The response of ionospheric convection in the polar cap to substorm activity

1995 ◽  
Vol 13 (2) ◽  
pp. 147-158 ◽  
Author(s):  
M. Lester ◽  
M. Lockwood ◽  
T. K. Yeoman ◽  
S. W. H. Cowley ◽  
H. Lühr ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Neutral Line ◽  
Flow Reversal ◽  
Polar Cap ◽  
Substorm Current Wedge ◽  
Expansion Phase ◽  
Ionospheric Convection ◽  
Eiscat Radar ◽  
Current Wedge

Abstract. We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.

scholarly journals Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events

2007 ◽  
Vol 25 (8) ◽  
pp. 1865-1876 ◽  
Author(s):  
A. D. DeJong ◽  
X. Cai ◽  
R. C. Clauer ◽  
J. F. Spann
Keyword(s):  
Magnetic Flux ◽  
Temporal Variations ◽  
Auroral Oval ◽  
Polar Cap ◽  
Expansion Phase ◽  
Magnetospheric Convection ◽  
Open Magnetic Flux ◽  
Open Flux ◽  
The Individual

Abstract. Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.

scholarly journals On the retreat of near-Earth neutral line during substorm expansion phase: a THEMIS case study during the 9 January 2008 substorm

2012 ◽  
Vol 30 (1) ◽  
pp. 143-151 ◽  
Author(s):  
X. Cao ◽  
Z. Y. Pu ◽  
A. M. Du ◽  
V. M. Mishin ◽  
X. G. Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Hall Current ◽  
Neutral Line ◽  
Tail Region ◽  
Expansion Phase ◽  
Reconnection Site

Abstract. The location of magnetic reconnection in the mid-tail during a substorm was studied in many researches. Here we present multi-point THEMIS observations of a reconnection event in the near-Earth magnetotail during substorm. In this event, THEMIS probes stayed in the near-Earth and mid-tail region aligning along the magnetotail. This allows reconnection evolution to be probed simultaneously from about −10 RE to −23 RE down tail. The Hall current related electron streams were observed at the same time by two probes far away from the reconnection site. Before near-Earth reconnection involved the tail lobe magnetic field, the reconnection site was restricted in earthward −23 RE. When reconnection involved into the tail lobe region, the reconnection site started to retreat gradually.

scholarly journals Seasonal and interplanetary magnetic field-dependent polar cap contraction during substorm expansion phase

2010 ◽  
Vol 115 (A11) ◽  
pp. n/a-n/a ◽  
Author(s):  
K. M. Laundal ◽  
N. Østgaard ◽  
H. U. Frey ◽  
J. M. Weygand
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Polar Cap ◽  
Expansion Phase ◽  
Field Dependent

scholarly journals Microwave indicator of potential geoeffectiveness and magnetic flux-rope structure of a solar active region

2021 ◽  
Vol 7 (1) ◽  
pp. 3-12
Author(s):  
Anastasiia Kudriavtseva ◽  
Ivan Myshyakov ◽  
Arkadiy Uralov ◽  
Victor Grechnev
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Flux ◽  
Neutral Line ◽  
Flux Rope ◽  
Coronal Magnetic Field ◽  
Horizontal Magnetic Field ◽  
Magnetic Flux Rope ◽  
Magnetic Flux Ropes ◽  
Class Flare

We analyze the presence of a microwave neutral-line-associated source (NLS) in a super-active region NOAA 12673, which produced a number of geo-effective events in September 2017. To estimate the NLS position, we use data from the Siberian Radioheliograph in a range 4–8 GHz and from the Nobeyama Radioheliograph at 17 GHz. Calculation of the coronal magnetic field in a non-linear force-free approximation has revealed an extended structure consisting of interconnected magnetic flux ropes, located practically along the entire length of the main polarity separation line of the photospheric magnetic field. NLS is projected into the region of the strongest horizontal magnetic field, where the main energy of this structure is concentrated. During each X-class flare, the active region lost magnetic helicity and became a CME source.

