2021
DOI: 10.1029/2021ja029207
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Embedded Regions 1 and 2 Field‐Aligned Currents: Newly Recognized From Low‐Altitude Spacecraft Observations

Abstract: Earth's magnetosphere is electromagnetically coupled to its ionosphere by field-aligned currents (FACs) comprising two large-scale elements, Region 1 (R1) and Region 2 (R2) currents, which were discovered by Potemra (1976a, 1976b) in the ionosphere (Figure 1a). Region 1 currents, which are at higher latitudes, consist of FACs flowing downward into the ionosphere in the dawn sector and upward out of the ionosphere in the dusk sector. Equatorward of R1 currents lie R2 currents, which flow in the opposite direc… Show more

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Cited by 10 publications
(22 citation statements)
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References 88 publications
(141 reference statements)
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“…Consistent with the suggested mechanism, the boundary between background and embedded FACs is within the plasma sheet (Liu et al, 2021) (note that the R1/R2 interface is also within the plasma sheet on both the nightside and dayside (Liu et al, 2016;Ohtani et al, 2010;Wing et al, 2010)), and most previously-reported embedded FAC events or embedded FAC-like signatures occurred during geomagnetically active times (Liu et al, 2018(Liu et al, , 2020(Liu et al, , 2021Saflekos et al, 1982). Such active-time occurrence was shown for only <10 events, however, so a statistical study, as in the following, is needed to establish the dependence of ER1 and ER2 FACs' occurrence on geomagnetic activity, and thus allow for tests of the validity of the mechanism suggested by Liu et al (2021).…”
supporting
confidence: 71%
See 1 more Smart Citation
“…Consistent with the suggested mechanism, the boundary between background and embedded FACs is within the plasma sheet (Liu et al, 2021) (note that the R1/R2 interface is also within the plasma sheet on both the nightside and dayside (Liu et al, 2016;Ohtani et al, 2010;Wing et al, 2010)), and most previously-reported embedded FAC events or embedded FAC-like signatures occurred during geomagnetically active times (Liu et al, 2018(Liu et al, , 2020(Liu et al, , 2021Saflekos et al, 1982). Such active-time occurrence was shown for only <10 events, however, so a statistical study, as in the following, is needed to establish the dependence of ER1 and ER2 FACs' occurrence on geomagnetic activity, and thus allow for tests of the validity of the mechanism suggested by Liu et al (2021).…”
supporting
confidence: 71%
“…Based on simulations of strong FAC generation in the magnetotail (e.g., Birn et al, 2004;Gkioulidou et al, 2009;Yang et al, 2014), Liu et al (2021) suggested that ER1 and ER2 FACs arise from plasma disturbances (pressure buildup and flow vortices) in the central plasma sheet caused by strong convection during active times. The strong convection can be either steady or, more likely, intermittent in the form of bursty bulk flows (Angelopoulos et al, 1992) that accompany dipolarizing flux bundles (Liu et al, 2013(Liu et al, , 2014.…”
mentioning
confidence: 99%
“…The FAC boundaries are estimated with a threshold value of 0.05 μA/m 2 . Note that the FACs show alternating upward and downward signatures on the duskside, which imply finer structures embedded in the large‐scale Region‐1/Region‐2 FACs (e.g., Liu et al., 2021; Xiong et al., 2014). Small‐scale FAC structures away from the equatorward auroral boundaries are not shaded for better visibility.…”
Section: Observations and Simulation Resultsmentioning
confidence: 99%
“…We would expect the strongest currents to occur on the side of the distribution that dominates the mean current of a given region, although it may be that our observations are consistent with the embedded Birkeland currents recently reported by Liu et al. (2021). In a future study, we will repeat this analysis based on times at which we see ring current intensifications in order to verify this inference.…”
Section: Discussionmentioning
confidence: 99%
“…We take maps of AMPERE data and analyze them statistically. We find that the mean current densities resemble the Regions 1 and 2 current systems which have been investigated throughout the history of the field (Birkeland, 1908; Iijima & Potemra, 1978; Liu et al., 2021; Weimer, 2001). However, we find that the modes of the current density distributions are displaced toward the pole relative to the means, and that the mean current densities traditionally interpreted as R1 and R2 are explained mainly by asymmetries in the distribution of the currents rather than by the mode current.…”
Section: Discussionmentioning
confidence: 99%