The spatial distribution of region 2 field-aligned currents relative to subauroral polarization stream

Abstract

Abstract. To test the current-generation model of subauroral polarization stream (SAPS), we have investigated the relative positions of field-aligned currents (FACs) with respect to SAPS in a statistical way by using CHAMP (CHAllenging Minisatellite Payload) and DMSP (Defense Meteorological Satellite Program) satellite observations as well as model simulations. Comparative studies have been performed for consecutive CHAMP observations in different magnetic local time (MLT) sectors with respect to SAPS. The latitude of the peak westward zonal wind deduced from CHAMP measurements has been used to represent the location of the SAPS peak. Both the density and the sheet current strength of R2 (region 2) FACs are enhanced when SAPS occur. Subsequently R2 FACs decay in intensity and correspondingly the centers retreat poleward. The latitudes of the center of the R2 FAC, small-and medium-scale FACs, and SAPS shift equatorward with increasing MLT. The SAPS peaks are located between R2 and R1 (region 1) FAC peaks in all MLT bins under study. The SAPS peaks are closer to R2 centers in the later MLT sectors. The peaks of small-and mediumscale FACs are located poleward of SAPS, mainly in the upward R1 FACs region. The upward R1 FACs are partly closed by the downward R1 FACs in the dawn-morning sector. Based on model simulation, when R2 shifts equatorward to the subauroral region, the plasma flow also shifts equatorward with its peak located poleward of that of R2 FACs. Both the model and observations provide evidence that SAPS behave as caused by a magnetospheric current source.

The Effect of Subauroral Polarization Streams on Ionosphere and Thermosphere During the 2015 St. Patrick's Day Storm: Global Ionosphere‐Thermosphere Model Simulations

“…In turn, the reduced conductance intensifies the polarization electric field leading to significant plasma stream in the subauroral region. This current generator model is consistent with extensive observations (He et al, ; Makarevich & Bristow, ; Wang et al, ) and has been widely accepted. In addition, other SAPS models, such as voltage generator model, have also been suggested (De Keyser, ; Lyatsky et al, ; Mishin, ).…”

A subauroral polarization stream driven by field‐aligned currents associated with precipitating energetic ions caused by EMIC waves: A case study

“…For the SAPS production mechanism, it is also proposed that a fraction of Region 2 FACs flow into regions of low ionospheric conductivities at subauroral latitudes so as to cause large polarization electric fields, driving the SAPS [ Heinemann et al ., ; Anderson et al ., ; Foster and Burke , ; H . Wang et al ., ]. As shown in Figures b and d, between 63.5° MLAT and 66.5° MLAT, Δ B z shows a positive gradient with increasing latitudes, implying Region 2 FACs flowing into the ionosphere in the evening sector.…”

Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic Field Components B<sub>X</sub>, B<sub>Y</sub> and B<sub>Z</sub> During Geomagnetic Storm

“…Interplanetary magnetic field (IMF) influences on the occurrence of large-scale FACs has been long recognized [31,19,1]. The IMF influence on the FACs is however not from only a single IMF component but a contribution from all the IMF components.…”

“…For northward IMF Bz, NBZ FACs dominate in the polar cap poleward of R1 FACs [17]. This current system, NBZ FACs, have been interpreted in terms of the antiparallel reconnection on field lines tailward of the dayside cusp [17,31,32]. When IMF B Y becomes dominant DPY FACs form around the noon sector while positive B Y , in the northern hemisphere results in upward field-aligned current located poleward of the downward current, and vice versa in the southern hemisphere [16,2].…”