Transcript 3 Cycles of Solar Activity

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 – 1975 - 2009
Rotation
Modulation
Observed
At < 10 uT
WSO Sensitivity Issues in ~2001
4 Solar Minima, 3 Polar Reversals
1976 - 2009
South stronger
In Cycles 21 + 22
Surge Arrival
WSO Large-scale Polar Aperture 55 to Pole
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
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
Axial, Equatorial, and Total Solar Dipole – 3 Cycles
1976 - 2009
Total
Axial
Equatorial
Total Solar Dipole, Quadrupole, Octupole – 3 Cycles
1976 - 2009
Dipole
Quadrupole
l=3
Magnitude @ 2.5Rs
Computed Source Surface
Magnetic Field
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
3 Cycles of the Computed HCS Inclination
Best SS Radius may be 1.8 Rs this minimum – Sun & Hoeksema SH11A-1487
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
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
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
The long decline of Solar Cycle 23 has been marked
by very few, well separated Active Regions
(GONG website
movie, MSFC
sunspot
illustrations)
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
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
Back to the Photospheric Field
Zonal Average of Total Flux and Net Flux – 3 Cycles
1976-2009 from WSO
~2001 WSO Sensitivity
Antisymmetric
Zonal
Symmetric
Zonal
Old
Polarity
Surge
2003/4
Work with Leyan Lo & Phil Scherrer
Toroidal (East-West) Field – 3 Cycles from WSO
Cycles overlap several years and are extended
Comparison of SSN for last 5 Cycles
From wattsupwiththat website
Perspective Comes from Taking the Long View
From Wikipedia website
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 antisymmetric 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