HelioWiki Home Page - Recent changes [en]

The Hale Sector Boundary links flares to global magnetic fields

Hhudson — Fri, 09 Oct 2026 19:53:34 GMT

Conclusions

← Older revision		Revision as of 19:53, 9 October 2026
(3 intermediate revisions by the same user not shown)
Line 24:		Line 24:
	[https://en.wikipedia.org/wiki/Heliospheric_current_sheet heliospheric current sheet].		[https://en.wikipedia.org/wiki/Heliospheric_current_sheet heliospheric current sheet].

	[[File:537f1.png\|center\|thumb\|~~800px~~\|caption\|Figure 1: <i>		[[File:537f1.png\|center\|thumb\|600px\|caption\|Figure 1: <i>
	Figure 1. The extremes of solar magnetism. Left, the "salt-and-pepper" of		Figure 1. The extremes of solar magnetism. Left, the "salt-and-pepper" of
	the polarity distribution in the photosphere.		the polarity distribution in the photosphere.
Line 51:		Line 51:
	active regions.		active regions.

	[[File:537f2.png\|center\|thumb\|~~800px~~\|caption\|Figure 2: <i>		[[File:537f2..png\|center\|thumb\|600px\|caption\|Figure 2: <i>
	Two examples from the		Two examples from the
	[https://www.astro.gla.ac.uk/users/iain/hsb/ HSB Web tool].		[https://www.astro.gla.ac.uk/users/iain/hsb/ HSB Web tool].
Line 66:		Line 66:
	where opposing polarities prevail and may enable		where opposing polarities prevail and may enable
	[https://svs.gsfc.nasa.gov/20310 magnetic reconnection].		[https://svs.gsfc.nasa.gov/20310 magnetic reconnection].

			This Nugget describes our [interactive HSB database], but if you are
			interested there have been earlier Nuggets: [1], [2]

	== Historical note ==		== Historical note ==
Line 74:		Line 77:
	== References ==		== References ==

	[1] [https://ui.adsabs.harvard.edu/abs/2011ApJ...733...49S/ "Flaring Hale Sector		[1] [https://ui.adsabs.harvard.edu/abs/2011ApJ...733...49S/ "Flaring Hale Sector Boundaries"]
	Boundaries"]

	[2] [https://ui.adsabs.harvard.edu/abs/2018A&A...618A...9L/ "The association of the Hale sector boundary with RHESSI solar flares and active longitudes"]		[2] [https://ui.adsabs.harvard.edu/abs/2018A&A...618A...9L/ "The association of the Hale sector boundary with RHESSI solar flares and active longitudes"]

The Hale Sector Boundary links flares to global magnetic fields

Hhudson — Fri, 09 Oct 2026 19:39:02 GMT

No. 537 initial upload

New page

{{Infobox Nugget
|name = Nugget
|title = The Hale Sector Boundary links flares to global magnetic fields
|number = 537
|first_author = Iain HANNAH
|second_author = Hugh HUDSON
|publish_date = October 12, 2026
|next_nugget =
|previous_nugget = {{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::536]]}}
}}

== Introduction ==

When spacecraft first began to observe the interplanetary field, they found
a remarkable property: the radial component appeared to alternate polarities on a few-day time scale.
This became known as the "sector structure", and can be understood from
the comparisons in Figure 1 (right panel).
Often there are two or four sectors per solar rotation, and
the scale of the homogenous field structures is many solar radii.
At the other extreme, the magnetic field at the surface of the Sun (left
panel) shows abundant fine structure "salt and pepper", at scales
"measureless to man" - including the fine structures of solar flares.
The surface separating the two polarities lies within the
[https://en.wikipedia.org/wiki/Heliospheric_current_sheet heliospheric current sheet].

[[File:537f1.png|center|thumb|800px|caption|Figure 1: <i>
Figure 1. The extremes of solar magnetism. Left, the "salt-and-pepper" of
the polarity distribution in the photosphere.
Note how the systematic EW patterns differ between the NS hemispheres.
Right, the iconic view of the heliospheric current sheet, which forms a
warped surface separating the two (+/-) polarities.
Because of the warps produced by field asymmetries, a fixed obsesrver see
alternating sectors.
</i>]]

In this Nugget we describe the "Hale sector boundary" (Ref. [1])
and provide an interactive tool showing how it links these two
extreme spatial scales.
We define the Hale boundary as the "portions
of the heliospheric magnetic-field polarity inversion structure
where the polarity change has the same sense as the leading-to-following
polarity transition of sunspot groups in that hemisphere" (Ref. [2])
This refers to the amazing hemispheric preference for the "leading" sunspot,
in the sense of first appearance as the Sun rotate, to have the opposite
polarity from the "trailing" sunspots in a group.
This is guaranteed to be somewhat confusing, but Figure 2 shows
examples that make it all very clear.
These are from our Web-based
[https://www.astro.gla.ac.uk/users/iain/hsb/ interactive database]
of Hale sector boundaries, solar flares, and
active regions.

[[File:537f2.png|center|thumb|800px|caption|Figure 2: <i>
Two examples from the
[https://www.astro.gla.ac.uk/users/iain/hsb/ HSB Web tool].
The purple symbols show where the Hale sector boundary occurs as the
heliospheric current sheet sweeps below the solar equator; green dots
show active regions, and red letters show flare locations.
</i>]]

== Conclusions ==

The tendency for the smallest magnetic features to occur at where the
largest-scale polarity structures meet is remarkable, but with a sketch
one can see that the Hale boundary, and not the non-Hale boundary, is
where opposing polarities prevail and may enable
[https://svs.gsfc.nasa.gov/20310 magnetic reconnection].

== Historical note ==

The authors became interested in this subject via the encouragement of our late
friend [https://solarnews.aas.org/2025/obituary-leif-svalgaard-1942-2025/ Leif Svalgaard].

== References ==

[1] [https://ui.adsabs.harvard.edu/abs/2011ApJ...733...49S/ "Flaring Hale Sector
Boundaries"]

[2] [https://ui.adsabs.harvard.edu/abs/2018A&A...618A...9L/ "The association of the Hale sector boundary with RHESSI solar flares and active longitudes"]

File:537f2..png

Hhudson — Fri, 09 Oct 2026 19:23:30 GMT

Hhudson uploaded File:537f2..png

New page

File:537f1.png

Hhudson — Fri, 09 Oct 2026 19:22:50 GMT

Hhudson uploaded File:537f1.png

New page