Plasma sheet expansion at r = 15 - 22 RE: A recovery phase or expansion phase phenomenon?

1994 ◽  
Vol 99 (A6) ◽  
pp. 10995 ◽  
Author(s):  
L. R. Lyons ◽  
C. Y. Huang
Keyword(s):  
Plasma Sheet ◽  
Recovery Phase ◽  
Expansion Phase

scholarly journals An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

2007 ◽  
Vol 25 (1) ◽  
pp. 59-76 ◽  
Author(s):  
M. L. Parkinson ◽  
J. A. Wild ◽  
C. L. Waters ◽  
M. Lester ◽  
E. A. Lucek ◽  
...  
Keyword(s):  
Plasma Sheet ◽  
Large Scale ◽  
Ring Current ◽  
Narrow Channel ◽  
Recovery Phase ◽  
Global Scale ◽  
Auroral Oval ◽  
Flow Channel ◽  
Expansion Phase ◽  
Field Aligned Current

Abstract. An auroral westward flow channel (AWFC) is a latitudinally narrow channel of unstable F-region plasma with intense westward drift in the dusk-to-midnight sector ionosphere. AWFCs tend to overlap the equatorward edge of the auroral oval, and their life cycle is often synchronised to that of substorms: they commence close to substorm expansion phase onset, intensify during the expansion phase, and then decay during the recovery phase. Here we define for the first time the relationship between an AWFC, large-scale field-aligned current (FAC), the ring current, and plasmapause location. The Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar, observed a jet-like AWFC during ~08:35 to 13:28 UT on 7 April 2001. The initiation of the AWFC was preceded by a band of equatorward expanding ionospheric scatter (BEES) which conveyed an intense poleward electric field through the inner plasma sheet. Unlike previous AWFCs, this event was not associated with a distinct substorm surge; rather it occurred during an interval of persistent, moderate magnetic activity characterised by AL~−200 nT. The four Cluster spacecraft had perigees within the dusk sector plasmasphere, and their trajectories were magnetically conjugate to the radar observations. The Waves of High frequency and Sounder for Probing Electron density by Relaxation (WHISPER) instruments on board Cluster were used to identify the plasmapause location. The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) EUV experiment also provided global-scale observations of the plasmapause. The Cluster fluxgate magnetometers (FGM) provided successive measurements specifying the relative location of the ring current and filamentary plasma sheet current. An analysis of Iridium spacecraft magnetometer measurements provided estimates of large-scale ionospheric FAC in relation to the AWFC evolution. Peak flows in the AWFC were located close to the peak of a Region 2 downward FAC, located just poleward of the plasmapause. DMSP satellite observations confirmed the AWFC was located equatorward of the nightside plasmasheet, sometimes associated with ~10 keV ion precipitation.

scholarly journals Temporal and spatial evolution of discrete auroral arcs as seen by Cluster

2005 ◽  
Vol 23 (7) ◽  
pp. 2531-2557 ◽  
Author(s):  
S. Figueiredo ◽  
G. T. Marklund ◽  
T. Karlsson ◽  
T. Johansson ◽  
Y. Ebihara ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Sheet ◽  
Large Scale ◽  
Potential Drop ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Expansion Phase ◽  
Electric Fields And Currents ◽  
Auroral Arcs

Abstract. Two event studies are presented in this paper where intense convergent electric fields, with mapped intensities up to 1350 mV/m, are measured in the auroral upward current region by the Cluster spacecraft, at altitudes between 3 and 5 Earth radii. Both events are from May 2003, Southern Hemisphere, with equatorward crossings by the Cluster spacecraft of the pre-midnight auroral oval. Event 1 occurs during the end of the recovery phase of a strong substorm. A system of auroral arcs associated with convergent electric field structures, with a maximum perpendicular potential drop of about ~10 kV, and upflowing field-aligned currents with densities of 3 µA/m2 (mapped to the ionosphere), was detected at the boundary between the Plasma Sheet Boundary Layer (PSBL) and the Plasma Sheet (PS). The auroral arc structures evolve in shape and in magnitude on a timescale of tens of minutes, merging, broadening and intensifying, until finally fading away after about 50 min. Throughout this time, both the PS region and the auroral arc structure in its poleward part remain relatively fixed in space, reflecting the rather quiet auroral conditions during the end of the substorm. The auroral upward acceleration region is shown for this event to extend beyond 3.9 Earth radii altitude. Event 2 occurs during a more active period associated with the expansion phase of a moderate substorm. Images from the Defense Meteorological Satellite Program (DMSP) F13 spacecraft show that the Cluster spacecraft crossed the horn region of a surge-type aurora. Conjugated with the Cluster spacecraft crossing above the surge horn, the South Pole All Sky Imager recorded the motion and the temporal evolution of an east-west aligned auroral arc, 30 to 50 km wide. Intense electric field variations are measured by the Cluster spacecraft when crossing above the auroral arc structure, collocated with the density gradient at the PS poleward boundary, and coupled to intense upflowing field-aligned currents with mapped densities of up to 20 µA/m2. The surge horn consists of multiple arc structures which later merge into one structure and intensify at the PS poleward boundary. The surge horn and the associated PS region moved poleward with a velocity at the ionospheric level of 0.5 km/s, following the large-scale poleward expansion of the auroral oval associated with the substorm expansion phase. Keywords. Ionosphere (Ionosphere-magnetosphere interacctions; Electric fields and currents; Particle acceleration)

scholarly journals IMF effect on the polar cap contraction and expansion during a period of substorms

