scholarly journals Studies of magnetotail dynamics and energy evolution during substorms using MHD simulations

2009 ◽  
Vol 27 (4) ◽  
pp. 1717-1727 ◽  
Author(s):  
S. Brogl ◽  
R. E. Lopez ◽  
M. Wiltberger ◽  
H. K. Rassoul
Keyword(s):  
Growth Phase ◽  
Plasma Sheet ◽  
Magnetic Energy ◽  
Substorm Onset ◽  
Energy Evolution ◽  
Polar Cap ◽  
Expansion Phase ◽  
Mhd Simulations ◽  
Hydrodynamic Code ◽  
Magnetotail Dynamics

Abstract. We examine the distribution and propagation of energy in the plasma sheet and lobes using observations and simulations for three substorms. The substorms occurred on 9 March 1995, 10 December 1996, and 27 August 2001 and have been simulated using the Lyon-Fedder-Mobarry magneto-hydrodynamic code. All three events occur over North America and show a clear substorm current wedge over the ground magnetometer chains of Alaska, Canada, and Greenland. The three simulations show the thinning of the plasma sheet during the growth phase of the event and an increase in the relative amount of thermal energy due to the compression of the plasma sheet. Generally, the total lobe energy, polar cap flux, and lobe magnetic field strength simultaneously increase during the growth phase, and polar cap flux and total lobe energy only start dropping at substorm onset, as measured by the CANOPUS magnetometer chain. Starting at time of onset and continuing throughout the expansion phase a transfer of magnetic energy from the lobes into the plasma sheet occurs, with the increase in the plasma sheet energy ranging from 30–40% of the energy that is released from the lobes.

scholarly journals Transition from substorm growth to substorm expansion phase as observed with a radial configuration of ISTP and Cluster spacecraft

2005 ◽  
Vol 23 (6) ◽  
pp. 2183-2198 ◽  
Author(s):  
V. A. Sergeev ◽  
M. V. Kubyshkina ◽  
W. Baumjohann ◽  
R. Nakamura ◽  
O. Amm ◽  
...  
Keyword(s):  
Transition Region ◽  
Growth Phase ◽  
Plasma Sheet ◽  
Magnetic Energy ◽  
Global Scale ◽  
Substorm Onset ◽  
Plasma Injection ◽  
Storms And Substorms ◽  
Auroral Phenomena ◽  
Inner Region

Abstract. Transition from the growth phase to the substorm expansion during a well-isolated substorm with a strong growth phase is investigated using a unique radial (THEMIS-like) spacecraft constellation near midnight, including the probing of the tail current at ~16 RE with Cluster, of the transition region at ~9 RE with Geotail and Polar, and of the inner region at 6.6 RE with two LANL spacecraft. The activity development on both a global scale and near the spacecraft footpoints was monitored with global auroral images (from the IMAGE spacecraft) and the ground network. Magnetospheric models, tuned using in-situ observations, indicated a strong tail stretching and plasma sheet thinning, which included the growth of the near-Earth current (approaching 30 nA/m2) and possible formation of a local B minimum in the neutral sheet (~5 nT) at ~10–12 RE near the substorm onset. However, there were no indications that the substorm onset was initiated just in this region. We emphasize the rather weak magnetic and plasma flow perturbations observed outside the thinned plasma sheet at Cluster, which could be interpreted as the effects of localized earthward-contracting newly-reconnected plasma tubes produced by the impulsive reconnection in the midtail plasma sheet. In that case the time delays around the distinct substorm onset are consistent with the activity propagation from the midtail to the inner magnetosphere. A peculiar feature of this substorm was that 12min prior to this distinct onset, a clear soft plasma injection to the GEO orbit was recorded which has little associated effects both in the ionosphere and in the transition region at ~9 RE. This pseudo-breakup was probably due to either a localized ballooning-type activity or due to the braking of a very narrow BBF whose signatures were also recorded by Cluster. This event manifested the (previously unknown) phenomenon, a strong tail overloading (excessive storage of magnetic energy) contrasted to the modest energy dissipation and plasma acceleration, which are both discussed and interpreted as the consequences of cold/dense and thick pre-substorm plasma sheet which often occurs after the long quiet period. The lessons of using the radial spacecraft configurations in substorm onset studies are also discussed. Keywords. Magnetospheric physics (Auroral phenomena, plasma sheet, storms and substorms)

scholarly journals Statistical study of high-latitude plasma flow during magnetospheric substorms

2004 ◽  
Vol 22 (10) ◽  
pp. 3607-3624 ◽  
Author(s):  
G. Provan ◽  
M. Lester ◽  
S. B. Mende ◽  
S. E. Milan
Keyword(s):  
Plasma Flow ◽  
Growth Phase ◽  
High Latitude ◽  
Large Scale ◽  
Flow Region ◽  
Substorm Onset ◽  
Return Flow ◽  
Polar Cap ◽  
Magnetospheric Substorms ◽  
Superposed Epoch Analysis

