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1
Predicting the Solar Cycle
Leif Svalgaard
Stanford University
SORCE 2010
Keystone, CO, May 20, 2010
2
State of the Art: Predicting Cycle 24What the Sun seems to be doing
3
Near Normal Distribution = No Skill?Some preference for Climatological Mean
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200 225
Distribution of Predicted Solar Cycle 24 Size
Climatological Mean
Rmax
4
Flux Transport Dynamo Models
• Dikpati, M., de Toma, G., Gilman, P.A.: Predicting the strength of solar cycle 24 using a flux-transport dynamo-based tool, Geophys. Res. Lett., 33, L05102, 2006.
Rmax24 = 160-185• Choudhuri, A.R., Chatterjee, P., Jiang, J.: Predicting
Solar Cycle 24 with a solar dynamo model, Phys. Rev. Lett., 98, 131103, 2007.
Rmax24 = 75
• Difference is primarily due to different assumptions about the diffusivity of magnetic flux into the Sun [high = weak cycle]
5
High Diffusivity: LeftLow Diffusivity (Advection): Right
Conveyor BeltP is a proxy for T
One year between dots
Dikpati et al.Choudhuri et al.
6
Grow-N-Crash ‘Model’Easy to get a high correlation
Dikpati et al. 2006
7
Supply a Scaled Standard Cycle Body to get ‘Stunning’ Correlation
Crash-N-GrowDikpati et al.
Dikpati et al. assumed constant Meridional Circulation, except for cycle 24
8
Meridional Circulation
Both (Dikpati, Choudhuri) of these Flux Transport Dynamo Models produce strong polar fields and short cycles when the meridional flow is fast. However: “Measurements of the meridional flow over Cycle 23 now show that on the approach to Cycle 24 minimum in 2008 to speeds significantly higher than were seen at the previous minimum (David Hathaway, SOHO-23)”
9
Meridional Circulation
Lisa Rightmire, David Hathaway (2009): Cross-correlating full-disk magnetograms
10
‘Flux Transport Models Not Ready Yet’
• “In these models this higher meridional flow speed should produce strong polar fields and a short solar cycle contrary to the observed behavior.
• “These observations, along with others, suggest that Flux Transport Dynamo Models do not properly capture solar cycle behavior and are not yet ready to provide predictions of solar cycle behavior.
Hathaway, 2009
11
Is This Too Harsh?
• The polar fields were built several years ago before the increase in the Meridional circulation [the polar fields were essentially established by mid-2003]
22 23
12
And Have Not Increased Since Then, rather Beginning to Show the expected
Decrease due to New Cycle Activity
-150
-100
-50
0
50
100
150
2003.0 2004.0 2005.0 2006.0 2007.0 2008.0 2009.0 2010.0 2011.0
S
N
N+S
WSO Polar Fields
Year
uT
N-S
model WF
Bad Filter
13
Issues with Meridional Circulation
• The question is not whether the M.C. is there or not (multiple cells?), but rather what role it plays in the solar cycle, probably hinging on the value of the turbulent diffusivity.
• An unknown is the degree to which M.C. is affected by back-reaction from the Lorentz force associated with the dynamo-generated magnetic field (chicken and egg).
• The form and speed of the equatorward return flow in the lower convective zone is at present unknown (possibly SDO/HMI will tell us).
14
Perhaps a Shallow Dynamo?
Ken Schatten [Solar Physics, 255, 3-38, 2009] explores the possibility of sunspots being a surface phenomenon [being the coalescence of smaller magnetic features as observations seem to indicate] and that the solar dynamo is shallow rather than operating at the tachocline, based on his Cellular Automata model of solar activity.
See poster
15
In his Model, the Polar Flux also Predicts the Sunspot Flux
16
Other Dynamo Models
Kitiashvili, 2009
The Ensemble Kalman Filter (EnKF) method has been used to assimilate the sunspot number data into a non-linear α-Ω mean-field dynamo model, which takes into account the dynamics of turbulent magnetic helicity.
17
Back to Empirical Predictions?
With predictions based on Flux Transport Dynamos in doubt or less enthusiastically embraced (and the Shallow Dynamo and the EnKF approach not generally pursued) we may be forced back to Precursor Techniques where some observed features are thought to presage future activity.
