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

H Wang,A Ridley,T Huang,H Lühr

doi:10.5194/angeo-32-533-2014

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 medium-scale 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.

Highlights

Two types of plasma flows have been classified in the literature: (1) polarization jets (PJ) (Galperin et al, 1974) or subauroral ion drifts (SAIDS) (Spiro et al, 1979), featured as more intense (∼ 1000 m s−1) and latitudinally confined (≤ 1◦ latitude) plasma flow; and (2) a wider latitudinal extent and longer duration of plasma flow (Yeh et al, 1991)
We looked at the small- and medium-scale field-aligned currents (FACs) (SSFAC) (10–150 km wavelengths), which are derived from the 1 Hz preprocessed CHAMP fluxgate magnetometer (FGM) data
Both the peak value and full strength of region 2 (R2) FACs get enhanced when subauroral polarization stream (SAPS) attain peaks, afterwards FACs tend to recover in magnitude and retreat poleward

Summary

Introduction

The subauroral polarization stream (SAPS) is one of the interesting and important features of the magnetosphere– ionosphere–thermosphere coupling processes in the subauroral region, representing the rapid westward plasma flow predominantly in the dusk and premidnight sector (16–24 magnetic local time, MLT) (e.g., Galperin et al, 1974; Spiro et al, 1979; Anderson et al, 1991, 1993, 2001; Yeh et al, 1991; Fejer and Scherliess, 1998; Scherliess and Fejer, 1998; Rowland and Wygant, 1998; Wygant et al, 1998; Ridley et al, 2002; Foster et al, 2002; Foster and Vo, 2002; Garner et al, 2004; Figueiredo et al, 2004; Liemohn et al, 2005; Jensen and Fejer, 2007; Zheng et al, 2008; Erickson et al, 2010, 2011; Clausen et al, 2012; Mishin, 2013). SAPS can deepen the F region trough density (e.g., Smiddy et al, 1977; Maynard, 1978; Spiro et al, 1978; Anderson et al, 1991, 2001; Foster et al, 2007), enhance the electron temperature (e.g., Wang and Lühr, 2013; Mishin, 2013), contribute to the ion upflow (e.g., Yeh and Foster, 1990; Anderson et al, 1991; Moffett et al, 1992; Erickson et al, 2010; Wang and Lühr, 2013), and Published by Copernicus Publications on behalf of the European Geosciences Union. Recent studies have disclosed that SAPS can cause westward wind jets and air density anomalies, which peak at the same location (e.g., Wang et al, 2012a, b; Wang et al, 2012)

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Discussion

Conclusion