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Title: On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution

Abstract

The influence of localized field-aligned current, associated with intense transpolar arcs mostly occurring during periods of northward interplaentary magnetic field (IMF), on the global electrodynamics has been investigated using a numerical simulation model. Idealized field-aligned current distributions representing both the region 1/2 system of the auroral oval and the transpolar arc as well as a corresponding ionospheric conductivity distribution are fed into the model to calculate the potential distributions. The transpolar arc has been represented by a few alternative field-aligned current distributions which are different in the way the downward return currents are distributed in the ionosphere. If the conductivity of the main auroral oval is comparable to that of the polar arc the dusk cell will have two local potential minima and thus a region of weak antisunward convection in between. Depending on the direction of the polar arc current sheets the dawn-dusk electric field will either be reversed (or weakened) or intensified at the location of the transpolar arc. The presence of a reversal depend, however, not only on the relative magnitude between the polar arc current sand those of the region 1/2 system but also on the characteristics of the acceleration region and of the conductivity distributionmore » associated with the polar arc. Comparisons are made between the model results and Viking electric field data for a number of polar arc crossings to reveal the most common electrodynamical signatures of these auroral phenomena.« less

Authors:
;  [1]
  1. (Royal Inst. of Tech., Stockholm (Sweden))
Publication Date:
OSTI Identifier:
5255923
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Geophysical Research; (United States); Journal Volume: 96:A8
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; POLAR-CAP AURORAE; ELECTRODYNAMICS; AURORAL OVAL; ELECTRIC CONDUCTIVITY; ELECTRIC CURRENTS; INTERACTIONS; INTERPLANETARY MAGNETIC FIELDS; MAGNETIC BAYS; MATHEMATICAL MODELS; MORPHOLOGY; SOLAR WIND; AURORAE; CURRENTS; ELECTRICAL PROPERTIES; MAGNETIC FIELDS; PHYSICAL PROPERTIES; SOLAR ACTIVITY; 640201* - Atmospheric Physics- Auroral, Ionospheric, & Magetospheric Phenomena

