and mid-latitude stations (Furstenfeldbruck, Toledo, and Argentine Island). These data provide them with a broad range of observations, including the latitudinal extent of the polar cap, visual identification of substorm aurorae and the magnetic perturbations produced directly beneath them, in situ magnetic field and energetic particle observations of the disruption of the cross-tail current sheet, and observations concerning the spatial expansion of the current disruption region from two radially aligned spacecraft. The DMSP data indicate that the event took place during a period when the polar cap was relatively contracted, yet the disruption of the current sheet was observed by CCE at 8.56 R{sub E}. They have been able to infer a considerable amount of detail concerning the structure and westward expansion of the auroral features associated with the event, and they show that those auroral surges were located more than 10{degree} equatorward of the boundary between open and closed field lines. Moreover, they present evidence that the current sheet disruption observed by CCE in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at Syowa. Furthermore, the observations strongly imply that disruption of the cross-tail current began in the near-Earth region and that it had a component of expansion which was radially antisunward.

  9. A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.; Mankofsky, A.; Chang, C.-L.; Papadopoulos, K.; Wu, C. S.

    1990-01-01

    A linear analysis is performed to investigate the kinetic cross-field streaming instability in the earth's magnetotail neutral sheet region. Numerical solution of the dispersion equation shows that the instability can occur under conditions expected for the neutral sheet just prior to the onset of substorm expansion. The excited waves are obliquely propagating whistlers with a mixed polarization in the lower hybrid frequency range. The ensuing turbulence of this instability can lead to a local reduction of the cross-tail current causing it to continue through the ionosphere to form a substorm current wedge. A substorm expansion onset scenario is proposed based on this instability in which the relative drift between ions and electrons is primarily due to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is within the range of electric field values detected in the neutral sheet region during substorm intervals. The skew in local time of substorm onset location and the three conditions under which substorm onset is observed can be understood on the basis of the proposed scenario.

  10. Characterizing the Magnetospheric State for Sawtooth Events

    NASA Astrophysics Data System (ADS)

    Fung, S. F.; Tepper, J. A.; Cai, X.

    2015-12-01

    Magnetospheric sawtooth events, first identified in the early 1990's, are named for their characteristic appearance of multiple quasi-periodic intervals of slow decrease followed by sharp increase of proton energy fluxes in the geosynchronous region. The successive proton flux decrease-and-increase intervals have been interpreted as recurrences of stretching and dipolarization, respectively, of the nightside geomagnetic field [Reeves et al., 2003]. Due to their often-extended intervals with 2- 10 cycles, sawteeth occurrences are sometimes referred to as a magnetospheric mode [Henderson et al., 2006]. Studies over the past two decades of sawtooth events (both event and statistical) have yielded a wealth of information on the conditions for the onset and occurrence of sawtooth events, but the occurrences of sawtooth events during both storm and non-storm periods suggest that we still do not fully understand the true nature of sawtooth events [Cai et al., 2011]. In this study, we investigate the characteristic magnetospheric state conditions [Fung and Shao, 2008] associated with the beginning, during, and ending intervals of sawtooth events. Unlike previous studies of individual sawtooth event conditions, magnetospheric state conditions consider the combinations of both magnetospheric drivers (solar wind) and multiple geomagnetic responses. Our presentation will discuss the most probable conditions for a "sawtooth state" of the magnetosphere. ReferencesCai, X., J.-C. Zhang, C. R. Clauer, and M. W. Liemohn (2011), Relationship between sawtooth events and magnetic storms, J. Geophys. Res., 116, A07208, doi:10.1029/2010JA016310. Fung, S. F. and X. Shao, Specification of multiple geomagnetic responses to variable solar wind and IMF input, Ann. Geophys., 26, 639-652, 2008. Henderson, M. G., et al. (2006), Magnetospheric and auroral activity during the 18 April 2002 sawtooth event, J. Geophys. Res., 111, A01S90, doi:10.1029/2005JA011111. Reeves, G. D., et al. (2004), IMAGE

  11. Association of plasma sheet variations with auroral changes during substorms

    SciTech Connect

    Hones, E.W. Jr.; Craven, J.D.; Frank, L.A.; Parks, G.K.

    1988-01-01

    Images of the southern auroral oval taken by the University of Iowa auroral imaging instrumentation on the Dynamics Explorer 1 satellite during an isolated substorm are correlated with plasma measurements made concurrently by the ISEE 1 satellite in the magnetotail. Qualitative magnetic field configuration changes necessary to relate the plasma sheet boundary location to the latitude of the auroras are discussed. Evidence is presented that the longitudinal advances of the auroras after expansive phase onset are mappings of a neutral line lengthening across the near-tail. We observe a rapid poleward auroral surge, occurring about 1 hour after expansive phase onset, to coincide with the peak of the AL index and argue that the total set of observations at that time is consistent with the picture of a /open quotes/poleward leap/close quotes/ of the electrojet marking the beginning of the substorm's recovery. 9 refs. 3 figs.

  12. The energy coupling function and the power generated by the solar wind-magnetosphere dynamo

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

    1980-01-01

    A solar wind parameter epsilon, known as the energy coupling function, has been shown to correlate with the power consumption in the magnetosphere. It is shown in the present paper that the parameter epsilon can be identified semi-quantitatively as the dynamo power delivered from the solar wind to an open magnetosphere. This identification not only provides a theoretical basis for the energy coupling function, but also constitutes an observational verification of the solar wind-magnetosphere dynamo along the magnetotail. Moreover, one can now conclude that a substorm results when the dynamo power exceeds 10 to the 18th erg/s.

  13. Plasmasphere pulsations observed simultaneously by midlatitude SuperDARN radars, ground magnetometers and THEMIS spacecraft during an auroral substorm

    NASA Astrophysics Data System (ADS)

    Ruohoniemi, J. M.; Shi, X.; Baker, J. B. H.; Frissell, N. A.; Hartinger, M.; Liu, J.

    2015-12-01

    We present simultaneous ground and space-based observations of ultra-low frequency (ULF) pulsations which occurred during an auroral substorm on September 25th, 2014. Expansion phase onset began at 06:04 UT at which time three midlatitude SuperDARN radars observed strong pulsations in the Pi2 frequency range with peak to peak amplitude reaching as high as 1km/s. Similar pulsations occurred during a later auroral intensification which started at 06:20 UT. Both sets of pulsations were detected in a region of radar backscatter located inside the subauroral polarization stream (SAPS) equatorward of the auroral oval specified by THEMIS all sky imagers and inside the midlatitude density trough as mapped by GPS/TEC measurements. The amplitude of the pulsations was large enough to reverse the direction of the SAPS flow from westward to eastward. Similar pulsations were detected by electric field instrument aboard the THEMIS probe D located inside the plasmasphere. Simultaneous observations from several low-latitude ground magnetometers (some located on the dayside) further illustrate the global nature of the pulsations and suggest they may have been associated with a plasmaspheric cavity resonance (PCR). Pulsed tailward plasma flow observed by THEMIS probe E at the geosynchronous orbit suggests that the compressional energy to generate the PCR was from the Bursty Bulk Flows (BBFs) braking against the magnetospheric dipolar region.

  14. Simultaneous ground-satellite observation of Pi 2 pulsations associated with upward/downward FACs of the substorm current wedge

    NASA Astrophysics Data System (ADS)

    Uozumi, T.; Yumoto, K.; Imajo, S.; Koga, K.; Obara, T.; Baishev, D. G.; Shevtsov, B. M.; Milling, D. K.; Mann, I. R.; Ikeda, A.; Abe, S.; Yoshikawa, A.; Kawano, H.

    2011-12-01

    The formation of a substorm current wedge (SCW) is one of the fundamental processes in the expansion phase of the magnetospheric substorm [e.g. McPherron et al., 1973]. Uozumi et al. [2011] found that the ground Pi 2 timeseries had high coherencies with simultaneously observed AKR timeseries, regardless of whether the Pi 2 timeseries were associated with upward FAC or downward FAC; this fact suggests that the upward SCW and the downward SCW oscillated in a synchronized manner. This aspect was deduced from ground observations, and should be verified by a simultaneous observation on the ground and in the magnetosphere. In order to clarify the timing relation of Pi 2s that are associated with SCW oscillations, we made a comparative study by combining the ground and satellite data. We analyzed simultaneous ground-satellite observation of Pi 2 pulsation at the ETS-VIII geosynchronous orbit [Koga and Obara, 2008] and at MAGDAS/CPMN [Yumoto and the MAGDAS Group, 2006] high-, middle- and low-latitude stations. We picked up a Pi 2 event that exhibited a high coherency in the waveform among the ground and satellite Pi 2. A typical Pi 2 occurred around 1121UT on July 28, 2008. MLT of each ground station and ETS-VIII at the occurrence of the Pi 2 was as follows: TIK: 19.5h, KUJ: 20.0h, ETS-VIII: 20.8h, ZYK: 20.9h, MGD: 21.0h, PTK: 21.5h and WAD: 3.7h. Characteristics of the Pi 2 event are summarized as follows: (1) the initial deflection of the ground Pi 2s and magnetic bay variations in the D (eastward) component indicate the signature of the upward (at TIK, ZYK, MGD and PTK) and downward (at WAD) FAC of the SCW. (2) Pi 2 oscillated in- or 180deg out-of-phase among the D on the ground and N (eastward) components at the geosynchronous altitude (correlation coefficient: |Υ|> 0.75, phase delay: |ΔT|<10s). (3) Pi 2 oscillations in the H (northward) and P (parallel to the earth rotation axis) component exhibited phase (time) difference among them (|ΔT| < ~50s). By taking into

  15. Some aspects of the relation between Pi 1-2 magnetic pulsations observed at L - 1. 3-2. 1 on the ground and substorm-associated magnetic field variations in the near-earth magnetotail observed by AMPTE CCE

    SciTech Connect

    Yumoto, K.; Saito, T. ); Takahashi, K.; Potemra, T.A.; Zanetti, L.J. ); Menk, F.W.; Fraser, B.J. )

    1989-04-01

    The relation between Pi 1-2 pulsations on the ground and substorm-associated magnetic field variations in space has been studied using data obtained on the ground at low-latitude conjugate stations (L = 1.3-2.1) and in the near-Earth magnetotail by the AMPTE CCE spacecraft. The ground-based data were acquired in a campaign period from July 20 to September 16, of 1986, during which the apogee of CCE (8.8 R{sub E}) was located between 2330 and 0230 hours magnetic local time. Of 16 clear magnetic field dipolarizations observed at CCE, all had a corresponding Pi 2 pulsation on the ground, with a time lag of +1 to {minus}7 min. For most (13) of these cases, the time lag was equal to or shorter than 2 min. However, the authors also found Pi 2 pulsations that do not accompany a dipolarization at CCE. These results are consistent with previous observations, which showed that Pi 2 pulsations are a global indicator of the expansion phase onset of a substorm, whereas dipolarizations occur in a limited region in the near-Earth magnetotail. One of the 16 events, which occurred on August 28, 1986, is studied in detail because a 13-s Pi 1 pulsation was observed on the ground in addition to an ordinary Pi 2 pulsation. For this event, CCE also observed a {approximately} 13-s oscillation at {approximately} 8.1 R{sub E} in the midplane of the magnetorail near midnight (Takahashi et a., 1987). They suggest that field line resonance driven by a quasi-monochromatic oscillation in the near-Earth tail is the cause of the Pi 1 pulsation observed on the ground. The commonly observed Pi 2 pulsations could be attributed to other wave excitation mechanisms including transient response of the magnetospheric cavity to a substorm-associated impulse.

  16. Elements of M-I Coupling in Repetitive Substorm Activity Driven by Interplanetary CMEs

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Sandholt, P. E.

    2014-12-01

    By means of case studies we explore key elements of the magnetosphere-ionosphere current system associated with repetitive substorm activity during persistent strong forcing by ICMEs. Our approach consists of a combination of the magnetospheric and ionospheric perspectives on the substorm activity. The first aspect is the near-Earth plasma sheet with its repetitive excitations of the substorm current wedge, as monitored by spacecraft GOES-10 when it traversed the 2100-0300 MLT sector, and its coupling to the westward auroral electrojet (WEJ) centered near midnight during the stable interplanetary (IP) conditions. The second aspect is the excitation of Bostrom type II currents maximizing at dusk and dawn and their associated ionospheric Pedersen current closure giving rise to EEJ (WEJ) events at dusk (dawn). As documented in our study, this aspect is related to the braking phase of Earthward-moving dipolarization fronts-bursty bulk flows. We follow the magnetospheric flow/field events from spacecraft Geotail in the midtail (X = - 11 Re) lobe to geostationary altitude at pre-dawn MLTs (GOES 10). The associated M-I coupling is obtained from ground-satellite conjunctions across the double auroral oval configuration along the meridian at dusk. By this technique we distinguish between ionospheric manifestations in three latitude regimes: (i) auroral oval south, (ii) auroral oval north, and (iii) polar cap. Regime (iii) is characterized by events of enhanced antisunward convection near the polar cap boundary (flow channel events) and in the central polar cap (PCN-index events). The repetitive substorm activity is discussed in the context of the level of IP driving as given by the geoeffective IP electric field (E_KL), magnetotail reconnection (inferred from the PCN-index and spacecraft Wind at X = - 77 Re) and the storm SYM-H index. We distinguish between different variants of the repetitive substorm activity, giving rise to electrojet (AL)-plasma convection (PCN) events

  17. Propagation of BBFs and Dipolarization Fronts in the Global MHD simulation of February 27, 2009 Substorm

    NASA Astrophysics Data System (ADS)

    Ge, Y.; Raeder, J.; Angelopoulos, V.; Gilson, M. L.; Runov, A.

    2010-12-01

    A global MHD simulation has been performed to investigate the THEMIS substorm on February 27, 2009. During this substorm the conjugated observations from the space and on the THEMIS ground observatories are available. The location and time of this substorm onset can be determined based on these observations. The initial auroral brightening is found at around 07:49 UT in the field of view of Fort Smith station (FSMI), with a pre-existing auroral arc located equatorward. A couple minutes later, the in situ observations recorded a sharp dipolarization front sunward passing through THEMIS spacecraft, which travels almost 10 RE in the magnetotail. In this study our global MHD model, i.e., OpenGGCM, driven by the real-time solar wind/IMF conditions, is able to reproduce the key features of these substorm signatures, including the auroral breakup at FSMI with the same onset time as the observations, and a strong earthward Bursty Bulk Flow (BBF) and dipolarization fronts that cause the substorm onset signatures. It is found in the simulation that the auroral breakup is caused by the strong flow shear and the flow vortices which form as the BBF moves earthward. Investigation of the tail BBF and its dipolarization front (DF) reveals that the bipolar change of the Bz component ahead of the DF can be produced by the interaction between two distinct plasmas from separate X lines: the anti-sunward moving southward flux tubes in the tailward flows emanating from an inner magnetic reconnection region, and the sunward traveling dipolarized tubes within the front of a strong earthward BBF that originates in a mid-tail reconnection region. The rebound and oscillations of the intruding BBF reported by the recent THEMIS observations are also seen in the simulation when the BBF encounters the high-pressure inner magnetosphere.

  18. The Differences in Onset Time of Conjugate Substorms

    NASA Astrophysics Data System (ADS)

    Weygand, J. M.; Zesta, E.; McPherron, R. L.; Hsu, T. S.

    2014-12-01

    The auroral electrojet (AE) index is traditionally calculated from 13 ground magnetometer stations located around the typical northern auroral oval location. Similar coverage in the Southern Hemisphere index (SAE) does not exist, so the AE calculation has only been performed using Northern Hemisphere data. In the present study, we use seven southern auroral region ground magnetometers as well as their conjugate Northern Hemisphere data to calculate conjugate AE indices for 274 days covering all four seasons. With this dataset over 1200 substorm onsets have been identified in the SAE index using the technique of Hsu et al. [2012]. A comparison of the SAE index with the world data center standard AE index shows that the substorm onsets do not always occur at the same time with differences on the order of several minutes. In this study we examine the differences in the onset time and the reason for those differences using our conjugate AE indices and using pairs of conjugate ground magnetometer stations. Specifically, we used the pair of stations at West Antarctica Ice Sheet Divide and Sanikiluaq, Canada and Syowa, Antarctica and Tjörnes, Iceland. The largest differences in onset time appear to be related to the IMF Bz and magnetic field line length. Differences on the order of minutes for the onset time of conjugate substorms have serious implications for substorm theories. The problem is that waves from a current disruption region to the mid tail, or flows from the mid tail to the current disruption region take the same amount of time (~2 minutes), which makes it difficult to decide where the onset disturbance is initiated, particularly when onset indicators have differences on the order of minutes.

  19. Acceleration of ions by electric field pulses in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Liu, J.; Angelopoulos, V.; Runov, A.

    2015-06-01

    Intense (˜5-15 mV/m), short-lived (≤1 min) electric field pulses have been observed to accompany earthward propagating, dipolarizing flux bundles (flux tubes with a strong magnetic field) before they are stopped by the strong dipole field. Using Time History of Events and Macroscale Interactions during Substorms observations and test particle modeling, we investigate particle acceleration around L shell ˜7-9 in the nightside magnetosphere and demonstrate that such pulses can effectively accelerate ions with tens of keV initial energy to hundreds of keV. This acceleration occurs because the ion gyroradius is comparable to the spatial scale of the localized electric field pulse at the leading edge of the flux bundle before it stops. The proposed acceleration mechanism can reproduce observed spectra of high-energy ions. We conclude that the electric field associated with dipolarizing flux bundles prior to their stoppage in the inner magnetosphere provides a natural site for intense local ion acceleration.

  20. Low energy electrons in the inner Earth's magnetosphere

    NASA Astrophysics Data System (ADS)

    Ganushkina, Natalia; Sillanpaa, Ilkka; Dugyagin, Stepan; Pitchford, David; Rodriguez, Juan; Runov, Andrei

    2016-04-01

    The fluxes of electrons with energies < 100 keV are not usually analyzed and modeled in details when studying the electron radiation belts. These fluxes constitute the low energy part of the seed population, which is critically important for radiation belt dynamics. Moreover, energetic electrons with energies less than about 100 keV are responsible for hazardous space-weather phenomena such as surface charging. The electron flux at these energies varies highly with geomagnetic activity and even during quiet-time periods. Significant variations in the low-energy electrons can be seen during isolated substorms, not related to any storm periods. Moreover, electron flux variations depend on the electron energy. Statistical analysis of AMC 12 CEASE II ESA instrument data (5-50 keV) and GOES MAGED data (40, 75, 150 keV) have revealed that electron fluxes increase by the same order of magnitude during isolated substorms with 200 nT of AE index and storm-time substorms with 1200 nT of AE index. If substorms are represented as electromagnetic pulses which transport and accelerate electrons additionally, how are their amplitudes determined, if not related directly to a substorm's strength? Another factor of crucial importance is the specification of boundary conditions in the electron plasma sheet. We developed a new model for electron number density and temperature in the plasma sheet as dependent on solar wind and IMF conditions based on THEMIS data analysis. We present observational and modeling results on low energy electrons in the inner magnetosphere with newly-developed, time-dependent boundary conditions with a special focus on the role of substorms for electron transport and acceleration.

  1. TEMPEST: Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories--A Proposal to the Medium Class Explorer Program

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The objective of the Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories (TEMPEST) mission is to understand the nature and causes of magnetic storm conditions in the magnetosphere whether they be manifested classically in the buildup of the ring current, or (as recently discovered) by storms of relativistic electrons that cause the deep dielectric charging responsible for disabling satellites in synchronous orbit, or by the release of energy into the auroral ionosphere and the plasma sheet during substorms.

  2. Multipoint observations by CUTLASS radar, Doppler and oblique ionospheric sounding methods during a magnetospheric storm

    NASA Astrophysics Data System (ADS)

    Blagoveshchensky, D. V.; Kornienko, V. A.; Lester, M.; Stocker, A. J.; Warrington, E. M.

    Experimental results during a magnetospheric storm on April 28-29, 2001, obtained in course of High-rate SolarMax IGS/GPS campaign are presented. The analysis completed to date has given rise to the following conclusions. (1) During the expansion and recovery phases of a substorm (which formed part of the storm) the width of the Doppler spectrum on two paths, Murmansk - St. Petersburg and London - St. Petersburg, has a maximum and lies within 10 - 30 Hz, whreas under quiet conditions it varied from 1 to 3 Hz. The wide spectrum is associated chiefly with increasing the intensity of ionospheric inhomogeneities during disturbed conditions, although to some extent, the spectral width also depends on the mechanism of propagation on the path. (2) Observations made by the CUTLASS radar located at Hankasalmi, Finland, during the magnetic storm illustrate some of the physical processes in the ionosphere and variations of parameters of its irregularities caused by an impact of geophysical disturbances. The characteristics of the ionospheric irregularities derived from the radar data are consistent with estimations made by the Doppler method. (3) The variations of radio wave propagation parameters observed on OIS data during the storm on high and middle latitude paths (Murmansk- St. Petersburg and Inskip - Leicester) have some similar features which occur when the signal is reflected from the F2-layer. Differences, however, occur for signals reflected from the ionospheric E-layer. (4) The results of these experiments and the derived characteristics could be useful in understanding magnetosphere-ionosphere coupling, in Space Weather problems, and for forecasting the ionospheric state during moderate intensity magnetospheric disturbances.

  3. Trajectory Traces of Charged Particles in the Magnetosphere

    NASA Technical Reports Server (NTRS)

    Ejiri, M.

    1976-01-01

    The characteristic enhancements of ring current particles with energies of about 1 to 100 keV, associated with magnetospheric substorms, were observed by Explorer 45 around the plasmapause in the afternoon to midnight region, and showed the characteristic structure called a 'nose' in the proton spectrograms. The motion of these particles in the equatorial magnetosphere, under a recently proposed convection electric field and a dipole magnetic field is described. Approximate equations of a bounce period, a second adiabatic invariant, and a bounce-average azimuthal velocity are given with inaccuracies less than about 0.001 for all pitch angles. The complete set of flow patterns of 90 deg pitch angle particles is also presented by means of stagnation lines through which radial drifts and/or azimuthal drifts change their directions. The particle tracings in the magnetosphere give a basic concept to explain the observed nose characteristics.

  4. Plasmas in Saturn's magnetosphere

    NASA Technical Reports Server (NTRS)

    Frank, L. A.; Burek, B. G.; Ackerson, K. L.; Wolfe, J. H.; Mihalov, J. D.

