Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations

Jiang Liu,Yukitoshi Nishimura,William A Bristow,Chih-Ping Wang,Larry R Lyons

doi:10.3389/fspas.2021.737946

Abstract

Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval).

Highlights

Bursts of flows with an equatorward component are seen within the nightside auroral oval (Sergeev et al, 1990; Kauriste et al, 1996; Yeoman & Lühr, 1999), these being the ionospheric counterpart of earthward flow bursts in the plasma sheet (Angelopoulos et al, 1992)
Available datasets were analyzed in this study. This data can be found here: SuperDARN data is accessible via http://vt
LL: All aspects of paper YN: Data coordination, analysis, and interpretation C-PW: Rice Convection Model simulations JL: Data analysis and interpretation WB: Two-dimensional radar flows and their interpretation

Summary

INTRODUCTION

Bursts of flows with an equatorward component are seen within the nightside auroral oval (Sergeev et al, 1990; Kauriste et al, 1996; Yeoman & Lühr, 1999), these being the ionospheric counterpart of earthward flow bursts in the plasma sheet (Angelopoulos et al, 1992). Flow bursts in the ionosphere have been observed to lead to a variety of other important geomagnetic disturbances as the reach to near the equatorward boundary of the auroral oval, which maps to the inner plasma sheet. These disturbances include thin substorm growth phase aurora arc formation or intensification (Nishimura et al, 2011), substorm onset (e.g., Nishimura et al, 2010), and omega bands (Henderson et al, 2002; Liu et al, 2018).

RCM RESULTS

SUMMARY AND CONCLUSION

DATA AVAILABILITY STATEMENT