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

From RHESSI Wiki

(Difference between revisions)
Jump to: navigation, search
(first bit of No. 386)
(first half, struggling with the humongous figure and its caption)
Line 1: Line 1:
{{Infobox Nugget
{{Infobox Nugget
|name = Nugget
|name = Nugget
-
|title = Relation of Non-neutralized electric currents and the activity in active regions
+
|title = Relation of Non-neutralized electric currents and the activity in active regions  
|number = 386
|number = 386
|first_author = P. VEMAREDDY
|first_author = P. VEMAREDDY
|second_author =  
|second_author =  
|publish_date = 24 August 2020
|publish_date = 24 August 2020
-
|next_nugget = TBD
+
|next_nugget = TBD  
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::385]]}}
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::385]]}}
}}
}}
Line 12: Line 12:
== Introduction ==
== Introduction ==
-
Transient eruptive events derive their energy from electrical
+
Transient eruptive events (flares, CMEs, jets etc.) derive their energy  
-
currents that pass through the solar atmosphere.  
+
from electrical currents that pass through the solar atmosphere.  
There are evidential reports that the strong electrical currents involved  
There are evidential reports that the strong electrical currents involved  
in major flares are embedded within magnetic flux that has emerged from the  
in major flares are embedded within magnetic flux that has emerged from the  
Line 21: Line 21:
[https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction Faraday's Law]
[https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction Faraday's Law]
as applied to the  
as applied to the  
-
[http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/zeeman.html Zeeman effect]  
+
[http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/zeeman.html Zeeman effect]
observed in the solar photosphere.
observed in the solar photosphere.
-
According to Parker (1996),
+
According to Parker (Ref. [1]), the net electric current at any cross-section  
-
the net electric current at any cross-section of a flux tube embedded
+
of a magnetic flux tube embedded in relatively field-free plasma must result  
-
in relatively field-free plasma must result in a zero value, which
+
in a zero value, which turns out not to be the case observationally  
-
is not the case observationally (Venkatakrishnan & Tiwari 2009).
+
(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.
-
[[File:386f1.png|600px|thumb|center|'''Figure 1''':
+
== Analysis ==
 +
 
 +
From the net vertical current distribution computed from vector field
 +
measurements in the photosphere, j<sub>z</sub> ~ (&nabla; x B)<sub>z</sub>,
 +
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.
 +
 
 +
 
 +
[[File:386f1.png|400px|thumb|center|'''Figure 1''':
 +
Degree of net electric current neutralization in AR 11429.
]]
]]
 +
 +
'''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
 +
(south) polarity regions.
 +
Axis units are 0.5 arcsec pixels.
 +
The Middle and bottom panels show the
 +
Evolution of |DC/RC| in north (B<sub>z</sub> > 0, top panel)
 +
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
 +
grey with y-axis scale on right of each panel.
 +
The horizontal dotted line marks current neutralization level of unity.
 +
Note that |DC/RC| for Jz<sub>ch</sub> (volume currents) is dominant than
 +
for J<sub>z</sub> indicating the additional contribution of
 +
Jz<sub>ch</sub> in the NCN.
 +
 +
 +
== References ==
 +
 +
[1] [http://adsabs.harvard.edu/abs/1996ApJ...471..485P "Inferring Mean Electric Currents in Unresolved Fibril Magnetic Fields"]
 +
 +
[2] [https://ui.adsabs.harvard.edu/abs/2009ApJ...706L.114V "On the Absence of Photospheric Net Currents in Vector Magnetograms of Sunspots Obtained from Hinode (Solar Optical Telescope/Spectro-Polarimeter)"]
 +
 +
[3] [http://adsabs.harvard.edu/abs/2012ApJ...761...61G "Non-neutralized Electric Current Patterns in Solar Active Regions: Origin of the Shear-generating Lorentz Force"]
 +
 +
[4] [https://ui.adsabs.harvard.edu/abs/2001JGR...10625185F "A prospective method for predicting coronal mass ejections from vector magnetograms"]

Revision as of 16:14, 23 September 2020


Nugget
Number: 386
1st Author: P. VEMAREDDY
2nd Author:
Published: 24 August 2020
Next Nugget: TBD
Previous Nugget: White-light emission and photospheric magnetic field changes in flares
List all



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, jz ~ (∇ 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.

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 (south) polarity regions. Axis units are 0.5 arcsec pixels. The Middle and bottom panels show the Evolution of |DC/RC| in north (Bz > 0, top panel) and south (Bz < 0, bottom panel) in emerging ARs. ]] The ratio is also plotted for Jzch (the red curve) in respective panels. Net magnetic flux (in units of 1021 Maxwell) is plotted in grey with y-axis scale on right of each panel. The horizontal dotted line marks current neutralization level of unity. Note that |DC/RC| for Jzch (volume currents) is dominant than for Jz indicating the additional contribution of Jzch 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"

Retrieved from "https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Relation_of_Non-neutralized_electric_currents_and_the_activity_in_active_regions"
Facts about Relation of Non-neutralized electric currents and the activity in active regionsRDF feed
RHESSI Nugget Date24 August 2020  +
RHESSI Nugget First AuthorP. VEMAREDDY  +
RHESSI Nugget Index386  +
Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox