predicting the solar cycle

8/7/2019 Predicting the Solar Cycle

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Predicting the Solar Cycle

Leif SvalgaardStanford University

Solar Analogs II

Flagstaff, AZ, Sept. 22, 2009


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State of the Art: Predicting Cycle 24Predictions sent to the Prediction Panel


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State of the Art: Predicting Cycle 24What the Sun seems to be doing


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Near Normal Distribution = No SkillSome preference for Climatological Mean

5

5

5

3

5 5 75 5 5 75 5

Distribution of Predicted Solar Cycle 24 Size

Climatological Mean

Rmax


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E arly Optimism and PR E ffort

The next sunspot cycle will be 3 0- 5 0%stronger than the last one and begin as

much as a year late, according to abreakthrough forecast using a computer model of solar dynamics developed byscientists at the National Center for Atmospheric Research (NCAR).

2004-2006


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Flux Transport Dynamo Models Dikpati, M., de Toma, G., Gilman, P.A.: Predicting the

strength of solar cycle 24 using a ux-transport dynamo-based tool, Geophys. Res. Lett., 33 , L0 5 102, 2006.

Rmax24

= 160-18 5 Choudhuri, A.R., Chatterjee, P., Jiang, J.: Predicting

Solar Cycle 24 with a solar dynamo model, Phys. Rev.Lett., 98, 1 3 110 3 , 200 .

Rmax 24 = 5

Difference is primarily due to different assumptions about thediffusivity of magnetic flux into the Sun [high = weak cycle]


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H igh Diffusivity: Left

Low Diffusivity (Advection): RightConveyor BeltP is a proxy for T

One year betweendots

Dikpati et al.Choudhuri et al.


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Grow-N-Crash ModelE asy to get a high correlation

Dikpati et al. 2006

Intermittency from threshold effects


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Grow-N-Crash ModelE asy to get a high correlation

Dikpati et al. 2006


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Supply a Scaled Standard Cycle

Body to get Stunning CorrelationCrash-N-GrowDikpati et al.

Dikpati et al. assumed constant Meridional Circulation, except for cycle 24


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Meridional Circulation

Both (Dikpati, Choudhuri) of these FluxTransport Dynamo Models produce strongpolar fields and short cycles when themeridional flow is fast .However : Measurements of the meridional flowover Cycle 2 3 now show that on the approach to

Cycle 24 minimum in 2008 to speedssignificantly higher than were seen at theprevious minimum (David H athaway, SO H O-2 3 )


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Meridional Circulation

Lisa Rightmire, David H athaway (2009):Cross-correlating full-disk magnetograms


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Flux Transport Models Not Ready Yet

In these models this higher meridionalflow speed should produce strong polar fields and a short solar cycle contrary tothe observed behavior.

These observations, along with others,suggest that Flux Transport Dynamo

Models do not properly capture solar cyclebehavior and are not yet ready to providepredictions of solar cycle behavior.

H athaway, 2009


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Is This Too H arsh?

The polar fields were built several yearsago before the increase in the Meridionalcirculation [the polar fields were essentiallyestablished by mid-200 3 ]

22 2 3


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And H ave Not Increased Since Then,rather Beginning to Show a Decrease

150

-100

-50

0

50

100

150

200 .0 2004.0 2005.0 2006.0 2007.0 2008.0 2009.0 20 10.0 20 11 .0

S

N

N+S

WSO Polar Fields

Y ear

T

N-S

ode

Bad i

ter


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Latitudes of Active Regions During

Cycle 23

were not Unusual

18 7 4-200 5


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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. isaffected by back-reaction from the Lorentz forceassociated with the dynamo-generated magneticfield (chicken and egg).

The form and speed of the equatorward returnflow in the lower convective zone is at presentunknown.


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Perhaps a Shallow Dynamo?

Ken Schatten [ S olar Physics, 255 , 3-38,2009 ] explores the possibility of sunspotsbeing a surface phenomenon [being thecoalescence of smaller magnetic featuresas observations seem to indicate] and thatthe solar dynamo is shallow rather than

operating at the tachocline, based on hisCellular Automata model of solar activity.


