Substorm influence on the ionospheric electric potentials and currents

Characteristic patterns of the high-latitude, ionospheric electric potential have been derived for two groups, with and without the occurrence of magnetospheric substorms, and for all orientations of the interplanetary magnetic field (IMF). These maps were derived from all available, simultaneous Dynamics Explorer 2 and solar wind data, using a least error fit technique. There are distinctive patterns for each orientation of the IMF, both with and without substorms in progress. In comparison to the nonsubstorm electric potential patterns, the substorm group tends to have a more pronounced Harang discontinuity near midnight. The averages of the AE indices that were measured simultaneously with the electric potentials have also been analyzed. The AU index is found to be linearly proportional to the electric potential in the dusk cell, while the |AL| index compared with the dawn cell's potential has a nonlinear trend. The |AL| index is distinctively greater for the substorm group, as expected, while the electric potential and AU index remain relatively unchanged. The measured electric potential patterns have been combined with a conductivity model in order to derive ionospheric and field-aligned currents. The Harang discontinuity is prominent in the horizontal ionospheric currents, particularly for the substorm group. Model calculations of |AL| indicate that some of the substorm increase can be accounted for by an enhanced auroral conductivity, while the changes in the electric field's magnitude and orientation near midnight, in distortions that do not significantly increase the overall potential drop, also contribute to the substorm electrojet. The field-aligned currents show a systematic evolution of the region 1 and region 2 current belts as the IMF changes from a +Y to −Y orientation. For negative BY the upward currents form a continuous oval, linking the region 2 current on the dawn side with the region 1 current on the dusk side, through both noon and midnight. For positive BY the upward currents are no longer continuous through noon and are divided by downward current linking the region 2 current on the duskside with the region 1 current on the dawnside. The “region 0” or cusp currents, which move from prenoon to postnoon as the IMF BY changes from positive to negative, appear to be continuations of the post/prenoon region 1 current belts.

[1]  M. L. Johnson,et al.  associated with the westward traveling surge and large-scale auroral spirals , 1998 .

[2]  Y. Kamide,et al.  Two‐component auroral electrojet: Importance for substorm studies , 1996 .

[3]  Y. Kamide,et al.  The average ionospheric electrodynamics for the different substorm phases , 1996 .

[4]  Y. Kamide,et al.  Substorm changes of the electrodynamic quantities in the polar ionosphere: CDAW 9 , 1995 .

[5]  D. Weimer,et al.  Models of high‐latitude electric potentials derived with a least error fit of spherical harmonic coefficients , 1995 .

[6]  J. S. Murphree,et al.  Four large-scale field-aligned current systems in the dayside high-latitude region , 1995 .

[7]  R. Hoffman,et al.  Satellite measurements through the center of a substorm surge , 1994 .

[8]  J. Slavin,et al.  Ground-based studies of ionospheric convection associated with substorm expansion , 1994 .

[9]  D. Weimer.  Substorm time constants , 1994 .

[10]  D. Weimer,et al.  The relationship between ionospheric convection and magnetic activity , 1994 .

[11]  P. Newell,et al.  Relationship between Birkeland current regions, particle precipitation, and electric fields , 1993 .

[12]  D. Weimer,et al.  Variations of the polar cap potential measured during magnetospheric substorms , 1992 .

[13]  M. Saunders.  The morphology of dayside Birkeland currents , 1992 .

[14]  Y. Kamide,et al.  Cross-polar cap potential difference, auroral electrojet indices, and solar wind parameters , 1992 .

[15]  Mike Lockwood,et al.  Dependence of convective flows and particle precipitation in the high‐latitude dayside ionosphere on the X and Y components of the interplanetary magnetic field , 1991 .

[16]  W. J. Burke,et al.  Polar cap potentials and the auroral electrojet indices , 1990 .

[17]  Mike Lockwood,et al.  The excitation of plasma convection in the high‐latitude ionosphere , 1990 .

[18]  T. Araki,et al.  Geomagnetic effects of the Hall and Pedersen current flowing in the auroral ionosphere , 1989 .

[19]  K. Szego,et al.  Pickup ions in the unshocked solar wind at comet Halley , 1989 .

[20]  R. Lundin,et al.  IMF By dependence of region 1 Birkeland currents near noon , 1988 .

[21]  J. D. Craven,et al.  Imaging results from Dynamics Explorer 1 , 1988 .

[22]  M. S. Gussenhoven,et al.  Statistical and functional representations of the pattern of auroral energy flux, number flux, and conductivity , 1987 .

[23]  Wolfgang Baumjohann,et al.  Estimation of electric fields and currents from international magnetospheric study magnetometer data for the CDAW 6 intervals: Implications for substorm dynamics , 1985 .

[24]  John D. Craven,et al.  Polar views of the Earth's aurora with Dynamics Explorer , 1982 .

[25]  H. F. Burdick,et al.  Instrumentation for vector electric field measurements from DE-B. [Dynamics Explorer-B satellite , 1981 .

[26]  T. Potemra,et al.  Large‐scale characteristics of field‐aligned currents associated with substorms , 1978 .

[27]  Y. Kamide,et al.  The location of the field‐aligned currents with respect to discrete auroral arcs , 1976 .

[28]  N. Fukushima.  Generalized theorem for no ground magnetic effect of vertical currents connected with Pedersen currents in the uniform-conductivity ionosphere , 1976 .

[29]  N. Maynard,et al.  Electric field measurements across the harang discontinuity. [of the auroral zone , 1974 .

[30]  J. Heppner.  The harang discontinuity in auroral belt ionospheric currents , 1971 .

[31]  D. A. Dunnett.  Classical Electrodynamics , 2020, Nature.

[32]  L. Harang.  The mean field of disturbance of polar geomagnetic storms , 1946 .