Organization of the magnetosphere during substorms (original) (raw)
Related papers
Substorms as nonequilibrium transitions of the magnetosphere
Journal of Atmospheric and Solar-Terrestrial Physics, 2001
The complexity of the magnetospheric dynamics during substorms has attracted continued attention and its understanding requires approaches beyond the conventional one based on plasma processes. Recognizing the nonequilibrium and open nature of the coupled solar wind-magnetosphere system, attempts have been made recently to interpret the observational data in terms of self-organization (SO) and self-organized criticality (SOC). The SO concept re ects the nonlinear organized behavior of the magnetosphere as a whole, while the SOC approach emphasizes its multi-scale aspects. Evidence of both SO and SOC in substorm dynamics inferred from ground-based and multi-spacecraft data, as well as the possible combination of these concepts within the framework of a more general approach of nonequilibrium phase transitions are presented in this paper. Like the real sandpiles and recent SOC models, the multi-scale manifestations of the substorm activity are more consistent with the phase transition behavior, viz. a system e ectively tuned to criticality rather than being self-organized. The problem of characterizing this critical behavior other than the widely used power-law frequency and scale spectra is discussed.
Geomagnetism and Aeronomy, 2007
The interval 0000-1400 UT of the superstorm of November 20, 2003, has been studies based on the ACE/WIND data and the MIT2 magnetogram inversion technique. The distributions of the electric potential and currents, field-aligned currents, and Joule heat in the ionosphere have been calculated. The variable magnetotail length and powers coming into the magnetosphere, ionosphere and ring current have been estimated. The selected superstorm intervals, when it became possible to identify the disturbance mode produced by the interaction between the variable solar wind dynamic pressure and IMF effects, have been described. Spontaneous substorms, two types of driven responses to changes in IMF or in the solar wind dynamic pressure ( P d ), zero events at simultaneous jumps of IMF and P d , and a previously unknown mode of saturation of the ionospheric electric field at a redistribution of the energy coming into the magnetosphere between the ionosphere and ring current are among the selected modes. PACS numbers: 94.30.Lr
Current understanding of magnetic storms: Storm-substorm relationships
Journal of geophysical …, 1998
activity indices on the basis of solar/solar wind/interplanetary magnetic field parameters continue to be upgraded, insuring reliable techniques for forecasting magnetic storms under real-time conditions, There is a need to evaluate the efficiency or predictability of georna~netic indices on the basis of' physical processes that occur during storm-time substorms. It is also crucial to differentiate between storms and non-storm-time substorms in terms of energy transfer/conversion processes, i.e., mechanical energy from the solar wind, electromagnetic energy in the rnagnetotail, and again, mechanical energy of panicles in the plasma sheet, ring current, and aurora.
Concurrent Effects between Geomagnetic Storms and Magnetospheric Substorms
Universe
An accurate understanding of dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve space weather diagnosis. In this work, we exploit some recently developed methods of dynamical system theory to provide new insights and conceptual ideas in space weather science. In particular, we study the co-variation and recurrence statistics of two geomagnetic indices, SYM-H and AL, that measure the intensity of the globally symmetric component of the equatorial electrojet and that of the westward auroral electrojet, respectively. We find that the number of active degrees of freedom, required to describe the phase space dynamics of both indices, depends on the geomagnetic activity level. When the magnetospheric substorm activity, as monitored by the AL index, increases, the active number of degrees of freedom increases at high latitudes above the dimension obtained through classical time delay embedding methods. Conversely, a reduced nu...
Time-dependent magnetospheric configuration and breakup mapping during a substorm
Journal of Geophysical Research, 2011
1] We analyze an isolated substorm on 29 March 2009 observed by the Thermal Emission Imaging System (THEMIS) and well monitored by ground-based observatories at and near station Gillam. The event provides a rare opportunity for monitoring the substorm magnetic topology thanks to fortuitous clustering of the THEMIS probes, complemented by the GOES 12 spacecraft. The neutral sheet position was found to be displaced by ∼0.5 R E northward from its average location. The peak cross-tail current density was estimated to be ∼20 nA/m 2 at the end of the growth phase, revealing the formation of a thin current sheet during the last 15 min prior to the expansion onset. The fortuitous spacecraft conjunction allowed us to construct an adjusted time-varying model based on magnetic field and pressure observations during the substorm. We then used the adjusted model to map the location of the spacecraft to the ionosphere and the breakup from the ionosphere to the equatorial region. Significant time-dependent differences between this and the standard models (e.g., T96) do exist, resulting in breakup mapping to ∼22 R E , compared to 12 R E if classical models are used. Moreover, we find that spacecraft footprints in the ionosphere move significantly equatorward (2°) over tens of minutes during the growth phase but jump poleward (2°-4°) after expansion onset. Since such motions are also typical for auroral arcs during substorms, we infer that magnetic field reconfiguration during various substorm phases, rather than plasma motion in the equatorial magnetosphere, is largely responsible for the observed motion of the aurora. Citation: Kubyshkina, M., V. Sergeev, N. Tsyganenko, V. Angelopoulos, A. Runov, E. Donovan, H. Singer, U. Auster, and W. Baumjohann (2011), Time-dependent magnetospheric configuration and breakup mapping during a substorm,
Magnetospheric substorms—definition and signatures
Journal of Geophysical Research, 1980
