Relation of Non-neutralized electric currents and the activity in active regions

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-	[[File:386f1.png|400px|thumb|center|'''Figure 1''':	+	[[File:386f1.png|700px|thumb|center|]]
		+
		+	'''Figure 1:'''
	Degree of net electric current neutralization in AR 11429.		Degree of net electric current neutralization in AR 11429.
-	]]	+	Left panel: A sample vector magnetogram is with traced SPILs (the blue curves).
-		+
-	'''Caption:''' Top panel: A sample vector magnetogram is with traced SPILs (the blue curves).	+
	Transverse field vectors are shown with the red (green) arrows in north		Transverse field vectors are shown with the red (green) arrows in north
	(south) polarity regions.		(south) polarity regions.
-	Axis units are 0.5 arcsec pixels.	+	Axis units are in 0.5 arcsec pixels.
-	The Middle and bottom panels show the	+	The right panel shows the evolution of |DC/RC| in the north polarity.
-	Evolution of |DC/RC| in north (B<sub>z</sub> > 0, top panel)	+	The right panel shows the evolution of |DC/RC| in the north (B<sub>z</sub> > 0 polarity.
-	and south (B<sub>z</sub> < 0, bottom panel) in emerging ARs.	+
-	]]	+
-	The ratio is also	+
-	plotted for Jz<sub>ch</sub> (the red curve) in respective panels.	+
	Net magnetic flux (in units of 10<sup>21</sup> Maxwell) is plotted in		Net magnetic flux (in units of 10<sup>21</sup> Maxwell) is plotted in
-	grey with y-axis scale on right of each panel.	+	grey with y-axis scale on right.
	The horizontal dotted line marks current neutralization level of unity.		The horizontal dotted line marks current neutralization level of unity.
	Note that |DC/RC| for Jz<sub>ch</sub> (volume currents) is dominant than		Note that |DC/RC| for Jz<sub>ch</sub> (volume currents) is dominant than
	for J<sub>z</sub> indicating the additional contribution of		for J<sub>z</sub> indicating the additional contribution of
	Jz<sub>ch</sub> in the NCN.		Jz<sub>ch</sub> in the NCN.
-
	== References ==		== References ==

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Revision as of 11:06, 24 September 2020

Nugget
Number:	386
1st Author:	P. VEMAREDDY
2nd Author:
Published:	24 August 2020
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Introduction

Transient eruptive events (flares, CMEs, jets etc.) derive their energy from electrical currents that pass through the solar atmosphere. There are evidential reports that the strong electrical currents involved in major flares are embedded within magnetic flux that has emerged from the convection zone through the photosphere into the corona. We identify these currents via the twisting of the field, or by other means such as Faraday's Law as applied to the Zeeman effect observed in the solar photosphere.

According to Parker (Ref. [1]), the net electric current at any cross-section of a magnetic flux tube embedded in relatively field-free plasma must result in a zero value, which turns out not to be the case observationally (Ref. [2]). A study of two active regions (Ref. [3]) appears to have resolved the debate. Intense polarity inversion lines (PILs) amid the compact polarities of these active regions contribute significantly to non-neutralized coronal currents. This also suggests that the length of strong magnetically sheared PIL (SPIL) may be proportional to the observed net current. In this context, a very early study in 2001 (Ref. [4]) was the basis for this well-proven relation of strong SPIL being an indicator for the occurrence of eruptions with its length a measure of the net vertical current.

Analysis

From the net vertical current distribution computed from vector field measurements in the photosphere, j_z ~ (∇ x B)_z, we deduce the net current by summing over the pixels of a particular polarity. In each polarity, the absolute ratio (|DC/RC|) of dominant and non-dominant net current is evaluated with the flux evolution in the active region. A ratio of unity indicates neutralized currents in that polarity. Higher than unity indicates non-neutralized net current and is a special case of non-potentiality. The breakdown of net current neutralization (NCN) implies a form of Lorentz force development leading to stability loss and CME eruption, according to flux-rope models of eruptions.

Figure 1: Degree of net electric current neutralization in AR 11429. Left panel: A sample vector magnetogram is with traced SPILs (the blue curves). Transverse field vectors are shown with the red (green) arrows in north (south) polarity regions. Axis units are in 0.5 arcsec pixels. The right panel shows the evolution of |DC/RC| in the north polarity. The right panel shows the evolution of |DC/RC| in the north (B_z > 0 polarity. Net magnetic flux (in units of 10²¹ Maxwell) is plotted in grey with y-axis scale on right. The horizontal dotted line marks current neutralization level of unity. Note that |DC/RC| for Jz_ch (volume currents) is dominant than for J_z indicating the additional contribution of Jz_ch in the NCN.

References

[1] "Inferring Mean Electric Currents in Unresolved Fibril Magnetic Fields"

[2] "On the Absence of Photospheric Net Currents in Vector Magnetograms of Sunspots Obtained from Hinode (Solar Optical Telescope/Spectro-Polarimeter)"

[3] "Non-neutralized Electric Current Patterns in Solar Active Regions: Origin of the Shear-generating Lorentz Force"

[4] "A prospective method for predicting coronal mass ejections from vector magnetograms"