    1980-01-01

    The solar wind plasma analyzer on board Pioneer 2 provides first observations of low-energy positive ions in the magnetosphere of Saturn. Measurable intensities of ions within the energy-per-unit charge (E/Q) range 100 eV to 8 keV are present over the planetocentric radial distance range about 4 to 16 R sub S in the dayside magnetosphere. The plasmas are found to be rigidly corotating with the planet out to distances of at least 10 R sub S. At radial distances beyond 10 R sub S, the bulk flows appear to be in the corotation direction but with lesser speeds than those expected from rigid corotation. At radial distances beyond the orbit of Rhea at 8.8 R sub S, the dominant ions are most likely protons and the corresponding typical densities and temperatures are 0.5/cu cm and 1,000,000 K, respectively, with substantial fluctuations. It is concluded that the most likely source of these plasmas in the photodissociation of water frost on the surface of the ring material with subsequent ionization of the products and radially outward diffusion. The presence of this plasma torus is expected to have a large influence on the dynamics of Saturn's magnetosphere since the pressure ratio beta of these plasmas approaches unity at radial distances as close to the planet as 6.5 R sub S. On the basis of these observational evidences it is anticipated that quasi-periodic outward flows of plasma, accompanied with a reconfiguration of the magnetosphere beyond about 6.5 R sub S, will occur in the local night sector in order to relieve the plasma pressure from accretion of plasma from the rings.

  5. Substorm classification with the WINDMI model

    NASA Astrophysics Data System (ADS)

    Horton, W.; Weigel, R. S.; Vassiliadis, D.; Doxas, I.

    The results of a genetic algorithm optimization of the WINDMI model using the Blanchard-McPherron substorm data set is presented. A key result from the large-scale computations used to search for convergence in the predictions over the database is the finding that there are three distinct types of vx Bs -AL waveforms characterizing substorms. Type I and III substorms are given by the internally-triggered WINDMI model. The analysis reveals an additional type of event, called a type II substorm, that requires an external trigger as in the northward turning of the IMF model of Lyons (1995). We show that incorporating an external trigger, initiated by a fast northward turning of the IMF, into WINDMI, a low-dimensional model of substorms, yields improved predictions of substorm evolution in terms of the AL index. Intrinsic database uncertainties in the timing between the ground-based AL electrojet signal and the arrival time at the magnetopause of the IMF data measured by spacecraft in the solar wind prevent a sharp division between type I and II events. However, within these timing limitations we find that the fraction of events is roughly 40% type I, 40% type II, and 20% type III.

  6. On the role of ground-based observations in substorm research: Can one recognize the beast from its foot prints?

    NASA Astrophysics Data System (ADS)

    Kauristie, K.

    2003-04-01

    The first coordinated efforts of ground-based auroral observations were carried out already during the International Geophysical Year (IGY) 1957-1958, during which all-sky camera pictures and magnetometer data were collected from several stations in the northern polar regions. This huge amount of data were later organized by Syun-Ichi Akasofu to describe the original auroral substorm concept, main parts of which belong also to the wider magnetospheric substorm schema which started to build up when satellite observations became available. Also the IGY concept is still living strong as versatile networks of ground-based instruments support the ambitious international satellite missions (like Cluster or ILWS) investigating the different solar-terrestrial coupling processes. Many magnetospheric substorm processes have their own specific ionospheric signatures. Consequently, ground-based observations are often used to provide the background context that helps the interpretation of the localized magnetospheric satellite observations. The possibility to analyse phenomena of very different scale sizes is a further advantage. With the modern high-resolution imagers auroral structures of less than kilometer-scale can be analysed. On the other hand, with the combination of the data of the global SuperDARN network and several magnetometer networks the entire polar cap convection and current pattern can be monitored. The development of various data analysis tools and assimilation methods has pushed the interpretation of ground-based data towards more quantitative analysis and resulted in several important findings. In the presentation we will discuss the benefits and pitfalls of ground-based observations, review the most important contributions to substorm research, and envisage some of the future challenges.

  7. Physics of Substorm Growth Phase, Onset, and Dipolarization

    SciTech Connect

    C.Z. Cheng

    2003-10-22

    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.

  8. Studies of the substorm on March 12, 1991: 1. Structure of substorm activity and auroral ions

    NASA Astrophysics Data System (ADS)

    Lazutin, L. L.; Kozelova, T. V.; Meredith, N. P.; Danielides, M.; Kozelov, B. V.; Jussila, J.; Korth, A.

    2007-02-01

    The substorm on March 12, 1991 is studied using the data of ground-based network of magnetometers, all-sky cameras and TV recordings of aurora, and measurements of particle fluxes and magnetic field onboard a satellite in the equatorial plane. The structure of substorm activity and the dynamics of auroral ions of the central plasma sheet (CPS) and energetic quasi-trapped ions related to the substorm are considered in the first part. It is shown that several sharp changes in the fluxes and pitch-angle distribution of the ions which form the substorm ion injection precede a dipolarization of the magnetic field and increases of energetic electrons, and coincide with the activation of aurora registered 20° eastward from the satellite. A conclusion is drawn about different mechanisms of the substorm acceleration (injection) of electrons and ions.

  9. Multi-Scale Modeling of Magnetospheric Dynamics

    NASA Technical Reports Server (NTRS)

    Kuznetsova, M. M.; Hesse, M.; Toth, G.

    2012-01-01

    Magnetic reconnection is a key element in many phenomena in space plasma, e.g. Coronal mass Ejections, Magnetosphere substorms. One of the major challenges in modeling the dynamics of large-scale systems involving magnetic reconnection is to quantifY the interaction between global evolution of the magnetosphere and microphysical kinetic processes in diffusion regions near reconnection sites. Recent advances in small-scale kinetic modeling of magnetic reconnection significantly improved our understanding of physical mechanisms controlling the dissipation in the vicinity of the reconnection site in collisionless plasma. However the progress in studies of small-scale geometries was not very helpful for large scale simulations. Global magnetosphere simulations usually include non-ideal processes in terms of numerical dissipation and/or ad hoc anomalous resistivity. Comparative studies of magnetic reconnection in small scale geometries demonstrated that MHD simulations that included non-ideal processes in terms of a resistive term 11 J did not produce fast reconnection rates observed in kinetic simulations. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is nongyrotropic pressure effects with spatial scales comparable with the particle Larmor radius. We utilize the global MHD code BATSRUS and replace ad hoc parameters such as "critical current density" and "anomalous resistivity" with a physically motivated model of dissipation. The primary mechanism controlling the dissipation in the vicinity of the reconnection site in incorporated into MHD description in terms of non-gyrotropic corrections to the induction equation. We will demonstrate that kinetic nongyrotropic effects can significantly alter the global magnetosphere evolution. Our approach allowed for the first time to model loading/unloading cycle in response to steady southward IMF driving. The role of solar wind parameters and

  10. DYNAMICS OF STRONGLY TWISTED RELATIVISTIC MAGNETOSPHERES

    SciTech Connect

    Parfrey, Kyle; Beloborodov, Andrei M.; Hui, Lam

    2013-09-10

    Magnetar magnetospheres are believed to be strongly twisted due to shearing of the stellar crust by internal magnetic stresses. We present time-dependent axisymmetric simulations showing in detail the evolution of relativistic force-free magnetospheres subjected to slow twisting through large angles. When the twist amplitude is small, the magnetosphere moves quasi-statically through a sequence of equilibria of increasing free energy. At some twist amplitude the magnetosphere becomes tearing-mode unstable to forming a resistive current sheet, initiating large-scale magnetic reconnection in which a significant fraction of the magnetic free energy can be dissipated. This ''critical'' twist angle is insensitive to the resistive length scale. Rapid shearing temporarily stabilizes the magnetosphere beyond the critical angle, allowing the magnetosphere of a rapidly differentially rotating star to store and dissipate more free energy. In addition to these effects, shearing the surface of a rotating star increases the spindown torque applied to the star. If shearing is much slower than rotation, the resulting spikes in spindown rate can occur on timescales anywhere from the long twisting timescale to the stellar spin period or shorter, depending both on the stellar shear distribution and the existing distribution of magnetospheric twists. A model in which energy is stored in the magnetosphere and released by a magnetospheric instability therefore predicts large changes in the measured spindown rate before soft gamma repeater giant flares.

  11. Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude

    NASA Astrophysics Data System (ADS)

    Nosé, M.; Iyemori, T.; Wang, L.; Hitchman, A.; Matzka, J.; Feller, M.; Egdorf, S.; Gilder, S.; Kumasaka, N.; Koga, K.; Matsumoto, H.; Koshiishi, H.; Cifuentes-Nava, G.; Curto, J. J.; Segarra, A.; ćElik, C.

    2012-08-01

    Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40-150 s and irregular (damped) waveforms. It is well-known that pulsations of this type are clearly observed at mid- and low-latitude ground stations on the nightside at substorm onset. Therefore, with 1-s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find that significant enhancements of the Wp index mostly coincide with those of the other data. Thus the Wp index can be considered a good indicator of substorm onset. The Wp index, other geomagnetic indices, and geosynchronous satellite data are plotted in a stack for quick and easy search of substorm onset. The stack plots and digital data of the Wp index are available at the Web site (http://s-cubed.info) for public use. These products would be useful to investigate and understand space weather events, because substorms cause injection of intense fluxes of energetic electrons into the inner magnetosphere and potentially have deleterious impacts on satellites by inducing surface charging.

  12. Mercury's Dynamic Magnetosphere: What Have We Learned from MESSENGER?

    NASA Astrophysics Data System (ADS)

    Slavin, James A.

    2016-04-01

    Mercury's magnetosphere is created by the solar wind interaction with its dipolar, spin-axis aligned, northward offset intrinsic magnetic field. Structurally it resembles that of the Earth in many respects, but the magnetic field intensities and plasma densities are all higher at Mercury due to conditions in the inner solar system. Magnetospheric plasma at Mercury appears to be primarily of solar wind origin, i.e. H+ and He++, but with 10% Na+ derived from the exosphere. Solar wind sputtering and other processes promote neutrals from the regolith into the exosphere where they may be ionized and incorporated into the magnetospheric plasma population. At this point in time, about one year after MESSENGER's impact and one year prior to BepiColombo's launch, we review MESSENGER's observations of magnetospheric dynamics and structure. In doing so we will provide our best answers to the following six questions: Question #1: How do magnetosheath conditions at Mercury differ from what is found at the other planets? Question #2: How do conditions in Mercury's magnetosheath contribute to the dynamic nature of Mercury's magnetosphere? How does magnetopause reconnection at Mercury differ from what is seen at Earth? Are flux transfer events (FTEs) a major driver of magnetospheric convection at Mercury? Question #3: Does reconnection ever erode the dayside magnetosphere to the point where the subsolar region of the surface is exposed to direct solar wind impact? To what extent do induction currents driven in Mercury's interior limit the solar wind flux to the surface? Do FTEs contribute significantly to the solar wind flux reaching the surface? Question #4: What effects do heavy planetary ions have on Mercury's magnetosphere? Question #5: Does Mercury's magnetotail store and dissipate magnetic energy in a manner analogous to substorms at Earth? How is the process affected by the lack of an ionosphere and the expected high electrical resistivity of the crust? Question #6: How

  13. The Plasma Physics Processes that Drive Ring Current Enhancements during Geomagnetic Storms and Substorms

    NASA Astrophysics Data System (ADS)

    Cash, Michele Diane

    Geomagnetic storms result when energetic particles of solar and ionospheric origin fill Earth's inner magnetosphere and create a strong westward current, known as the ring current. This dissertation presents results from investigating the plasma dynamics that contribute to the development of Earth's ring current from ionospheric outflow of H+ and O+ ions, and the role of ring current enhancements in the generation of geomagnetic storms and substorms. Modeling was carried via a combined multifluid and particle approach, which enables us to resolve the small-scale dynamics that are key to particle energization within the context of the global magnetosphere. The results presented in this dissertation substantially contribute to our understanding of the development and composition of the ring current during geomagnetic storms and substorms, and offer insight into the ionospheric sources regions for ring current ions, as well as the processes through which these particles are energized, injected, and trapped within the inner magnetosphere. This thesis presents results that show how small-scale particle dynamics within the current sheet, boundary layers, and reconnection regions drive the acceleration of ring current particles within the larger global context of the magnetosphere. Small-scale structures within the magnetotail are shown to be more important in determining when particles are accelerated than the time after particles are initialized in the ionosphere. It is also found that after a period of southward IMF, in which particle energization is observed, a northerly turning of the IMF is necessary in order to trap energetic particles in orbit around the Earth and form a symmetric ring current. Asymmetries in the acceleration mechanisms between ionospheric H+ and O + ions were observed with oxygen ions convecting duskward according to the cross-tail current and gaining more energy than protons, which moved earthward on reconnecting field lines and were accelerated

  14. IMF effect on the polar cap contraction and expansion during a period of substorms

    NASA Astrophysics Data System (ADS)

    Aikio, A. T.; Pitkänen, T.; Honkonen, I.; Palmroth, M.; Amm, O.

    2013-06-01

    The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase. In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

  15. A New Paradigm for Multi-Scale Geospace Dynamics Inspired by Recent Observations of the Substorm

    NASA Astrophysics Data System (ADS)

    Donovan, E.

    2014-12-01

    Ground-based observations of the spatio-temporal evolution of the aurora and related processes have played a critical role in the dramatic advances in substorm research that have unfolded over the THEMIS era. For example, with its unique combination of extent of coverage, and time and space resolution, THEMIS-ASI has shown dynamics unfolding rapidly across surprisingly large distances. Its image sequences show the substorm as part of a system-level dynamic that connects the inner magnetosphere to the distant tail, and perhaps even the dayside. Together with simultaneous observations by the THEMIS spacecraft, the auroral images have also transformed our understanding of magnetic mapping during the growth phase. In this talk I will review some true science highlights that have been enabled by ground-based observations since the launch of THEMIS. I will also highlight how these ground-based observations fall short of capturing key aspects of the dynamics around expansion phase onset. This creates difficulties, for example, in understanding why, how and where dispersionless injections begin. I finish with a discussion of how ground-based observations targeting the substorm have impacted geospace research in general.

  16. Nonlinear stability of the near-Earth plasma sheet during substorms: 9 February 1995 event

    NASA Astrophysics Data System (ADS)

    Dobias, P.; Wanliss, J. A.; Samson, J. C.

    2006-12-01

    It has been previously demonstrated that several minutes prior to an onset of a magnetospheric substorm the near-Earth plasma sheet becomes unstable to resonance-type perturbations. The next logical step, examined here, is an assumption that the velocity shear in the resonance would lead to a development of a Kelvin-Helmholtz (KH) instability. Using a Grad-Shafranov equilibrium constrained by CANOPUS data, we analyze the stability properties of the near-Earth plasma sheet in the presence of a field-line resonance-generated KH instability at around 10 Earth radii. The results of the analysis are in general agreement with observations and computer modeling of substorms. As a part of the analysis, we discuss the importance of the proper distinction between the stability properties of the magnetotail, and the trigger mechanism responsible for the instability. While these two aspects of a substorm may be (and likely are) related, it is possible that they involve different types of processes that work in a complementary fashion.

  17. Magnetospheric Convection as a Global Force Phenomenon

    NASA Astrophysics Data System (ADS)

    Siscoe, G.

    2007-12-01

    Since 1959 when Thomas Gold showed that motions in the magnetosphere were possible despite plasma being frozen to the magnetic field, magnetospheric convection as a subject of study has gone through several stages (to be reviewed) leading to a recent one that integrates convection into a global system of balance of forces. This area of research has opened by focusing on the region 1 current system as a carrier of force between the solar wind and the ionosphere/thermosphere fluid. An important result to emerge from it is the realization that the force that the solar wind delivers to the magnetosphere in being transferred by the region 1 current system to the ionosphere/thermosphere fluid is amplified by about an order of magnitude. (Vasyliunas refers to this as "leveraging.") The apparent violation of Newton's Third Law results from the main participants in the force balance being not the solar wind force but the JxB force on the ionosphere/thermosphere fluid and the mu-dot-grad-B force on the Earth's dipole. This talk extends the study by considering the global force-balance problem separately for the Pedersen current (a completion of the region 1 problem), the Hall current (thus introducing the region 2 current system), and the Cowling current (bringing in the substorm current wedge). The approach is through representing the ionosphere/thermosphere fluid by the shallow water equations. Novelties that result include force balance by means of tidal bulges and tidal bores.

  18. Observations of plasma sheet expansion at substorm onset, R = 15 to 22 Re

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.; Huang, C. Y.

    1992-01-01

    We have used a large number of auroral magnetograms to identify four isolated substorms and estimate their onset times. At the onsets, ISEE-1 was in the vicinity of magnetic midnight at radial distances of 15.6 to 21.8 Re and very near the outer boundary of the plasma sheet. We find that, for each event, the plasma sheet expanded, and the magnetic field dipolarized at the inferred onset time. Our most definitive event occurred while ISEE was at a geocentric radial distance of 21.8 Re. This result conflicts with previous understanding, though further verification of the result is required. Our observations show very similar characteristics to those observed at synchronous orbit, and they are consistent with an extension of a portion of the substorm current wedge to the radial distance of the satellite. If this explanation is correct, ISEE must have been within the longitude range of the substorm current wedge at the onsets.

  19. Evolution of auroral acceleration region field-aligned current systems, plasma, and potentials observed by Cluster during substorms

    NASA Astrophysics Data System (ADS)

    Hull, A. J.; Chaston, C. C.; Fillingim, M. O.; Frey, H. U.; Goldstein, M. L.; Bonnell, J. W.; Mozer, F.

    2015-12-01

    The auroral acceleration region is an integral link in the chain of events that transpire during substorms, and the currents, plasma and electric fields undergo significant changes driven by complex dynamical processes deep in the magnetotail. The acceleration processes that occur therein accelerate and heat the plasma that ultimately leads to some of the most intense global substorm auroral displays. Though this region has garnered considerable attention, the temporal evolution of field-aligned current systems, associated acceleration processes, and resultant changes in the plasma constituents that occur during key stages of substorm development remain unclear. In this study we present a survey of Cluster traversals within and just above the auroral acceleration region (≤3 Re altitude) during substorms. Particular emphasis is on the spatial morphology and developmental sequence of auroral acceleration current systems, potentials and plasma constituents, with the aim of identifying controlling factors, and assessing auroral emmission consequences. Exploiting multi-point measurements from Cluster in combination with auroral imaging, we reveal the injection powered, Alfvenic nature of both the substorm onset and expansion of auroral particle acceleration. We show evidence that indicates substorm onsets are characterized by the gross-intensification and filamentation/striation of pre-existing large-scale current systems to smaller/dispersive scale Alfven waves. Such an evolutionary sequence has been suggested in theoretical models or single spacecraft data, but has not been demonstrated or characterized in multispacecraft observations until now. It is also shown how the Alfvenic variations over time may dissipate to form large-scale inverted-V structures characteristic of the quasi-static aurora. These findings suggest that, in addition to playing active roles in driving substorm aurora, inverted-V and Alfvenic acceleration processes are causally linked. Key

  20. A proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution

    SciTech Connect

    Anderson, P.C.; Baker, D.N. ); Hanson, W.B.; Heelis, R.A. ); Frank, L.A.; Craven, J.D. )

    1993-04-01

    The authors conduct a study of subauroral ion drifts (SAID), to examine their correlation with magnetic storms. By a SAID one means a latitudinally narrow band of westward drifting ions located on the equatorial side of the auroral oval in the evening ionosphere. They look at the relationship of SAID to various stages in the development of a substorm. Data comes from DE 1, which provided auroral images, DE 2 which measured ionospheric parameters by means of magnetometers, an ion drift meter, a low altitude plasma instrument, and a retarding potential analyzer, and measurements of particle injection made by instruments at geosynchronous orbit. Analysis of the data showed very low ion drifts or field aligned currents in regions equatorward of the auroral oval before or after substorms. After substorm onset ion drifts and field aligned currents were observed extending well equatorward of the oval. There was no clear drift spike in these observations suggesting a SAID. They never saw a SAID occuring within 30 minutes of substorm onset. In almost all observations of a SAID which could be correlated with the recovery phase of the substorm, the SAID was initiated in the recovery phase. The authors then propose a model to explain the SAID which draws upon a decrease in the conductivity in the E and F regions between the band of electron precipitation in the oval and the equatorward band of ion precipitation. Several factors play into this decrease, but its occurance allows the growth of large electric fields which can drive the plasma drift as the equatorward extent of the substorm expansion shrinks in the recovery phase.

  1. Energy storage and dissipation in the magnetotail during substorms 2. MHD simulations

    NASA Astrophysics Data System (ADS)

    Steinolfson, R. S.; Winglee, R. M.

    1993-05-01

    The effects of temporal and spatial variations in the plasma resistivity on the evolution of the magnetosphere during substorms are examined with numerical solutions of the two-dimensional magnetohydrodynamic (MHD) equations. The global MHD simulations self-consistently consider the interaction of the solar wind with the dayside magnetosphere as well as the evolution of the tail region. These solutions are used to study how various solar wind states generate conditions in the tail, such as pressure gradients and cross-tail currents, that have the potential of leading to a substorm. Although the MHD formalism does provide information on the large-scale evolution, the essential mechanism for substorm development may involve microscopic or particle processes not present in an MHD approach. As a result, this MHD study is carried out in association with particle simulations (Winglee and Steinolfson, this issue). Since one connection between the MHD and particle approaches is through the resistivity, the effects of various resistivity distributions on the global MHD configuration are examined. The resistivity distributions considered here are (1) a temporally constant and spatially uniform resistivity, (2) a resistivity proportional to the square of the local current density, and (3) a resistivity proportional to the square of the local magnetic field strength. The latter distribution is suggested by the above particle simulations and represents effects produced by the increased magnetization of particles and the differential motion between electrons and ions. For all three cases a plasmoid is formed and ejected tailward. However, when the resistivity depends on the field strength, considerably more energy is stored in the tail prior to plasmoid formation, and plasmoid formation is delayed relative to the results for the other two resistivity distributions. Furthermore, when the plasmoid is eventually ejected, it moves down the tail with a higher speed. The MHD results

  2. Lower thermospheric wind variations in auroral patches during the substorm recovery phase

    NASA Astrophysics Data System (ADS)

    Oyama, Shin-ichiro; Shiokawa, Kazuo; Miyoshi, Yoshizumi; Hosokawa, Keisuke; Watkins, Brenton J.; Kurihara, Junichi; Tsuda, Takuo T.; Fallen, Christopher T.

    2016-04-01

    Measurements of the lower thermospheric wind with a Fabry-Perot interferometer (FPI) at Tromsø, Norway, found the largest wind variations in a night during the appearance of auroral patches at the substorm recovery phase. Taking into account magnetospheric substorm evolution of plasma energy accumulation and release, the largest wind amplitude at the recovery phase is a fascinating result. The results are the first detailed investigation of the magnetosphere-ionosphere-thermosphere coupled system at the substorm recovery phase using comprehensive data sets of solar wind, geomagnetic field, auroral pattern, and FPI-derived wind. This study used three events in November 2010 and January 2012, particularly focusing on the wind signatures associated with the auroral morphology, and found three specific features: (1) wind fluctuations that were isolated at the edge and/or in the darker area of an auroral patch with the largest vertical amplitude up to about 20 m/s and with the longest oscillation period about 10 min, (2) when the convection electric field was smaller than 15 mV/m, and (3) wind fluctuations that were accompanied by pulsating aurora. This approach suggests that the energy dissipation to produce the wind fluctuations is localized in the auroral pattern. Effects of the altitudinal variation in the volume emission rate were investigated to evaluate the instrumental artifact due to vertical wind shear. The small electric field values suggest weak contributions of the Joule heating and Lorentz force processes in wind fluctuations. Other unknown mechanisms may play a principal role at the recovery phase.