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Schattens Cellular Automata Model


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In the CA Model, the Polar Fluxalso Predicts the Sunspot Flux


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Other Dynamo Models

Kitiashvili, 2009

The E nsemble Kalman Filter ( E nKF) method has beenused to assimilate the sunspot number data into a non-linear - mean-field dynamo model, which takes intoaccount the dynamics of turbulent magnetic helicity.


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Back to E mpirical Predictions?

With predictions based on Flux TransportDynamos in doubt or less enthusiasticallyembraced (and the Shallow Dynamo andthe E nKF approach not generally pursued)we may be forced back to Precursor Techniques where some observed

features are thought to presage futureactivity.


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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


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Green Corona Brightnessto Determine Time of Maximum

?

?

Altrock, 2009


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Torsional Oscillation Polar BranchWhere is it? (Chicken & E gg)

H owe, 2009


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Large-Scale Magnetic Field fromNeutral Lines on H Maps

Tlatov et al., 2006

Assigning fields of +1 and -1 toareas between neutral lines,calculate the global dipole 1 andoctupole 3 components . Theypredict the cycle 69 months ahead

McIntosh

A(t)


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Geomagnetic Activity DuringDescending Phase of Cycle

Bhatt et al., 2009


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Or Just at Minimum

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8 8 8 8 8 88 8 2 8 2 2 2 20

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Rmax = 22.5 + 13.42 Apmin R 2=0.88

Rmax = 24.85 * Apmin 0.7956 R2=0.89

Rmax Apmins

Sunspot Number at Maximum Following Ap at Minimum

Svalgaard, 2


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AA-index as Proxy for OpenH eliospheric Magnetic Flux

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Wang & Sheeley, 2009

Min AA based on last 12 months


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Recurrent H igh-Speed Streams Nearing Solar Minimum Create H igh Geomagnetic Activity

-0

-0

-0

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0 0

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0 0

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3 0

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0 000 0 0

Sargent's Recurrence Index

0

0

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3 0

0

0

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0

0 0 0 0 00 0 0 3 0 0 0 0 0 0 0 000 0 0

Geomagnetic Activity (aa*)


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The Size of these Activity Peaks[Corrected for Sunspot Activity] has

been used as a Precursor of the NextCycle [Physics is Obscure Though]

Solar Activity (IHV R) and Interplanetary (IHV I)

1860 1880 1900 1920 1940 1960 1980 2000Date

0

10

20

30

40

50

60

Ge

omagnetic IHV Index (nT)

IHVR = 19.2 + 0.140 RIHVI = IHV - IHV R

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1213

1415

1617

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19

20

21 2223

H athaway et al.


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Picking the Wrong Peak [FromFiltered Data] Can Lead You Astray

2

2

!

!

!

!

2 !

3

1!

1! "

1!

1!

1!

1! !

2 2 1

Sargent's Recurrence Index

1

2

3

1 1 1 1 1 1 1 1 2 1 3 1 1 1 1 1 1 2 2 1

Geomagnetic Activity (aa*)


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Picking the Peak Using the large peak in 200 3 predicted a largecycle [Rmax ~ 160], but perhaps the peak to use

[based on the Recurrence Index] is the one in2008 that predicts a small cycle [Rmax ~ 80]

0

10

20

3 0

0

0

60

0

80

1 6 1 1 8 1 2000 2001 2002 200 3 200 200 2006 200 2008 200 2010

Geomagnetic Acti v it y

Fl ares

"Recurrence

Peak"LargeCycle Small

cycle


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Definition of Polar Fields


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Measurements of Polar Fields

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-3

-

-

3

5 5 5 5 5

MSO* WSO

N rth - Sou th Sola r ola r f lds [mic r oTesla]

53 5


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Another Measure of the Polar fields

Nobeyama Radioheliograph, Japan

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Polar Field Scaled by Size of NextCycle is Possibly an Invariant

1

2 3 3

1 33 3

1

4 3 3

1

5

3 3

3

5

3 3

4 3 3

33 3

2 3 3

5

6 7 8

5

6

70 1975 1980 1985 1990 1995 2000 2005 2010

MSO* WSO

North - South Solar Polar fields [microTesla]

