Transcript Predicting the Solar Cycle

Predicting the Solar Cycle
Leif Svalgaard
Stanford University
Solar Analogs II
Flagstaff, AZ, Sept. 22, 2009
1
State of the Art: Predicting Cycle 24
Predictions sent to the Prediction Panel
2
State of the Art: Predicting Cycle 24
What the Sun seems to be doing
3
Near Normal Distribution = No Skill
Some preference for Climatological Mean
Distribution of Predicted Solar Cycle 24 Size
30
25
20
Climatological Mean
15
10
5
0
0
25
50
75
100
125
Rmax
150
175
200
225
4
Early Optimism and PR Effort
• “The next sunspot cycle will be 30-50%
stronger than the last one and begin as
much as a year late, according to a
breakthrough forecast using a computer
model of solar dynamics developed by
scientists at the National Center for
Atmospheric Research (NCAR).”
2004-2006
5
Flux Transport Dynamo Models
• Dikpati, M., de Toma, G., Gilman, P.A.: Predicting the
strength of solar cycle 24 using a flux-transport dynamobased 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]
6
High Diffusivity: Left
Low Diffusivity (Advection): Right
P is a proxy for T
Conveyor Belt
One year
between
dots
Choudhuri et al.
Dikpati et al.
7
Grow-N-Crash ‘Model’
Easy to get a high correlation
Dikpati et al. 2006
Intermittency from threshold effects
8
Grow-N-Crash ‘Model’
Easy to get a high correlation
Dikpati et al. 2006
9
Supply a Scaled Standard Cycle
Body to get ‘Stunning’ Correlation
Crash-N-Grow
Dikpati et al.
Dikpati et al. assumed constant Meridional Circulation, except for cycle 24
10
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)”
11
Meridional Circulation
Lisa Rightmire, David Hathaway (2009):
Cross-correlating full-disk magnetograms
12
‘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
13
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
14
And Have Not Increased Since Then,
rather Beginning to Show a Decrease
150
WSO Polar Fields
uT
Bad Filter
100
S
50
0
N+S
model
WF
-50
N
-100
-150
2003.0
N-S
2004.0
2005.0
2006.0
2007.0
Year
2008.0
2009.0
2010.0
2011.0
15
Latitudes of Active Regions During
Cycle 23 were not Unusual
1874-2005
16
Issues with Meridional Circulation
• The question is not whether the M.C. is there or
not, 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.
17
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.
18
Schatten’s Cellular Automata Model
19
In the CA Model, the Polar Flux
also Predicts the Sunspot Flux
20
Other Dynamo Models
The Ensemble Kalman Filter (EnKF) method has been
used to assimilate the sunspot number data into a nonlinear α-Ω mean-field dynamo model, which takes into
account the dynamics of turbulent magnetic helicity.
Kitiashvili, 2009
21
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.
22
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
23
Green Corona Brightness
to Determine Time of Maximum
?
?
Altrock, 2009
24
Torsional Oscillation Polar Branch
Where is it? (Chicken & Egg)
Howe, 2009
25
Large-Scale ‘Magnetic’ Field from
Neutral Lines on Hα Maps
Assigning fields of +1 and -1 to
areas between neutral lines,
calculate the global dipole μ1 and
octupole μ3 components. They
McIntosh
predict the cycle 69 months ahead
A(t)
Tlatov et al., 2006
26
Geomagnetic Activity During
Descending Phase of Cycle
Bhatt et al., 2009
27
Or Just at Minimum
Sunspot Number at Maximum Following Ap at Minimum
180
obs
Rmax
Apmin
16
160
14
140
12
120
10
100
8
80
6
60
4
40
2
Rmax = 22.5 + 13.42 Apmin R =0.88
20
Rmax = 24.85 * Apmin0.7956 R2=0.89
0
2
0
1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Svalgaard, 2009
28
AA-index as Proxy for Open
Heliospheric Magnetic Flux
24
Min AA based on last 12 months
Wang & Sheeley, 2009
29
Recurrent High-Speed Streams Nearing Solar
Minimum Create High Geomagnetic Activity
Geomagnetic Activity (aa*)
70
60
50
40
30
20
10
0
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
1960
1970
1980
1990
2000
2010
Sargent's Recurrence Index
1
0.8
0.6
0.4
0.2
0
-0.21860
1870
1880
1890
1900
1910
1920
1930
1940
1950
-0.4
-0.6
30
The Size of these Activity Peaks
[Corrected for Sunspot Activity] has
been used as a Precursor of the Next
Cycle [Physics is Obscure Though]
Hathaway et al.