  3. Van Allen Probes observations of dipolarization and its associated O+ flux variations in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Nose, M.; Keika, K.; Kletzing, C.; Smith, C. W.; MacDowall, R. J.; Reeves, G. D.; Spence, H. E.

    2015-12-01

    Recent study employing the MDS-1 satellite reveals that magnetic field dipolarization in the deep inner magnetosphere is not unusual. When the MDS-1 satellite was located at L=3.5-5.0 near the auroral onset longitude (MLT difference of ≤2.5 h), the occurrence probability of local dipolarization was about 16%. Surprisingly, an event was found at L~3.6, far inside the geosynchronous altitude. It was also shown that after the dipolarization, the oxygen ENA flux in the nightside ring current region measured by the IMAGE satellite was predominantly enhanced by a factor of 2-5 and stayed at an enhanced level for more than 1 h, while clear enhancement was scarcely seen in the hydrogen ENA flux. To better understand mechanisms of the selective acceleration of O+ ions during dipolarization, an in-situ measurement of ion fluxes is needed. However, there are few studies investigating H+ and O+ flux variations during dipolarization in the deep inner magnetosphere. In this study we investigate magnetic field dipolarization and its associated ion flux variations in the deep inner magnetosphere, using magnetic field and ion flux data obtained by the Van Allen Probes. From the magnetic field data recorded on the nightside (1800-0600 MLT) in the inner magnetosphere (L=3.0-6.6) in VDH coordinates, we select substorm-related dipolarization events in which the H component increases by more than 20 nT and the absolute value of the V component decreases by more than 8 nT in 5 minutes. About 150 dipolarization events are identified from 1 October 2012 to 30 June 2015. We find that the dipolarization mostly occurs at L=4.5-6.5 in the premidnight sector (2100-0000 MLT). No events are found at L<4.0. Some dipolarization events are accompanied by O+ flux enhancements in the energy range higher than a few keV, which have the pitch angle distribution peaked around 45 or 135 degrees. We also find that low energy O+ ions often appear after dipolarization with an energy dispersion starting from

  4. Dynamics of the 1054 UT March 22, 1979, substorm event: CDAW 6

    SciTech Connect

    McPherron, R.L.; Manka, R.H.

    1985-02-01

    The physical processes involved in the transfer of energy from the solar wind to the magnetosphere, and release associated with substorms, have been examined in a sequence of Coordinated Data Analysis Workshops (CDAW 6). Magnetic storms of March 22 and 31, 1979, were chosen to study the problem, using a data base from 13 spacecraft and about 130 ground-based magnetometers. This paper describes the March 22 storm, in particular the large, isolated substorm at 1054 UT which followed an interval of magnetic calm. We summarize the observations in the solar wind, in various regions of the magnetosphre, and at the ground, synthesizing these observations into a description of the substorn development. We then give our interpretation of these observations and test their consistency with the reconnection model. The substorm appears to have been generated by a southward turning of the interplanetary magnetic field associated with a current sheet crossing. Models of ionospheric currents derived from ground data show the substorm had three phases of development. During the first phase, a two-celled convection current system developed in the polar cap as synchronous spacecraft on the nightside recorded an increasingly tailike field and the ISEE measurements show that the near-earth plasma sheet thinned. In the second phase, possibly triggered by sudden changes in the solar wind, a one-celled current system was added to the first, enhancing the westward electrojet. During this phase the synchronous orbit field became more dipolar, and the plasma sheet magnetic field turned strongly southward as rapid tailward flow developed soon after expansion onset, suggesting that a neutral line formed in the near-earth plasma sheet with subsequent plasmoid ejection.

  5. Activation of the tail open part during the magnetospheric storm

    NASA Astrophysics Data System (ADS)

    Mishin, V. M.; Karavaev, Yu. A.; Sapronova, L. A.; Solovyev, S. I.

    2012-07-01

    In each polar cap (PC) we mark out "old PC" observed during quiet time before the event under consideration, and "new PC" that emerges during the substorm framing the old one and expanding the PC total area. Old and new PCs are the areas for the magnetosphere old and new tail lobes, respectively. The new lobe variable magnetic flux Ψ1 is usually assumed to be active, i.e. it provides the electromagnetic energy flux (Poynting flux) ɛ' transport from solar wind (SW) into the magnetosphere. The old lobe magnetic flux Ψ2 is supposed to be passive, i.e. it remains constant during the disturbance and does not participate in the transporting process which would mean the old PC electric field absolute screening from the convection electric field created by the magnetopause reconnection. In fact, screening is observed, but far from absolute. We suggest a model of screening and determine its quantitative characteristics in the selected superstorm. The coefficient of a screening is the β = Ψ2/Ψ02, where Ψ02 = const is open magnetic flux through the old PC measured prior to the substorm, and Ψ2 is variable magnetic flux through the same area measured during the substorm. We consider three various regimes of disturbance. In each, the coefficient β decreased during the loading phase and increased at the unloading phase, but the rates and amplitudes of variations exhibited a strong dependence on the regime. We interpreted decrease in β as a result of involving the old PC magnetic flux Ψ2, which was considered to be constant earlier, in the Poynting flux ɛ' transport process from solar wind into the magnetosphere. Transport process weakening at the subsequent unloading phase creates increase in β. Estimates showed that coefficient β during each regime and the computed Poynting flux ɛ' varied manifolds. In general, unlike the existing substorm conception, the new scenario describes an unknown earlier of tail lobe activation process during a substorm growth phase that

  6. Formation and evolution of high-plasma-pressure region in the near-Earth plasma sheet: Precursor and postcursor of substorm expansion onset

    NASA Astrophysics Data System (ADS)

    Yao, Y.; Ebihara, Y.; Tanaka, T.

    2015-08-01

    Cause of substorm expansion onset is one of the major problems in the magnetospheric study. On the basis of a global magnetohydrodynamic (MHD) simulation, Tanaka et al. (2010) suggested that formation and evolution of a high-pressure region (HPR) in the near-Earth plasma sheet could result in sudden intensification of the Region 1 field-aligned current and the westward auroral electrojet. In this sense, the formation and evolution of the HPR are a key in understanding the cause of the onset. On 5 April 2009, three probes of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) were located at XGSM~-11 Re around the equator, which provide unique opportunity to investigate the spatial-temporal evolution of the HPR near the substorm expansion onset. Just before the onset, a positive excursion of the plasma pressure appeared at the outermost probe first, followed by the inner ones. Just after the onset, the opposite sequence took place. A positive excursion of the Y component of the current density was observed near the onset by the THEMIS probes and followed by a decrease trend. A similar variation was also found in the MHD simulation. All these features are consistent with the simulation result that a squeeze of the plasma from the plasma sheet results in the formation of the HPR before the onset and that the accumulated plasma spreads outward after the onset. The HPR is shown to be important for the dynamics of the magnetosphere during a substorm.

  7. Integrated Observations of ICME - Driven Substorm - Storm Evolution on 7 August 1998: Traditional and Non-Traditional Aspects.

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Sandholt, P. E.; Torbert, R. B.

    2015-12-01

    The aim of this study is to obtain an integrated view of substorm-storm evolution in relation to well-defined interplanetary (IP) conditions, and to identify traditional and non-traditional aspects of the DP1 and DP2 current systems during substorm activity. Specifically, we report a case study of substorm/storm evolution driven by an ICME from ground observations around the oval in relation to geoeffective IP parameters (Kan-Lee electric field, E-KL, and dynamic pressure, Pdyn), geomagnetic indices (AL, SYM-H and PCN) and satellite observations (from DMSP F13 and F14, Geotail, and GOES spacecraft). A sudden enhancement of E-KL at a southward turning of the IMF led to an initial transient phase (PCN-enhancement) followed by a persistent stage of solar wind-magnetosphere-ionosphere coupling. The persistent phase terminated abruptly at a steep E-KL reduction when the ICME magnetic field turned north after a 3-hour-long interval of enhanced E-KL. The persistent phase consisted of (i) a 45-min-long substorm growth phase (DP2 current) followed by (ii) a classical substorm onset (DP1 current) in the 0100 - 0300 MLT sector, (ii) a 30-min-long expansion phase, maximizing in the same sector, and (iii) a phase lasting for 1.5 hr of 10-15 min-long DP1 events in the 2100 - 2300 and 0400 - 0600 MLT sectors. In the morning sector the expansion phase was characterized by Ps6 pulsations and omega bands. The SYM-H evolution reached the level of a major storm after a 2.5-hour-long interval of E-KL ˜5 mV/m and elevated Pdyn in the substorm expansion phase. Magetosphere - Ionosphere (M - I) coupling during a localized electrojet event at 0500 MLT in the late stage of the substorm expansion is studied by ground - satellite conjunction data (Iceland - Geotail). The DP1 and DP2 components of geomagnetic activity are discussed in relation to M - I current systems and substorm current wedge morphology.

  8. Magnetospheres: Jupiter, Satellite Interactions

    NASA Astrophysics Data System (ADS)

    Neubauer, F.; Murdin, P.

    2000-11-01

    Most of the satellites of Jupiter, notably the large Galilean satellites Io, Europa, Ganymede and Callisto (see JUPITER: SATELLITES), orbit deep inside the magnetosphere of Jupiter (see JUPITER: MAGNETOSPHERE) and are therefore immersed in the flow of magnetospheric plasma (made of a mixture of electrons and ions) and subjected to an interaction with the strong Jovian magnetic field. These intera...

  9. Substorm effects in auroral spectra. [electron spectrum hardening

    NASA Technical Reports Server (NTRS)

    Eather, R. H.; Mende, S. B.

    1973-01-01

    A substorm time parameter is defined and used to order a large body of photometric data obtained on aircraft expeditions at high latitudes. The statistical analysis demonstrates hardening of the electron spectrum at the time of substorm, and it is consistent with the accepted picture of poleward expansion of aurora at the time of substorm and curvature drift of substorm-injected electrons. These features are not evident from a similar analysis in terms of magnetic time. We conclude that the substorm time concept is a useful ordering parameter for auroral data.

  10. Observations of Plasma Transient on the Lobe Field Line During the Substorm. Interball Tail Observations on October 3, 1995

    NASA Technical Reports Server (NTRS)

    Avanov, L. A.; Smimov, V. N.; Chandler, M. O.

    2004-01-01

    On October 3, 1995 Interball Tail spacecraft was located on tail lobe field lines. Solar wind conditions monitored by WIND and Getail spacecraft were quiet stable. During the time of operation of SCA-1 plasma spectrometer typical plasma mantle is observed. However, at approx. 15:07 UT strong plasma transient with duration of approx. 10 minutes was detected. We found that magnetic field profile of this plasma transient correlates well with ground based H component of magnetic field measured by Tixie Bay station. Ground base data indicates that this transient is observed during strong substorm. We argue that this transient is probably more dense mantle plasma which can be observed at the Interball Tail location provided that the current on the magnetopause is depressed. This depression probably reflects response of the tail magnetopause to changing of the global current system of the magnetosphere caused by the substorm.

  11. Formation of a very thin current sheet in the near-earth magnetotail and the explosive growth phase of substorms

    NASA Technical Reports Server (NTRS)

    Lee, L. C.; Zhang, L.; Choe, G. S.; Cai, H. J.

    1995-01-01

    A magnetofricional method is used to construct two-dimensional MHD equilibria of the Earth's magnetosphere for a given distribution of entropy functions(S = pV(exp gamma), where p is the plasma pressure and V is the tube volume per unit magnetic flux. It is found that a very thin current sheet with B (sub zeta) is less than 0.5 nu T and thickness less than 1000 km can be formed in the near-earth magnetotail (x is approximately -8 to -20R(sub e) during the growth phase of substorm. The tail current sheets are found to become thinner as the entropy or the entropy gradient increases. It is suggested that the new entropy anti-diffusion instability associated with plasma transport across field lines leads to magnetic field dipolarization and accelerates the formation of thin current sheet, which may explain the observed explosive growth phase of substorms.

  12. Ionospheric Irregularities at High Latitudes During Geomagnetic Storms and Substorms: Simultaneous Observations of Magnetic Field Perturbations and GPS Scintillations

    NASA Astrophysics Data System (ADS)

    Kim, H.; Deshpande, K.; Clauer, C. R.; Bust, G. S.; Crowley, G.; Humphreys, T. E.; Kim, L.; Lessard, M.; Weatherwax, A. T.; Zachariah, T. P.

    2012-12-01

    Plasma instability in the ionosphere is often observed as disturbance and distortion of the amplitude and phase of radio signals, which are known as ionospheric scintillations. High-latitude ionospheric plasma, closely connected to solar wind and magnetospheric dynamics, produce very dynamic and short-lived GPS scintillations, making it challenging to characterize them. This study reports simultaneous observations of geomagnetic pulsations and GPS signal scintillations during geomagnetic storms and substorms using a newly designed Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) installed at the South Pole. A statistical investigation of the AAL-PIP data recorded from January through May 2012 is presented to study local time distribution of scintillation events and a correlation between GPS scintillation and magnetic field perturbations. This report discusses a possible connection between magnetic field perturbations associated with the ionospheric currents and the creation of plasma instability by examining relative contribution of storm/substorm activity to ionospheric irregularities.

  13. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    NASA Technical Reports Server (NTRS)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  14. Dying Flow Bursts as Generators of the Substorm Current Wedge

    NASA Astrophysics Data System (ADS)

    Haerendel, Gerhard

    2016-07-01

    Many theories or conjectures exist on the driver of the substorm current wedge, e.g. rerouting of the tail current, current disruption, flow braking, vortex formation, and current sheet collapse. Magnitude, spatial scale, and temporal development of the related magnetic perturbations suggest that the generator is related to the interaction of the flow bursts with the dipolar magnetosphere after onset of reconnection in the near-Earth tail. The question remains whether it is the flow energy that feeds the wedge current or the internal energy of the arriving plasma. In this presentation I argue for the latter. The current generation is attributed to the force exerted by the dipolarized magnetic field of the flow bursts on the preceding layer of high-beta plasma after flow braking. The generator current is the grad-B current at the outer boundary of the compressed high-beta plasma layers. It needs the sequential arrival of several flow bursts to account for duration and magnitude of the ionospheric closure current.

  15. Modeling Substorm Injections with a Simple Magnetotail model

    NASA Astrophysics Data System (ADS)

    Kabin, Konstantin; Spanswick, Emma; Donovan, Eric; Kalugin, German

    2016-07-01

    Magnetotail dipolarizations, often associated with substorms, produce significant energetic particle enhancements in the night-time magnetosphere. We developed a simple yet self-consistent model for the electric and magnetic fields during dipolarizations, which is based on our earlier work (Kabin et al., JGR 2010). This model is very flexible and is particularly well suited for describing transition from the dipole-like to tail-like magnetic fields. We perform test particle simulations in the electric and magnetic fields specified by the model and find substantial energization of both electron and protons associated with the motion of this transition region. This energy gain is sufficient to explain many features of Dispersionless Injections. The energization of the particles is caused by betatron acceleration due to both the local increases in the magnetotail field strength during a dipolarization and to the particles drift closer to the Earth. In some cases the energy of an electron was found to increase by a factor of 25 or more. Our results are particularly well suited for comparison with riometer observations which often show clear signatures of Dispersionless Injections.

  16. A new model for auroral breakup during substorms

    SciTech Connect

    Rothwell, P.L.; Block, L.P.; Falthammar, C.G.; Silevitch, M.B.

    1989-04-01

    A model for substorm breakup is developed, based on the relaxation of stretched (closed) dipolar field lines, and the formation of an incipient current wedge within a single arc structure. It is argued that the establishment of a coupled current structure within a single arc leads to a quasi-stable system; i.e., the pre-breakup regime. Perturbation of the pre-breakup structure leads to an instability criterion. It is found, consistent with observations, that narrower auroral arcs at lower L shells undergo the most explosive poleward expansion. According to this model, the precise location at which breakup occurs depends on the O/sup +/ density in the plasma sheet, the level of magnetic activity (K/sub p/), and the intensity of the substorm westward electrojet in the ionosphere. An enhancement of any of these features will cause breakup to occur at lower L shells. Comparison of our model with the Heppner-Maynard polar-cap potential model indicates that breakup is restricted to the west of the Harang discontinuity consistent with recent observations from the Viking satellite.

  17. Magnetospheric vortices and their global effect after a solar wind dynamic pressure decrease

    NASA Astrophysics Data System (ADS)

    Zhao, H. Y.; Shen, X. C.; Tang, B. B.; Tian, A. M.; Shi, Q. Q.; Weygand, J. M.; Yao, Z. H.; Zong, Q.-G.; Fu, S. Y.; Yao, S. T.; Xiao, T.; Pu, Z. Y.

    2016-02-01

    Using multipoint data from three Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites, we report a magnetospheric flow vortex driven by a negative solar wind dynamic pressure pulse. The observed vortex rotated in a direction opposite to that associated with positive solar wind dynamic pressure pulses. The vortex was moving tailward, as confirmed by a global magnetohydrodynamics (MHD) simulation. In addition, the equivalent ionospheric currents (EICs) deduced from ground magnetometer station data reveal that a current vortex in the ionosphere near the foot point of the satellites has a rotation sense consistent with that observed in the magnetosphere. The field-aligned current (FAC) density estimated from three THEMIS satellites is about 0.15 nA/m2, and the total FAC of the vortex is about 1.5-3 × 105 A, on the order of the total FAC in a pseudobreakup, but less than the total FAC in most moderate substorms, 106 A.

  18. Energy cascade in the magnetosphere-ionosphere system: A case study

    NASA Astrophysics Data System (ADS)

    Semeter, J. L.; Dahlgren, H.; Akbari, H.; Swoboda, J.; Hampton, D. L.; Anderson, B. J.; Dyrud, L. P.; Fentzke, J.

    2013-12-01

    Common to all geomagnetic storms and substorms is the phenomenon of energy cascade, wherein an impulsive change in magnetospheric free energy is dissipated in a hierarchy of spatial and temporal scales at the ionospheric footprint, extending down to the fundamental scales available in the system (electron gyro-radius, electron inertial length). This paper investigates energy cascade through a synthesis of multi-scale measurements of a particular substorm (onset at ~10 UT on 01 March 2011). Fortuitous space-based measurements from the AMPERE experiment document the regional intensification of field-aligned currents. Conjugate ground-optical measurements of the subsequent auroral breakup are found to represent the optical manifestation of time-energy dispersive field-aligned electron bursts (FABs) [Dahlgren et al., 2013]. The 449-MHz Poker Flat Incoherent Scatter Radar connects these features with ion-acoustic turbulence at the expanding edge of the substorm. The connection of large scale substorm currents with decameter-scale ionospheric turbulence fills an important observational gap in our understanding of magnetosphere-ionosphere coupling under disturbed conditions.

  19. Nightside magnetospheric current circuit: Time constants of the solar wind-magnetosphere coupling

    NASA Astrophysics Data System (ADS)

    Ohtani, S.; Uozumi, T.

    2014-05-01

    This study addresses the characteristics of the nightside magnetospheric current system using the analogy of an electric circuit. The modeled circuit consists of the generator (V: solar wind), inductor (L: tail lobes), capacitor (C: plasma sheet convection), and resistor (R: particle energization). The electric circuit has three time constants: τCR(=CR), τLC(=√LC), and τL/R(=L/R). Here τCR is of the order of the ion gyroperiod in the plasma sheet, τLC is a global timescale (2πτLC is several tens of minutes), and τL/R is even longer (several hours). Despite uncertainty in the estimate of each circuit element, τCR ≪ τLC ≪ τL/R holds generally for the magnetosphere, which characterizes the electric circuit as overdamped. The following implications are obtained: (1) During the substorm growth phase the cross-tail current increases continuously even if interplanetary magnetic field (IMF) BZ does not change after southward turning; (2) the magnetotail current weakens following northward turnings if the change of IMF BZ is comparable to the preceding southward IMF BZ; otherwise it may strengthen continuously if more gradually; (3) during the early main phase of magnetospheric storms the enhancement of the lobe magnetic energy is far more prominent than the enhancements of the kinematic and kinetic energies of the plasma sheet plasma; (4) The efficiency of the solar wind-magnetosphere coupling changes on a timescale of several hours (τL/R) through the change of the tail flaring, and so does the cross polar-cap potential; and (5) the magnetospheric current system does not resonate to an oscillatory external driver, and therefore, the periodicity of some magnetotail phenomena reflects that of their triggers.

  20. Particle acceleration in pulsar magnetospheres

    NASA Technical Reports Server (NTRS)

    Baker, K. B.

    1978-01-01

    The structure of pulsar magnetospheres and the acceleration mechanism for charged particles in the magnetosphere was studied using a pulsar model which required large acceleration of the particles near the surface of the star. A theorem was developed which showed that particle acceleration cannot be expected when the angle between the magnetic field lines and the rotation axis is constant (e.g. radial field lines). If this angle is not constant, however, acceleration must occur. The more realistic model of an axisymmetric neutron star with a strong dipole magnetic field aligned with the rotation axis was investigated. In this case, acceleration occurred at large distances from the surface of the star. The magnitude of the current can be determined using the model presented. In the case of nonaxisymmetric systems, the acceleration is expected to occur nearer to the surface of the star.

  1. Observations of Earthward and tailward propagating flux rope plasmoids: Expanding the plasmoid model of geomagnetic substorms

    NASA Technical Reports Server (NTRS)

    Moldwin, Mark B.; Hughes, W. Jeffrey

    1994-01-01

    A survey of Interplanetary Monitoring Platform (IMP 8) magnetometer data for plasmoid signatures during magnetospheric intervals from 1981 through 1983 found 16 plasmoids and 37 traveling compression regions as well as two earthward propagating flux ropes and 19 south-north bipolar lobe signatures. The properties of these relatively near-Earth plasmoids, traveling compression regions, and earthward propagating flux ropes and a qualitative model for their formation are presented. The plasmoids have estimated sizes, durations, magnetic field signatures, downtail velocities, and substorm associations very similar to those of the plasmoids identified in International Sun-Earth Explorer (ISEE) 3 deep-tail observations. The occurrence frequency of these near-Earth plasma sheet plasmoids is significantly smaller than that of plasmoids found in the mid- and deep tail with ISEE 3. The earthward propagating flux ropes are characterized by a south-north bipolar turning in the Geocentric Solar Magnetospheric (GSM) B(sub z) component, are localized near the noon-midnight meridional plane, and are strongly correlated with interplanetary magnetic field B(sub z) north and small isolated high latitude geomagnetic substorms. These events are also apparently very rare and/or spatially localized. We propose that these structures are 'proto-plasmoids,' i.e., plasmoids for which near-Earth magnetic reconnection stopped before all the closed plasma sheet field lines were reconnected. The proto-plasmoids are then 'trapped' inside closed magnetic field lines and propagate earthward owing to the effect of the distant X-line's earthward plasma flow. We suggest that the two different 'types' of plasmoids are due to the different energy states of the magnetosphere during periods of southward and northward interplanetary magnetic field.

