1 long-term solar synoptic measurements with implications for the solar cycle leif svalgaard...
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Long-term Solar Synoptic Measurements with Implications
for the Solar Cycle
Leif Svalgaard
Stanford University23 April 2013
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Dimensions of Synoptic Observations
• Time Dimension (long-term data sets)• Spatial Dimension (distribution over the
disk of activity, synoptic maps, height, depth)
Most efficient are visualizations combining the two dimensions, e.g.
• Movies, Butterfly diagram, Rotation sequences, …
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Classes of Synoptic Observations
• Single Point (e.g. Center Disk spectra)• Full-Disk (e.g. Sunspot Number, F10.7 flux,
Mean Field, Total Solar Irradiance)• Image-based (e.g. Sunspot Area, Ca K line
index, Magnetograms, Synoptic charts)
And aggregate views derived from images, e.g.• Polar Field Evolution• Hemispheric Asymmetries• Meridional and ‘Torsional’ circulations
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Synoptic Observations are Important for Understanding and Predicting the Solar Cycle
• With limited time for this presentation Leif can only touch upon some aspects that have been important for his own research
• It should, however, be clear how those relate to the wider issues, like constraining dynamo theories, forming inner boundary conditions for space weather, affecting the environment of the Earth and our space assets and technological infrastructure.
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Predicting Solar Activity
Sunspots
Polar Fields
Solar Prediction Panel, 2006
Observations and theory suggest that the magnetic field at the poles of the Sun at solar minimum is a good predictor of the next solar cycle.
Theory:Deep circu-lation?
The low polar fields at the recent solar minimum predicted a small cycle 24
-400
-300
-200
-100
0
100
200
300
400
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
MSO* WSO
North - South Solar Polar fields [microTesla]
Sunspots 2423
2221
MWO* WSO
?
WSO
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050
100150200250300350400450500
1980 1985 1990 1995 2000 2005 2010 2015 2020
232221
Active Region Count
24
Numbered Active Regions per Month
How is Cycle 24 Evolving? As predicted 9 years ago using the polar field precursor method
D. Hathaway
Prediction
14
24
Cycle 24 is beginning to look like Cycle 14
Lowest in a 100 years
SIDC
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A different view of polar fields: Nobeyama Image of 17GHz Emission
ν17 GHz = λ1.76 cm
νe = B (Tesla) × 28 GHz
Beam width 10”
1. General Limb brightening: Bremsstralung (free-free) from hot atmosphere [10,000 – 13,000 K]
2. Active regions bright: Gyro-resonance from strong fields
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Coronal Holes Everywhere Show Same Behavior as the Polar Holes
3 Days later
When a coronal hole is at the limb, the bright 17GHz patches appear, otherwise not
Quantifying the Brightening:
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Evolution of Patches over the Cycle
Reversal
Reversal
E
W
W
S
N
Pol
es
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Excess Tb over 10,800K, signed according to WSO polar field sign
WSO Sensitivity in 2001
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Using Polar Faculae Count to determine Polar Magnetic Flux and HMF Field Strength
1905-2011
Andrés Muñoz-Jaramillo, Neil Sheeley, et al., 2013
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Observed Polar Field Reversals
MWO: Roger Ulrich, 2012
Supersynoptic charts MWO
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And the ‘Rush to the Pole’ of Coronal Emissions
Measurements of the location of ‘peaks’ of Fe XIV coronal emission at 503 nm (the ‘Green Line Corona’) over 7 solar cycles. The plots show the probability of observing a ‘peak’ at a given latitude as a function of time.
Is there an ‘extended’ cycle of 17 years?
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Asymmetric Solar Activity Spots & Groups
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Comparing Cycles 14 and 24
Cycle 14 suggests that the activity in the South might pick up in cycle 24
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70-100 Year ‘Gleissberg Cycle’ in Solar Activity Asymmetry?
Zolotova et al., 2010
Is this a ‘regular’ cycle or just over-interpretation of noisy data [like Waldmeier’s]?
‘Prediction’ from this: South will lead in cycle 25 or 26 and beyond. We shall see…
Extreme Asymmetry during the Maunder Minimum…
There are various dynamo theoretical ‘explanations’ of N-S asymmetry. E.g. Pipin, 1999. I can’t judge these…
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Cosmic Ray Modulation Depends on the Sign of Solar Pole Polarity
Miyahara, 2011
The shape of the modulation curve [alternating ‘peaks’ and ‘flat tops’] shows the polar field signs.
North pole
North pole
Ice cores contain a long record of 10Be atoms produced by cosmic rays. The record can be inverted to yield the cosmic ray intensity. The technique is not yet good enough to show peaks and flats, but might with time be refined to allow this.Svalgaard
& Wilcox, 1976
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The Butterfly Diagram
1825 1867
SchwabeStaudach
Arlt
Arlt
Hathaway
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We Observe Fewer Spots per Sunspot Group
431,000 daily obs.
There is a weak solar cycle variation on top of a general downward trend seen by all observers
As the sunspot number is primarily determined by the number of spots, the SSN will be too low as a measure of solar activity
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TSI and CME-rate no longer following the Sunspot Number
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Conclusions
• To enable practical prediction of solar activity synoptic observations in both space and time are indispensable
• The long-term evolution of the solar cycle can only be tracked [and eventually understood] by sustained and calibrated synoptic observations
• I must be preaching to the choir today