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Substorm

About: Substorm is a research topic. Over the lifetime, 5035 publications have been published within this topic receiving 153456 citations. The topic is also known as: magnetospheric substorm & auroral substorm.


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Journal ArticleDOI
TL;DR: In this paper, a working model of simultaneous auroral activity over the entire polar region is presented in terms of the auroral substorm, which has two characteristic phases, an expansive phase and a recovery phase.

1,460 citations

Journal ArticleDOI
TL;DR: The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is the fifth NASA Medium-class Explorer (MIDEX), launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms as discussed by the authors.
Abstract: The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is the fifth NASA Medium-class Explorer (MIDEX), launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. The mission employs five identical micro-satellites (hereafter termed “probes”) which line up along the Earth’s magnetotail to track the motion of particles, plasma and waves from one point to another and for the first time resolve space–time ambiguities in key regions of the magnetosphere on a global scale. The probes are equipped with comprehensive in-situ particles and fields instruments that measure the thermal and super-thermal ions and electrons, and electromagnetic fields from DC to beyond the electron cyclotron frequency in the regions of interest. The primary goal of THEMIS, which drove the mission design, is to elucidate which magnetotail process is responsible for substorm onset at the region where substorm auroras map (∼10 RE): (i) a local disruption of the plasma sheet current (current disruption) or (ii) the interaction of the current sheet with the rapid influx of plasma emanating from reconnection at ∼25 RE. However, the probes also traverse the radiation belts and the dayside magnetosphere, allowing THEMIS to address additional baseline objectives, namely: how the radiation belts are energized on time scales of 2–4 hours during the recovery phase of storms, and how the pristine solar wind’s interaction with upstream beams, waves and the bow shock affects Sun–Earth coupling. THEMIS’s open data policy, platform-independent dataset, open-source analysis software, automated plotting and dissemination of data within hours of receipt, dedicated ground-based observatory network and strong links to ancillary space-based and ground-based programs. promote a grass-roots integration of relevant NASA, NSF and international assets in the context of an international Heliophysics Observatory over the next decade. The mission has demonstrated spacecraft and mission design strategies ideal for Constellation-class missions and its science is complementary to Cluster and MMS. THEMIS, the first NASA micro-satellite constellation, is a technological pathfinder for future Sun-Earth Connections missions and a stepping stone towards understanding Space Weather.

1,456 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a phenomenological model of the magnetospheric substorm sequence, which can be divided into three main phases: the growth phase, the expansion phase, and the recovery phase.
Abstract: 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 most 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, flux transport to the geomagnetic tail, and thinning and inward motion of the plasma sheet. Our observations indicate, furthermore, that the expansionmore » phase of substorms can originate near the inner edge of thc plasm sheet as a consequence of rapid plasma sheet thinnig. 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 tailward. However, the onset of the expansion phase of substorms is found to be far from a simple process. Expansion phases 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 indicates that, in comparing observations occurring in different substorms, careful note should be made of the localization and central meridian of cach substorm. (auth)« less

1,138 citations

Journal ArticleDOI
TL;DR: In this paper, the authors determined the statistical features of field-aligned currents during a large number of substorms from the magnetic field observations acquired with the Triad satellite, including the following: (1) the large-scale regions of fieldaligned currents determined previously by the authors (Iijima and Potemra, 1976a) persist during all phases of sub-storm activity, namely, region 1, located near the poleward boundary of the fieldaligned current region, and region 2, positioned near the equatorward boundary.
Abstract: Characteristics of field-aligned currents have been determined during a large number of substorms from the magnetic field observations acquired with the Triad satellite. The statistical features of field-aligned currents include the following: (1) The large-scale regions of field-aligned currents determined previously by the authors (Iijima and Potemra, 1976a) persist during all phases of substorm activity, namely, region 1, located near the poleward boundary of the field-aligned current region, and region 2, located near the equatorward boundary. Field-aligned currents flow into region 1 on the morningside and away from region 1 on the eveningside. The current flow in region 2 is reversed to region 1 at any given local time except in the Harang discontinuity region (∼2000–2400 MLT), where the flow patterns are more complicated. (2) During active periods (|AL| ≥ 100 γ) the average latitude width of regions 1 and 2 increases by 20–30%, and the centers of these regions shift equatorward by 2°–3° with respect to the quiet time values. (3) The current density in region 1 is statistically larger than the current density in region 2 at all local times except during active periods and in the midnight to morning local time sector. In this region, where the westward electrojet is most active, the current density in region 2 can exceed the current density in region 1. (4) During relatively quiet conditions (|AL| < 100 γ) the largest field-aligned current densities occur in two areas of region 1 near noon (near ∼ 1030 MLT and ∼ 1300 MLT) with an average value of ∼1.6µA/m². During active periods (|AL| ≥ 100 γ) the regions of peak current density shift toward the nightside (the region near 1030 MLT shifts to ∼0730 MLT, and the region near ∼1300 MLT shifts to ∼1430 MLT), and the average current density increases to ∼2.2 µA/m². (5) The average total amount of field-aligned current flowing into the ionosphere always equals the current flow away from the ionosphere during a wide range of quiet and disturbed conditions. The average total current during quiet periods is ∼2.7 × 106 A and during disturbed periods is ∼5.2 × 106 A. (6) A three-region pattern of field-aligned current flow persists in the Harang discontinuity region (∼2000–2400 MLT) during undisturbed and disturbed periods, when the westward auroral electrojet does not intrude into this sector. This flow pattern consists of an upward flowing field-aligned current surrounded to the north and south by downward flowing currents. During periods when the westward auroral electrojet has intruded deeply into the evening sector the Triad magnetometer data exhibit complicated and fine-structured variations indicating the presence of complex field-aligned currents in this sector. (7) The alignment of current sheets is generally along the boundary of the auroral oval (rather than in the east-west direction), but noticeable distortions of this alignment occur during very disturbed periods. The alignment of field-aligned currents is different in region 1 and region 2 during active periods. The different behavior of field-aligned currents in region 1 and 2 during substorms actively suggests that they are controlled by different source regions in the magnetosphere or ionosphere. The region 1 field-aligned currents map to the outermost part of the magnetosphere and magnetotail region, whereas the region 2 currents map to regions of the plasma sheet closer to the earth.

899 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that epsilon is the primary factor controlling the time development of magnetospheric substorms and storms and that the power generated by the dynamo can be identified as ϵ through the use of a dimensional analysis, indicating 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.
Abstract: 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.

840 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202386
2022182
202171
202084
201978
201888