  2. Auroral fading in ionosphere-magnetosphere coupling model: Implications for possible mechanisms

    SciTech Connect

    Janhunen, P.; Pulkkinen, T.I.; Kauristie, K.

    1995-08-01

    The authors present results from a numerical model which includes coupling between the magnetosphere and ionosphere, and in which they observe indications similar to observations which occasionally show a fading of auroral arcs and electrojets during the later phases of substorm onset. The model shows that the magnetospheric plasma shifts toward the earth at this point, and at least the poleward part of the precipitation region is cooled. These effects combine to suppress the precipitation of hot dense plasma, for at least a short time.

  3. Electron precipitation pattern and substorm morphology

    NASA Technical Reports Server (NTRS)

    Hoffman, R. A.; Burch, J. L.

    1972-01-01

    Patterns of the precipitation of low energy electrons observed by polar satellites were examined as functions of substorm phase. Precipitation boundaries are generally identifiable at the low latitude edge of polar cusp electron precipitation and at the poleward edge of precipitation in the premidnight sector. Both of these boundaries move equatorward when the interplanetary magnetic field turns southward.

  4. Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD

    NASA Astrophysics Data System (ADS)

    Pickett, J. S.; Chen, L.-J.; Santolík, O.; Grimald, S.; Lavraud, B.; Verkhoglyadova, O. P.; Tsurutani, B. T.; Lefebvre, B.; Fazakerley, A.; Lakhina, G. S.; Ghosh, S. S.; Grison, B.; Décréau, P. M. E.; Gurnett, D. A.; Torbert, R.; Cornilleau-Wehrlin, N.; Dandouras, I.; Lucek, E.

    2009-06-01

    Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 RE and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2) the EDI instrument detected bursts of field-aligned electron currents, 3) the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4) the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5) CIS detected nearly comparable densities of H+ and O+ ions and a large tailward H+ velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD) with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in more detail using the space

  5. Dynamic Agents of Magnetosphere-Ionosphere Coupling

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.; Rowland, Douglas E.; Moore, Thomas E.; Collier, Michael

    2011-01-01

    VISIONS sounding rocket mission (VISualizing Ion Outflow via Neutral atom imaging during a Substorm) has been awarded to NASA/GSFC (PI Rowland) in order to provide the first combined remote sensing and in situ measurements of the regions where ion acceleration to above 5 e V is occurring, and of the sources of free energy and acceleration mechanisms that accelerate the ions. The key science question of VISIONS is how, when, and where, are ions accelerated to escape velocities in the auroral zone below 1000 km, following substorm onset? Sources of free energy that power this ion acceleration process include (but not limited) electron precipitation, field-aligned currents, velocity shears, and Alfvenic Poynting flux. The combine effect of all these processes on ionospheric ion outflows will be investigated in a framework of the kinetic model that has been developed by Khazanov et al. in order to study the polar wind transport in the presence of photoelectrons.

  6. New Understanding of Mercury's Magnetosphere from MESSENGER'S First Flyby

    NASA Technical Reports Server (NTRS)

    Slavin, James A.; Acuna, Mario H.; Anderson, Brian J.; Baker, Daniel N.; Benna, Mehdi; Gloeckler, George; Gold, Robert E.; Ho, George C.; Killen, M.; Korth, Haje; Krimigis, Stamatios M.; McNutt, Ralph L., Jr.; Raines, James M.; Schriver, David; Somomon, Sean C.; Starr, Richard; Travnicek, Pavel; Zurbuchen, Thomas H.

    2008-01-01

    Observations by the MESSENGER spacecraft on 14 January 2008 have revealed new features of the solar system's smallest planetary magnetosphere. The interplanetary magnetic field orientation was unfavorable for large inputs of energy from the solar wind and no evidence of magnetic substorms, internal magnetic reconnection, or energetic particle acceleration was detected. Large-scale rotations of the magnetic field were measured along the dusk flank of the magnetosphere and ultra-tow frequency waves were frequently observed beginning near closest approach. Outbound the spacecraft encountered two current-sheet boundaries across which the magnetic field intensity decreased in a step-like manner. The outer current sheet is the magnetopause boundary. The inner current sheet is similar in structure, but weaker and -1000 km closer to the planet. Between these two current sheets the magnetic field intensity is depressed by the diamagnetic effect of planetary ions created by the photo-ionization of Mercury's exosphere.

  7. Computer modeling of events in the inner magnetosphere

    NASA Technical Reports Server (NTRS)

    Harel, M.; Wolf, R. A.; Reiff, P. H.; Smiddy, M.

    1979-01-01

    The first effort at computer simulating the behavior of the inner magnetosphere during a substorm-type event on 19 September 1976 was completed. The computer model simulates many aspects of the behavior of the closed-field-line portion of the earth's magnetosphere, and the auroral and subauroral ionosphere. For these regions, the program self-consistently computes electric fields, electric currents, hot-plasma densities, plasma flow velocities and other parameters. Highlights of the results of our event simulation are presented. Predicted electric fields for several times during the event agree reasonably well with corresponding data from satellite S3-2. Detailed discussion is presented for a case of rapid subauroral flow that was observed on one S3-2 pass and is predicted by the computer runs. The computed global distribution of Birkeland current agrees reasonably well with the observations of Iijima and Potemra.

  8. Electric field variations during substorms: OGO-6 measurements

    NASA Technical Reports Server (NTRS)

    Heppner, J. P.

    1972-01-01

    The OGO-6 electric field measurements make it clear that the general pattern of high latitude electric fields in magnetic time-invariant latitude coordinates is not highly variable and that when unusual variations, or field distributions, occur they are relatively isolated in time and spatial extent. Thus, electric field changes on a global scale cannot, in general, be evoked as a direct cause of substorms. Polar traverses along the 18(h) to 6(h) magnetic time meridian show that the sum of potential drops across the evening auroral belt and morning auroral belt approximately equals the potential drop across the polar cap. The integrated polar cap potential drop ranges from 20 to 100 keV and values in the center of this range are most common under conditions of moderate magnetic disturbance. Roughly near 18(h) magnetic local time, a latitudinally narrow strip at the transition between auroral belt and polar cap fields exhibits unusually large field fluctuations immediately following the sudden onset of a negative bay at later magnetic local times. It appears likely that this spatially isolated correlation is related to an effect rather than a cause of substorm enhancement.

  9. Energy density of ionospheric and solar wind origin ions in the near-Earth magnetotail during substorms

    SciTech Connect

    Daglis, I.A.; Livi, S.; Sarris, E.T.

    1994-04-01

    The authors present a study of hydrogen, oxygen, and helium ions observed in the magnetotail, where measurements of enegy densities were made, and correlated with indexes related to substorm behaviour. The objective is to study relations between the solar wind/magnetosphere/ionosphere. Data were collected using an instrument on the AMPTE/CCE satellite. Strong correlations were observed between different ions and auroral indexes. Energetic ions are found to be increasing in density in the magnetotail in periods when auroral currents are dissipating.

  10. Using the Virtual Heliospheric and Magnetospheric Observatories for geospace studies

    NASA Astrophysics Data System (ADS)

    Merka, J.; Szabo, A.; Narock, T. W.; Walker, R. J.; King, T.; Slavin, J. A.; Imber, S.; Karimabadi, H.; Faden, J.

    2008-12-01

    Finding and retrieving space physics data is a rather daunting task even when the data are publicly available on the Internet because there are thousands of relatively small and many large data sets stored in various formats and accompanied often only by terse documentation. Virtual Heliospheric and Magnetospheric Observatories (VHO and VMO) are being developed to help researches by creating a single point of uniform discovery, access, and use of heliospheric (VHO) and magnetospheric (VMO) data. Available data can be searched based on various criteria as, for example, spatial location, time of observation, measurement type, parameter values, etc. The VHO and VMO also utilize event lists to quickly narrow down searches by specific events, e.g. bow shock crossings, flux transfer events (FTEs) or CMEs/ICMEs. We will demonstrate the utility of VHO/VMO for geospace studies by reprising some multi-spacecraft, multi- instrument analyzes from the literature. For example, simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms were identified by visual inspection of several years of ISTP measurements by Slavin et al. [2002]. Using the VHO/VMO we show how studies such as these can be carried out with substantial time savings and often with the added value of accessing additional relevant data sets that would not have been available to scientist performing the analysis. http://vho.nasa.gov http://vmo.nasa.gov Slavin et al., Simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms, J. of Geophysical Research, 107 (A7), 10.1029/2000JA003501, 2002

  11. Freja Studies of the Current-Voltage Relation in Substorm-Related Events

    NASA Technical Reports Server (NTRS)

    Olsson, A.; Andersson, Laila; Eriksson, A. I.; Clemmons, J.; Erlandsson, R. E.; Reeves, G.; Hughes, T.; Murphee, J. S.

    2000-01-01

    Field-aligned currents and electrostatic potentials play important roles in the coupling between the magnetosphere and the ionosphere. If one assumes that the ionosphere-magnetosphere potential difference is mainly due to the mirror force, one can use the single particle adiabatic kinetic theory to describe the system. From this theory, a linear relationship j(sub II) = KV between field-aligned current density j(sub II) and potential drop V along the same field line can be derived, provided that the potential drop is not too large and not too small. With rare exceptions, observational tests of this relation have mainly concentrated on quiet magnetospheric situations, with acceleration voltages V approx. less than 5 kV. Here we use observations from the Freja satellite of precipitating auroral electrons at 1.700 km altitude to study substorm related events, with acceleration voltages up to 20 keV. The observations are found to be consistent with a linear current-voltage relation even i n these conditions, although with values of the field aligned K lower than previously reported (1-5 x 10(exp 11 S/sq m). This can be explained by lower densities and higher characteristic electron energies in the magnetospheric source region of the precipitating electrons. We analyze the data by three different methods, which are all found to be in general agreement. The results are in agreement with a previous study, where the spectra of precipitating electrons --were indirectly inferred by inversion of data from the EISCAT incoherent scatter radar, thereby validating the use of radar data for studies of auroral electrons. Comparisons with previous studies are made, emphasizing the dependence of the results on the type of auroral structure and magnetospheric conditions.

  12. On the role of pre-onset streamers in substorm onset and development

    NASA Astrophysics Data System (ADS)

    Kepko, L.

    2014-12-01

    A large body of THEMIS-era research has made significant progress in studying both the morphology and the impact on substorm development of pre-onset auroral streamers. Specifically, beginning in 2010, a series of papers by Nishimura, Lyons, and others has laid out a scenario in which pre-onset white light streamers that appear to move from hight to low latitude represent low entropy flux tubes propagating to the near-Earth transition region. These entropy depleted flux tubes trigger an instability which then grows exponentially, rapidly leading to substorm onset. In the context of previously established terminology, this is considered a hybrid triggered inside-out scenario. More recent work has also challenged the traditional interpretation that Pi2 pulsations, the initiation of the substorm current wedge, and auroral onset are nearly simultaneous, as predicted by a model of onset driven by magnetotail flow bursts. Instead, it has been argued that auroral onset occurs many minutes earlier, and that further development is fed by post-onset auroral streamer activity. In this talk, I assess the role of of pre-onset auroral streamers in substorm onset and development, and review how the observations and interpretations relate to our current understanding of magnetotail processes.

  13. Interhemispheric Differences in Substorm Onsets as Determined from Pi1B Pulsations

    NASA Astrophysics Data System (ADS)

    Lessard, M. R.; Kim, H.; Engebretson, M. J.; Posch, J.; Weatherwax, A. T.

    2006-05-01

    The relationship between phenomena of solar origin and the climate of Earth depends, to some degree, on the transport of electromagnetic energy to the upper atmosphere. The processes that enable this energy transfer are complex (and often interrelated) and typically include storms and substorms and, more specifically, the transport of energy via waves and particle precipitation. Not surprisingly, the effectiveness of the coupling often changes with season as well as the variability of parameters within the solar wind, an effect noted especially with regard to substorms. In this talk, recent work regarding interhemispheric differences in substorm onset arrival times is discussed, with a focus on new results showing interesting differences in arrival times of Pi1B pulsations, characterized by broadband bursts in the ULF range (periods of 1 to 40 s). Previous work has shown that these pulsations provide an onset signature with timing precision the order of a few seconds and, also, that the ground stations that detect this signature need only be located within a couple hours in MLT of the onset. In a detailed study, observations at nominally conjugate stations (South Pole and Iqaluit) are used to determine differences in substorm onsets in opposite hemispheres. This is a statistical study spanning a few years and includes several tens of events, where the presence of substorms are confirmed using fluxgate magnetometer and other data. The raw results show a wide range in onset times, with no clear seasonal dependence that might indicate a tendency for onset to occur in one hemisphere or the other. For periods of perhaps a few weeks, however, there are times when onset does occur preferentially in one hemisphere, suggesting that coupling is somehow mediated by solar wind parameters.

  14. Intense energetic-electron flux enhancements in Mercury's magnetosphere: An integrated view with high-resolution observations from MESSENGER

    NASA Astrophysics Data System (ADS)

    Dewey, R. M.; Baker, D. N.; Slavin, J. A.; Raines, J. M.; Lawrence, D. J.; Goldsten, J. O.; Peplowski, P. N.; Korth, H.; Krimigis, S. M.; Anderson, B. J.; Ho, G. C.; McNutt, R. L., Jr.; Schriver, D.; Solomon, S. C.

    2015-12-01

    One of the surprising observations by Mariner 10 during its March 1974 flyby of Mercury was the detection of intense bursts of energetic particles in Mercury's magnetosphere in association with substorm-like magnetic field reconfigurations. A full understanding of where, when, and how such particle bursts occur was not possible from the limited Mariner 10 data. The MESSENGER mission to Mercury has provided a wealth of new data about energetic particle phenomena. With observations from MESSENGER's Energetic Particle Spectrometer (EPS), as well as data arising from energetic electrons recorded by the X-Ray Spectrometer (XRS) and Gamma-Ray and Neutron Spectrometer (GRNS) instruments, recent work has greatly extended our record of the acceleration, transport, and loss of energetic electrons at Mercury. The combined data sets include measurements from a few keV up to several hundred keV in electron kinetic energy and have permitted relatively good spatial and temporal resolution for many events. We focus here on the detailed nature of energetic electron bursts measured by the GRNS system, and we place these events in the context of solar wind and magnetospheric forcing at Mercury. Our examination of data at high temporal resolution (10 ms) during the period March 2013 through October 2014 supports strongly the view that energetic electrons are accelerated in the near-tail region of Mercury's magnetosphere and are subsequently "injected" onto closed magnetic field lines on the planetary night side. The electrons evidently fill the plasma sheet volume and drift rapidly eastward toward the dawn and pre-noon sectors, at time executing multiple complete drifts around the planet to form "quasi-trapped" populations.

  15. Comprehensive survey of energetic electron events in Mercury's magnetosphere with data from the MESSENGER Gamma-Ray and Neutron Spectrometer

    NASA Astrophysics Data System (ADS)

    Lawrence, David J.; Anderson, Brian J.; Baker, Daniel N.; Feldman, William C.; Ho, George C.; Korth, Haje; McNutt, Ralph L.; Peplowski, Patrick N.; Solomon, Sean C.; Starr, Richard D.; Vandegriff, Jon D.; Winslow, Reka M.

    2015-04-01

    Data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20 min. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call "quasi-permanent structures." Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons.

  16. The enhancement of cosmic radio noise absorption due to hiss-driven energetic electron precipitation during substorms

    NASA Astrophysics Data System (ADS)

    Li, Haimeng; Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Wang, Zhenzhen; Qiao, Zheng; Wygant, John R.

    2015-07-01

    The Van Allen probes, low-altitude NOAA satellite, MetOp satellite, and riometer are used to analyze variations of precipitating energetic electron fluxes and cosmic radio noise absorption (CNA) driven by plasmaspheric hiss with respect to geomagnetic activities. The hiss-driven energetic electron precipitations (at L ~ 4.7-5.3, magnetic local time (MLT) ~ 8-9) are observed during geomagnetic quiet condition and substorms, respectively. We find that the CNA detected by riometers increased very little in the hiss-driven event during quiet condition on 6 September 2012. The hiss-driven enhancement of riometer was still little during the first substorm on 30 September 2012. However, the absorption detected by the riometer largely increased, while the energies of the injected electrons became higher during the second substorm on 30 September 2012. The enhancement of CNA (ΔCNA) observed by the riometer and calculated with precipitating energetic electrons is in agreement during the second substorm, implying that the precipitating energetic electrons increase CNA to an obviously detectable level of the riometer during the second substorm on 30 September 2012. The conclusion is consistent with Rodger et al. (2012), which suggest that the higher level of ΔCNA prefers to occur in the substorms, because substorms may produce more intense energetic electron precipitation associated with electron injection. Furthermore, the combination of the observations and theory calculations also suggests that higher-energy electron (>55 keV) precipitation contributes more to the ΔCNA than the lower energy electron precipitation. In this paper, the higher-energy electron precipitation is related to lower frequency hiss.

  17. CDAW 9 analysis of magnetospheric events on May 3, 1986 - Event C

    NASA Technical Reports Server (NTRS)

    Baker, D. N.; Pulkkinen, T. I.; Mcpherron, R. L.; Craven, J. D.; Frank, L. A.; Elphinstone, R. D.; Murphree, J. S.; Fennell, J. F.; Lopez, R. E.; Nagai, T.

    1993-01-01

    An intense geomagnetic substorm event on May 3, 1986, occurring toward the end of a strong storm period, is studied. The auroral electrojet indices and global imaging data from both the Northern and Southern Hemispheres clearly revealed the growth phase and expansion phase development for a substorm with an onset at 0111 UT. An ideally located constellation of four spacecraft allowed detailed observation of the substorm growth phase in the near-tail region. A realistic time-evolving magnetic field model provided a global representation of the field configuration throughout the growth and early expansion phase of the substorm. Evidence of a narrowly localized substorm onset region in the near-earth tail is found. This region spread rapidly eastward and poleward after the 0111 UT onset. The results are consistent with a model of late growth phase formation of a magnetic neutral line. This reconnection region caused plasma sheet current diversion before the substorm onset and eventually led to cross-tail current disruption at the time of the substorm onset.

  18. Magnetospheric Multiscale (MMS) Orbit

    NASA Video Gallery

    This animation shows the orbits of Magnetospheric Multiscale (MMS) mission, a Solar-Terrestrial Probe mission comprising of four identically instrumented spacecraft that will study the Earth's magn...

  19. Is there a strange attractor in the magnetosphere?

    NASA Technical Reports Server (NTRS)

    Roberts, D. A.

    1991-01-01

    This paper reviews recent attempts to determine if some aspects of magnetospheric dynamics, and in particular substorms as measured by AE and AL geomagnetic indices, can be represented by a low-dimensional dynamical system. If true, this result would imply that a small set of ordinary differential equations could describe important aspects of substorm dynamics, greatly simplifying modeling and prediction efforts and providing significant input to more detailed modeling. The "embedding" and "correlation dimension" methods used to investigate the dimensionality of a physical process from a single time series are considered in detail with an emphasis on what can go wrong and what can be done about it. Two main conclusions of this work, which includes some new results on the particular case of AL, are (1) that a low-dimensional and probably strange attractor does exist in magnetospheric dynamics, and (2) that there is no reliable substitute for using large numbers of data points in performing analyses leading to this conclusion.

  20. Low energy particle signature of substorm dipolarization

    SciTech Connect

    Liu, C.; Perez, J.D. ); Moore, T.E.; Chappell, C.R. )

    1994-02-01

    The low energy particle signature of substorm dipolarization is exhibited through a case study of RIMS data on DE-1 at [approximately]2100 MLT, ILAT = 59[degrees][approximately]65[degrees], L = 3.8 [approximately] 5.4 R[sub E], and geocentric distances 2.6[approximately]2.9 R[sub E]. A strong cross-field-line, poleward outflow that lasts for a few minutes with a velocity that reaches at least 50 km/s is correlated with substorm activity evidenced in the AE index and the MAG-1 data. All the major species (H[sup +], He[sup +], O[sup +]) are observed to have the same bulk velocity. The parallel velocities are strongly correlated with the perpendicular velocities. The parallel acceleration is shown to result from the centrifugal force of the ExB drift induced by the dipolarizing perturbation of the magnetic field. 9 refs., 4 figs.

  1. Location and propagation of the magnetotail current disruption during substorm expansion: Analysis and simulation of an ISEE multi-onset event

    SciTech Connect

    Jacquey, C.; Sauvaud, J.A.; Dandouras, J. )

    1991-03-01

    Magnetic field variations measured onboard the ISEE-1 spacecraft in the tail northern lobe ({approximately}22 R{sub E} geocentric distance) during a substorm with multiple onsets are analyzed and simulated using a model current sheet shows that substorm onsets are associated with a partial disruption of the cross-tail current that begins in the near-earth plasma sheet ({approximately}7 R{sub E}) and that expands tailward during substorm expansion with a velocity of the order of 300 km/s. The two consecutive substorm onsets, which occur during a very active period (AE > 500 nT), correspond to a similar partial disruption of the near-earth current sheet that expands tailwards over a distance of the order of 80 R{sub E}.

  2. Generation mechanism of L-value dependence of oxygen flux enhancements during substorms

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Ebihara, Y.; Tanaka, T.; Ohtani, S.; Gkioulidou, M.; Takahashi, K.; Kistler, L. M.; Kletzing, C.

    2015-12-01

    The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures charged particles with an energy range from ~eV to ~ tens of keV. The observation shows that the energy flux of the particles increases inside the geosynchronous orbit during substorms. For some night-side events around the apogee, the energy flux of O+ ion enhances below ~10 keV at lower L shell, whereas the flux below ~8 keV sharply decreases at higher L shells. This structure of L-energy spectrogram of flux is observed only for the O+ ions. The purpose of this study is to investigate the generation mechanism of the structure by using numerical simulations. We utilized the global MHD simulation developed by Tanaka et al (2010, JGR) to simulate the electric and magnetic fields during substorms. We performed test particle simulation under the electric and magnetic fields by applying the same model introduced by Nakayama et al. (2015, JGR). In the test particle simulation each test particle carries the real number of particles in accordance with the Liouville theorem. Using the real number of particles, we reconstructed 6-dimensional phase space density and differential flux of O+ ions in the inner magnetosphere. We obtained the following results. (1) Just after the substorm onset, the dawn-to-dusk electric field is enhanced to ~ 20 mV/m in the night side tail region at L > 7. (2) The O+ ions are accelerated and transported to the inner region (L > ~5.5) by the large-amplitude electric field. (3) The reconstructed L-energy spectrogram shows a similar structure to the Van Allen Probes observation. (4) The difference in the flux enhancement between at lower L shell and higher L shells is due to two distinct acceleration processes: adiabatic and non-adiabatic. We will discuss the relationship between the particle acceleration and the structure of L-energy spectrogram of flux enhancement in detail.