18
Precursors
• Coronal Structure [Rush to the Poles]
• Torsional Oscillation [At Depth]
• H-alpha Maps [Magnetic Field Proxy]
• Geomagnetic Activity [Solar Wind Proxies]
• Open Flux at Minimum
And that old stand-by:
• Polar Fields
19
Green Corona Brightnessto Determine Time of Maximum
?
?
Altrock, 2009
20
Torsional Oscillation Polar BranchWhere is it? (Chicken & Egg)
Howe, 2009
21
Large-Scale ‘Magnetic’ Field from Neutral Lines on Hα Maps
Tlatov et al., 2006
Assigning fields of +1 and -1 to areas between neutral lines, calculate the global dipole μ1 and octupole μ3 components. They predict the cycle 69 months aheadMcIntosh
A(t)
22
Geomagnetic Activity at MinimumPolar Field Proxy?
0
20
40
60
80
100
120
140
160
180
1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 20200
2
4
6
8
10
12
14
16
Rmax = 22.5 + 13.42 Apmin R2=0.88
Rmax = 24.85 * Apmin0.7956 R2=0.89
Rmax Apminobs
Sunspot Number at Maximum Following Ap at Minimum
Svalgaard, 2009
23
AA-index as Proxy for Open Heliospheric Magnetic Flux
24
Wang & Sheeley, 2009
Min AA based on last 12 months
24
The Size of Recurrent Activity Peaks [Corrected for Sunspot Activity] has
been used as a Precursor of the Next Cycle [Physics is Obscure Though]
Hathaway et al.
25
Picking the Wrong Peak [From Filtered Data] Can Lead You Astray
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Sargent's Recurrence Index
0
10
20
30
40
50
60
70
1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Geomagnetic Activity (aa*)
26
“Picking the Peak”• Using the large peak in 2003 predicted a large
cycle [Rmax ~ 160], but perhaps the peak to use [based on the Recurrence Index] is the one in 2008 that predicts a small cycle [Rmax ~ 70]
0
10
20
30
40
50
60
70
80
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Geomagnetic Activity
Flares
"Recurrence Peak"
Large Cycle Small
cycle
27
Definition of Polar Fields
28
Measurements of Polar Fields
1953 1965
-400
-300
-200
-100
0
100
200
300
400
1970 1975 1980 1985 1990 1995 2000 2005 2010
Mount Wilson Solar Obs. Wilcox Solar Obs.
Solar Polar Magnetic Fields (N-S, microTesla)
29
Another Measure of the Polar fields
Nobeyama Radioheliograph, Japan
-1500
-1000
-500
0
500
1000
1500
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
K
Year
Polar Field Proxy from Nobeyama 17 GHz Brightness Temperature
North
South
-200
-150
-100
-50
0
50
100
150
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Data Bad
WSO Polar Fields
North
South
uT
Year
17 GHz Radio Flux
30
Polar Field Scaled by Size of Next Cycle is Possibly an Invariant
Rmax24 = 72
Our Prediction-400
-300
-200
-100
0
100
200
300
400
1970 1975 1980 1985 1990 1995 2000 2005 2010
Mount Wilson Solar Obs. Wilcox Solar Obs.
Solar Polar Magnetic Fields (N-S, microTesla)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
45
72
165
Solar Dipole Divided by Sunspot Number for Following Maximum
R24
21 22 23 2420
31
Cycle TransitionsThe current minimum is very low [the lowest in a century], and it is clear that Minimum is now behind us.Dashed line: Hathaway New Prediction
2007.0422007.1212007.2032007.2852007.37
2007.4522007.5372007.6222007.7042007.7892007.8712007.9562008.0412008.1232008.2052008.2872008.3722008.4542008.5392008.6242008.7062008.7912008.8732008.9582009.0422009.1212009.203
050
100150200250300350400450500
1980 1985 1990 1995 2000 2005 2010 2015
232221
Active Region Count
24
0
20
40
60
80
100
120
140
1983 1984 1985 1986 1987 1988 1989
21 22
0
20
40
60
80
100
120
140
1993 1994 1995 1996 1997 1998 1999
22 23
0
20
40
60
80
100
120
140
2005 2006 2007 2008 2009 2010 2011
23 240
10
20
30
40
50
60
70
80
90
100
2007.75 2008.25 2008.75 2009.25 2009.75 2010.25
23
24
Active Region Days (per Month)
3 Ri
23+24
32
The Diverse 23-24 Minima:Mean Field, TSI, F10.7, SSN(s)
8383838383838383
1359.0
1359.5
1360.0
1360.5
1361.0
1361.5
1362.0
2008.00
2008.07
2008.15
2008.22
2008.30
2008.37
2008.45
2008.52
2008.60
2008.67
2008.75
2008.82
2008.90
2008.97
2009.05
2009.12
2009.19