Rmax 24 = 75

Our Prediction


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Cycle Transitions9

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B

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S R

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3R

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R

V R

W R

X R

8 R Y R

S R R

S Y 8 3 S Y 8U

S Y 8 V S Y 8 W S Y 8 X S Y 88 S Y 8 Y

21 22

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T R

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R

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W R

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8 R Y R

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S Y Y

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S Y Y V S Y Y W S Y Y X S Y Y 8 S Y Y Y

22 23

R

S R

T R

3R

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R

V R

W R

X R

8 R Y R

S R R

T R R V T R R W T R R X T R R 8 T R R Y T R S R T R S S

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23

24

g

e h ioni

ays p q er r ont s t

g

i/`

e 323+24

T e current minimumis very low [t e lowestin a century], and itlooks like inimum isnow be ind us


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What Will Cycle 24 Look Like? Perhaps like cycle 14, starting 10 7 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


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If We Can Just See the Spots

Sunspots are getting warmer, thus becomingharder to see. Will they disappear? Or will theSunspot Number just be biased and too small

William Livingston, Pers. Comm. 2010

dy - 4 d

dy 0.01 d

1 00

2000

2 00

000

00

4000

1 0 1 2000 200 2010 201 20200

0.2

0.4

0.

0.

1B Gauss In t nsi t

ear

Livingston Penn mbral ata


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F10. 7 Flux Relationship withSunspot Numbers is Changing

u v -9 .16 7E -1w

x 6 x 1.1 9 4E-0 8 xy

-

.9 00 E-0 6 x 4 x 1.4

1E -0

x

- 1. 9 00E -01x

x 1.

7 8 E+ 01x -

.9 7 8 E+ 0w

R

v 9 .77 0E -01

0

0

100

1

0

00

0

0

0 100 1

0

00

0

00

F10.7 s

R

s e r s. F10.7 Flu x M nth ly A e r a es

1951 1988

1996 2009

Ratio of observed SSNand SSN computedfrom F10. 7 usingformula for 1 9 1-1 988

Recent SSN alreadtoo low ?

Svalgaard & H udson, 00 9

0

1

19 0 1 9 196 0 1 96 19 70 1 97 198 0 198 199 0 199 2000

00

010

se r ej

Rk ,l

/ Calcul atej

Rk ,l

[f m r Rk ,l

>4]

S n o C

mmmmm

rich

m


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So What Do We Predict? SSN or F10. 7 Flux or Magnetic Regions?

Since the prediction is based on themagnetic 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?


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Conclusion"It cannot be said that much progress has been madetowards the disclosure of the cause, or causes, of thesun-spot cycle. Most thinkers on this difficult subjectprovide a quasi-explanation of the periodicity throughcertain assumed vicissitudes affecting internalprocesses. In all these theories, however, the course of transition is arbitrarily arranged to suit a period, whichimposes itself as a fact peremptorily claimingadmittance, while obstinately defying explanation"

Agnes M. Clerke, A Popular H istory of Astronomy Duringthe Nineteenth Century, page 16 3 , 4 th edition, A. & C.Black, London, 1902.


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AbstractWe discuss a number of aspects related to our understanding of the solar dynamo. We begin by illustrating the lack of our understanding. Perhaps asexemplified by SWPC's Solar Cycle 24 Prediction Panel. They received andevaluated ~ 7 5 prediction papers with predicted sunspot number maxima rangingfrom 40 to 200 and with a near normal distribution around the climatologicalmean indicative of the poor State of the Art. Flux Transport Dynamo Modelswere recently hyped? or hoped? to promise significant progress, but they givewidely differing results and thus seem inadequate in their current form. In thesemodels, higher meridional flow speed should produce strong polar fields and ashort solar cycle, contrary to the observed behavior of increased meridional flowspeed, low polar fields, and long-duration cycle 2 3 . Poorly understoodPrecursor-methods again seem to work as they have in previous cycles. I reviewthe current status of these methods. Predictions are usually expressed in termsof maximum Sunspot Number or maximum F10. 7 radio flux, with the implicitassumption that there is a fixed [and good] relation between these measures of

solar activity. If Livingston & Penns observations of a secular change in sunspotcontrast 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 maychallenge cherished and long-held beliefs and paradigms. .

predicting the solar cycle

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