  3. Dynamics of Storms and Substorms from the multi-scale WINDMI models

    NASA Astrophysics Data System (ADS)

    Horton, W.; Mithaiwala, M.; Doxas, I.; Wong, V.

    The 14 parameter WINDMI magnetosphere-ionosphere dynamics model is upgraded to include nightside region 2 shielding currents closing in the partial ring current and is tested on the seven GEM storms selected for community wide study. These geomagnetic storms last several days and typically contain many substorms. First we review the performance of the well known base model optimized with a genetic algorithm carried out over the 14 physics based parameters using the Blanchard-McPherron database of 117 isolated substorms. We then compare the performance for those standard parameters with those obtained for the seven GEM storms. Then we turn to the high dimensionality spatially resolved WINDMI-SR model and examine the Earthward and tailward propagation of current disruption type events. This is a multi-scale dynamics model that contains micro-scale instabilities in a global synthesis (or multimode) model driven by the solar wind. Due to global lobe inductance and the central plasma sheet plasma capacitance evaluated with Tsyganenko-87 field geometry, we find that the dipolarization pulses travel Earthward at speeds of order 50 km/s comparable to the observed dipolarization pulses. Currently the leading hypothesis for the slow sub-Alfven speed is that of Moore et al. who invoke high values of oxygen loading to lower the Alfven speed. Our lower pulse speed is from the global 3D cavity eigenmodes of the WINDMI-Tysganenko system. We present the results of integrating ensembles of central plasma sheet electrons first in the standard Li et al. 1998 dipolarization pulse model and then in the closely related WINDMI sub-Alfven pulses. The results for the substorm injection fluxes are estimated and compared with geosynchronous data. The nonlinear Dst of the Burton-McPherron equation and the Temerin-Li model are also discussed in view of the generalized WINDMI model.

  4. Electric field evidence for tailward flow at substorm onset

    NASA Technical Reports Server (NTRS)

    Nishida, A.; Tulunay, Y. K.; Mozer, F. S.; Cattell, C. A.; Hones, E. W., Jr.; Birn, J.

    1983-01-01

    Electric field observations made near the neutral sheet of the magnetotail provide additional support for the view that reconnection occurs in the near-earth region of the tail. Southward turnings of the magnetic field that start at, or shortly after, substorm onsets are accompanied by enhancements in the dawn-to-dusk electric field, resulting in a tailward E x B drift velocity. Both the magnetic and the electric fields in the tailward-flowing plasma are nonuniform and vary with inferred spatial scales of several earth radii in the events examined in this paper. These nonuniformities may be the consequence of the tearing-mode process. The E x B flow was also towards the neutral sheet and away from midnight in the events studied.

  5. The formation and evolution of a plasmoid flux rope using a global MHD simulation of an actual substorm event

    NASA Astrophysics Data System (ADS)

    Farr, Nathan; Baker, Daniel N.; Wiltberger, Michael

    We present the results of a global magnetohydrodynamic (MHD) simulation of a pair of substorms on August 11, 2002. Comparisons of data with simulation results reveal an agreement regarding the timing and sequence of events in the magnetosphere. We then present the results in the simulation of a plasmoid flux rope formed during the second substorm. Unlike standard 2-D depictions of reconnection and plasmoid release during a substorm, the simulation shows a highly complex structure that has considerable winding of both closed and open field lines. Additionally, the flux rope does not move tailward uniformly, but rather has a asymmetric motion in which the dawn flank portion moves tailward prior to the dusk end of the flux rope, resulting in a a skewed flux rope that runs almost downtail instead of crosstail. The flux rope structure begins on closed field lines, then progresses through open field lines and finally onto IMF field lines. Using the global simulation we can connect the large scale magnetotail reconfiguration with features on the auroral boundary of the model. The results shown here are in agreement with existing MHD tail simulations as well as flux rope observations from satellite data.

  6. MESSENGER Observations of Extreme Magnetic Tail Loading and Unloading During its Third Flyby of Mercury: Substorms?

    NASA Technical Reports Server (NTRS)

    Slavin, James A.; Anderson, Brian J.; Baker, Daniel N.; Benna, Mehdi; Gloeckler, George; Krimigis, Stamatios M.; McNutt, Ralph L., Jr.; Schriver, David; Solomon, Sean C.; Zurbuchen, Thomas H.

    2010-01-01

    During MESSENGER's third flyby of Mercury on September 29, 2009, a variable interplanetary magnetic field produced a series of several minute enhancements of the tail magnetic field hy factors of approx. 2 to 3.5. The magnetic field flaring during these intervals indicates that they result from loading of the tail with magnetic flux transferred from the dayside magnetosphere. The unloading intervals were associated with plasmoids and traveling compression regions, signatures of tail reconnection. The peak tail magnetic flux during the smallest loading events equaled 30% of the magnetic flux emanating from Mercury, and may have reached 100% for the largest event. In this case the dayside magnetic shielding is reduced and solar wind flux impacting the surface may be greatly enhanced. Despite the intensity of these events and their similarity to terrestrial substorm magnetic flux dynamics, no energetic charged particles with energies greater than 36 keV were observed.

  7. Substorm effects in MHD and test particle simulations of magnetotail dynamics

    SciTech Connect

    Birn, J.; Hesse, M.

    1998-12-31

    Recent magnetohydrodynamic simulations demonstrate that a global tail instability, initiated by localized breakdown of MHD, can cause plasmoid formation and ejection as well as dipolarization and the current diversion of the substorm current wedge. The connection between the reconnection process and the current wedge signatures is provided by earthward flow from the reconnection site. Its braking and diversion in the inner magnetosphere causes dipolarization and the magnetic field distortions of the current wedge. The authors demonstrate the characteristic properties of this process and the current systems involved. The strong localized electric field associated with the flow burst and the dipolarization is also the cause of particle acceleration and energetic particle injections. Test particle simulations of orbits in the MHD fields yield results that are quite consistent with observed injection signatures.

  8. Analysis of the linear response function relating AL to VB{sub s} for individual substorms

    SciTech Connect

    Blanchard, G.T.; McPherron, R.L.

    1995-10-01

    Time series of the AL index and rectified solar wind electric field are used to study solar wind coupling to auroral ionospheric currents during individual substorms. Calculation of the individual filters is accompanied by representing them as the product of two simple filters: a low-pass filter that accounts for the response of the ionospheric electric field to the reconnection electric field, and a filter composed of delta function. The delta functions each have the effect of delaying and scaling the response of AL relative to VB{sub s} without distorting the waveform of VB{sub s}. Nearly all significant correlation between AL and VB{sub s} can be accounted for when the second filter contains only two components. This result suggests that the westward electrojet indexed by AL is controlled by two distinct processes, both proportional to VB{sub s}. For an ensemble of 117 isolated substorms the average prediction efficiency of a filter with two delays is 71%. If one were able to determine the exact values of the two delays and the two gain factors prior to an event, then one would be able to estimate the instantaneous magnetospheric response function. The authors examined season, universal time, and prior activity as possible factors controlling the magnitude of the parameters but found no apparent relationships. Until such relations are found the average parameters provide the best estimate but account for only 47% of the variance in the AL index. 20 refs., 10 figs.

  9. Ionospheric signatures of a plasma sheet rebound flow during a substorm onset

    NASA Astrophysics Data System (ADS)

    Juusola, L.; Kubyshkina, M.; Nakamura, R.; PitkäNen, T.; Amm, O.; Kauristie, K.; Partamies, N.; RèMe, H.; Snekvik, K.; Whiter, D.

    2013-01-01

    Magnetic reconnection in Earth's magnetotail produces fast earthward flows in the plasma sheet. Tailward flows are often observed associated with the earthward flows. Both return flow vortices at the flanks of an earthward flow channel and rebound of the earthward flow from the intense dipolar magnetic field of the inner magnetosphere have been shown to explain tailward flows observed near Earth. We combine plasma sheet measurements from Cluster with conjugate ground-based magnetic and auroral data to examine the development of earthward and tailward flow signatures during a substorm onset. We show for the first time observations of ionospheric signatures that appear to be associated with rebound flows. Because of the highly dynamic magnetotail configuration, special care is taken with the satellite footprint mapping. The ionospheric footprints produced by the event oriented AM02 model drift equatorward and poleward in response to tail magnetic field stretching and dipolarization, respectively. The footprint motion matches that of the ambient ionospheric structures, and the plasma flow measured by Cluster agrees with that inferred from the conjugate ionospheric observations, confirming the validity of the AM02 mapping. The ionospheric signatures of fast earthward flows during a substorm onset are shown to resemble the known signatures of quiet-time flows, including equatorward propagating auroral streamers inside a channel of enhanced poleward equivalent current. However, the large-scale dipolarization results in additional poleward expansion of the signatures, as has been predicted by simulations.

  10. Near-earth Thin Current Sheets and Birkeland Currents during Substorm Growth Phase

    SciTech Connect

    Sorin Zaharia; C.Z. Cheng

    2003-04-30

    Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (|X| {approx} 9 R{sub E}) thin cross-tail current sheet, as well as the equatorward shift of the ionospheric Birkeland currents. Our study is performed by solving the 3-D force-balance equation with realistic boundary conditions and pressure distributions. The results show a cross-tail current sheet with large current (J{sub {phi}} {approx} 10 nA/m{sup 2}) and very high plasma {beta} ({beta} {approx} 40) between 7 and 10 R{sub E}. The obtained region-1 and region-2 Birkeland currents, formed on closed field lines due to pressure gradients, move equatorward and become more intense (J{sub {parallel}max} {approx} 3 {micro}A/m{sup 2}) compared to quiet times. Both results are in agreement with substorm growth phase observations. Our results also predict that the cross-tail current sheet maps into the ionosphere in the transition region between the region-1 and region-2 currents.

  11. CURRENT SHEET THINNING AND ENTROPY CONSTRAINTS DURING THE SUBSTORM GROWTH PHASE

    NASA Astrophysics Data System (ADS)

    Otto, A.; Hall, F., IV

    2009-12-01

    A typical property during the growth phase of geomagnetic substorms is the thinning of the near-Earth current sheet, most pronounced in the region between 6 and 15 R_E. We propose that the cause for the current sheet thinning is convection from the midnight tail region to the dayside to replenish magnetospheric magnetic flux which is eroded at the dayside as a result of dayside reconnection. Adiabatic convection from the near-Earth tail region toward the dayside must conserve the entropy on magnetic field lines. This constraint prohibits a source of the magnetic flux from a region further out in the magnetotail. Thus the near-Earth tail region is increasingly depleted of magnetic flux (the Erickson and Wolf [1980] problem) with entropy matching that of flux tubes that are eroded on the dayside. It is proposed that the magnetic flux depletion in the near-Earth tail forces the formation of thin current layers. The process is documented by three-dimensional MHD simulations. It is shown that the simulations yield a time scale, location, and other general characteristics of the current sheet evolution during the substorm growth phase.

  12. Convection Constraints and Current Sheet Thinning During the Substorm Growth Phase

    NASA Astrophysics Data System (ADS)

    Otto, A.; Hsieh, M.

    2012-12-01

    A typical property during the growth phase of geomagnetic substorms is the thinning of the near-Earth current sheet, most pronounced in the region between 6 and 15 RE. We propose that the cause for this current sheet thinning is convection from the midnight tail region to the dayside to replenish magnetospheric magnetic flux that is eroded at the dayside as a result of dayside reconnection. Slow (adiabatic) convection from the near-Earth tail region toward the dayside must conserve the entropy on magnetic field lines. This constraint prohibits a source of magnetic flux from a region further out in the magnetotail. Thus the near-Earth tail region is increasingly depleted of magnetic flux (the Erickson and Wolf [1980] problem) with entropy matching that of flux tubes that are eroded on the dayside. It is proposed that the magnetic flux depletion in the near-Earth tail forces the formation of thin current layers. The process is illustrated and examined by three-dimensional meso-scale MHD simulations. It is shown that the simulations yield a time scale, location, and other general characteristics of the current sheet evolution consistent with observations during the substorm growth phase. The developing thin current sheet is easily destabilized and can undergo localized reconnection events. We present properties of the thinning current sheet, the associated entropy evolution, examples of localized reconnection onset and we discuss the dependence of this process on external parameters such the global reconnection rate.

  13. MHD simulations using average solar wind conditions for substorms observed under northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Park, K. S.; Lee, D.-Y.; Ogino, T.; Lee, D. H.

    2015-09-01

    Substorms are known to sometimes occur even under northward interplanetary magnetic field (IMF) conditions. In this paper, we perform three-dimensional global magnetohydrodynamic simulations to examine dayside reconnection, tail, and ionospheric signatures for two cases of substorm observations under prolonged northward and dawnward IMF conditions: (1) a strongly northward/dawnward IMF case with BIMF = (0, -20, 20) nT; (2) a weakly northward/dawnward IMF case with BIMF = (0, -2, 2) nT. Throughout the simulations, we used the constant solar wind conditions to reflect the prolonged solar wind conditions around the substorm times. We found that, in both cases, the tail reconnection occurred after the usual high-latitude reconnection on the dayside, providing a possible energy source for later triggered substorm observations under northward IMF conditions. The presence of an equal amount of IMF By allows the high-latitude reconnected magnetic field lines to transport to the tail lobe, eventually leading to the tail reconnection. The simulation results also revealed the following major differences between the two cases: First, the reconnection onset (both on dayside and in the tail) occurs earlier in the strongly northward IMF case than in the weakly northward IMF case. Second, the polar cap size, which is finite in both cases despite the northward IMF conditions and thus supports the lobe energy buildup needed for the substorm occurrences, is larger in the strongly northward IMF case. Accordingly, the polar cap potential is far larger in the strongly northward IMF case (hundreds of kilovolt) than in the weakly northward IMF case (tens of kilovolt). Third, in the strongly northward IMF case, the strong earthward tail plasma flow appears to be caused by the enhanced convection (so enhanced duskward Ey) due to the tail reconnection. In contrast, in the weakly northward IMF case, the earthward tail plasma flow increases gradually in association with a modestly increased

  14. The irregular Pi3 geomagnetic pulsations and its connection with the energetic particles in the magnetosphere and ionosphere

    NASA Astrophysics Data System (ADS)

    Belakhovsky, Vladimir; Pilipenko, Vjacheslav

    2015-04-01

    In this study we investigate the nighttime irregular Pi3 type geomagnetic pulsations generated as during strong single substorms as during sawtooth events using modern satellite (GOES, THEMIS) and ground-based observations (CARISMA, THEMIS, NORSTAR). These pulsations developed during all substorm period but not only during substorm growth phase as ordinary Pi2 pulsations. The maximum intensity of these pulsations lies in auroral zone (~66° CGL). It is seen a good correspondence between Pi3 geomagnetic pulsations on the ground-based magnetometers of the CARISMA network and on the GOES geostationary spacecraft, THEMIS spacecrafts which located at ~10 Re in the magnetosphere tail. It is seen strong increase of the fluxes of the electrons on GOES, THEMIS spacecrafts, increase of CNA on the NORSTAR riometers, increase of the aurora intensity on the THEMIS all-sky imagers during the beginning of the substrom. The considered irregular Pi3 pulsations strongly modulate the fluxes of the electrons in the magnetosphere at GOES, THEMIS spacecrafts and CNA, aurora intensity. But there is no close phase correspondence between the Pi3 pulsations in the geomagnetic field and fluxes of the trapped and precipitated electrons. At the same time there is no simultaneous geomagnetic pulsations in the same frequency rage was observed on the dayside (IMAGE network). We suppose that these Pi3 pulsations have another physical nature than dayside Pc5 pulsations. The Pi3 geomagnetic pulsations may be generated due to proper geomagnetic tail oscillations during substorm development.

  15. Magnetosphere-Ionosphere Convection as a Compound System

    NASA Astrophysics Data System (ADS)

    Tanaka, T.

    2007-12-01

    Convection is the most fundamental process in understanding the structure of geospace and disturbances observed in the magnetosphere-ionosphere (M-I) system. In this paper, a self-consistent configuration of the global convection system is considered under the real topology as a compound system. Investigations are made based on the M-I coupling scheme by analyzing numerical results obtained from magnetohydrodynamic (MHD) simulations which guarantee the self-consistency in the whole system under the Bv (magnetic field and velocity) paradigm. It is emphasized in the M-I coupling scheme that convection and field-aligned current (FAC) are different aspects of same physical process characterizing the open magnetosphere. Special attention is given in this paper to the energy supplying (dynamo) process that drives the FAC system. In the convection system, the dynamo must be constructed from shear motion together with plasma population regimes to steadily drive the convection. Convection patterns observed in the ionosphere are also the manifestation of achievement in global self-consistency. A primary approach to apply these concepts to the study of geospace is to consider how the M-I system adjusts the relative motion between the compressible magnetosphere and the incompressible ionosphere when responding to given solar-wind conditions. The above principle is also applicable for the study of disturbance phenomena such as the substorm as well as for the study of apparently unique processes such as the flux transfer event (FTE), the sudden commencement (SC), and the theta aurora. Finally, an attempt is made to understand the substorm as the extension of enhanced convection under the southward interplanetary magnetic field (IMF) condition.

  16. Generation of Alfven waves by deceleration of magnetospheric convection and broadband Pi pulsations

    NASA Technical Reports Server (NTRS)

    Kan, J. R.; Lee, L. C.; Longenecker, D. U.; Chiu, Y. T.

    1982-01-01

    The generation of Alfven waves by the deceleration of magnetospheric convection caused by ionospheric loading effects in the magnetospheric dynamo is considered. A one-dimensional model of that region of the plasma sheet where convection is decelerated due to the dynamo process in the magnetosphere-ionosphere coupling is formulated, and the stability of the region is analyzed in order to derive the growth rate of unstable Alfven waves. The effects of ionospheric damping on unstable Alfven wave packets bounding between hemispheres are estimated. It is found that the overall growth rate is proportional to the height-integrated Pedersen conductivity and the convection speed in the dynamic region, but changes into a damping rate when the Pedersen conductivity is reduced below a specific threshold. The unstable Alfven waves thus generated are also found to contribute to both burstlike and relatively continuous Pi pulsations observed during substorms.

  17. Magnetospheres in the solar system

    SciTech Connect

    Mcnutt, R.L.

    1984-11-01

    Intrinsic and induced magnetospheres of planets, moons, and comets in the solar system are described. Magnetospheric electric fields, the plasmasphere, rotational effects, and corotation and convection dominated intrinsic magnetospheres are considered. Supersonic and subsonic interactions in induced magnetospheres are discussed. (ESA)

  18. Suprathermal O/sup +/ and H/sup +/ ion behavior during the March 22, 1979 (CDAW 6), substorms

    SciTech Connect

    Ipavich, F.M.; Galvin, A.B.; Scholer, M.; Gloeckler, G.; Hovestadt, D.; Klecker, B.

    1985-02-01

    We present measurements of energetic (approx.130 keV) O/sup +/ ions in the earth's magnetosphere during the two Coordinated Data Analysis Workshop 6 substorms on March 22, 1979. The behavior of thermal and suprathermal H/sup +/ (10--130 keV) and suprathermal He/sup + +/ (30--130 keV/e) ions is also discussed. The observations were made with the University of Maryland/Max-Planck-Institut ultralow energy charge analyzer (ULECA) sensor on ISEE 1 at geocentric distances approx.16 to 7 R/sub E/ in the earth's magnetotail. Approximately 15 min before the 1054 UT onset of the first substorm, energetic O/sup +/ ions are observed streaming tailward. H/sup +/ and He/sup + +/ ions at all energies were generally streaming tailward from approx.1059 to 1115 UT, consistent with the presence of a near-earth neutral line during this interval. From 1117 to 1124 UT the H/sup +/ and He/sup + +/ ions were observed flowing earthward, suggesting that at approx.1117 UT the neutral line retreated tailward. A brief interval in the southern tail lobe, from approx.1124 to 1126 UT, was highlighted by an intense O/sup +/ beam streaming tailward; the O/sup +//H/sup +/ ratio at 130 keV was 7 +- 2. This suggests that high energy O/sup +/ ions may be accelerated directly out of the ionosphere. The recovery phase of the first substorm began a few minutes later and was characterized by large intensities of nearly isotropic suprathermal ions. The O/sup +//H/sup +/ differential intensity ratio at 130 keV was quite large (approx.1) during the recovery phase of both substorms.

  19. Saturn's Magnetospheric Cusp: Cassini Observations

    NASA Astrophysics Data System (ADS)

    Jasinski, J. M.; Arridge, C. S.; Sergis, N.; Coates, A. J.; Jones, G. H.

    2015-12-01

    The first in-situ analysis of the high-latitude magnetospheric cusp region at Saturn is presented using data from the Cassini spacecraft. The cusp is a funnel-shaped region where shocked solar wind plasma is able to enter the magnetosphere via the process of magnetic reconnection. The analysis is presented in three sections: Firstly, a high-latitude spacecraft trajectory is shown to cross the northern cusp where magnetosheath plasma is observed in-situ. The ion observations are shown to be a result of `bursty' reconnection occurring at the dayside magnetopause. A different interval is also presented where the southern cusp is observed to oscillate with a period the same as Saturn's rotational period. Secondly, the locations of all the cusp crossings are shown. The field-aligned distances (calculated from observed ion energy-pitch angle dispersions) from the reconnection site are presented. The cusp events are also compared to solar wind propagation models to investigate any correlations. Finally, the magnetic field observations of the cusps are analysed focusing on the diamagnetic depressions. The data are subtracted from a magnetic field model, and the calculated magnetic pressure deficits are compared to the particle pressures. A high plasma pressure layer in the magnetosphere adjacent to the cusp is discovered to also depress the magnetic field.

  20. Magnetospheric-ionospheric Poynting flux

    NASA Technical Reports Server (NTRS)

    Thayer, Jeffrey P.

    1994-01-01

    Over the past three years of funding SRI, in collaboration with the University of Texas at Dallas, has been involved in determining the total electromagnetic energy flux into the upper atmosphere from DE-B electric and magnetic field measurements and modeling the electromagnetic energy flux at high latitudes, taking into account the coupled magnetosphere-ionosphere system. This effort has been very successful in establishing the DC Poynting flux as a fundamental quantity in describing the coupling of electromagnetic energy between the magnetosphere and ionosphere. The DE-B satellite electric and magnetic field measurements were carefully scrutinized to provide, for the first time, a large data set of DC, field-aligned, Poynting flux measurement. Investigations describing the field-aligned Poynting flux observations from DE-B orbits under specific geomagnetic conditions and from many orbits were conducted to provide a statistical average of the Poynting flux distribution over the polar cap. The theoretical modeling effort has provided insight into the observations by formulating the connection between Poynting's theorem and the electromagnetic energy conversion processes that occur in the ionosphere. Modeling and evaluation of these processes has helped interpret the satellite observations of the DC Poynting flux and improved our understanding of the coupling between the ionosphere and magnetosphere.

