Rapid Solar Cycle Onset - Potential
New Climate Study Tool?
By
Julia L. R. Saba, Keith T. Strong, Gregory L. Slater
Lockheed Martin Advanced Technology Center
SORCE Meeting in Orcas Island
20
-22 September 2006
20-22
Abstract
Investigation of long-term variability in flux from the Yohkoh Soft Xray Telescope revealed a sudden intensity rise in August 1997, from
solar minimum values to about 25% of the Cycle 23 maximum within
two solar rotations. The step-function increase was mirrored in several
other activity measures, including strong-field (>25 G) magnetic flux.
The onset appeared to be global in nature, rather than localized, and to
reflect a transition in active region character (number, size, longevity,
complexity, connectivity, flare productivity).
Preliminary results show that Cycle 22 had a similar sharp rise. Besides
constraining dynamo-transport theories, the sudden onset of the solar
activity cycle might offer a useful fiducial marker for studying solar
input to Earth climate.
The Yohkoh SXT Data
• 10-yr chronological
database of 72,000
full-disk solar images
in thin Al filter
• Selection towards
quieter times
(Flares > C-level
trigger high-cadence,
small-FOV mode)
• Calibrated, despiked,
background subtracted,
and aligned
Yohkoh Full-Sun Image in Thin Al Filter
• Total solar X-ray flux
from summed rows &
columns
• Yields: one datum per
image
• Pass band: 3 to 50 Å
• Temperature: 1 to 50 MK
• 5-arcsec spatial resolution
Yohkoh SXT X-Ray Data Reveal an Abrupt
Step-Like Onset to Cycle 23 (the “Step”)
27-Day Running Average
GOES XRS Confirms the SXT Result
• GOES XRS 1– 8 Å data
C
• Minimum flux determined
for each day
– Selects against flares
B
• 28-day averaged
• Step found similar to that
seen by Yohkoh SXT
A
– Steps are simultaneous
– XRS significantly
“harder” than SXT
The Origin Of Solar Activity is the Magnetic
Field. Does it Reflect the Step?
• SOHO Michelson Doppler Imager (MDI)
17 Jul 97
– Full-disk line-of-sight magnetograms
provide total (unsigned) flux
Central
Meridian
Strip for
Synoptic
Maps
– Northern vs. Southern hemisphere
– Active latitude bands compared
– Strong field (>25G) vs. weak fields (<25B)
• Kitt Peak Confirms the MDI Results
– Weak field flux shows gradual ramp
– Weak field dominates until after Step
4 Sep 97
MDI Synoptic Magnetic Map Shows
Global Onset of Activity
How “Global” Was the Outbreak?
• Synoptic maps divided into 4 quadrants in N and S hemisphere
• Level of activity assessed in each quadrant independently
Step Present during
CR1926/7
No Step Observed
during CR1926/7
Northern
Hemisphere
3
1
Southern
Hemisphere
2
2
Over 60% of the active longitudes were
involved with the initial outbreak of activity
Magnetic Flux from MDI & KPNO has Step in
Strong Fields Simultaneous with SXT Step
Step in
Southern
Hemisphere
Step in
Northern
Hemisphere
Evolution of Photospheric and Coronal Magnetic
Fields Shows Global Nature of the Step
1997-07-10
1997-08-07
1997-09-04
1997-10-02
Yohkoh SXT
SOHO MDI
1997-06-12
STEP
• Small, Isolated Regions
• Large, Interconnected Regions
• Mixed Old /New Cycle
• Only New Cycle
Flare Rate Increases Sharply at Step
1000
Weighted Number of Flares (C + 10*M + 100*X)
Total Number of Flares (C + M + X)
100
10
1
Jan-97
Apr-97
Jul-97
Oct-97
Jan-98
In the 7 months before the step: 30 flares
In the 7 months after the step: 430 flares
No Old Cycle Regions Emerge After Step
10
9
8
7
6
5
OLD
4
NEW
3
2
1
OLD
1935
1933
1931
1929
1927
1925
1923
1921
1919
1917
1915
1913
1911
0
Monthly Averaged Sunspot Area Shows the Step
But Monthly Sunspot Number Change is Gradual
Sunspot
Number
• Monthly Averages
– Sunspot Number (SN)
• Onset appears gradual
• No obvious step*
• SN is NOT good proxy for
activity
Sunspot
Area
– Sunspot Area (SA)
• Clear increase in base level
after time of Step*
* SXT Step interval shown by vertical dotted lines
Any Step in Total Solar Irradiance (TSI)
is at Best Subtle (and Delayed)
The Sun Changed Fundamentally
BEFORE THE STEP (7 months):
AFTER THE STEP (4 months):
•
Few Regions (<10 per CR)
•
More Regions (>10 per CR)
•
Active Regions Small
•
Regions Larger (x 3)
•
Regions Isolated
•
Region-Region & Region-Pole
Connections
•
Mix of New & Old Cycle Regions
•
No Old Cycle Regions Emerge
•
Regions Short-Lived (few days)
•
More Longer-Lived Regions ( x 2;
some last for over a rotation)
•
A Few Flares of Modest Intensity
•
Increasing Flare Rate (x 15)
– 4.0 C-flares / month
– 58.3 C-flares / month
– 0.3 M-flares / month
–
4.5 M-flares / month
– 0.0 X-flares / month
–
0.8 X-flares / month
Do Other Independent Activity
Indicators Show the Same Effect?