Abstract. We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF Bz component was increasing (becoming less negative) during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.

scholarly journals Correlation between ground-based observations of substorm signatures and magnetotail dynamics

2005 ◽  
Vol 23 (3) ◽  
pp. 997-1011 ◽  
Author(s):  
E. Borälv ◽  
H. J. Opgenoorth ◽  
K. Kauristie ◽  
M. Lester ◽  
J.-M. Bosqued ◽  
...  
Keyword(s):  
Solar Wind ◽  
Event Study ◽  
Plasma Sheet ◽  
Sheet Thickness ◽  
Substorm Onset ◽  
Boundary Motion ◽  
Thickness Variations ◽  
Magnetotail Dynamics

Abstract. We present a substorm event study using the four Cluster spacecraft in combination with ground-based instruments, in order to perform simultaneous observations in the ionosphere and magnetotail. We show good correlation between substorm signatures on the ground and in the magnetotail, even though data from the northern-ground and southern-tail hemispheres are compared. During this event ground-based magnetometers show a substorm onset over Scandinavia in the pre-midnight sector. Within 1.5h the onset and three intensifications are apparent in the magnetograms. For all the substorm signatures seen on the ground, corresponding plasma sheet boundary motion is visible at Cluster, located at a downtail distance of 18.5 RE. As a result of the substorm onset and intensifications, Cluster moves in and out between the southern plasma sheet and lobe. Due to the lack of an apparent solar wind driver and the good correlation between substorm signatures on the ground, we conclude the substorm itself is the driver for these plasma sheet dynamics. We show that in the scales of Cluster inter-spacecraft distances (~0.5 RE) the inferred plasma sheet motion is often directed in both Ygsm- and Zgsm-directions, and discuss this finding in the context of previous studies of tail flapping and plasma sheet thickness variations.

Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs

2013 ◽  
Vol 118 (5) ◽  
pp. 2034-2042 ◽  
Author(s):  
Y. Nishimura ◽  
L. R. Lyons ◽  
K. Shiokawa ◽  
V. Angelopoulos ◽  
E. F. Donovan ◽  
...  
Keyword(s):  
Substorm Onset ◽  
Polar Cap ◽  
Expansion Phase

scholarly journals The relationship between the magnetosphere and magnetospheric/auroral substorms

2013 ◽  
Vol 31 (3) ◽  
pp. 387-394 ◽  
Author(s):  
S.-I. Akasofu
Keyword(s):  
Electric Field ◽  
Growth Phase ◽  
Magnetic Energy ◽  
Dissipative System ◽  
Satellite Observation ◽  
Recovery Phase ◽  
Release Process ◽  
Expansion Phase ◽  
Auroral Substorms ◽  
The Relationship

Abstract. On the basis of auroral and polar magnetic substorm studies, the relationship between the solar wind-magnetosphere dynamo (the DD dynamo) current and the substorm dynamo (the UL dynamo) current is studied. The characteristics of both the DD and UL currents reveal why auroral substorms consist of the three distinct phases after the input power ε is increased above 1018 erg s−1. (a) The growth phase; the magnetosphere can accumulate magnetic energy for auroral substorms, when the ionosphere cannot dissipate the power before the expansion phase. (b) The expansion phase; the magnetosphere releases the accumulated magnetic energy during the growth phase in a pulse-like manner in a few hours, because it tries to stabilize itself when the accumulated energy reaches to about 1023 erg s−1. (c) The recovery phase; the magnetosphere becomes an ordinary dissipative system after the expansion phase, because the ionosphere becomes capable of dissipating the power with the rate of 1018 ~ 1019 erg s−1. On the basis of the above conclusion, it is suggested that the magnetosphere accomplishes the pulse-like release process (resulting in spectacular auroral activities) by producing plasma instabilities in the current sheet, thus reducing the current. The resulting contraction of the magnetic field lines (expending the accumulated magnetic energy), together with break down of the "frozen-in" field condition at distances of less than 10 RE, establishes the substorm dynamo that generates an earthward electric field (Lui and Kamide, 2003; Akasofu, 2011). It is this electric field which manifests as the expansion phase. A recent satellite observation at a distance of as close as 8.1 RE by Lui (2011) seems to support strongly the occurrence of the chain of processes suggested in the above. It is hoped that although the concept presented here is very crude, it will serve in providing one way of studying the three phases of auroral substorms. In turn, a better understanding of auroral substorms will also be useful in studying the magnetosphere, because various auroral activities can be the visible guide for this endeavor.