Citation Formats

Marklund, G.T., and Blomberg, L.G. On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution. United States: N. p., 1991. Web. doi:10.1029/91JA01120.
Marklund, G.T., & Blomberg, L.G. On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution. United States. doi:10.1029/91JA01120.
Marklund, G.T., and Blomberg, L.G. 1991. "On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution". United States. doi:10.1029/91JA01120.
@article{osti_5255923,
title = {On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution},
author = {Marklund, G.T. and Blomberg, L.G.},
abstractNote = {The influence of localized field-aligned current, associated with intense transpolar arcs mostly occurring during periods of northward interplaentary magnetic field (IMF), on the global electrodynamics has been investigated using a numerical simulation model. Idealized field-aligned current distributions representing both the region 1/2 system of the auroral oval and the transpolar arc as well as a corresponding ionospheric conductivity distribution are fed into the model to calculate the potential distributions. The transpolar arc has been represented by a few alternative field-aligned current distributions which are different in the way the downward return currents are distributed in the ionosphere. If the conductivity of the main auroral oval is comparable to that of the polar arc the dusk cell will have two local potential minima and thus a region of weak antisunward convection in between. Depending on the direction of the polar arc current sheets the dawn-dusk electric field will either be reversed (or weakened) or intensified at the location of the transpolar arc. The presence of a reversal depend, however, not only on the relative magnitude between the polar arc current sand those of the region 1/2 system but also on the characteristics of the acceleration region and of the conductivity distribution associated with the polar arc. Comparisons are made between the model results and Viking electric field data for a number of polar arc crossings to reveal the most common electrodynamical signatures of these auroral phenomena.},
doi = {10.1029/91JA01120},
journal = {Journal of Geophysical Research; (United States)},
number = ,
volume = 96:A8,
place = {United States},
year = 1991,
month = 8
}
  • The comparison of the distribution of field-aligned currents and ionospheric currents on a very quiet day and a moderately disturbed day, obtained on the basis of the International Magnetosphere Study Alaska meridian chain of magnetometers, reveals that the field-aligned currents (region I and II currents) consist of two systems: the part I system in the dayside and the part II system in the nightside. On a very quiet day the part II system is either absent or very weak. On the other hand, on a moderately disturbed day the part II system becomes a dominant feature. It is also shownmore » that both the ionospheric currents and the electric fields on quiet and disturbed days can be understood in terms of the response of the ionosphere to changes of the part I and II systems.« less
  • It has been common to suppose that polar region field-aligned currents for southward interplanetary magnetic fields (IMF) consist of two parts: region 1 and region 2 currents. It is often suggested that both of these current systems flow on closed field lines. In this pilot study the limited data available from the ISIS 2 satellite are used to examine region 1 currents with the objective of establishing whether or not they can exist partially on open field lines (i.e., inside the polar caps) for southward IMF. Magnetic field perturbations were used to identify the field-aligned currents (FACs). The absence ofmore » {ge}keV electrons but the presence of {le}200 eV electrons in the polar cap or background polar rain is considered as the signature of open field lines. On some passes, region 1 sense FACs appear to be composed of two parts. The poleward part of the current signature is accompanied by electron fluxes at energies {le}200 eV or occasionally by fluxes at background levels while the equatorward part of the interval is accompanied by electron fluxes at energies both {le}200 eV and {ge}keV. On other passes, region 1 sense currents are accompanied by both {le}200 eV and {ge}keV electron fluxes during the entire pass. The authors propose that region 1 sense FACs flow on both closed and open field lines for the first situation and on closed field lines for the second situation. In seeking to understand why region 1 currents sometimes flow only on closed field lines and sometimes flow on open as well as closed field lines, the authors suggest a control by the IMF B{sub y}. The IMF B{sub y} may also shift the region 1 currents on open field lines to one side (dawn or dusk) of the polar cap like the convection cells. Such a shift provides a consistent model of the data taken on the dayside and the authors discuss why night side observations may be different. 47 refs., 6 figs., 1 tab.« less
  • Computer simulation studies of the electric fields and currents in the global ionosphere produced by field-aligned electric currents for quiet periods are conducted. The steady state equations for current conservation are solved numerically by assuming (1) several divided regions of the global earth (such as the polar cap, auroral zone, and middle-low latitudes), (2) exponentially distributed anisotropic electric conductivities for each zone with a continuous change at the boundaries of the regions, and (3) exponentially distributed downward and upward field-aligned current intensities in the auroral region, assumptions based on our current knowledge of auroral phenomena and geomagnetic variations as wellmore » as rocket and satellite measurements of field-aligned currents. Resultant computer-plotted diagrams include equipotential contours of the electric fields, vector distributions of the electric fields and currents, and electric current patterns equivalent to the magnetic field effect produced by the field-aligned and real ionospheric currents.neity alters considerably the electric field pattern that has previously been obtained by assuming the uniform conductivity distribution. (2) Even a slight conductivity enhancement along the nightside auroral belt results in a large modification of the electric field. (3) The existence of the strong conductivity gradients and the field-aligned currents in the equatorward half of the auroral oval reduces the electric field in the middle and low latitudes. This corresponds to the 'shielding' effect of the electric field inside the Alfven layer in the magnetotail. (4) Seasonal changes in the polar cap conductivities cause surprisingly large effects on the electric fields and currents. (5) The equivalent ionospheric currents differ significantly from real ionospheric currents in both intensity and direction.« less
  • The computer simulation scheme for calculating the electric fields and currents in the global ionosphere in relation to field-aligned currents for quiet periods that we previously developed is extended to disturbed conditions. In a series of numerical simulations representing various substorms we take into account our current knowledge of characteristics of auroral enhancement in the ionospheric electric conductivities as well as changes in the intensity and location of field-aligned currents. The possible effects of these variable parameters in producing the observed complexity of the electric field and current patterns are studied, with the following main results: The conductivity inhomogeneity inmore » the auroral belt can reproduce the observed local time dependence of the electric fields and currents. The amount of the return currents from the auroral electrojets flowing within the ionosphere is small, an indication that the major part of the electrojets is connected directly to the field-aligned currents. Therefore the ground magnetic perturbations in the polar cap and also in the middle and low latitudes during substorms can be ascribed mainly to the magnetic effects of the field-aligned currents. Even when the intensities of the field-aligned currents and the associated auroral electrojets do increase considerably during substorms over their values of quiet times, the total potential difference across the polar cap does not increase very much, because of a simultaneous increase in the ionospheric conductivities along the nightside auroral oval. No special field-aligned current system in the Harang discontinuity region is required to reproduce this feature. The distribution pattern of the equivalent ionospheric current differs significantly from that of the real ionospheric current vectors. The maximum electrojet intensity seen in the equivalent current system is weaker than that of the real auroral electrojets.« less