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

Evolution of the Large-Scale Magnetic Field Over Three Solar Cycles Global Properties Corona & Heliosphere Zonal Magnetic Field Toroidal Magnetic Field

Daily Solar Mean Magnetic Field – Sun as a Star 3 Cycles – WSO Sensitivity Issues in ~2001 Rotation Modulation Observed At < 10 uT

4 Solar Minima, 3 Polar Reversals WSO Large-scale Polar Aperture 55 to Pole Surge Arrival South stronger In Cycles

MDI Measured Polar Field during Cycle Movie shows observed and Interpolated polar field above 62 Smaller 75+ Polar Field Is More Symmetric & Reverses Later Difference in Strength is Significant, but Smaller

MDI Measured Polar Field during Cycle Movie shows observed and Interpolated polar field above 62 Smaller 75+ Polar Field Is More Symmetric & Reverses Later Difference in Strength is Significant, but Smaller

Axial, Equatorial, and Total Solar Dipole – 3 Cycles Total Axial Equatorial

Total Solar Dipole, Quadrupole, Octupole – 3 Cycles Dipole Quadrupole l = 3 2.5Rs

Computed Source Surface Magnetic Field

The Computed Coronal Field & HCS During Cycle Every 10 th Rotation Each panel 2 Rots wide Reversal in Stable Structures Dipole and Quadrupole Dominate

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 Structure During Solar Minimum in 1996 compared with 2008 Low-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 this Minimum 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 Proxy Each Panel shows ~10 years starting Low latitude holes are relatively more important during this solar minimum

(GONG website movie, MSFC sunspot illustrations) The long decline of Solar Cycle 23 has been marked by very few, well separated Active Regions

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 21Cycle 23

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 22Cycle 23

Back to the Photospheric Field

Zonal Average of Total Flux and Net Flux – 3 Cycles from WSO ~2001 WSO Sensitivity

Antisymmetric Zonal Symmetric Zonal Old Polarity Surge 2003/4

Toroidal (East-West) Field – 3 Cycles from WSO Cycles overlap several years and are extended Work with Leyan Lo & Phil Scherrer

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 Toroidal flux pattern about the same New flux emerges just after previous max at high latitude and expands equatorward