31
Picking the Wrong Peak [From
Filtered Data] Can Lead You Astray
Geomagnetic Activity (aa*)
70
60
50
40
30
20
10
0
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
1960
1970
1980
1990
2000
2010
Sargent's Recurrence Index
1
0.8
0.6
0.4
0.2
0
-0.21860
1870
1880
1890
1900
1910
1920
1930
1940
1950
-0.4
-0.6
32
“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 ~ 80]
Geomagnetic Activity
80
70
60
Flares
50
40
"Recurrence
Peak"
30
Large
Cycle
20
10
0
1996
1997
1998
1999
2000
2001
2002
2003
2004
Small
cycle
2005
2006
2007
2008
2009
2010
33
Definition of Polar Fields
34
Measurements of Polar Fields
1953
1965
North - South Solar Polar fields [microTesla]
400
300
WSO
MSO*
200
100
0
1965
-100
1970
1975
1980
1985
1990
1995
2000
2005
2010
-200
-300
-400
35
Another Measure of the Polar fields
17 GHz Radio Flux
1500
K
Polar Field Proxy from Nobeyama 17 GHz Brightness Temperature
North
1000
500
0
South
-500
-1000
-1500
1993
150
Year
1994
1995
1996
1997
1998
uT
1999
2000
2001
2002
2003
2004
2005
2006
2007
2003
2004
2005
2006
2007
WSO Polar Fields
100
50
North
0
-50
Data Bad
South
-100
-150
Nobeyama Radioheliograph, Japan
-200
1993
Year
1994
1995
1996
1997
1998
1999
2000
2001
2002
36
Polar Field Scaled by Size of Next
Cycle is Possibly an Invariant
North - South Solar Polar fields [microTesla]
400
300
WSO
MSO*
200
100
0
1965
-100
-200
-300
1970
1975
1980
1985
1990
1995
2000
2005
2010
Rmax24 = 75
Our Prediction
-400
37
500
450
400
350
300
250
200
150
100
21
50
0
1980
100
90
80
70
60
50
40
30
20
10
0
1983
100
90
80
70
60
50
40
30
20
10
0
1993
Active Region Count
2007.285
2007.37
2007.452
2007.537
2007.622
2007.704
2007.789
2007.871
2007.956
2008.041
2008.123
2008.205
2008.287
2008.372
2008.454
2008.539
2008.624
2008.706
2008.791
2008.873
2008.958
2009.042
2009.121
2009.203
2009.285
2009.366
2009.448
2009.529
2009.611
2009.692
Cycle Transitions
22
1985
23
1990
1995
2000
24
2005
21
2010
2015
The current minimum
is very low [the lowest
in a century], and it
looks like Minimum is
now behind us
22
1984
1985
1986
1987
22
1988
1989
23
Region Days (per Month)
30
1994
1995
1996
1997
1998
1999
25
100
90
80
70
60
50
40
30
20
10
0
2005
20
23+24
15
10
Ri/0.3
23
5
23
24
24
0
2007.75
2006
2007
2008
2009
2010
2008
2008.25
2008.5
2008.75
2009
2009.25
2009.5
2009.75
2010
2011
38
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
39
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…
Livingston & Penn Umbral Data
4000
1
B Gauss
Intensity
3500
0.8
3000
0.6
dy = 0.0186 dx
2500
0.4
dy = -54 dx
2000
1500
1990
0.2
1995
2000
2005
2010
2015
Year
0
2020
William Livingston, Pers. Comm. 2010
40
F10.7 Flux Relationship with
Sunspot Numbers is Changing
Sunspot Number vs. F10.7 Flux Monthly Averages
250
R
Ratio of observed SSN
and SSN computed
from F10.7 using
formula for 1951-1988
y = -9.167E-12x 6 + 1.194E-08x 5 - 5.900E-06x 4 + 1.451E-03x 3 - 1.900E-01x 2 + 1.378E+01x - 3.978E+02
R2 = 9.770E-01
200
150
1951-1988
100
1996-2009
50
Recent SSN already
too low ?
F10.7 sfu
0
0
50
100
150
200
250
300
Observed Rz,i / Calculated Rz,i [for Rz,i >4]
2
Zürich
SIDC
1
0
1950
m
1955
m
1960
1965
m
1970
1975
m
1980
1985
m
1990
Svalgaard & Hudson, 2009
1995
m
2000
2005
2010
41
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
6
• Sunspot Number
Who knows?
• Was the Maunder Minimum like this?
42
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.
43
Abstract
We 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. .
44