2013 ◽  
Vol 31 (6) ◽  
pp. 1021-1034 ◽  
Author(s):  
A. T. Aikio ◽  
T. Pitkänen ◽  
I. Honkonen ◽  
M. Palmroth ◽  
O. Amm
Keyword(s):  
Recovery Phase ◽  
Bow Shock ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Early Recovery ◽  
Mhd Simulation ◽  
Expansion Phase ◽  
Contraction And Expansion ◽  
Good Agreement ◽  
The Imf

Abstract. 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.

scholarly journals Ionospheric signatures during a magnetospheric flux rope event

2008 ◽  
Vol 26 (12) ◽  
pp. 3967-3977 ◽  
Author(s):  
L. Juusola ◽  
O. Amm ◽  
H. U. Frey ◽  
K. Kauristie ◽  
R. Nakamura ◽  
...  
Keyword(s):  
Flux Rope ◽  
Recovery Phase ◽  
Expansion Phase ◽  
Northern Fennoscandia ◽  
Ionospheric Region ◽  
Image Satellite ◽  
Imaging Camera ◽  
Flux Ropes ◽  
Field Aligned Current ◽  
Upward Current

Abstract. On 13 August 2002, during a substorm, Cluster encountered two earthward moving flux ropes (FR) in the central magnetotail. The first FR was observed during the expansion phase of the substorm, and the second FR during the recovery phase. In the conjugate ionospheric region in Northern Fennoscandia, the ionospheric equivalent currents were observed by the MIRACLE network and the auroral evolution was monitored by the Wideband Imaging Camera (WIC) on-board the IMAGE satellite. Extending the study of Amm et al. (2006), we examine and compare the possible ionospheric signatures associated with the two FRs. Amm et al. studied the first event in detail and found that the ionospheric footprint of Cluster coincided with a region of downward field-aligned current. They suggested that this region of downward current, together with a trailing region of upward current further southwestward, might correspond to the ends of the FR. Unlike during the first FR, however, we do not see any clear ionospheric features associated with the second one. In the GSM xy-plane, the first flux rope axis was tilted with respect to the y-direction by 29°, while the second flux rope axis was almost aligned in the y-direction, with an angle of 4° only. It is possible that due to the length and orientation of the second FR, any ionospheric signatures were simply mapped outside the region covered by the ground-based instruments. We suggest that the ground signatures of a FR depend on the orientation and the length of the structure.

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 Storm Time EMIC Waves Observed by Swarm and Van Allen Probe Satellites

2021 ◽  
Author(s):  
Yangfan He ◽  
Hui Wang ◽  
Lühr Hermann ◽  
Kistler Lynn ◽  
Saikin Anthony ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Recovery Phase ◽  
Early Recovery ◽  
Expansion Phase ◽  
Van Allen Probes ◽  
Substorm Activity ◽  
Temporal And Spatial ◽  
Maximum Occurrence ◽  
Winter Hemisphere ◽  
Emic Waves

<p>The temporal and spatial evolution of electromagnetic ion cyclotron (EMIC) waves during<br>the magnetic storm of 21–29 June 2015 was investigated using high-resolution magnetic field observations<br>from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric<br>EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during<br>the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral<br>regions occurred more frequently in the nighttime than during the day and exhibited less obvious<br>latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere<br>and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were<br>absent in the magnetosphere and ionosphere around the minimum SYM-H. During the early recovery<br>phase, He<sup>+ </sup>band EMIC waves were observed in the ionosphere and magnetosphere. During the late<br>recovery phase, H<sup>+</sup> band EMIC waves emerged in response to enhanced earthward convection during<br>substorms in the premidnight sector. The occurrence of EMIC waves in the noon sector was affected by<br>the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer<br>hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 hr with a<br>duration of less than 186 min from coordinated observations. The results could provide additional insights<br>into the spatial characteristics and propagation features of EMIC waves during storm periods</p>

scholarly journals Substorm behavior of the auroral electrojet indices

2004 ◽  
Vol 22 (6) ◽  
pp. 2135-2149 ◽  
Author(s):  
J. W. Gjerloev ◽  
R. A. Hoffman ◽  
M. M. Friel ◽  
L. A. Frank ◽  
J. B. Sigwarth
Keyword(s):  
Current System ◽  
Three Dimensional ◽  
Recovery Phase ◽  
Auroral Electrojet ◽  
Spatial Behavior ◽  
Early Recovery ◽  
Substorm Current Wedge ◽  
Expansion Phase ◽  
Systematic Behavior ◽  
Current Wedge

