New Views of Global Solar Magnetic Field Evolution Over Four Solar Cycles

{{Infobox Nugget
|name = Nugget
|title = New Views of Global Solar Magnetic Field Evolution Over Four Solar Cycles
|number = 331
|first_author = David Webb
|second_author = 
|publish_date = 20 August 2018
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== Introduction ==

The magnetic field of the Sun originates in the solar interior, driven by a 
[dynamo] mechanism. 
It then emerges through the [photosphere], ultimately
permeating the entire heliosphere. 
The evolution of this field at the Sun's
surface is manifested in large-scale features such as filaments,
active regions and sunspots, polarity boundaries, and coronal holes.
Surface diffusion and transport produces an evolving pattern of
positive and negative magnetic polarity regions that encompass the
global magnetic field.  
The Sun exhibits characteristic migration
patterns of all of these these features. 
One is the equatorward movement of the
latitude zone of sunspots, a fundamental feature of the 11-year
activity cycle that resembles the wings of a butterfly (Figure 1),
as first described by [Maunder].
Another is the poleward movement of high-latitude filaments and
their related unipolar magnetic cells.  
It is clear that observing
the evolution of such surface features over long, solar cycle-time
scales is important for understanding the internal fluid dynamics
of the Sun.  
The newly-established McIntosh Archive of solar synoptic
maps now permits tracking these features over four consecutive solar
cycles.

[[File:331f1.png|600px|thumb|center|Figure 1:
A) Scanned image of an original synoptic map in from March 2002
created by Pat McIntosh.  (B) Processed colorized map from the new
McIntosh Archive with negative (gray) and positive (white) polarity
magnetic fields, negative (red) and positive (blue) coronal holes,
filaments (green), and polarity inversion lines (black).  
]]

== Discussion ==

This Archive consists of a set of hand-drawn solar Carrington maps
created by 
[https://aas.org/obituaries/patrick-s-mcintosh-1940-2016 Patrick McIntosh], 
who passed away in 2016, from 1964 to 2009 (Figure 1A).  
Pat used mainly H, He-I 10830 &Acirc;  and photospheric
magnetic measurements from both ground-based and NASA satellite
observations.  
With these he traced the phenomena of the
[https://en.wikipedia.org/wiki/Stellar_magnetic_field solar magnetic field]:
polarity inversion lines, filaments, sunspots and plage and, later, 
coronal holes, over a 45-year period.  
This yielded a unique record of synoptic maps of features associated with the 
large-scale solar magnetic field.  
With NSF support we have preserved and are digitizing this archive in
an IDL-based, searchable format (Figure 1B). We have created a
website
(https://www2.hao.ucar.edu/mcintosh-archive/four-cycles-solar-synoptic-maps),
and an archival repository at NOAAs National Centers for Environmental
Information (NCEI).  
This work is reviewed in the References, most recently in Ref [1].  

Figure 2 combines the sunspot, filament and coronal hole locations
for the entire McIntosh Archive ("McA") data processed to date, 
showing at a glance how
the patterns repeat in each cycle.  
In addition, the plot illustrates
how the positive and negative-polarity open magnetic fields surround
the closed-field filaments and sunspots globally.  

 The open field is that part connected into the solar wind, and the
 closed field is that part forming loop-like connections between two
 points in the photosphere.

Despite the data gaps, this demonstrates well how the dual cells of 
opposite-polarity in the higher latitudes of each hemisphere track each 
other through each cycle, and how consistent the offset is between 
the higher-latitude open and closed regions and the lower-latitude 
closed regions (sunspots and plage).  
Of interest is the evolution of the polar magnetic regions of the Sun and 
how the 
[https://www.noao.edu/noao/noaonews/mar99/node38.html "rush to the poles"]
and other patterns occur during the period when the polar fields reverse near
each cycle maximum.  
Figure 2 shows that we have data coverage
during these epochs for three consecutive solar cycles: in the North
in Cycle 21 around CR 1700, Cycle 22  CR 1830, and Cycle 23  CR 1970.  
In the South the reversals lag those in the north, as has been the case 
in recent solar cycles.  
We are working to fill in the data for the incomplete or missing CRs. 
The Carrington rotation number (CR) counts solar rotations since an
epoch defined by 
[https://en.wikipedia.org/wiki/Richard_Christopher_Carrington Carrington], 
at a rate he also devised.
This framework is necessary because of the
[https://en.wikipedia.org/wiki/Differential_rotation differential rotation].

[[File:331f2.png|600px|thumb|center|Figure 2:
"Butterfly" plot of all of the McA data processed to date starting
with CR 1513 in October 1966 and ending with CR 2086 in July 2009.
The Year scale is at the top and the Carrington Rotation scale at
the bottom.  
This plots for each CR all sunspots (orange), the
poleward-most filament boundaries (green), and the poleward-most
coronal hole boundaries (red and blue).  
Closed (open) circles
indicate the most northward (southward) extensions of hole boundaries
for each CR, and red and blue indicate magnetic polarity.  
]]

Finally, Figure 3 is a sequence of equatorial slices stacked along a 
curving, snake-like axis advancing in time using the Archive data for 
all of Cycle 23 (CRs 1910-2084).  
Active longitudes are evident in the quiet sun, sunspots, and coronal holes.  
A near 180<sup>&circ;</sup> longitudinal asymmetry is particularly evident 
just after solar maximum, consistent with studies spanning 100 years of 
sunspot active longitudes. 

[[File:331f3.png|600px|thumb|center|Figure 3:
A sequence of equatorial slices (20 to +20 heliolatitude) is stacked
along a curving axis, like a snake, advancing in time through CRs
1910-2084 (Cycle 23).  
The width of the snake is the 360 heliolongitude range for 
for each CR.  The colors follow the key as in Figure 1B.  The panels
on the right show how an equatorial latitude strip from one CR is
patched into a stackplot which in turn becomes a curvilinear part
of the entire snake that traverses all of Cycle 23 ]] 

== References ==

[1] [https://pdfs.semanticscholar.org/14f7/fc86de5c76b01df4c8d171d338874e7b4868.pdf "Global Solar Magnetic Field Evolution Over 4 Solar Cycles: Use of the McIntosh Archive"]

[2] [http://adsabs.harvard.edu/abs/2017SpWea..15.1442W "Preserving a unique archive for long-term solar variability studies"]
 
[3] [http://adsabs.harvard.edu/abs/2017IAUS..328...93G "Beyond Sunspots: Studies Using the McIntosh Archive of Global Solar Magnetic Field Patterns"]