•
Strong B Fields:
YES
•
Active Regions:
YES
•
Flare Statistics:
YES
•
Sunspot Area:
YES
•
EUV Flux:
YES
•
F10.7:
YES
•
Green- Line Flux:
YES
•
Sunspot Number:
NO?
•
CME Number:
NO
•
Weak B Fields:
NO
•
TSI:
NO
Conclusions
• Significant, sharp, global increase in soft X-rays
• Large coincident increase in strong B flux
• Fundamental change in solar activity after the Step
–
–
–
–
15-fold increase in flare rate
No old-cycle regions emerged
Number of high-latitude new-cycle regions increased
Sunspot area increased sharply
• North and South asymmetry
– North starts first and dominates initially
– South followed a rotation later, dominates eventually
• Smoother increases in:
– Sunspot Number, CMEs, weak B flux, and TSI
The Solar Cycle in Operation
January
2008
139 CRs
140 CRs
Prediction
- Rotation and Convection interact to produce Differential Rotation & Helicity
- Differential Rotation converts Poloidal B to Toroidal B
- Helicity twists the Toroidal B regenerating Poloidal B
The SXT Data Are Provocative!
• Initial Discovery
• New Result:
Decay ≈ – Rise Slope!
• Intersection of:
First New Cycle
Region Detected
End of cycle 22
Start of minimum
Start of Cycle 23
Coincidence?
CONJECTURE: Suppression of new cycle by old until:
(1) flux build-up reaches critical value, or (2) old cycle flux depleted
HOW DOES THE SUN CREATE A STEP?
Solar Minimum Profile for Two Cycles Superposed
(A) Cycle 1 + Cycle 2 (same exponent)
(B) Cycle 1 (slow ) + Cycle 2 (fast)
Solar Minimum Profile Changes if the Two Cycles Interact
(C) Cycle 1 (slow) inhibits Cycle 2 (fast)
(D) Cycle 1 inhibits Cycle 2 + 50% noise
Prediction?
• The size of the next cycle should
DOES IT WORK?
depend on:
– Size of previous cycle(s)
5.00
4.50
4.00
3.50
3.00
– Length of solar minimum
and level of activity during
solar minimum*
2.50
2.00
1.50
1.00
Length of Min (years)
– Decay rate of previous cycle
0.50
– Rise rate of new cycle
Average Sunspot Area Over Cycle
0.00
0
500
1000
1500
2000
2500
Possibly!
*Solar minimum length defined as time from end of
the previous cycle to Step
3000
3500
4000
Future Work (I)
•
“Has this happened before?”
Look at previous cycles
– Available data types more
limited
140 CRs
(10.45 Years)
– Less coverage
Cycle 22
Cycle 23
– Calibration less well
established
•
Initial indications:
– Similar step onsets in
Cycles 21 & 22, about
140 CRs apart
– Predict Next Step:
Jan 2008 (± 2 months)
GOES 1-8 Å Minimum Daily Flux
with 1-Month Boxcar Smooth
Future Work (II)
•
Examine other solar activity indicators:
– Does the nature of CMEs change?
– EUV, UV, green-line, F10.7, …
•
Improve the predictability of solar cycles?
– Help determine risk level for long-term deep-space exploration
– STEREO will establish if onset truly global
•
Do solar cycles turn off suddenly?
– Anecdotal evidence (e.g., April 1984): Probably not
•
Implications for dynamo and flux transport models
– Is there a helioseismic signature?
•
Linkage to the Earth?
– Sharp discontinuity provides a potential fiducial for atmospheric changes
(composition, scale height, dynamics, etc.)
– The implications of the Step for climate and weather changes?
• Can we differentiate between various Sun-Climate linkage mechanisms?
• Can we derive the climate sensitivity to solar activity changes?
Acknowledgements
KPNO data:
Jack Harvey, NSO
MDI processing:
Jeneen Sommers, Stanford
IDL / SolarSoft:
Sam Freeland, LMATC
Funding Support:
MDI Grant,
SXT Contract, &
Lockheed Martin IRAD Programme