Abstract. The behavior of the auroral electrojet indices AU and AL during classical substorms is investigated by the use of global auroral images. A superposition of the 12 AE stations onto global auroral images and identification of the AL and AU contributing stations enable an understanding of the temporal as well as spatial behavior of the indices with respect to the substorm coordinate system and timeframe. Based on this simple technique it was found that at substorm onset the AL contributing station makes a characteristic jump from a location near the dawn terminator to the onset region, typically bypassing one or more AE stations. During the expansion phase this station typically lies at the poleward edge of the surge region. This is the location of the intense substorm current wedge electrojet in the semiempirical self-consistent substorm model of the three-dimensional current system by Gjerloev and Hoffman (2002). This current wedge is fed primarily pre-midnight by an imbalance of the Region 0 and Region 1 field-aligned currents, not from the dawnside westward electrojet. Then during the early recovery phase the AL contributing station jumps back to the dawn sector. The defining AU station does not show any similar systematic behavior. We also find that the dawn side westward electrojet seems to be unaffected by the introduction of the substorm current wedge. According to our model, much of this current is closed to the magnetosphere as it approaches midnight from dawn. Based on the characteristics of the AL station jumps, the behavior of the dawn-side electrojet, and the understanding of the three-dimensional substorm current system from our model, we provide additional experimental evidence for, and an understanding of, the concept of the two component westward electrojet, as suggested by Kamide and Kokubun (1996).

scholarly journals Brightening of onset arc precedes the dipolarization onset: THEMIS observations of two events on 1 March 2008

2011 ◽  
Vol 29 (11) ◽  
pp. 2045-2059 ◽  
Author(s):  
J. R. Kan ◽  
H. Li ◽  
C. Wang ◽  
H. U. Frey ◽  
M. V. Kubyshkina ◽  
...  
Keyword(s):  
Time Delay ◽  
Plasma Sheet ◽  
Coupling Model ◽  
Mhd Waves ◽  
Current Loop ◽  
Expansion Phase ◽  
Tail Current ◽  
Electrojet Current ◽  
The Cross ◽  
Poleward Expansion

Abstract. We present a new M-I coupling model of substorm during southward IMF based on the THEMIS observations of two events on 1 March 2008. The first event (E-1) was classified as a pseudo-breakup: brightening of the onset arc preceded the first dipolarization onset by ∼71 ± 3 s, but the breakup arcs faded within ∼5 min without substantial poleward expansion and the dipolarization stopped and reversed to thinning. The second event (E-2) was identified as a substorm: brightening of the second onset arc preceded the second dipolarization onset by ∼80 ± 3 s, leading to a full-scale expanding auroral bulge during the substorm expansion phase for ∼20 min. The Alfvén travel time from the ionosphere to the dipolarization onset region is estimated at ∼69.3 s in E-1; at ∼80.3 s in E-2, which matched well with the observed time delay of the dipolarization onset after the brightening of the onset arc, respectively in E-1 and E-2. Brightening of the onset arc precedes the dipolarization onset suggest that the onset arc brightening is caused by the intense upward field-aligned currents originating from the divergence of the Cowling electrojet in the ionosphere. The Cowling electrojet current loop (CECL) is formed to close the field-aligned currents at all times. The closure current in the Alfvén wavefront is anti-parallel to the cross-tail current. Dipolarization onset occurs when the Alfvén wavefront incident on the near-Earth plasma sheet to disrupt the cross-tail current in the dipolarization region. Slow MHD waves dominate the disruption of the cross-tail current in the dipolarization region.

scholarly journals Observations of an auroral streamer in a double oval configuration

2011 ◽  
Vol 29 (4) ◽  
pp. 701-716 ◽  
Author(s):  
O. Amm ◽  
R. Nakamura ◽  
T. Takada ◽  
K. Kauristie ◽  
H. U. Frey ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Recovery Phase ◽  
Auroral Oval ◽  
Expansion Phase ◽  
Optical Instruments ◽  
Image Satellite ◽  
Bursty Bulk Flow ◽  
Polarization Electric Field ◽  
Late Evening ◽  
Eiscat Radar

Abstract. During the late evening and night of 14 September 2004, the nightside auroral oval shows a distinct double oval configuration for several hours after a substorm onset at ~18:45 UT. This structure is observed both by the IMAGE satellite optical instruments focusing on the Southern Hemisphere, and by the MIRACLE ground-based instrument network in Scandinavia. At ~21:17 UT during the recovery phase of the substorm, an auroral streamer is detected by these instruments and the EISCAT radar, while simultaneously the Cluster satellites observe a bursty bulk flow in the conjugate portion of the plasma sheet in the magnetotail. Our combined data analysis reveals significant differences between the ionospheric equivalent current signature of this streamer within a double oval configuration, as compared to previously studied streamer events without such a configuration. We attribute these differences to the presence of an additional poleward polarization electric field between the poleward and the equatorward portions of the double oval, and show with a simple model that such an assumption can conceptually explain the observations. Further, we estimate the total current transferred in meridional direction by this recovery phase streamer to ~80 kA, significantly less than for previously analysed expansion phase streamer events. Both results indicate that the development of auroral streamers is dependent on the ambient background conditions in the magnetosphere-ionosphere system. The auroral streamer event studied was simultaneously observed in the conjugate Northern and Southern Hemisphere ionosphere.

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