  1. Magnetospheric Image Unfolding

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The Grant was a three year grant funded under the Space Physics Supporting Research and Technology and Suborbital Program. Our objective was to develop automated techniques needed to unfold or "invert" global images of the magnetospheric ion populations obtained by the new magnetospheric imaging techniques (ENA, EUV) in anticipation of future missions such as the Magnetospheric Imager and, now, IMAGE. Our focus on the present three year grant is to determine the degree to which such images can quantitatively constrain the global electromagnetic properties of the magnetosphere. In a previous three year grant period we successfully automated a forward modeling inversion algorithm, demonstrated that these inversions are robust in the face of realistic instrumental considerations such as counting statistics and backgrounds, applied error analysis techniques to the extracted parameters using variational procedures, implemented very realistic magnetospheric test images to test the inversion algorithms using the Rice University Magnetospheric Specification Model, and began the process of generating parametric models with the flexibility to handle the realistic magnetospheric images (e.g. Roelof et al, 1992; 1993). Our plan for the present 3 year grant period was to complete the development of the inversion tools needed to handle realistic magnetospheric images, assess the degree to which global electrodynamics is quantitatively constrained by ENA images of the magnetosphere, and bring the inversion of EUV images up to the maturity that we will have achieved for the ENA imaging. Below the accomplishments of our three year effort are present followed by a list of our presentations and publications. The accomplishments of all three years are presented here, and thus some of these items appeared on interim progress reports.

  2. Substorm Bulge/Surge Controlled by Polar Cap Flow Channels

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Nishimura, T.; Zou, Y.; Gallardo-Lacourt, B.; Donovan, E.; Shiokawa, K.; Nicolls, M. J.; Chen, S.; Ruohoniemi, J. M.; Nishitani, N.; McWilliams, K. A.

    2015-12-01

    Previous studies have provided evidence that localized channels of enhanced polar cap flow drive plasma sheet/auroral oval flow channels, auroral poleward boundary intensifications and streamers, and substorm onset. Evidence has also indicated that a persistence of such flow channels after substorm onset may enhance post-onset auroral poleward expansion and activity. Here, we combine auroral imager and radar observations to show evidence that polar-cap flow channels can directly feed the substorm bulge westward motion, i.e., the westward traveling surge, and its poleward expansion well into the pre-existing polar cap. By taking advantage of the capability of tracing polar cap arcs and patches over long distances with red line imaging, we are able to trace flow features that strongly affect the substorm bulge across the polar cap for up to ~1-1.5 hr prior to their impacting and affecting the substorm bulge.

  3. Spatial distribution of magnetic fluctuation power with period 40 to 600 s in the magnetosphere observed by THEMIS

    NASA Astrophysics Data System (ADS)

    Wang, G. Q.; Zhang, T. L.; Ge, Y. S.

    2015-11-01

    Ultralow frequency (ULF) fluctuations are ubiquitous in the magnetosphere and have significant influence on the energetic particle transport. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) data to give the spatial distribution of the Pi2/Pc4 and Pc5 band magnetic fluctuation amplitude near the magnetic equator in the magnetosphere. Statistical results can be summarized as follows: (1) strong ULF fluctuations are common in the magnetotail plasma sheet; the amplitude of all three components of magnetic fluctuations decreases with decreasing radial distance; (2) during periods of high AE index, fluctuations can propagate toward the Earth as far as the data cutoff in the nightside of the magnetosphere, and the amplitude of magnetic fluctuations is clearly stronger near the dusk sector of the synchronous orbit than that near the dawn sector, suggesting that the substorm particle injection has significant contribution to these fluctuations; (3) intense compressional Pc5 band magnetic fluctuations are a persistent feature near two flanks of the magnetosphere. Clear peaks of the compressional Pi2/Pc4 band magnetic fluctuation power near two flanks can be found during periods of fast solar wind, while the power of compressional Pi2/Pc4 band fluctuations is weak when the solar wind is slow. (4) Solar wind dynamic pressure and its variations can globally affect the ULF fluctuation power in the magnetosphere. Magnetic fluctuations near the noonside can penetrate from the magnetopause to the synchronous orbit or inner when solar wind pressure variations are large.

  4. Spatial distribution of magnetic fluctuation power with period 40 to 600 s in the magnetosphere observed by THEMIS

    NASA Astrophysics Data System (ADS)

    Wang, Guoqiang; Zhang, Tielong; Ge, Yasong

    2016-04-01

    Ultralow frequency (ULF) fluctuations are ubiquitous in the magnetosphere and have significant influence on the energetic particle transport. We use Time History of Events and Macroscale Interactions During Substorms (THEMIS) data to give the spatial distribution of the Pi2/Pc4- and Pc5-band magnetic fluctuation amplitude near the magnetic equator in the magnetosphere. Statistical results can be summarized as follows: (1) Strong ULF fluctuations are common in the magnetotail plasma sheet; The amplitude of all three components of magnetic fluctuations decreases with decreasing radial distance; (2) During periods of high AE index, fluctuations can propagate toward the Earth as far as the data cutoff in the nightside of the magnetosphere, and the amplitude of magnetic fluctuations is clearly stronger near the dusk sector of the synchronous orbit than that near the dawn sector, suggesting that the substorm particle injection has significant contribution to these fluctuations; (3) Intense compressional Pc5-band magnetic fluctuations are a persistent feature near two flanks of the magnetosphere. Clear peaks of the compressional Pi2/Pc4-band magnetic fluctuation power near two flanks can be found during periods of fast solar wind, while the power of compressional Pi2/Pc4-band fluctuations is weak when the solar wind is slow. (4) Solar wind dynamic pressure and its variations can globally affect the ULF fluctuation power in the magnetosphere. Magnetic fluctuations near the noon side can penetrate from the magnetopause to the synchronous orbit or inner when solar wind pressure variations are large.

  5. The magnetosphere of Saturn

    NASA Technical Reports Server (NTRS)

    Schardt, A. W.

    1982-01-01

    Information about the magnetosphere of Saturn is provided: the magnetic dipole moment is axisymmetric, the bow shock stand-off distance is about 22 R sub S. The satellites Titan, Dione, and Tethys are probably the primary sources of magnetospheric plasma. Outside of approx. 4 R sub S, energetic particles are energized by diffusing inward while conserving their first and second adiabatic invariants. Particles are lost by satellite sweep-out, absorption byt the E ring and probably also by plasma interactions. The inner magnetosphere is characterized.

  6. Multiradar observations of substorm-driven ULF waves

    NASA Astrophysics Data System (ADS)

    James, M. K.; Yeoman, T. K.; Mager, P. N.; Klimushkin, D. Yu.

    2016-06-01

    A recent statistical study of ULF waves driven by substorm-injected particles observed using Super Dual Auroral Radar Network (SuperDARN) found that the phase characteristics of these waves varied depending on where the wave was observed relative to the substorm. Typically, positive azimuthal wave numbers, m, were observed in waves generated to the east of the substorms and negative m to the west. The magnitude of m typically increased with the azimuthal separation between the wave observation and the substorm location. The energies estimated for the driving particles for these 83 wave events were found to be highest when the waves were observed closer to the substorm and lowest farther away. Each of the 83 events studied by James et al. (2013) involved just a single wave observation per substorm. Here a study of three individual substorm events are presented, with associated observations of multiple ULF waves using various different SuperDARN radars. We demonstrate that a single substorm is capable of driving a number of wave events characterized by different azimuthal scale lengths and wave periods, associated with different energies, W, in the driving particle population. We find that similar trends in m and W exist for multiple wave events with a single substorm as was seen in the single wave events of James et al. (2013). The variety of wave periods present on similar L shells in this study may also be evidence for the detection of both poloidal Alfvén and drift compressional mode waves driven by substorm-injected particles.

  7. Ionospheric and magnetospheric plasmapauses'

    NASA Technical Reports Server (NTRS)

    Grebowsky, J. M.; Hoffman, J. H.; Maynard, N. C.

    1977-01-01

    During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of about 5.2 R sub e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2-5.4. The locations of the Explorer 45 plasmapause crossings during this month were compared to the latitudinal decreases of the H(+) density observed on ISIS 2 near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Vertical flows of the H(+) ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 kilometers/sec near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H(+) trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause.

  8. Van Allen Probe Observations: Near-Earth injections of Mev Electrons Associated with Intense Substorm Electric Fields

    NASA Astrophysics Data System (ADS)

    Dai, L.; Wygant, J. R.; Bonnell, J. W.; Cattell, C. A.; Kletzing, C.; Baker, D. N.; Li, X.; Malaspina, D.; Blake, J. B.; Fennell, J.; Claudepierre, S. G.; Takahashi, K.; Funsten, H. O.; Reeves, G. D.; Spence, H. E.; Angelopoulos, V.; Glassmeier, K. H.; Turner, D. L.; Thaller, S. A.; Breneman, A. W.; Kersten, K.; Tang, X.; Tao, X.

    2014-12-01

    With their unique orbit, the Van Allen Probes (RBSP) spacecraft are well suited to investigate near-Earth substorm injections that penetrate into the heart of outer radiation belts. Substorms are generally conceived to inject 10s-100s keV electrons but intense substorm electric fields have been shown capable of injecting ~MeV electrons as well at the geosynchronous altitude. An intriguing question is whether such MeV electron injections can penetrate to lower L shells and directly contribute to the relativistic electron population of the outer radiation belt. In this talk, we present RBSP observations of near-Earth substorm injection of MeV relativistic particles and associated intense dipolarization electric field at L ~5.5. The substorm injection occurred during a moderate storm (DST~-30 to -20) with steady solar wind conditions. RBSP-A observed dispersionless injection of electrons from 10s keV up to 3 MeV in the pre-mid night sector (MLT=22UT). The injection was associated with unusually large (60mV/m) dipolarization electric fields that lasted 1 minute. At about the same time, THEMIS-D observed energy-dispersive injection of electrons at energies as high as at least 720keV at L~6.8 in the pre-dawn sector. Injection of energetic protons (~1MeV) and proton drift echos were observed at RBSP-A as well. RBSP-A observed a broad spectrum of nonlinear electric field structures but no whistler waves at the injection. The properties of the observed dipolarization electric field constrain the acceleration mechanism responsible for the MeV electron injection. We will discuss the implications of these observations on the direct impact of substorms on the outer radiation belt.

  9. 0.5-4 Å X-RAY BRIGHTENINGS IN THE MAGNETOSPHERE OBSERVED BY THE GEOSTATIONARY OPERATIONAL ENVIRONMENTAL SATELLITES

    SciTech Connect

    Yamamoto, Tetsuya T.; Miyoshi, Y.

    2013-10-01

    We found 217 X-ray brightening events in Earth's magnetosphere. These events occur in the high-energy band (0.5-4 Å) of the Geostationary Operational Environmental Satellite (GOES) X-ray light curves, although GOES X-ray light curves are frequently used as indices of solar flare magnitudes. We found that (1) brightening events are absent in the low-energy band (1-8 Å), unlike those associated with solar flares; and (2) the peak fluxes, durations, and onset times of these events depend on the magnetic local time (MLT). The events were detected in 2006, 2010, and 2011 at around 19-10 MLT, that is, from night to morning. They typically lasted for 2-3 hr. Their peak fluxes are less than 3 × 10{sup –8} W m{sup –2} in the 0.5-4 Å band and are maximized around 0-5 MLT. From these MLT dependencies, we constructed an MLT time profile of X-ray brightening events. Because 0.5-4 and 1-8 Å fluxes were observed and had the same order of magnitude when GOES 14 passed through Earth's shadow, we expected that X-ray brightening events in the 1-8 Å band are obscured by high-background X-ray fluxes coming from the Sun. We also found coincidence between X-ray brightening events and aurora substorms. In the majority of our events, the minimum geomagnetic field values (AL index) are below –400 nT. From these results and consideration of the GOES satellite orbit, we expect that these X-ray brightening events occur in the magnetosphere. We cannot, however, clarify the radiative process of the observed X-ray brightening events.

  10. LANL Studies Earth's Magnetosphere

    ScienceCinema

    Daughton, Bill

    2014-08-12

    A new 3-D supercomputer model presents a new theory of how magnetic reconnection works in high-temperature plasmas. This Los Alamos National Laboratory research supports an upcoming NASA mission to study Earth's magnetosphere in greater detail than ever.

  11. Solar and magnetospheric science

    NASA Technical Reports Server (NTRS)

    Timothy, A. F.; Schmerling, E. R.; Chapman, R. D.

    1976-01-01

    The current status of the Solar Physics Program and the Magnetospheric Physics Program is discussed. The scientific context for each of the programs is presented, then the current programs and future plans are outlined.

  12. Magnetospheric and auroral processes

    NASA Technical Reports Server (NTRS)

    Reiff, Patricia H.

    1990-01-01

    Progress was made on the following two projects within the semiannual period: (1) simulations of the magnetic storm of April 1988 using the Magnetospheric Specification Model; and (2) improvement of a user-oriented electric-field model.

  13. LANL Studies Earth's Magnetosphere

    SciTech Connect

    Daughton, Bill

    2011-04-15

    A new 3-D supercomputer model presents a new theory of how magnetic reconnection works in high-temperature plasmas. This Los Alamos National Laboratory research supports an upcoming NASA mission to study Earth's magnetosphere in greater detail than ever.

  14. The Pulsating Pulsar Magnetosphere

    NASA Astrophysics Data System (ADS)

    Tsui, K. H.

    2015-06-01

    Following the basic principles of a charge-separated pulsar magnetosphere, we consider the magnetosphere to be stationary in space, instead of corotating, and the electric field to be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the plasma of the magnetosphere undergoes guiding center drifts of the gyromotion due to the forces transverse to the magnetic field. These forces are the electric force, magnetic gradient force, and field line curvature force. Since these plasma velocities are of drift nature, there is no need to introduce an emf along the field lines, which would contradict the {{E}\\parallel }={\\boldsymbol{E}} \\cdot {\\boldsymbol{B}} =0 plasma condition. Furthermore, there is also no need to introduce the critical field line separating the electron and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms of plasma velocities. The fields and velocities are then connected through the space-charge densities self-consistently. We solve the pulsar equation analytically for the fields and construct the standard steady-state pulsar magnetosphere. By considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar pumping rate exceeds the Poynting flux in the open field lines, plasma pressure can build up in the magnetosphere, in particular, in the closed region. This could cause a periodic opening up of the closed region, leading to a pulsating magnetosphere, which could be an alternative to pulsar beacons. The closed region can also be opened periodically by the build up of toroidal magnetic field through a positive feedback cycle.

  15. A current disruption mechanism in the neutral sheet for triggering substorm expansions

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.; Mankofsky, A.; Chang, C.-L.; Papadopoulos, K.; Wu, C. S.

    1989-01-01

    Two main areas were addressed in support of an effort to understand mechanism responsible for the broadband electrostatic noise (BEN) observed in the magnetotail. The first area concerns the generation of BEN in the boundary layer region of the magnetotail whereas the second area concerns the occassional presence of BEN in the neutral sheet region. For the generation of BEN in the boundary layer region, a hybrid simulation code was developed to perform reliable longtime, quiet, highly resolved simulations of field aligned electron and ion beam flow. The result of the simulation shows that broadband emissions cannot be generated by beam-plasma instability if realistic values of the ion beam parameters are used. The waves generated from beam-plasma instability are highly discrete and are of high frequencies. For the plasma sheet boundary layer condition, the wave frequencies are in the kHz range, which is incompatible with the observation that the peak power in BEN occur in the 10's of Hz range. It was found that the BEN characteristics are more consistent with lower hybrid drift instability. For the occasional presence of BEN in the neutral sheet region, a linear analysis of the kinetic cross-field streaming instability appropriate to the neutral sheet condition just prior to onset of substorm expansion was performed. By solving numerically the dispersion relation, it was found that the instability has a growth time comparable to the onset time scale of substorm onset. The excited waves have a mixed polarization in the lower hybrid frequency range. The imposed drift driving the instability corresponds to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is in the 10 mV/m range which is well within the observed electric field values detected in the neutral sheet during substorms. This finding can potentially account for the disruption of cross-tail current and its diversion to

  16. Enabling Breakthrough Kinetic Simulations of the Magnetosphere Using Petascale Computing

    NASA Astrophysics Data System (ADS)

    Vu, H. X.; Karimabadi, H.; Omelchenko, Y.; Tatineni, M.; Majumdar, A.; Krauss-Varban, D.; Dorelli, J.

    2009-12-01

    Currently global magnetospheric simulations are predominantly based on single-fluid magnetohydrodynamics (MHD). MHD simulations have proven useful in studies of the global dynamics of the magnetosphere with the goal of predicting eminent features of substorms and other global events. But it is well known that the magnetosphere is dominated by ion kinetic effects, which is ignored in MHD simulations, and many key aspects of the magnetosphere relating to transport and structure of boundaries await global kinetic simulations. We are using our recent innovations in hybrid (electron fluid, kinetic ions) simulations, as being developed in our Hybrid3D (H3D) code, and the power of massively parallel machines to make, breakthrough 3D global kinetic simulations of the magnetosphere. The innovations include (i) multi-zone (asynchronous) algorithm, (ii) dynamic load balancing, and (iii) code adaptation and optimization to large number of processors. In this presentation we will show preliminary results of our progress to date using from 512 to over 8192 cores. In particular, we focus on what we believe to be the first demonstration of the formation of a flux rope in 3D global hybrid simulations. As in the MHD simulations, the resulting flux rope has a very complex structure, wrapping up field lines from different regions and appears to be connected on at least one end to Earth. Magnetic topology of the FTE is examined to reveal the existence of several separators (3D X-lines). The formation and growth of this structure will be discussed and spatial profile of the magnetic and plasma variables will be compared with those from MHD simulations.

  17. From the bow shock to the magnetosphere-ionosphere coupling

    NASA Astrophysics Data System (ADS)

    Ponomarev, E. A.; Sedykh, P. A.

    We suggest a description of magnetospheric processes in the form of a model consisting of three blocks 1 Block of electric current generation in the bow shock where the solar wind energy converts to electric energy This current closes through the magnetosphere in the form of the dawn-dusk current The bow shock can be a sufficient source of power for supplying energy to substorm processes The direction of current behind the bow shock front depends on the sign of the IMF Bz-component Ponomarev et al 2000 2003 It is this current which sets convection in motion by an Ampere force Any change in external current through the magnetosphere causes a convection restructuring within a time on the order of the travel time of the magnetosonic wave from the magnetopause to the center of the system because the restructuring wave comes from both flanks 2 Block of gas pressure relief formation The combined action of convection and strong pitch-angle diffusion of electrons and protons is responsible for the formation of gas pressure distribution in the magnetosphere Kennel C F 1969 Ponomarev E A 1985 that is steady bulk currents The divergence of these bulk currents brings about a spatial distribution of field-aligned currents i e magnetospheric sources of ionospheric current systems The combined action leads also to the formation of particle precipitation regions in the form of an oval corresponding to the location of the auroral zone The nonstationary solution of this problem with time-dependent boundary conditions reproduces the

  18. Black Hole Magnetospheres

    NASA Astrophysics Data System (ADS)

    Punsly, Brian

    This chapter compares and contrasts winds and jets driven by the two distinct components of the black magnetosphere: the event horizon magnetosphere (the large scale magnetic field lines that thread the event horizon) and the ergospheric disk magnetosphere associated with poloidal magnetic flux threading plasma near the equatorial plane of the ergosphere. The power of jets from the two components as predicted from single-fluid, perfect MHD numerical simulations are compared. The decomposition of the magnetosphere into these two components depends on the distribution of large scale poloidal magnetic flux in the ergosphere. However, the final distribution of magnetic flux in a black hole magnetosphere depends on physics beyond these simple single-fluid treatments, non-ideal MHD (eg, the dynamics of magnetic field reconnection and radiation effects) and two-fluid effects (eg, ion coupled waves and instabilities in the inner accretion flow). In this chapter, it is emphasized that magnetic field line reconnection is the most important of these physical elements. Unfortunately, in single-fluid perfect MHD simulations, reconnection is a mathematical artifact of numerical diffusion and is not determined by physical processes. Consequently, considerable calculational progress is required before we can reliably assess the role of each of these components of black hole magnetospheres in astrophysical systems.

  19. Geomagnetic Storm and Substorm Predictions with the Real-Time WINDMI Model

    NASA Astrophysics Data System (ADS)

    Mays, Mona; Horton, Wendell; Kozyra, Janet

    The Real-Time WINDMI model is an implementation of WINDMI, a low dimensional, plasma physics-based, nonlinear dynamical model of the coupled magnetosphere-ionosphere system. The system of nonlinear ordinary differential equations, which describes energy transfer into, and between dominant components of the nightside magnetosphere and ionosphere, is solved numerically to determine the state of each component. The model characterizes the energy stored in the ring current and the region 1 field-aligned current which are compared to the Dst and AL indices. Solar wind parameter measurements from ACE are automatically downloaded every 10 minutes and used to derive the input solar wind driving voltage to the model. This allows the computation of model Dst and AL values by Real-Time WINDMI about 1-2 hours before index data is available at the Kyoto WDC Quicklook website. Model results are shown on the website (http://orion.ph.utexas.edu/ windmi/realtime/). The model has captured about 15 storm and/or substorm events in the past 2 years it has been running. Model validation for the AL and Dst predictions is being implemented. Real-Time WINDMI performance is also studied for the rectified driving voltage compared to the Siscoe et al. voltage as input. We plan to compare the database of Real-Time WINDMI Dst predictions with other ring current models which contain different loss and energization processes. The work is supported by NSF grant ATM-0638480.

  20. Statistical characterization of the growth and spatial scales of the substorm onset arc

    NASA Astrophysics Data System (ADS)

    Kalmoni, N. M. E.; Rae, I. J.; Watt, C. E. J.; Murphy, K. R.; Forsyth, C.; Owen, C. J.

    2015-10-01

    We present the first multievent study of the spatial and temporal structuring of the aurora to provide statistical evidence of the near-Earth plasma instability which causes the substorm onset arc. Using data from ground-based auroral imagers, we study repeatable signatures of along-arc auroral beads, which are thought to represent the ionospheric projection of magnetospheric instability in the near-Earth plasma sheet. We show that the growth and spatial scales of these wave-like fluctuations are similar across multiple events, indicating that each sudden auroral brightening has a common explanation. We find statistically that growth rates for auroral beads peak at low wave number with the most unstable spatial scales mapping to an azimuthal wavelength λ≈ 1700-2500 km in the equatorial magnetosphere at around 9-12 RE. We compare growth rates and spatial scales with a range of theoretical predictions of magnetotail instabilities, including the Cross-Field Current Instability and the Shear Flow Ballooning Instability. We conclude that, although the Cross-Field Current instability can generate similar magnitude of growth rates, the range of unstable wave numbers indicates that the Shear Flow Ballooning Instability is the most likely explanation for our observations.

