Comparing the Large-Scale Magnetic Field During the Last Three Solar Cycles

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Comparing the Large-Scale Magnetic Field During
the LastThree Solar Cycles

• Todd Hoeksema

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Evolution of the Large-Scale Magnetic Field
OverThree Solar Cycles

• Global Properties
• Corona Heliosphere
• Zonal Magnetic Field
• Toroidal Magnetic Field

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Daily Solar Mean Magnetic Field Sun as a Star 3
Cycles 1975 - 2009
Rotation Modulation Observed At lt 10 uT
WSO Sensitivity Issues in 2001
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4 Solar Minima, 3 Polar Reversals 1976 - 2009
South stronger In Cycles 21 22
Surge Arrival
WSO Large-scale Polar Aperture 55 to Pole
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MDI Measured Polar Field during Cycle 23 1996-2008
Smaller 75 Polar Field Is More Symmetric
Reverses Later Difference in Strength is
Significant, but Smaller
Movie shows observed and Interpolated polar field
above 62
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MDI Measured Polar Field during Cycle 23 1996-2008
Smaller 75 Polar Field Is More Symmetric
Reverses Later Difference in Strength is
Significant, but Smaller
Movie shows observed and Interpolated polar field
above 62
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Axial, Equatorial, and Total Solar Dipole 3
Cycles 1976 - 2009
Total
Axial
Equatorial
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Total Solar Dipole, Quadrupole, Octupole 3
Cycles 1976 - 2009
Dipole
Quadrupole
l 3
Magnitude _at_ 2.5Rs
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Computed Source Surface Magnetic Field
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The Computed Coronal Field HCS During Cycle
23 1996-2009 Every 10th Rotation Each panel 2
Rots wide Reversal in 1999-2000 Stable
Structures Dipole and Quadrupole Dominate
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3 Cycles of the Computed HCS Inclination
Best SS Radius may be 1.8 Rs this minimum Sun
Hoeksema SH11A-1487
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Ulysses Observed Different Solar Wind
Structure During Solar Minimum in 1996 compared
with 2008 Low-latitude is more complex and wider
due to Decreased importance of Polar Coronal
Holes
Note Coronal snapshot useful, but may mislead
since structure reflects rotation
From McComas et al., GRL 2008
Thanks to J. Luhmann
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IMF Measured at L1 is Significantly Weaker
this Minimum than the Previous Three
Ulysses also saw low IMF at high heliolatitudes
in 2007 (Smith et al., GRL, 2008) OMNI data
from NSSDC
IMF observed to be uniform at all latitudes away
from HCS
Thanks to J. Luhmann
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Computed open flux foot points Coronal Hole
Proxy Each Panel shows 10 years starting
1972. Low latitude holes are relatively more
important during this solar minimum
1973
1983
1993
2003
Thanks to J. Luhmann
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The long decline of Solar Cycle 23 has been
marked by very few, well separated Active Regions
(GONG website movie, MSFC sunspot illustrations)
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• Comparison of
• Large-Scale
• Corona in
• Cycles 21 23
• Panels spaced
• By 12 rotations.
• CYCLE 23
• Longer
• Fewer Contours
• Gradual Flattening
• Structures Persist
• More Dipole in
• Declining Phase

Cycle 21
Cycle 23
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• Comparison of
• Large-Scale
• Corona in
• Cycles 22 23
• Panels spaced
• By 12 rotations.
• Cycle 23
• Fewer Contours
• Slower Flattening
• Structures Persist
• Thanks to Weak Poles
• Both Dipolar During
• Reversal

Cycle 22
Cycle 23
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Back to the Photospheric Field
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Zonal Average of Total Flux and Net Flux 3
Cycles 1976-2009 from WSO
2001 WSO Sensitivity
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Antisymmetric Zonal
Old Polarity Surge 2003/4
Symmetric Zonal
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Toroidal (East-West) Field 3 Cycles from WSO
Work with Leyan Lo Phil Scherrer
Cycles overlap several years and are extended
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Comparison of SSN for last 5 Cycles
From wattsupwiththat website
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Perspective Comes from Taking the Long View
From Wikipedia website
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• Summary - 1
• Cycle 23 was longer and weaker (relative to 21
  and 22)
• MF, pole, meridional flow, corona, solar wind,
  dipole
• Polar Reversal on time, but no subsequent growth
  no organized poleward migration
• Corona/Heliosphere not as constrained by dominant
  Polar Coronal Holes

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• Summary - 2
• Corona/Heliosphere not constrained by dominant
  Polar Coronal Holes in declining phase of Cycle
  23
• HCS continued to reach high latitude
• Mid latitude structure in solar wind and low
  latitude coronal holes
• Very few spots in last few years.

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• Summary - 3
• Zonal Flux Reduced
• Poleward flows small
• Antisymmetric flows at low latitude only
• 2002 not like 1991, 1981
• Old polarity anti-symmetric flow in 2003
• Interesting to learn what was absent in
  2003-2004
• Toroidal flux pattern about the same
• New flux emerges just after previous max at high
  latitude and expands equatorward