For many years, researchers have utilized definitions of the substorm phenomenon that are not consistent among one another, and this has created great difficulties in comparing the results reported in the literature by the various researchers. In August 1978, nine magnetospheric physicists active in the field of substorm research met in Victoria, British Columbia, Canada, to attempt to reach a consensus on an acceptable definition for a magnetospheric substorm. This paper reports the agreements reached at the Victoria workshop and presents an operational definition of the magnetospheric substorm and a critique of the various signatures by which researchers can identify the time sequence and spatial extent of the substorm. [ 1964]. Since that time a vast amount of research has been carried out that has greatly enhanced our understanding of the substorm phenomenon. However, it has become clear over this decade of research that the substorm phenomenon is more complex than it was originally envisaged. The scattered arrays of monitoring equipment have provided a complicated combination of spatial and temporal variations that are just now beginning to be appreciated. Furthermore, different groups have used different signatures to define the occurrence
The development of the magnetospheric substorm and its influence on the magnetopause motion
Planetary and Space Science, 2005
The time development of the magnetospheric substorm on February 10, 1997 and its influence on motion of low-latitude magnetospheric boundary was studied. The plasma and magnetic data obtained on 4 spacecraft (WIND, Interball-1, Geotail, GOES 8) are compared to measurements at ground based stations. The observations show that the release of energy stored in the magnetotail was initiated by tail current disruption in the near-Earth region and that neutral line formation occurred a few minutes after the tail current disruption. Almost simultaneously with the substorm onset, a series of four rapid magnetopause crossings was observed by the Interball-1 on the evening flank of low-latitude magnetosphere. Some of the possible causes of the observed magnetopause motion, such as variations of the solar wind parameters, the Kelvin-Helmholtz instability and substorm processes are considered in the paper. The fast magnetopause motion is observed almost simultaneously with magnetic field variations in the near-Earth magnetotail and geomagnetic Pi2 pulsations on the ground. The results suggest the possible connection of short-time motion of the magnetospheric boundary with tail current disruption and the substorm current wedge formation. r
Satellite studies of magnetospheric substorms on August 15, 1968: 1. State of the magnetosphere
Journal of Geophysical Research, 1973
In the eight preceding papers, two magnetospheric substorms on August 15, 1968, were studied with data derived from many sources. In this, the concluding paper, we attempt a synthesis of these observations, presenting a phenomenological model of the magnetospheric substorm. On the basis of our results for August 15, together with previous reports, we believe that the substorm sequence can be divided into three main phases: the growth phase, the expansion phase, and the recovery phase. Observations for each of the first three substorms on this day are organized according to this scheme. We present these observations as three distinct chronologies, which we then summarize as a phenomenological model. This model is consistent with most of our observations on August 15, as well as with rhost previous reports. In our interpretation we expand our phenomenological model, briefly described in several preceding papers. This model follows closely the theoretical ideas presented more quantitatively in recent. papers by Coroniti and Kennel (1972a, b; 1973). A southward turning of the interplanetary magnetic field is accompanied by erosion of the dayside magnetosphere, flu x transport to the geomagnetic tail, and •hinning and inwhrd motion of the plasma sheet. Our observations indicate, furthermore., that the expansion phase of substorms can originate near the inner edge of the plasma sheet as a consequence Of rapid plasma sheet th{nning. At this time a portion of the inner edge of the tail current is 'shOrt circuited' through the ionosphere. This process is consistent with the formation of a neutral point in the near-tail region and its subsequent propagation taftward. However, the onset of the expansion phase of substorms is found to be far from a simple process. Expansion phase• can be centered at local times far from midnight, can apparently be localized to one meridian, and can have multiple onsets centered at different local times. Such behavior indicat;es that., in comparing observations occurring in different substorms, careful note should be made of the localization and central meridian of each substorm. In the preceding papers we have examined in detail many features of two magnetospheric substorms that occurred on August 15, 1968. We have chosen these substorms because of the near ideal location of the Ogo 5 spacecraft during this interval. Our main purpose in this study has been to establish the sequence of events that occurs during a single substorm,
Substorm study based on the Paraboloid model of the magnetosphere
A substorm is widely accepted to be a global phenomenon in magnetospheric physics. It is a large-scale process consisting of coherent phenomena. It is very interesting to study individual phenomena such as reconnection during the onset of a substorm flows in the tail, ionospheric precipitation, particle injection, etc. However, we would like to emphasize that it is important to investigate the substorm as a unified process depending on the conditions in the solar wind and within the magnetosphere. For this purpose we should use a global magnetospheric model. In this case it is the Paraboloid model. It is important to note that the Paraboloid model comprises all the necessary sources of the magnetic field in the magnetosphere which can be distinguished from each other. This enables calculation of the magnetic field of different sources with different timescales. By using this model, we can also calculate global characteristics of the magnetosphere, such as the magnetic fluxes in the polar cap and in the auroral oval as a function of model parameters depending on time and solar wind conditions. This makes it possible to find the criteria of magnetosphere transformation into the metastable configuration, when development of a substorm becomes inevitable. Using these criteria, constrains were found which should be imposed on the model parameters to determine the substorm onset. The results obtained make it feasible to explain the external substorm triggering by the northward turning of the interplanetary magnetic field in the solar wind. A case study of the 10 January 1997, substorm event confirms our findings.