2009.27
2009.34
2009.42
2009.49
2009.57
2009.64
2009.72
2009.79
2009.87
2009.94
2010.02
2010.09
2010.17
2010.24
2010.31
2010.39
2010.46
2010.54
30
40
50
60
70
80
90
100
110
120
130
140
150
160
TSI
F10.7
23SN24
0
60
MF
NOAA
SIDC
0
Fractional Year
33
F10.7 at minimum between two large
cycles 18 & 19 and two smallish cycles
23 & 2460
80
100
120
140
160
180
200
2006 2007 2008 2009 2010
F10.7 at Minima 1954 and 2008-2009
A
34
What Will Cycle 24 Look Like?• Perhaps like cycle 14, starting 107 years ago• Note the curious oscillations, will we see some this time?• If so, I can just imagine the confusion there will be with
‘verification’ of the prediction
Cycle 14
Alvestad, 2009
35
If We Can Just See the Spots…
• Sunspots are getting warmer, thus becoming harder to see. Will they disappear? Or will the Sunspot Number just be biased and too small…
William Livingston, Pers. Comm. 2010
1500
2000
2500
3000
3500
4000
1990 1995 2000 2005 2010 2015 2020
0
0.2
0.4
0.6
0.8
1B Gauss Intensity
Year
Livingston & Penn Umbral Data
36
F10.7 Flux Relationship with Sunspot Numbers is Changing
Ratio of observed SSN and SSN computed from F10.7 using formula for 1951-1990
Recent SSN already too low ?
Svalgaard & Hudson, 2009
0
1
2
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Observed Rz,i / Calculated Rz,i [for Rz,i >4]
SIDC
mmmmm
Zürich
mm
y = -1.4940E-11x6 + 1.6779E-08x5 - 7.4743E-06x4 + 1.7030E-03x3 - 2.1083E-01x2 + 1.4616E+01x - 4.1029E+02
R2 = 0.9759
0
50
100
150
200
250
0 50 100 150 200 250 300
F10.7 sfu
R
Sunspot Number vs. F10.7 Flux Monthly Averages
1951-1990
1996-2010
37
So What Do We Predict? SSN or F10.7 Flux or Magnetic Regions?
• Since the prediction is based on the magnetic field, we are really predicting a proxy for the field:
• F10.7 120 sfu
• Magnetic Regions 72/12 = 6
• Sunspot Number Who knows?
• Was the Maunder Minimum like this?
38
Conclusion"It cannot be said that much progress has been made towards the disclosure of the cause, or causes, of the sun-spot cycle. Most thinkers on this difficult subject provide a quasi-explanation of the periodicity through certain assumed vicissitudes affecting internal processes. In all these theories, however, the course of transition is arbitrarily arranged to suit a period, which imposes itself as a fact peremptorily claiming admittance, while obstinately defying explanation"
Agnes M. Clerke, A Popular History of Astronomy During the Nineteenth Century, page 163, 4th edition, A. & C. Black, London, 1902.
39
AbstractWe discuss a number of aspects related to our understanding of the solar dynamo. We begin by illustrating the lack of our understanding. Perhaps as exemplified by SWPC's Solar Cycle 24 Prediction Panel. They received and evaluated ~75 prediction papers with predicted sunspot number maxima ranging from 40 to 200 and with a near normal distribution around the climatological mean indicative of the poor State of the Art. Flux Transport Dynamo Models were recently hyped? or hoped? to promise significant progress, but they give widely differing results and thus seem inadequate in their current form. In these models, higher meridional flow speed should produce strong polar fields and a short solar cycle, contrary to the observed behavior of increased meridional flow speed, low polar fields, and long-duration cycle 23. Poorly understood Precursor-methods again seem to work as they have in previous cycles. I review the current status of these methods. Predictions are usually expressed in terms of maximum Sunspot Number or maximum F10.7 radio flux, with the implicit assumption that there is a fixed [and good] relation between these measures of solar activity. If Livingston & Penn’s observations of a secular change in sunspot contrast hold up, it becomes an issue which of these two measures of solar activity should be predicted and what this all means. The coming cycle 24 may challenge cherished and long-held beliefs and paradigms. .