  1. Energy storage and dissipation in the magnetotail during substorms. 2. MHD simulations

    SciTech Connect

    Steinolfson, R.S. ); Winglee, R.M. )

    1993-05-01

    The authors present a global MHD simulation of the magnetotail in an effort to study magnetic storm development. They address the question of energy storage in the current sheet in the early phases of storm growth, which previous simulations have not shown. They address this problem by dealing with the variation of the resistivity throughout the magnetosphere. They argue that MHD theory should provide a suitable representation to this problem on a global scale, even if it does not handle all details adequately. For their simulation they use three different forms for the resistivity. First is a uniform and constant resistivity. Second is a resistivity proportional to the current density, which is related to argument that resistivity is driven by wave-particle interactions which should be strongest in regions where the current is the greatest. Thirdly is a model where the resistivity varies with the magnetic field strength, which was suggested by previous results from particle simulations of the same problem. The simulation then gives approximately the same response of the magnetosphere for all three of the models. Each results in the formation and ejection of plasmoids, but the energy stored in the magnetotail, the timing of substorm onset in relation to the appearance of a southward interplanetary magnetic field, and the speed of ejection of the plasmoids formed differ with the resistivity models.

  2. Resonance nature of the magnetosphere

    NASA Astrophysics Data System (ADS)

    Alpert, Ya. L.

    2001-01-01

    A new approach toward an understanding of the nature of low frequency e.m. waves ( f≪,magnetosphere is given in this essay. It is based on detailed studies of Fourier spectra of magnetic field records obtained at 14 observation points, with L=2.6-13, around the world: in Antarctica, Canada, Italy, Iceland, Russia, and the USA in the frequency band f≈1-250 mHz. It overlaps the frequency band of so-called Pc2-Pc5 micropulsations. Repetitive and non-repetitive single Pc1 micropulsations at f≈0.4-2.2 Hz are also briefly discussed here. Under different conditions they should be created, respectively, by interaction of a non-linear and/or only linear gyro-resonance instability mechanism. The oscillations considered exist at any time both in quiet (QC) and disturbed (DC) conditions. Their spectra possess a line structure. The background is composed of resonance oscillations, and weaker oscillations caused by noise. The resonance oscillations may occur in the entire magnetosphere or in its parts. In the frequency range examined 12, 20-25, and more resonance frequencies fs,res were accordingly found in the spectra of the NP and SP observation points ( L≃13) and in the Tuckerton and Point Arena ( L≃2.6) data. The higher-order resonance maxima are overlapped by the noise oscillations. All these oscillations can be set swinging, producing strong non-repetitive wave packets with durations τ0≈20-300 s and longer. The conditions for producing the swinging background can be impulse/shock excitations of the magnetospheric plasma, a gyro-resonance instability, etc. Thus, the well-known multiple manifestations of hydromagnetic wave packets observed in our research in the magnetosphere at f<0.25 Hz are considered to be the result of a single physical phenomenon: the fundamental resonance e.m. oscillatory nature of the background magnetospheric plasma environment. It is shown that the observed waves and the spectral

  3. Response of northern winter polar cap to auroral substorms

    NASA Astrophysics Data System (ADS)

    Liou, Kan; Sotirelis, Thomas

    2016-05-01

    The three-phase substorm sequence has been generally accepted and is often tied to the Dungey cycle. Although previous studies have mostly agreed on the increase and decrease in the polar cap area during an episode of substorm, there are disparate views on when the polar cap starts to contract relative to substorm onset. Here we address this conflict using high-resolution (~1-3 min) snapshot global auroral images from the ultraviolet imager on board the Polar spacecraft. On the basis of 28 auroral substorm events, all observed in the Northern Hemispheric winter, it is found that the polar cap inflated prior to onset in all events and it attained the largest area ~6 min prior to the substorm expansion phase onset, while the dayside polar cap area remained steady around the onset. The onset of nightside polar cap deflation is found to be attributed to intensifications of aurora on the poleward edge of the nightside oval, mostly in the midnight sector. Although this result supports the loading-unloading and reconnection substorm models, it is not clear if the initial polar cap deflation and the substorm expansion are parts of the same process.

  4. Global ULF Wave Energy Transport in the Magnetosphere

    NASA Astrophysics Data System (ADS)

    Rae, I. J.; Mann, I. R.; Donovan, E. F.; Fenrich, F. R.; Watt, C. E. J.; Milling, D. K.; Lester, M.; Singer, H. J.; Reme, H.; Balogh, A.

    Transport of ULF wave energy via large-scale wave modes is extremely important in terms of solar wind-magnetosphere-ionosphere coupling In this paper we present a study in which we fully characterise and diagnose large-scale ULF wave dynamics on a near-global scale We present a study using a favourable radial alignment of the Cluster Polar and geosynchronous satellites in the dusk sector during a high solar wind speed interval We infer that magnetopause undulations observed by Cluster drove compressional waves perhaps in the form of Kelvin-Helmholtz unstable magnetospheric waveguide modes that propagate inward from the magnetopause These compressional waves couple to resonant field lines close to location of Polar and geosynchronous orbit and are observed as a field line resonance on the ground Further we analyse the magnetopause boundary oscillations on both large- and small-scales using the minimum variance technique to identify the planar nature of the boundary layer magnetopause This has important implications for both the DoubleStar and THEMIS missions together with measurements from other satellites such as Cluster Geotail and the geosynchronous satellite fleet flank and dayside conjunctions of these satellites will be able to characterise the full radial and multi-scale nature of Global ULF wave events This technique is valuable for the investigation of tail phenomena excited via the same K-H activity at the flanks for example in the boundary layer model for magnetospheric substorms

  5. Mageis Observations in the Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Fennell, J. F.; Claudepierre, S. G.; O'Brien, T. P., III; Blake, J. B.; Clemmons, J. H.; Roeder, J. L.; Spence, H. E.; Reeves, G. D.

    2014-12-01

    We examine two aspects of the 10's of keV to MeV electron conditions in the inner magnetosphere. First is the observation of wave-particle interactions associated with substorm injections in the midnight to dawn region of the magnetosphere. Second is the electron content of the inner radiation zone and slot regions prior to and during storm times using background corrected MagEIS data. The wave-particle observations take advantage of the MagEIS high rate data mode in conjuction with the HOPE and EMFISIS burst mode data to show the tight relationship between the <70 keV electron fluxes and chorus waves. Both electron flux enhancements and flux depletions are observed during temporally localized chorus wave events. The ability to remove the penetrating backgrounds caused by energetic protons in the inner zone and electron generated bremsstrahlung in the slot and outer zone allows one to put limits on the electron fluxes in these regions, especially for energies greater than a few hundred keV. We find that deep in the inner zone the electrons fluxes at >800 keV are very low or non-existent while there are significant fluxes of electrons at lower energies, down to MagEIS limit of ~30 keV. The more dynamic slot region fluxes have been similarly dominated by such lower energy electron fluxes thus far during the Van Allen Probes mission. We will also show evidence that during storm times the seed population electrons, <200 keV, can penetrate deep into the slot region and, at times, even into the inner zone.

  6. Principal component analysis of Birkeland currents determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment

    NASA Astrophysics Data System (ADS)

    Milan, S. E.; Carter, J. A.; Korth, H.; Anderson, B. J.

    2015-12-01

    Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. Principal component analysis (PCA) identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The regions 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly reconnected field lines. The cusp currents are strongly modulated by season, indicating that their strength is regulated by the ionospheric conductance at the foot of the field lines. PCA does not identify a pattern that is clearly characteristic of a substorm current wedge. Rather, a superposed epoch analysis of the currents associated with substorms demonstrates that there is not a single mode of response, but a complicated and subtle mixture of different patterns.

  7. Nonlinear, relativistic Langmuir waves in astrophysical magnetospheres

    NASA Technical Reports Server (NTRS)

    Chian, Abraham C.-L.

    1987-01-01

    Large amplitude, electrostatic plasma waves are relevant to physical processes occurring in the astrophysical magnetospheres wherein charged particles are accelerated to relativistic energies by strong waves emitted by pulsars, quasars, or radio galaxies. The nonlinear, relativistic theory of traveling Langmuir waves in a cold plasma is reviewed. The cases of streaming electron plasma, electronic plasma, and two-streams are discussed.

  8. First-Principles Simulations of Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Spitkovsky, Anatoly

    simulations of pulsar magnetospheres using particle-in-cell (PIC) method. PIC is an established technique for plasma simulations that represents the plasma as charged macroparticles that are advanced in electromagnetic fields. The fields are evolved with particle currents as sources, completing the cycle. We recently demonstrated that self-consistent PIC simulations with particle extraction from the star and pair production in the magnetosphere lead to solutions that resemble the force-free state, but carry information about particle acceleration and beaming. We will perform a numerical survey of pulsar magnetospheres with a multitude of pair production prescriptions in order to ascertain the regimes of pulsar parameter space where magnetospheres with abundant plasma occur. Further, we will use the plasma distribution function from these simulations to calculate the gamma-ray light curves and phase-resolved spectra, comparing them with our previous work on emission from force-free magnetic geometries. These results will be applied to interpret the library of pulsar light curves from Fermi. 45 years after discovery of pulsars, the study of pulsar magnetospheres is now undergoing an exciting transformation, where a calculable standard model is being formulated. The advent of global kinetic simulations that we will utilize in this research will enable us to produce the first complete ab-initio models of pulsar magnetospheres and their emission, solving one of the oldest unsolved problems in astrophysics.

  9. Solar wind-magnetosphere coupling and the distant magnetotail: ISEE-3 observations

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Smith, E. J.; Sibeck, D. G.; Baker, D. N.; Zwickl, R. D.; Akasofu, S. I.; Lepping, R. P.

    1985-01-01

    ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from absolute value of X = 120 to 140 R/sub e near the center of the tail to beyond absolute value of X = 200 R/sub e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B/sub z in the solar wind as observed by IMP-8. V/sub x in the distant plasma sheet is also found to be proportional to IMF B/sub z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 +- 5% is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B/sub z and tailward V/sub x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-Earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.

  10. Particle scattering and current sheet stability in the geomagnetic tail during the substorm growth phase

    SciTech Connect

    Pulkkinen, T.I.; Pellinen, R.J.; Koskinen, H.E.J. ); Baker, D.N. ); Buechner, J. ); Lopez, R.E. ); Dyson, R.L.; Frank, L.A. )

    1992-12-01

    The degree of pitch angle scattering and chaotization of various particle populations in the geomagnetic tail during the substorm growth phase is studied by utilizing the Tsyganenko 1989 magnetic field model. A temporally evolving magnetic field model for the growth phase is constructed by enhancing the near-Earth currents and thinning the current sheet from the values given by the static Tsyganenko model. Changing the field geometry toward an increasingly taillike configuration leads to pitch angle scattering of particles whose Larmor radii become comparable to the field line radius of curvature. Several different cases representing substorms with varying levels of magnetic disturbance have been studied. In each case, the field development during the growth phase leads to considerable scattering of the thermal electrons relatively close to the Earth. The current sheet regions where the electron motion is chaotic are magnetically mapped to the ionosphere and compared with low-altitude measurements of electron precipitation. The chaotization of the thermal electron population occurs within a few minutes of the substorm onset, and the ionospheric mappings of the chaotic regions in the equatorial plane compare well with the region of brightening auroras. Even though the temporal evolution of the complex plasma system cannot be self-consistently described by the temporal evolution of the empirical field model, these models can provide the most accurate estimates of the field parameters for tail stability calculations.

  11. Observations of plasma sheet expansion at substorm onset, R = 15 to 22 R[sub e

    SciTech Connect

    Lyons, L.R.; Huang, C.Y.

    1992-09-23

    The authors have used a large number of auroral magnetograms to identify four isolated substorms and estimate their onset times. At the onsets, ISEE-1 was in the vicinity of magnetic midnight at radial distances of 15.6 to 21.8 R[sub e] and very near the outer boundary of the plasma sheet. They find that, for each event, the plasma sheet expanded, and the magnetic field dipolarized at the inferred onset time. Their most definitive event occurred while ISEE was at a geocentric radial distance of 21.8 R[sub e]. This result conflicts with previous understanding, though further verification of the result is required. The observations show very similar characteristics to those observed at synchronous orbit, and they are consistent with an extension of a portion of the substorm current wedge to the radial distance of the satellite. If this explanation is correct, ISEE must have been within the longitude range of the substorm current wedge at the onsets. 13 refs., 8 figs.

  12. Characteristics of magnetospheric radio noise spectra

    NASA Technical Reports Server (NTRS)

    Herman, J. R.

    1976-01-01

    Magnetospheric radio noise spectra (30 kHz to 10 MHz) taken by IMP-6 and RAE-2 exhibit time-varying characteristics which are related to spacecraft position and magnetospheric processes. In the mid-frequency range (100-1,000 kHz) intense noise peaks rise by a factor of 100 or more above background; 80% of the peak frequencies are within the band 125 kHz to 600 kHz, and the peak occurs most often (18% of the time) at 280 kHz. This intense mid-frequency noise has been detected at radial distances from 1.3 Re to 60 Re on all sides of the Earth during magnetically quiet as well as disturbed periods. Maximum occurrence of the mid-frequency noise is in the evening to midnight hours where splash-type energetic particle precipitation takes place. ""Magnetospheric lightning'' can be invoked to explain the spectral shape of the observed spectra.

  13. Ion observations at Mercury's Magnetospheric Cusp

    NASA Astrophysics Data System (ADS)

    Jasinski, Jamie; Raines, Jim; Slavin, James

    2016-04-01

    The magnetospheric cusp is a region of direct entry for solar wind mass, energy and momentum into a planetary magnetosphere. Dayside magnetic reconnection between the interplanetary magnetic field and the planetary field allows shocked solar wind plasma to flow down open magnetospheric field lines. Whilst this is occurring these magnetic field lines convect poleward. For a spacecraft travelling through the high latitudes, this causes a velocity filter effect to be observed in the ion data, whereby higher energy ions are observed at lower latitudes. Here we present the ion observations from the MESSENGER spacecraft at Mercury's cusp, specifically focusing on ions latitudinally dispersed in energy. From these dispersions, the distance to the reconnection site is calculated and used to better understand the process of reconnection at Mercury's dayside magnetopause.

  14. Using Global Simulations of the Magnetosphere for Multi-Satellite Mission Planning and Data Analysis

    NASA Technical Reports Server (NTRS)

    Raeder, Joachim; Angelopoulos, Vassilis

    1998-01-01

    We use global simulations of Earth's magnetosphere to assess the scientific return from a multi-satellite mission in the magnetosphere. We examine 4 different scenarios with 20, 40, 80, and 160 satellites, respectively. The satellite orbits are randomized with perigee distances ranging from 2 to 5R(sub E), apogee distances between 10 and 50 R(sub E), and within +/-5R(sub E) of the geocentric solar ecliptic (GSE) equator. For each of these satellite configurations we examine the expected observations during a typical substorm by using time traces obtained from a global simulation at the satellite positions. The 160 satellite configuration yields sufficient information to distinguish between different substorm models without any temporal/spatial ambiguities. An 80 satellite configuration still provides sufficient information for this task, however for fewer events with good satellite conjunctions and with less statistical certainty. For constellations with fewer than 40 satellites time-space ambiguities are likely to remain in the observation. However, any multi-satellite constellation would be a quantum leap in magnetospheric research because of the unprecedented coverage of other regions, because it would enable new measurement techniques that are unique to multi-satellite missions, and because it would enable the use of data assimilation techniques in global models for the first time.

  15. Saturn's Magnetospheric Boundaries

    NASA Astrophysics Data System (ADS)

    Kurth, W. S.; Gurnett, D. A.; Hospodarsky, G. B.; Dougherty, M. K.; Arridge, C. S.; Achilleos, N. A.; Andre, N.; Crary, F. J.; McAndrews, H. J.; Szego, K.; Rymer, A. M.; Krimigis, S. M.; Mitchell, D. G.; Krupp, N.; Hamilton, D. C.; Hansen, K. C.

    2005-12-01

    Cassini has now been in orbit at Saturn for more than a year, making more than 12 passes through Saturn's magnetosphere. While the apoapses of these orbits have so far remained clustered near dawn and the inclinations have been mostly below about 20 degrees, progress has been made in mapping and understanding various magnetospheric boundaries. For example, initial modeling of the bow shock and magnetopause by Hendricks et al. [GRL, 32, 2005] suggest the magnetosphere is somewhat more inflated than thought from Pioneer- and Voyager-based models. Of perhaps even more interest are internal boundaries within the magnetosphere. These boundaries separate various magnetospheric regions and are less rigorously defined than the external boundaries. In fact, a number of authors have identified different regions based on particular sets of measurements; we review some of these and attempt to integrate these into a scheme of general utility, realizing that ongoing work on interpretation of existing observations and high inclination orbits to come will likely modify any such scheme we may devise this early in Cassini's tour.

  16. Geospace Magnetospheric Dynamics Mission

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Kluever, C.; Burch, J. L.; Fennell, J. F.; Hack, K.; Hillard, G. B.; Kurth, W. S.; Lopez, R. E.; Luhmann, J. G.; Martin, J. B.; Hanson, J. E.

    1998-01-01

    The Geospace Magnetospheric Dynamics (GMD) mission is designed to provide very closely spaced, multipoint measurements in the thin current sheets of the magnetosphere to determine the relation between small scale processes and the global dynamics of the magnetosphere. Its trajectory is specifically designed to optimize the time spent in the current layers and to minimize radiation damage to the spacecraft. Observations are concentrated in the region 8 to 40 R(sub E) The mission consists of three phases. After a launch into geostationary transfer orbit the orbits are circularized to probe the region between geostationary orbit and the magnetopause; next the orbit is elongated keeping perigee at the magnetopause while keeping the line of apsides down the tail. Finally, once apogee reaches 40 R(sub E) the inclination is changed so that the orbit will match the profile of the noon-midnight meridian of the magnetosphere. This mission consists of 4 solar electrically propelled vehicles, each with a single NSTAR thruster utilizing 100 kg of Xe to tour the magnetosphere in the course of a 4.4 year mission, the same thrusters that have been successfully tested on the Deep Space-1 mission.

  17. Unusual satellite-electron signature within the Uranian magnetosphere and its implications regarding whistler electron loss processes

    NASA Technical Reports Server (NTRS)

    Mauk, B. H.; Keath, E. P.; Krimigis, S. M.

    1994-01-01

    It has been reported that during the outbound (nightside) portion of the Voyager 2 encounter with the Uranian magnetosphere, intense whistler mode emissions were observed near the magnetic equator (lambda(sub m) approx. 16 deg) and at L shell values between approx. 5.5 and approx. 9 R(sub U). Comprehensive calculations of whistler-driven pitch angle diffusion, in previous work, have yielded strong diffusion electron lifetimes of approx. 1 hour for 20 to 40 keV electrons. In this paper we report on an unusual and sharply defined charged particle feature that: (1) involved electrons between 22 and 35 keV, (2) was observed during the time period of the intense whistler mode observations, (3) was aligned very accurately and sharply with the minimum L shell position (L approx. 7.5) of the satellite Ariel, and (4) has an appearance that suggests that electrons were removed only at and beyond Ariel's minimum-L. On the basis of our conclusion that the signature was caused by electron interactions with either Ariel or materials distributed along Ariel's orbit, the signature could not have been generated for at least 10 hours prior to its observation. Thus the calculated whistler loss times are in apparent conflict with the signature observation. A scenario of events is proposed to explain the data that involves substormlike electron acceleration on the Uranian nightside and a subsequent sculpting of the electron spatial distributions via interactions with Ariel or materials distributed along Ariel's orbit. The possibility exists that the accurate alignment of the sharp electron feature with Ariel's minimum-L, and the absorptionlike character of the feature, are accidental, and that the feature is caused by dynamical processes (e.g., substorms). In this case the dynamical processes must be quite dissimilar to those occurring in the Earth's magnetosphere.

  18. Field-Aligned Current Reconfiguration and Magnetospheric Response to an Impulse in the Interplanetary Magnetic Field BY Component

    NASA Astrophysics Data System (ADS)

    Wilder, F. D.; Eriksson, S.; Korth, H.; Hairston, M. R.; Baker, J. B.; Heinselman, C. J.

    2013-12-01

    When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the DMSP spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawn-side FAC pair. We find there is a delay of approximately 1.25 hours between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

  19. Dione's Magnetospheric Interaction

    NASA Astrophysics Data System (ADS)

    Kurth, W. S.; Hospodarsky, G. B.; Schippers, P.; Moncuquet, M.; Lecacheux, A.; Crary, F. J.; Khurana, K. K.; Mitchell, D. G.

    2015-12-01

    Cassini has executed four close flybys of Dione during its mission at Saturn with one additional flyby planned as of this writing. The Radio and Plasma Wave Science (RPWS) instrument observed the plasma wave spectrum during each of the four encounters and plans to make additional observations during the 17 August 2015 flyby. These observations are joined by those from the Cassini Plasma Spectrometer (CAPS), Magnetospheric Imaging Instrument (MIMI), and the Magnetometer instrument (MAG), although neither CAPS nor MAG data were available for the fourth flyby. The first and fourth flybys were near polar passes while the second and third were near wake passes. The second flyby occurred during a time of hot plasma injections which are not thought to be specifically related to Dione. The Dione plasma wave environment is characterized by an intensification of the upper hybrid band and whistler mode chorus. The upper hybrid band shows frequency fluctuations with a period of order 1 minute that suggest density variations of up to 10%. These density variations are anti-correlated with the magnetic field magnitude, suggesting a mirror mode wave. Other than these periodic density fluctuations there appears to be no local plasma source which would be observed as a local enhancement in the density although variations in the electron distribution are apparent. Wake passages show a deep density depletion consistent with a plasma cavity downstream of the moon. Energetic particles show portions of the distribution apparently absorbed by the moon leading to anisotropies that likely drive both the intensification of the upper hybrid band as well as the whistler mode emissions. We investigate the role of electron anisotropies and enhanced hot electron fluxes in the intensification of the upper hybrid band and whistler mode emissions.

  20. Global electric field determination in the Earth's outer magnetosphere using energetic charged particles

    NASA Technical Reports Server (NTRS)

    Eastman, Timothy E.; Sheldon, R.; Hamilton, D.

    1995-01-01

    Although many properties of the Earth's magnetosphere have been measured and quantified in the past 30 years since it was discovered, one fundamental measurement (for zeroth order MHD equilibrium) has been made infrequently and with poor spatial coverage - the global electric field. This oversight is due in part to the neglect of theorists. However, there is renewed interest in the convection electric field because it is now realized to be central to many magnetospheric processes, including the global MHD equilibrium, reconnection rates, Region 2 Birkeland currents, magnetosphere ionosphere coupling, ring current and radiation belt transport, substorm injections, and several acceleration mechanisms. Unfortunately the standard experimental methods have not been able to synthesize a global field (excepting the pioneering work of McIlwain's geostationary models) and we are left with an overly simplistic theoretical field, the Volland-Stern electric field model. Single point measurements of the plasmapause were used to infer the appropriate amplitudes of this model, parameterized by K(sub p). Although this result was never intended to be the definitive electric field model, it has gone nearly unchanged for 20 years. The analysis of current data sets requires a great deal more accuracy than can be provided by the Volland-Stern model. The variability of electric field shielding has not been properly addressed although effects of penetrating magnetospheric electric fields has been seen in mid-and low-latitude ionospheric data sets. The growing interest in substorm dynamics also requires a much better assessment of the electric fields responsible for particle injections. Thus we proposed and developed algorithms for extracting electric fields from particle data taken in the Earth's magnetosphere. As a test of the effectiveness of these new techniques, we analyzed data taken by the AMPTE/CCE spacecraft in equatorial orbit from 1984 to 1989.

