comparing the large-scale magnetic field during the last three solar cycles todd hoeksema
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Comparing the Large-Scale Magnetic Field During the Last
Three Solar Cycles
Todd Hoeksema
Evolution of the Large-Scale Magnetic Field OverThree Solar Cycles
Global Properties
Corona & Heliosphere
Zonal Magnetic Field
Toroidal Magnetic Field
Daily Solar Mean Magnetic Field – Sun as a Star3 Cycles – 1975 - 2009
WSO Sensitivity Issues in ~2001
RotationModulationObservedAt < 10 uT
4 Solar Minima, 3 Polar Reversals1976 - 2009
WSO Large-scale Polar Aperture 55 to Pole
Surge Arrival
South strongerIn Cycles 21 + 22
MDI MeasuredPolar Field during Cycle 231996-2008
Movie shows observed andInterpolated polar field above 62
Smaller 75+ Polar Field IsMore Symmetric & ReversesLater
Difference in Strength is Significant, but Smaller
MDI MeasuredPolar Field during Cycle 231996-2008
Movie shows observed andInterpolated polar field above 62
Smaller 75+ Polar Field IsMore Symmetric & ReversesLater
Difference in Strength is Significant, but Smaller
Axial, Equatorial, and Total Solar Dipole – 3 Cycles1976 - 2009
Total
Axial
Equatorial
Total Solar Dipole, Quadrupole, Octupole – 3 Cycles1976 - 2009
Dipole
Quadrupole
l = 3
Magnitude @ 2.5Rs
Computed Source Surface Magnetic Field
The ComputedCoronal Field & HCS
During Cycle 231996-2009
Every 10th RotationEach panel 2 Rots wide
Reversal in 1999-2000
Stable Structures
Dipole and QuadrupoleDominate
3 Cycles of the Computed HCS Inclination
Best SS Radius may be 1.8 Rs this minimum – Sun & Hoeksema SH11A-1487
From McComas et al., GRL 2008
Ulysses Observed Different Solar Wind StructureDuring Solar Minimum in 1996 compared with 2008Low-latitude is more complex and wider due to Decreased importance of Polar Coronal Holes
Thanks to J. Luhmann
Note: Coronal snapshot useful, but may mislead since structure reflects rotation
Ulysses also saw low IMF at high heliolatitudes in 2007 (Smith et al., GRL, 2008) –OMNI data from NSSDC
Thanks to J. Luhmann
IMF Measured at L1 is Significantly Weaker thisMinimum than the Previous Three
IMF observed to be uniform at all latitudes away from HCS
Thanks to J. Luhmann
Computed open flux foot points – Coronal Hole ProxyEach Panel shows ~10 years starting 1972.
Low latitude holes are relatively more important during this solar minimum
1973
1983
1993
2003
(GONG websitemovie, MSFC sunspotillustrations)
The long decline of Solar Cycle 23 has been marked by very few, well separated Active Regions
Comparison ofLarge-ScaleCorona in Cycles 21 & 23
Panels spacedBy 12 rotations.
CYCLE 23:
•Longer•Fewer Contours•Gradual Flattening•Structures Persist•More Dipole in Declining Phase
Cycle 21 Cycle 23
Comparison ofLarge-ScaleCorona in Cycles 22 & 23
Panels spacedBy 12 rotations.
Cycle 23:
•Fewer Contours•Slower Flattening•Structures Persist Thanks to Weak Poles•Both Dipolar During Reversal
Cycle 22 Cycle 23
Back to the Photospheric Field
Zonal Average of Total Flux and Net Flux – 3 Cycles1976-2009 from WSO
~2001 WSO Sensitivity
Antisymmetric Zonal
Symmetric Zonal
OldPolaritySurge2003/4
Toroidal (East-West) Field – 3 Cycles from WSO
Cycles overlap several years and are extendedWo
rk w
ith
Ley
an L
o &
Ph
il S
cher
rer
From wattsupwiththat website
Comparison of SSN for last 5 Cycles
From Wikipedia website
Perspective Comes from Taking the Long View
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
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.
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