scholarly journals Temporal variations in a four-sheet field-aligned current system and associated aurorae as observed during a Polar-ground magnetic conjunction in the midmorning sector

2003 ◽  
Vol 108 (A6) ◽  
Author(s):  
C. J. Farrugia
Keyword(s):  
Current System ◽  
Temporal Variations ◽  
Field Aligned Current ◽  
Ground Magnetic

scholarly journals Mesoscale ionospheric electrodynamics of omega bands determined from ground-based electromagnetic and satellite optical observations

2005 ◽  
Vol 23 (2) ◽  
pp. 325-342 ◽  
Author(s):  
O. Amm ◽  
A. Aksnes ◽  
J. Stadsnes ◽  
N. Østgaard ◽  
R.R. Vondrak ◽  
...  
Keyword(s):  
Method Of Characteristics ◽  
Current System ◽  
Optical Observations ◽  
Hall Conductance ◽  
Electromagnetic Data ◽  
Ionospheric Electrodynamics ◽  
Magnetic Signature ◽  
Field Aligned Current ◽  
Ground Magnetic ◽  
Polar Satellite

Abstract. We present ground-based electromagnetic data from the MIRACLE and BEAR networks and satellite optical observations from the UVI and PIXIE instruments on the Polar satellite of an omega band event over Northern Scandinavia on 26 June 1998, which occured close to the morning side edge of a substorm auroral bulge. Our analysis of the data concentrates on one omega band period from 03:18-03:27 UT, for which we use the method of characteristics combined with an analysis of the UVI and PIXIE data to derive a time series of instantaneous, solely data-based distributions of the mesoscale ionospheric electrodynamic parameters with a 1-min time resolution. In addition, the AMIE method is used to derive global Hall conductance patterns. Our results show that zonally alternating regions of enhanced ionospheric conductances ("tongues") up to ~60S and low conductance regions are associated with the omega bands. The tongues have a poleward extension of ~400km from their base and a zonal extension of ~380km. While they are moving coherently eastward with a velocity of ~770ms-1, the structures are not strictly stationary. The current system of the omega band can be described as a superposition of two parts: one consists of anticlockwise rotating Hall currents around the tongues, along with Pedersen currents, with a negative divergence in their centers. The sign of this system is reversing in the low conductance areas. It causes the characteristic ground magnetic signature. The second part consists of zonally aligned current wedges of westward flowing Hall currents and is mostly magnetically invisible below the ionosphere. This system dominates the field-aligned current (FAC) pattern and causes alternating upward and downward FAC at the flanks of the tongues with maximum upward FAC of ~25µA m-2. The total FAC of ~2MA are comparable to the ones diverted inside a westward traveling surge. Throughout the event, the overwhelming part of the FAC are associated with gradients of the ionospheric conductances, and 66-84% of the FAC are connected with ionospheric Hall currents.

Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study

2021 ◽  
Author(s):  
Dong Wei ◽  
Malcolm Dunlop ◽  
Junying Yang ◽  
Xiangcheng Dong ◽  
Yiqun Yu ◽  
...  
Keyword(s):  
Large Scale ◽  
Current System ◽  
Geomagnetically Induced Currents ◽  
Inner Magnetosphere ◽  
Wide Range ◽  
Ground System ◽  
Induced Currents ◽  
Ground Magnetic ◽  
Bursty Bulk Flows

<p>During geomagnetically disturbed times the surface geomagnetic field often changes abruptly, producing geomagnetically induced currents (GICs) in a number of ground based systems. There are, however, few studies reporting GIC effects which are driven directly by bursty bulk flows (BBFs) in the inner magnetosphere. In this study, we investigate the characteristics and responses of the magnetosphere-ionosphere-ground system during the 7 January 2015 storm by using a multi-point approach which combines space-borne measurements and ground magnetic observations. During the event, multiple BBFs are detected in the inner magnetosphere while the magnetic footprints of both magnetospheric and ionospheric satellites map to the same conjugate region surrounded by a group of magnetometer ground stations. It is suggested that the observed, localized substorm currents are caused by the observed magnetospheric BBFs, giving rise to intense geomagnetic perturbations. Our results provide direct evidence that the wide-range of intense dB/dt<strong> </strong>(and dH/dt) variations are associated with a large-scale, substorm current system, driven by multiple BBFs.</p>

27-Day Recurrence Phenomena in the Geomagnetic Field at Alert

1971 ◽  
Vol 8 (11) ◽  
pp. 1382-1387 ◽  
Author(s):  
R. N. Edwards ◽  
R. D. Kurtz
Keyword(s):  
Power Spectrum ◽  
Geomagnetic Storm ◽  
Amplitude Modulation ◽  
Geomagnetic Field ◽  
Current System ◽  
Temporal Variations

The temporal variations of the geomagnetic field at Alert are studied for a two-year period during a minimum of the 11-year sun-spot cycle. During this period (27 August 1962 to 21 September 1964), a recurrent geomagnetic storm is observed, persisting for 29 solar rotations. It produces lines in the geomagnetic power spectrum at frequencies corresponding to the harmonics of 27 days. A further 13 lines, equispaced in frequency by (1/27) cycles/day, are associated with sidebands of the daily line and are believed to result from amplitude modulation of the SqP/DS current system.

scholarly journals Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

1999 ◽  
Vol 17 (5) ◽  
pp. 692-706 ◽  
Author(s):  
S. Tsunomura
Keyword(s):  
Magnetic Fields ◽  
Electric Field ◽  
Current System ◽  
Equatorial Region ◽  
Iri Model ◽  
Ionospheric Layer ◽  
Ionospheric Current ◽  
New Model ◽  
Ionospheric Current System ◽  
Field Aligned Current