scholarly journals On storm weakening during substorm expansion phase

1997 ◽  
Vol 15 (2) ◽  
pp. 211-216 ◽  
Author(s):  
G. L. Siscoe ◽  
H. E. Petschek
Keyword(s):  
Energy Storage ◽  
Kinetic Energy ◽  
Growth Phase ◽  
Virial Theorem ◽  
Ring Current ◽  
Magnetic Energy ◽  
Energy Partitioning ◽  
Negative Contribution ◽  
Expansion Phase ◽  
Energy Dissipated

Abstract. Iyemori and Rao recently presented evidence that the strength of a magnetic storm, as measured by -Dst, weakens, or its rate of growth slows, during the substorm expansion phase. Yet the expansion phase is known to inject energetic particles into the ring current, which should strengthen the storm. We propose to reconcile these apparently contradictory results by combining the virial theorem and a principle of energy partitioning between energy storage elements in a system with dissipation. As applied to the unloading description of the substorm expansion phase, the virial theorem states that -Dst is proportional to the sum of the total magnetic energy and twice the total kinetic energy in the magnetosphere including the tail. Thus if expansion phase involves converting magnetic energy stored in the tail into kinetic energy stored in the ring current, a drop in -Dst during expansion phase requires that less than half the drop in magnetic energy goes into the ring current, the rest going into the ionosphere. Indeed Weiss et al., have estimated that the energy dissipated in the ionosphere during expansion phase is twice that injected into the ring current. This conclusion is also consistent with the mentioned energy partitioning principle, which requires that more energy be dissipated than transferred between storage elements. While Iyemori and Rao's observations seem to contradict the hypothesis that storms consist at least in part of a sum of substorms, this mode of description might nonetheless be preserved by including the substorm's growth-phase contribution. Then the change in storm strength measured from before the growth phase to after the expansion phase is positive, even though the expansion phase alone makes a negative contribution.

scholarly journals The electric field response to the growth phase and expansion phase onset of a small isolated substorm

1997 ◽  
Vol 15 (3) ◽  
pp. 289-299 ◽  
Author(s):  
R. V. Lewis ◽  
M. P. Freeman ◽  
A. S. Rodger ◽  
G. D. Reeves ◽  
D. K. Milling
Keyword(s):  
Electric Field ◽  
Growth Phase ◽  
Auroral Oval ◽  
Substorm Onset ◽  
Field Of View ◽  
Radar Backscatter ◽  
Expansion Phase ◽  
Ionospheric Convection ◽  
Flow Component ◽  
Field Response

Abstract. We capitalise on the very large field of view of the Halley HF radar to provide a comprehensive description of the electric field response to the substorm growth phase and expansion phase onset of a relatively simple isolated substorm ( |AL| < 250 nT) which occurred on 13 June 1988. The substorm phases are identified by their standard ground magnetic and spacecraft energetic particle signatures, which provide a framework for the radar measurements. The substorm is preceded by a prolonged period (>12 h) of magnetic quiescence, such that prior to the start of the growth phase, the apparent latitudinal motion of the radar backscatter returns is consistent with the variation in latitude of the quiet-time auroral oval with magnetic local time. The growth phase is characterised by an increasing, superimposed equatorward motion of the equatorward edge of the radar backscatter as the auroral oval expands. Within this backscatter region, there is a poleward gradient in the Doppler spectral width, which we believe to correspond to latitudinal structure in auroral emissions and magnetospheric precipitation. During the growth phase the ionospheric convection is dominated by a relatively smooth large-scale flow pattern consistent with the expanding DP2 (convection) auroral electrojets. Immediately prior to substorm onset the ionospheric convection observed by the radar in the midnight sector has a predominantly equatorward flow component. At substorm onset a dramatic change occurs and a poleward flow component prevails. The timing and location are quite remarkable. The timing of the flow change is within one minute of the dispersionless injection observed at geostationary orbit and the Pi2 magnetic signature on the ground. The location shows that this sudden change in flow is due to the effect of the upward field aligned current of the substorm current wedge imposed directly within the Halley radar field of view.

OBSERVATIONS OF SUBSTORM ACTIVITY FROM THE DATA OF MAIN CAMERA SYSTEM AND THD SATELLITE IN THE PLASMA SHEET

2021 ◽  
Vol 44 ◽  
pp. 16-19
Author(s):  
I.V. Despirak ◽  
◽  
T.V. Kozelova ◽  
B.V. Kozelov ◽  
A.A. Lubchich ◽  
...  
Keyword(s):  
Kola Peninsula ◽  
Growth Phase ◽  
Plasma Sheet ◽  
Space Time ◽  
Interesting Case ◽  
Camera System ◽  
Expansion Phase ◽  
Energetic Electrons ◽  
Time Dynamics ◽  
Substorm Activity