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 Development and validation of inversion technique for substorm current wedge using ground magnetic field data

2014 ◽  
Vol 119 (3) ◽  
pp. 1909-1924 ◽  
Author(s):  
Xiangning Chu ◽  
Tung-Shin Hsu ◽  
Robert L. McPherron ◽  
Vassilis Angelopoulos ◽  
Zuyin Pu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Substorm Current Wedge ◽  
Magnetic Field Data ◽  
Inversion Technique ◽  
Ground Magnetic ◽  
Development And Validation ◽  
Current Wedge

scholarly journals Saturation of the magnetosphere during superstorms: new results from magnetogram inversion technique

2017 ◽  
Vol 3 (3) ◽  
pp. 15-19
Author(s):  
Владимир Мишин ◽  
Vladimir Mishin ◽  
Юрий Караваев ◽  
Yuriy Karavaev
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Flux ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Field ◽  
Dynamic Pressure ◽  
Magnetic Clouds ◽  
Polar Cap ◽  
Thermal Pressure ◽  
Dayside Magnetopause

From data of three three superstorms we study new features of the saturation process of the polar cap magnetic flux deceleration of its area at strengthening the solar wind (SW). It is shown that the saturation of the polar cap is observed at growth of the SW dynamic pressure and vertical IMF component for both signs. Saturation is realized not only during the passage of interplanetary magnetic clouds, but also at significant enhancement of SW density, when the SW thermal pressure is comparable with the pressure of the interplanetary magnetic field. We assume that at such condiitions the saturation is caused not only by a decrease in the efficiency of reconnection at the dayside magnetopause, but mainly by a finite magnetosphere compressibility –stopping the magnetopause compression due to the rapid Eathward growth of the geomagnetic field, ie, interior magnetospheric structure of the geomagnetic field

SABRE observations of structured ionospheric flows during substorm expansion phase onset

1994 ◽  
Vol 12 (10/11) ◽  
pp. 1027-1038
Author(s):  
E. G. Bradshaw ◽  
M. Lester ◽  
T. B. Jones
Keyword(s):  
Magnetic Activity ◽  
Substorm Onset ◽  
Field Of View ◽  
Substorm Current Wedge ◽  
Expansion Phase ◽  
Pi2 Pulsation ◽  
Pi2 Pulsations ◽  
Generation Region ◽  
Coherent Radar ◽  
Current Wedge

Abstract. The irregularity velocity patterns observed by the SABRE coherent radar at substorm expansion phase onset, which is identified by magnetometer observations of Pi2 pulsations, are occasionally highly structured. In all the examples of structured velocity patterns examined, the SABRE viewing area is located at longitudes within the inferred substorm current wedge. Three types of structured velocity regime are apparent depending on the level of magnetic activity and the position of the radar viewing area relative to the substorm enhanced currents and the Pi2 pulsation generation region. Firstly, vortex-like velocity patterns are observed and these may be caused by the field-aligned currents associated with the substorm current wedge. Secondly, regions of equatorward velocity are also observed at times of substorm expansion phase onset moving longitudinally across the SABRE viewing area. The longitudinal movement is usually westward although an example of eastward motion has been observed. The phase velocity of these regions of equatorward flow is typically 1-3 km s-1. The observed equatorward velocities occur at the poleward edge or poleward of the background convection velocities observed by SABRE. These equatorward velocities may be related to the westward travelling surge and to the expansion (eastwards as well as westwards) of the brightening arc region at substorm onset. Thirdly, the flow rotates equatorward within the field of view but does not then appear to move longitudinally. These equatorward velocities may relate to the earthward surge of plasma from the magnetotail at substorm onset.

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

2015 ◽  
Vol 33 (4) ◽  
pp. 505-517 ◽  
Author(s):  
A. V. Nikolaev ◽  
V. A. Sergeev ◽  
N. A. Tsyganenko ◽  
M. V. Kubyshkina ◽  
H. Opgenoorth ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Latitude ◽  
Current Loop ◽  
Loop Model ◽  
Total Current ◽  
Substorm Current Wedge ◽  
Secondary Importance ◽  
Background Magnetic Field ◽  
Auroral Expansion ◽  
Current Wedge

Abstract. 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.

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