  1. Building a Coupled Kinetic Framework for the Magnetosphere-Ionosphere-Plasmasphere-Polar Wind-Superthermal Electron System

    NASA Astrophysics Data System (ADS)

    Omelchenko, Y.; Karimabadi, H.; Schunk, R. W.; Barakat, A. R.; Gardner, L. C.; Khazanov, G. V.; Glocer, A.; Kistler, L. M.

    2013-12-01

    Recent spacecraft observations have revealed that the critical plasma processes regulating mass and energy transfer in the magnetosphere take place at relatively thin ion-scale regions (e.g., bow shock, magnetopause, magnetotail) where kinetic ions control the physics. All parts of the magnetosphere are strongly coupled: the ionosphere's finite conductivity affects the field line tying as well as the size of the magnetosphere; multi-species ionospheric outflows limit the cross-polar cap potential, provide a sink for the energy flowing into the auroral region, modify the open/closed boundary during storms and substorms and determine the distribution of energetic particles in the ring current and plasma sheet. We propose to develop the next generation global modeling framework which will, for the first time, retain full ion kinetic effects throughout the entire magnetosphere. This will be achieved through coupling independent hybrid models for two separate parts of the magnetosphere: (i) the outer magnetosphere, modeled with a new asynchronous (event-driven) global hybrid code, HYPERS, and (ii) the ionosphere-plasmasphere-polar-wind (IPPW) system, modeled with a different hybrid code coupled with a new superthermal electron (SE) transport model. Thus, in our asynchronous framework the HYPERS code will provide self-consistent electric field and ion flows (sinks) to the IPPW-SE model which will self-consistently compute ionospheric kinetic ion flows (sources) and conductivity to enable seamless continuation of the kinetic-ion physics towards the outer magnetosphere.

  2. Planet/magnetosphere/satellite couplings: Observations from the moon

    NASA Astrophysics Data System (ADS)

    Prange, Renee

    1994-06-01

    The general characteristics of planetary magnetospheres depend upon a few key parameters, such as the magnetic dipole strength, the planetary rotation rate, and the strength of the internal plasma sources (satellites, rings, ionosphere). The present knowledge of the acceleration and of the large scale circulation of plasma in these magnetospheres is still rather poor. Plasma and energetic particle losses occur largely through precipitation into the atmosphere along magnetic field lines, giving rise to the planetary aurorae. These losses can be initiated by various kinds of magnetospheric processes, and, if clearly understood, could give major insights into the physics of the global magnetospheric system. After a brief comparative review of the planetary magnetospheres, it will be shown how our understanding of their dynamics could benefit from increased instrumental performances in terms of remote sensing in the X rays, UV to IR, and radio wavelength range, and what breakthroughs could be expected from lunar based observations.

  3. Magnetospheres of the outer planets

    NASA Technical Reports Server (NTRS)

    Vanallen, James A.

    1987-01-01

    The five qualitatively different types of magnetism that a planet body can exhibit are outlined. Potential sources of energetic particles in a planetary magnetosphere are discussed. The magnetosphere of Uranus and Neptune are then described using Pioneer 10 data.

  4. Comparison of substorms near two solar cycle maxima: (1999-2000 and 2012-2013)

    NASA Astrophysics Data System (ADS)

    Despirak, I.; Lubchich, A.; Kleimenova, N.

    2016-05-01

    We present the comparative analysis of the substorm behavior during two solar cycle maxima. The substorms, observed during the large solar cycle maximum (1999- 2000, with Wp> 100) and during the last maximum (2012-2013 with Wp~60), were studied. The considered substorms were divided into 3 types according to auroral oval dynamic. First type - substorms which are observed only at auroral latitudes ("usual" substorms); second type - substorms which propagate from auroral latitudes (<70?) to polar geomagnetic latitudes (>70°) ("expanded" substorms, according to expanded oval); third type - substorms which are observed only at latitudes above ~70° in the absence of simultaneous geomagnetic disturbances below 70° ("polar" substorms, according to contracted oval). Over 1700 substorm events have been analyzed. The following substorm characteristics have been studied: (i) the seasonal variations, (ii) the latitudinal range of the occurrence, (iii) solar wind and IMF parameters before substorm onset, (iiii) PC-index before substorm onset. Thus, the difference between two solar activity maxima could be seen in the difference of substorm behavior in these periods as well.

  5. On permanent and sporadic pulsations of the magnetosphere

    NASA Astrophysics Data System (ADS)

    Guglielmi, A. V.

    2015-05-01

    A question concerning the influence of permanent Pc3-band pulsations (periods from 10 to 45 s) on the excitation of sporadic Pi2-band pulsations (40 to 150 s) is raised. It is hypothesized that, being generated ahead of the front of the Earth's magnetosphere, the Pc3 penetrate into the geomagnetic tail where they cause local depression in the electric current in the neutral sheet and, under favorable conditions, initiate tearing instability. This leads to the reconnection of the magnetic field lines and explosion-like release of the magnetic energy stored in the tail. As a result, a substorm arises with the sporadic Pi2 pulsations being its important element. Ways are suggested to theoretically substantiate and experimentally validate this hypothesis.

  6. Kinetic Simulation and Energetic Neutral Atom Imaging of the Magnetosphere

    NASA Technical Reports Server (NTRS)

    Fok, Mei-Ching H.

    2011-01-01

    Advanced simulation tools and measurement techniques have been developed to study the dynamic magnetosphere and its response to drivers in the solar wind. The Comprehensive Ring Current Model (CRCM) is a kinetic code that solves the 3D distribution in space, energy and pitch-angle information of energetic ions and electrons. Energetic Neutral Atom (ENA) imagers have been carried in past and current satellite missions. Global morphology of energetic ions were revealed by the observed ENA images. We have combined simulation and ENA analysis techniques to study the development of ring current ions during magnetic storms and substorms. We identify the timing and location of particle injection and loss. We examine the evolution of ion energy and pitch-angle distribution during different phases of a storm. In this talk we will discuss the findings from our ring current studies and how our simulation and ENA analysis tools can be applied to the upcoming TRIO-CINAMA mission.

  7. Particle Transport and Energization Associated with Disturbed Magnetospheric Events

    SciTech Connect

    C.Z. Cheng; J.R. Johnson; S. Zaharia

    1999-11-01

    Energetic particle flux enhancement events observed by satellites during strongly disturbed events in the magnetosphere (e.g., substorms, storm sudden commencements, etc.) are studied by considering interaction of particles with Earthward propagating electromagnetic pulses of westward electric field and consistent magnetic field of localized radial and azimuthal extent in a background magnetic field. The energetic particle flux enhancement is mainly due to the betatron acceleration process: particles are swept by the Earthward propagating electric field pulses via the EXB drift toward the Earth to higher magnetic field locations and are energized because of magnetic moment conservation. The most energized particles are those which stay in the pulse for the longest time and are swept the longest radial distance toward the Earth. Assuming a constant propagating velocity of the pulse we obtain analytical solutions of particle orbits. We examine substorm energetic particle injection by computing the particle flux and comparing with geosynchronous satellite observations. Our results show that for pulse parameters leading to consistency with observed flux values, the bulk of the injected particles arrive from distances less than 9 R(subscript E), which is closer to the Earth than the values obtained by the previous model and is also closer to the distances obtained by the injection boundary model.

  8. Magnetotail Plasma Signatures of Pseudobreakups and Substorms

    NASA Technical Reports Server (NTRS)

    Fillingim, M. O.; Brittnacher, M. J.; Parks, G. K.; Chen, L. J.; Germany, G. A.; Spann, J. F.; Lin, R. P.

    1999-01-01

    Using Polar/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass through the near-Earth magnetotail. On the basis of images, these auroral brightenings are interpreted to be pseudobreakups due to the lack of significant global expansion. Large magnetic by the WIND spacecraft show a nearly one-to-one correspondence auroral intensifications. During intervals of large field auroral brightenings, energized ions have an Earthward velocity energized electrons generally remain isotropic. Closer inspection ion distribution functions indicate that the high velocity moments are not due to convective flows. Rather, the plasma is composed of a component and a stagnate cold component. We also trace the observed by WIND backwards in time to determine the source regions for the particles. Based upon these observations, we find that to zeroth order there is no difference in the behavior of the plasma during as compared to substorm expansive phase events.

  9. Modeling Saturn's Magnetospheric Field

    NASA Astrophysics Data System (ADS)

    Khurana, K. K.; Leinweber, H. K.; Russell, C. T.; Dougherty, M. K.

    2015-12-01

    The Cassini spacecraft has now provided an excellent coverage of radial distances, local times and latitudes in Saturn's magnetosphere. The magnetic field observations from Cassini continue to provide deep insights on the structure and dynamics of Saturn's magnetosphere. Two of the unexpected findings from Saturn's magnetosphere are that the current sheet of Saturn assumes a shallow saucer like shape from the forcing of the solar wind on the magnetosphere and that rotational diurnal periodicities are ubiquitous in a magnetosphere formed by an axisymmetric internal field from Saturn. We have used the comprehensive magnetic field data from Cassini to construct a versatile new model of Saturn's magnetospheric field for use in current and future data analysis. Our model consists of fully shielded modules that specify the internal spherical harmonic field of Saturn, the ring current and the magnetotail current systems and the interconnection magnetic field from the solar wind IMF. The tilt and hinging of the current sheet is introduced by using the general deformation technique [Tsyganenko, 1998]. In the new model, Saturn's current sheet field is based on Tsyganenko and Peredo [1994] formalism for disk-shaped current sheets. The shielding field from the magnetopause for the equatorial current sheet and the internal field is specified by Cartesian and cylindrical harmonics, respectively. To derive the shielding fields we use a model of the magnetopause constructed from magnetopause crossings observed by both Cassini and Voyager (Arridge et al. 2006). The model uses observations from Pioneer, Voyager and Cassini. A comparison of model field with the observations will be presented. Finally, we discuss both the applications of the new model and its further generalization using data from the proximal orbit phase of Cassini.

  10. Multipoint observations of the spatial distribution and temporal evolution of the "Nose-like" structures in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Luo, Hao; Du, Aimin; Ge, Yasong; Cao, Xin; Zhang, Ying; Huang, Sheng

    2016-04-01

    The "Nose-like" ion spectral structures are formed by ions in the near-Earth plasma sheet penetrating into the inner magnetosphere. Many studies had shown that the distribution of the Nose structures was controlled by the large-scale convection electric field, gradient-curvature drift and corotation electric field in the inner magnetosphere during geomagnetic quiet condition. However, during geomagnetic active periods, especially during the storms and substorms, the spatial and temporal characteristics and formation mechanism of different ions are still under debate. In this study, joint observations from Van Allen Probes, THEMIS, and Cluster will be used to statistically study the spatial distribution and temporal evolution of the "Nose-like" ion spectral structures in the inner magnetosphere. Backward tracing method based on Weimer 96 electric field and dipole magnetic field model was applied to simulate the ion structures and compared to the observations. The results show some important characteristics of the ion structures and will help us understand the injection mechanism of the ions from the plasma sheet into the inner magnetosphere and the relation between the storm and substorm, and thus provide important information for ring current formation.

  11. Magnetic field drift shell splitting: Cause of unusual dayside particle pitch angle distributions during storms and substorms

    SciTech Connect

    Sibeck, D.G.; McEntire, R.W.; Lui, A.T.Y.; Lopez, R.E.; Krimigis, S.M.

    1987-12-01

    We present a magnetic field drift shell--splitting model for the unusual butterfly and head-and-shoulder energetic (E>25 keV) particle pitch angle distributions (PADs) which appear deep within the dayside magnetosphere during the course of storms and substorms. Drift shell splitting separates the high and low pitch angle particles in nightside injections as they move to the dayside magnetosphere, so that the higher pitch angle particles move radially away from Earth. Consequently, butterfly PADs with a surplus of low pitch angle particles form on the inner edge of the injection, but head-and-shoulder PADs with a surplus of high pitch angle particles from on the outer edge. A similar process removes high pitch angle particles from the inner dayside magnetosphere during storms, leaving the remaining lower pitch angle particles to form butterfly PADs on the inner edge of the ring current. A detailed case and statistical study of CCE/MEPA observations, as well as a review of previous work, shows most examples of unusual PADs to be consistent with the model. copyright American Geophysical Union 1987

  12. Magnetic field drift shell splitting - Cause of unusual dayside particle pitch angle distributions during storms and substorms

    NASA Technical Reports Server (NTRS)

    Sibeck, D. G.; Mcentire, R. W.; Lui, A. T. Y.; Lopez, R. E.; Krimigis, S. M.

    1987-01-01

    This paper presents a magnetic field drift shell-splitting model for the unusual butterfly and head-and-shoulder energetic (E greater than 25 keV) particle pitch angle distributions (PADs) which appear deep within the dayside magnetosphere during the course of storms and substorms. Drift shell splitting separates the high and low pitch angle particles in nightside injections as they move to the dayside magnetosphere, so that the higher pitch angle particles move radially away from earth. Consequently, butterfly PADs with a surplus of low pitch angle particles form on the inner edge of the injection, but head-and-shoulder PADs with a surplus of high pitch angle particles form on the outer edge. A similar process removes high pitch angle particles from the inner dayside magnetosphere during storms, leaving the remaining lower pitch angle particles to form butterfly PADs on the inner edge of the ring current. A detailed case and statistical study of Charge Composition Explorer/Medium-energy Particle Analyzer observations, as well as a review of previous work, shows most examples of unusual PADs to be consistent with the model.

  13. Storm/substorm signatures in the outer belt

    SciTech Connect

    Korth, A.; Friedel, R.H.W.; Mouikis, C.; Fennell, J.F.

    1998-12-01

    The response of the ring current region is compared for periods of storm and substorm activity, with an attempt to isolate the contributions of both processes. The authors investigate CRRES particle data in an overview format that allows the display of long-term variations of the outer radiation belt. They compare the evolution of the ring current population to indicators of storm (Dst) and substorm (AE) activity and examine compositional changes. Substorm activity leads to the intensification of the ring current at higher L (L {approximately} 6) and lower ring current energies compared to storms (L {approximately} 4). The O{sup +}/H{sup +} ratio during substorms remains low, near 10%, but is much enhanced during storms (can exceed 100%). They conclude that repeated substorms with an AE {approximately} 900 nT lead to a {Delta}Dst of {approximately} 30 nT, but do not contribute to Dst during storm main phase as substorm injections do not form a symmetric ring current during such disturbed times.

  14. Substorm-induced energetic electron precipitation: Morphology and prediction

    NASA Astrophysics Data System (ADS)

    Beharrell, M. J.; Honary, F.; Rodger, C. J.; Clilverd, M. A.

    2015-04-01

    The injection, and subsequent precipitation, of 20 to 300 keV electrons during substorms is modeled using parameters of a typical substorm found in the literature. When combined with onset timing from, for example, the SuperMAG substorm database, or the Minimal Substorm Model, it may be used to calculate substorm contributions to energetic electron precipitation in atmospheric chemistry and climate models. Here the results are compared to ground-based data from the Imaging Riometer for Ionospheric Studies riometer in Kilpisjärvi, Finland, and the narrowband subionospheric VLF receiver at Sodankylä, Finland. Qualitatively, the model reproduces the observations well when only onset timing from the SuperMAG network of magnetometers is used as an input and is capable of reproducing all four categories of substorm associated riometer spike events. The results suggest that the different types of spike event are the same phenomena observed at different locations, with each type emerging from the model results at a different local time, relative to the center of the injection region. The model's ability to reproduce the morphology of spike events more accurately than previous models is attributed to the injection of energetic electrons being concentrated specifically in the regions undergoing dipolarization, instead of uniformly across a single-injection region.

  15. Comparison between the two basic modes of magnetospheric convection

    NASA Astrophysics Data System (ADS)

    Siscoe, George L.; Farrugia, Charlie J.; Sandholt, Per Even

    2011-05-01

    Magnetic flux in the magnetosphere can circulate in a forward sense (southward IMF) and a reverse sense (northward IMF). The point of this paper is to compare and contrast these two modes of circulation. Both have transient and persistent phases in response to a suddenly applied southward or northward IMF that then is held steady. In the initial, transient phases, reconnection voltage exceeds transpolar potential in the ionosphere because for forward circulation there is an inductive-like time lag while the region 1 current builds up in association with a net flow of magnetic flux from the dayside to the tail (magnetospheric erosion). For the transient phase of reverse convection, reconnection voltage exceeds transpolar potential because instead of over-the-pole, night-to-day transport to undo preexisting magnetospheric erosion, magnetic flux accretes directly onto the dayside magnetosphere. The persistent phase of forward circulation almost always manifests substorms, which modulate the amounts of open and closed flux on the nightside by about 25% in a zero-sum game that leaves the dayside flux mostly unaltered. Energy to power the transient and persistent phases of forward circulation comes from the solar wind flow through magnetic stresses created as the field advects tailward. Energy to power the transient phase of reverse convection, however, comes from tapping magnetic energy stored inductively in association with the region 1 and tail current systems. The persistent phase of reverse circulation is driven possibly by the Song-Russell mechanism, which operates on a day-to-night pressure gradient of plasma entrained by dayside flux accretion. The resulting circulation is slow.

  16. The Two Basic Modes of Magnetospheric Convection Compared

    NASA Astrophysics Data System (ADS)

    Siscoe, G. L.; Farrugia, C. J.; Sandholt, P. E.

    2010-12-01

    Magnetic flux in the magnetosphere can circulate in a forward sense (southward IMF) and a reverse sense (northward IMF). The point of this presentation is to compare and contrast these two modes of circulation. Both have transient and persistent phases. In the transient phases, reconnection voltage exceeds transpolar potential because for forward circulation there is an inductive time-lag while the region 1 current builds up in association with a net flow of magnetic flux from the dayside to the tail (magnetospheric erosion). For the transient phase of reverse convection, reconnection voltage exceeds transpolar potential because magnetospheric erosion is undone by magnetic flux accretion directly onto the dayside magnetosphere with no night-to-day flow of magnetic flux needed. Energy to power the transient and persistent phases of forward circulation comes from the solar wind flow by means of the creation of magnetic stresses as the field is advected tailward. Energy to power the transient phase of reverse convection comes from tapping magnetic energy stored inductively in association with the region 1 and tail current systems. The persistent phase of forward circulation almost always manifests substorms, which modulate the amounts of open and closed flux on the nightside by about 25% in a zero-sum game that leaves the dayside flux mostly unaltered. Having exhausted its driving energy source during the transient phase, the persistent phase of reverse circulation is powered possibly by the Song-Russell mechanism, which operates on a day-to-night pressure gradient of plasma entrained by dayside flux accretion. The resulting circulation is slow. We present observations that show a predicted winter-summer asymmetry in polar cap precipitation diagnostic of a rare occurrence of the persistent phase of reverse convection.

  17. Magnetospheric conditions near the equatorial footpoints of proton isotropy boundaries

    NASA Astrophysics Data System (ADS)

    Sergeev, V. A.; Chernyaev, I. A.; Angelopoulos, V.; Ganushkina, N. Y.

    2015-12-01

    Data from a cluster of three THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft during February-March 2009 frequently provide an opportunity to construct local data-adaptive magnetospheric models, which are suitable for the accurate mapping along the magnetic field lines at distances of 6-9 Re in the nightside magnetosphere. This allows us to map the isotropy boundaries (IBs) of 30 and 80 keV protons observed by low-altitude NOAA POES (Polar Orbiting Environmental Satellites) to the equatorial magnetosphere (to find the projected isotropy boundary, PIB) and study the magnetospheric conditions, particularly to evaluate the ratio KIB (Rc/rc; the magnetic field curvature radius to the particle gyroradius) in the neutral sheet at that point. Special care is taken to control the factors which influence the accuracy of the adaptive models and mapping. Data indicate that better accuracy of an adaptive model is achieved when the PIB distance from the closest spacecraft is as small as 1-2 Re. For this group of most accurate predictions, the spread of KIB values is still large (from 4 to 32), with the median value KIB ~13 being larger than the critical value Kcr ~ 8 expected at the inner boundary of nonadiabatic angular scattering in the current sheet. It appears that two different mechanisms may contribute to form the isotropy boundary. The group with K ~ [4,12] is most likely formed by current sheet scattering, whereas the group having KIB ~ [12,32] could be formed by the resonant scattering of low-energy protons by the electromagnetic ion-cyclotron (EMIC) waves. The energy dependence of the upper K limit and close proximity of the latter event to the plasmapause locations support this conclusion. We also discuss other reasons why the K ~ 8 criterion for isotropization may fail to work, as well as a possible relationship between the two scattering mechanisms.

  18. Electron pitch angle distributions throughout the magnetosphere as observed on Ogo 5.

    NASA Technical Reports Server (NTRS)

    West, H. I., Jr.; Buck, R. M.; Walton, J. R.

    1973-01-01

    A survey of the equatorial pitch angle distributions of energetic electrons is provided for all local times out to radial distances of 20 earth radii on the night side of the earth and to the magnetopause on the day side of the earth. In much of the inner magnetosphere and in the outer magnetosphere on the day side of the earth, the normal loss cone distribution prevails. The effects of drift shell splitting - i.e., the appearance of pitch angle distributions with minimums at 90 deg, called butterfly distributions - become apparent in the early afternoon magnetosphere at extended distances, and the distribution is observed in to 5.5 earth radii in the nighttime magnetosphere. Inside about 9 earth radii the pitch angle effects are quite energy-dependent. Beyond about 9 earth radii in the premidnight magnetosphere during quiet times the butterfly distribution is often observed. It is shown that these electrons cannot survive a drift to dawn without being considerably modified. The role of substorm activity in modifying these distributions is identified.

  19. Origins of magnetospheric plasma

    SciTech Connect

    Moore, T.E. )

    1991-01-01

    A review is given of recent (1987-1990) progress in understanding of the origins of plasmas in the earth's magnetosphere. In counterpoint to the early supposition that geomagnetic phenomena are produced by energetic plasmas of solar origin, 1987 saw the publication of a provocative argument that accelerated ionospheric plasma could supply all magnetospheric auroral and ring current particles. Significant new developments of existing data sets, as well as the establishment of entirely new data sets, have improved the ability to identify plasma source regions and to track plasma through the magnetospheric system of boundary layers and reservoirs. These developments suggest that the boundary between ionospheric and solar plasmas, once taken to lie at the plasmapause, actually lies much nearer to the magnetopause. Defining this boundary as the surface where solar wind and ionosphere contribute equally to the plasma, it is referred to herein as the 'geopause'. It is now well established that the infusion of ionospheric O(+) plays a major role in the storm-time distention of the magnetotail and inflation of the inner magnetosphere. After more than two decades of observation and debate, the question remains whether magnetosheric are protons of solar or terrestrial origin. 161 refs.

  20. Magnetosphere of Mercury

    N