We investigated an interesting case of the space-time dynamics of substorm activations (AL ~ 800 nT) on December 24, 2014, when there were simultaneous observations on the THEMIS D satellite in the plasma sheet (|X| ~ 6.2 RE) and ground-based observations on the Kola Peninsula. The development of the substorm activity in the interval of ~ 19:00 to ~ 20:00 UT was considered. In this interval, at Lovozero station (LOZ), three peaks in the Pi1B pulsations were recorded, associated with the brightening of arcs near LOZ. The first peak was observed in connection with the appearance of beads structures in the auroras along the growth phase arc to the south from LOZ latitude. The second and third peaks in Pi1B pulsations were associated with the expansion phase, when three dipolarization fronts (DFs) were registered according THD data. DFs and injection of energetic electrons into the magnetosphere were observed near the moments of sudden intensification of auroras: brightening of arcs, breakup in aurora. Besides, it was shown that the development of substorm occurs near the Harang discontinuity (HD) according to the IMAGE magnetometers data. In this case, we can follow the development of aurora around the HD according to the data of the all sky camera in Apatity. It was shown that the pre-onset auroral forms were moved accordingly the two-cell ionospheric convection developed during the growth phase of the substorm.

scholarly journals Multiple magnetic dipolarizations observed by THEMIS during a substorm

2011 ◽  
Vol 29 (2) ◽  
pp. 331-339 ◽  
Author(s):  
S. P. Duan ◽  
Z. X. Liu ◽  
J. Liang ◽  
Y. C. Zhang ◽  
T. Chen
Keyword(s):  
Plasma Sheet ◽  
High Speed ◽  
Onset Time ◽  
Substorm Onset ◽  
Bulk Flow ◽  
Small Scale ◽  
Expansion Phase ◽  
Ae Index ◽  
The Magnetic Field ◽  
Bulk Speed

Abstract. The magnetic field dipolarization in the vicinity of substorm onset and during substorm expansion phase during the period of 06:00–06:40 UT on 15 February 2008 is investigated with observations from multiple probes of THEMIS. It is found that the magnetic dipolarization at the substorm onset (the onset time was about 06:14 UT) was not accompanied by obvious magnetic disturbance and ion bulk speed variation. The magnetic dipolarizations taking place during the substorm expansion phase observed by P4~(−10.97, 2.04, −3.03) RE and P3~(−11.32, 1.15, −3.10) RE were mostly accompanied by high speed earthward ion bulk flow, but the magnetic dipolarizations occurring during the substorm expansion phase observed by P5~(−9.45, 1.07, −2.85) RE were not accompanied by high speed earthward ion bulk flow. Before substorm onset THEMIS P3, P4, P5 all observed the Bx component fluctuation with a period of about 300 s. After substorm onset earthward high speed ion bulk flow and significant magnetic disturbances both occurred at P3 and P4 locations. These results indicate that there is no one-to-one relationship between the near-Earth magnetic dipolarization and the earthward ion bulk flow. In particular, the magnetic dipolarization occurring on the earthward side of the inner near-Earth plasma sheet is not accompanied by high speed earthward ion bulk flow. The dipolarization at substorm onset is a local and small scale phenomenon. There are multiple magnetic dipolarizations occurring during the substorm expansion phase. The dipolarization process is very complex and is not simply an MHD process. It is accompanied by some kinds of plasma instabilities, the plasma sheet azimuthal expansion not only by earthward ion bulk flow during substorm. A sharp increase of the AE index does not always give an accurate substorm onset time for substorm analysis.

CHOICE OF CONDITIONS FOR MHD SIMULATIONS ABOVE THE ACTIVE REGION, ALLOWING THE STUDY OF THE SOLAR FLARE MECHANISM

2021 ◽  
Vol 44 ◽  
pp. 92-95
Author(s):  
A.I. Podgorny ◽  
◽  
I.M. Podgorny ◽  
A.V. Borisenko ◽  
N.S. Meshalkina ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Solar Flare ◽  
Magnetic Energy ◽  
Solar Radius ◽  
Computational Domain ◽  
Mhd Simulations ◽  
Flare Energy ◽  
Numerical Instabilities ◽  
The Magnetic Field

Primordial release of solar flare energy high in corona (at altitudes 1/40 - 1/20 of the solar radius) is explained by release of the magnetic energy of the current sheet. The observed manifestations of the flare are explained by the electrodynamical model of a solar flare proposed by I. M. Podgorny. To study the flare mechanism is necessary to perform MHD simulations above a real active region (AR). MHD simulation in the solar corona in the real scale of time can only be carried out thanks to parallel calculations using CUDA technology. Methods have been developed for stabilizing numerical instabilities that arise near the boundary of the computational domain. Methods are applicable for low viscosities in the main part of the domain, for which the flare energy is effectively accumulated near the singularities of the magnetic field. Singular lines of the magnetic field, near which the field can have a rather complex configuration, coincide or are located near the observed positions of the flare.

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