Abstract. A modeling method is proposed to derive a two-dimensional ionospheric layer conductivity, which is appropriate to obtain a realistic solution of the polar-originating ionospheric current system including equatorial enhancement. The model can be obtained by modifying the conventional, thin shell conductivity model. It is shown that the modification for one of the non-diagonal terms (Σθφ) in the conductivity tensor near the equatorial region is very important; the term influences the profile of the ionospheric electric field around the equator drastically. The proposed model can reproduce well the results representing the observed electric and magnetic field signatures of geomagnetic sudden commencement. The new model is applied to two factors concerning polar-originating ionospheric current systems. First, the latitudinal profile of the DP2 amplitude in the daytime is examined, changing the canceling rate for the dawn-to-dusk electric field by the region 2 field-aligned current. It is shown that the equatorial enhancement would not appear when the ratio of the total amount of the region 2 field-aligned current to that of region 1 exceeds 0.5. Second, the north-south asymmetry of the magnetic fields in the summer solstice condition of the ionospheric conductivity is examined by calculating the global ionospheric current system covering both hemispheres simultaneously. It is shown that the positive relationship between the magnitudes of high latitude magnetic fields and the conductivity is clearly seen if a voltage generator is given as the source, while the relationship is vague or even reversed for a current generator. The new model, based on the International Reference Ionosphere (IRI) model, can be applied to further investigations in the quantitative analysis of the magnetosphere-ionosphere coupling problems.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionosphere-magnetosphere interactions)

scholarly journals Dynamics of thin current sheets: Cluster observations

2007 ◽  
Vol 25 (6) ◽  
pp. 1365-1389 ◽  
Author(s):  
W. Baumjohann ◽  
A. Roux ◽  
O. Le Contel ◽  
R. Nakamura ◽  
J. Birn ◽  
...  
Keyword(s):  
Large Scale ◽  
Current System ◽  
Three Dimensional ◽  
Low Frequency ◽  
Active Period ◽  
Ion Flow ◽  
Magnetic Signatures ◽  
Field Aligned Current ◽  
Flow Reversals ◽  
Azimuthal Modulation

Abstract. The paper tries to sort out the specific signatures of the Near Earth Neutral Line (NENL) and the Current Disruption (CD) models, and looks for these signatures in Cluster data from two events. For both events transient magnetic signatures are observed, together with fast ion flows. In the simplest form of NENL scenario, with a large-scale two-dimensional reconnection site, quasi-invariance along Y is expected. Thus the magnetic signatures in the S/C frame are interpreted as relative motions, along the X or Z direction, of a quasi-steady X-line, with respect to the S/C. In the simplest form of CD scenario an azimuthal modulation is expected. Hence the signatures in the S/C frame are interpreted as signatures of azimuthally (along Y) moving current system associated with low frequency fluctuations of Jy and the corresponding field-aligned currents (Jx). Event 1 covers a pseudo-breakup, developing only at high latitudes. First, a thin (H≈2000 km≈2ρi, with ρi the ion gyroradius) Current Sheet (CS) is found to be quiet. A slightly thinner CS (H≈1000–2000 km≈1–2ρi), crossed about 30 min later, is found to be active, with fast earthward ion flow bursts (300–600 km/s) and simultaneous large amplitude fluctuations (δB/B~1). In the quiet CS the current density Jy is carried by ions. Conversely, in the active CS ions are moving eastward; the westward current is carried by electrons that move eastward, faster than ions. Similarly, the velocity of earthward flows (300–600 km/s), observed during the active period, maximizes near or at the CS center. During the active phase of Event 1 no signature of the crossing of an X-line is identified, but an X-line located beyond Cluster could account for the observed ion flows, provided that it is active for at least 20 min. Ion flow bursts can also be due to CD and to the corresponding dipolarizations which are associated with changes in the current density. Yet their durations are shorter than the duration of the active period. While the overall ∂Bz∂t is too weak to accelerate ions up to the observed velocities, short duration ∂Bz∂t can produce the azimuthal electric field requested to account for the observed ion flow bursts. The corresponding large amplitude perturbations are shown to move eastward, which suggests that the reduction in the tail current could be achieved via a series of eastward traveling partial dipolarisations/CD. The second event is much more active than the first one. The observed flapping of the CS corresponds to an azimuthally propagating wave. A reversal in the proton flow velocity, from −1000 to +1000 km/s, is measured by CODIF. The overall flow reversal, the associated change in the sign of Bz and the relationship between Bx and By suggest that the spacecraft are moving with respect to an X-line and its associated Hall-structure. Yet, a simple tailward retreat of a large-scale X-line cannot account for all the observations, since several flow reversals are observed. These quasi-periodic flow reversals can also be associated with an azimuthal motion of the low frequency oscillations. Indeed, at the beginning of the interval By varies rapidly along the Y direction; the magnetic signature is three-dimensional and essentially corresponds to a structure of filamentary field-aligned current, moving eastward at ~200 km/s. The transverse size of the structure is ~1000 km. Similar structures are observed before and after. These filamentary structures are consistent with an eastward propagation of an azimuthal modulation associated with a current system Jy, Jx. During Event 1, signatures of filamentary field-aligned current structures are also observed, in association with modulations of Jy. Hence, for both events the structure of the magnetic fields and currents is three-dimensional.

Deformation of plasma bubbles and the associated field aligned current system during substorm recovery phase

2012 ◽  
Vol 117 (A9) ◽  
pp. n/a-n/a ◽  
Author(s):  
Y. Pang ◽  
M. H. Lin ◽  
X. H. Deng ◽  
M. Zhou ◽  
S. Y. Huang
Keyword(s):  
Current System ◽  
Recovery Phase ◽  
Plasma Bubbles ◽  
Field Aligned Current
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