The Forgotten Sun

Leif Svalgaard Stanford University SHINE-2011, Snowmass, CO 13 July 2011 [email protected]

1

Solar Activity 1835-2011

Sunspot Number

Monthly Average Ap Index B nT

10 60 50 40 30 20 10 0 1840 8 Ap Geomagnetic Index (mainly solar wind speed) 1850

Heliospheric Magnetic Field Strength B (at Earth) Inferred from IDV and Observed B (IDV)

1990 2000 2010 6 13 23 4

B (obs)

Heliospheric Magnetic Field at Earth 2 0 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2 2000 2010

Year

Summary of How the Sun is Similar Now to a Century ago

• Sunspot Number at Minimum was as low • Minimum lasted as long • Solar Wind Speed was Similarly Small • Heliospheric Magnetic Field was as small • Mid-century Solar Activity was Similarly High • Ca II Network was Similar to Today’s • Cycle 24 is now Predicted to be Low [‘lowest in a hundred years…] 3

Reminder of the Near Zero Skill in Predicting the Solar Cycle (24)

We seem to be here now 30 25 20 15 10 5 0 0

Distribution of Predicted Solar Cycle 24 Size Climatological Mean

25 50 75 100

Rmax

125 150 175 200 225 4

Active Region Count

500 450 400 350 300 250 200 150 100 50 0 1980

21

1985

22

1990 1995 2000

23

2005 2010

24

2015 200 180 160 140 120 100 80 60 40 20 0 1983 200 180 160 140 120 100 80 60 40 20 0 1993 200 180 160 140 120 100 80 60 40 20 0 2005

21

1984 2006

23

1985 1994

22

1995 2007 1986 1996 2008 1987 1988 1997 1998

22

1989

23

1999 1990 2000 2009 2010

24

2011 2012 2007.042

2007.121

2007.203

2007.285

We have been there before, 108 years ago, 2007.452

2007.537

but have largely forgotten how it was 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

2010.611

2010.692

2010.774

2010.855

2010.937

2011.042

2011.121

2011.203

2011.285

2011.366

2011.448

2011.529

2011.611

5

Shapiro

et al

., 2011 Total Solar Irradiance has only been measured since 1978 and must be ‘reconstructed’ for times before that. Such reconstructions have a curious history as the ‘background’ variation on which the obvious solar cycle variation of only 0.1% seems to ride had become smaller and smaller.

Recently, this issue has become ‘hot’ again with an inferred very large ‘secular’ trend since 1900.

This in spite of the Sun being so similar back then to now. What have we forgotten?

6

How Much of Climate Variation is

0.6

Due to Variation of Solar Activity?

Global Temperature Anomaly Reconstructions

30-yr Averages 0.4

0.2

ºC Loehle Moberg GISS Average 0 0 -0.2

200 400 600 800 1000 1200 1400 1600 1800 2000 -0.4

-0.6

-0.8

-1 TSI (Steinhilber

et al

., 2009) dTemp/Temp = ¼ * dTSI/TSI, so dTSI/TSI = 0.5% means dTemp = 0.4º 7

1367 1366 1365 1364 1363 1362 1361 1360 1361.4

1361.2

1361.0

1360.8

1360.6

1360.4

1360.2

2004 2005 2006

Degradation of PMOD

2007 Monthly values 2008

SORCE/TIM

2009

Difference

2010

PMOD - 4.51

2011 0.2

0 -0.2

-0.4

2012 1 0.8

0.6

0.4

Comparison PMOD and SORCE-TIM

Is it that recent TSI is perhaps significantly smaller now? As claimed by Fröhlich [his PMOD composite] and that a ‘fourth’ [non-magnetic] parameter is needed: “It could be due to a global temperature change of Sun of 0.25K” SOHO Keyholes

PMOD Ratio SORCE

1.003550

1.003500

1.003450

1.003400

1.003350

1.003300

1.003250

1.003200

1.003150

1.003100

1.003050

Comparison with SORCE/TIM suggests that PMOD has uncompensated degradation, and that there is no evidence for TSI this minimum being lower than at previous minima 8

Steinhilber et al., 2009 Recent TSI Reconstructions are partly calibrated using the PMOD smaller values the past minimum (and they were likely not smaller) and an assumed secular change in the (Group) Sunspot Number. And herein lies another problem: do we know the sunspot number well enough for this?

9

HMF From Ice Core 10Be

Steinhilber 10

The Sunspot Number(s)

• • • Wolf Number =

k W G

(10* = number of groups

G

+

S

)

S

= number of spots Rudolf Wolf (1816-1893) Observed 1849-1893 • Group Number = 12

k G

Different Observers Have Different Group Counts

14 12 10 8 6 4 2 0 1845 1850 1855 1860 1865 1870 1875

G

1880 1885 The ’12’ is to make the mean for the past ~100 years the same as the mean Wolf Number Ken Schatten 1890 11

And Now, The Problem: Discordant Sunspot Numbers

Hoyt & Schatten, GRL

21

, 1994 12

Major Adjustments to Wolf Number

2x‘1857’ Wolfer 0.58x‘1874’ 1.23x‘1874’

Wolf Wolf published several versions of his series over time, but did not modify his own data 13

.

Justification of the Adjustments rests on Wolf’s Discovery:

rD

=

a

+

b R W

North X rY Morning H rD D Evening Y = H sin(D) dY = H cos(D) dD For small D, dD and dH East Y A current system in the ionosphere [E-layer] is created and maintained by solar FUV radiation. Its magnetic effect is measured on the ground.

14

The Diurnal Variation of the Declination for Low, Medium, and High Solar Activity

Diurnal Variation of Declination at Praha (Pruhonice)

9 10 8 6 -4 -6 -8 -10 4 2 0 -2

dD'

Jan

1957-1959 1964-1965

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Diurnal Variation of Declination at Praha

0 -2 -4 -6 8 6 4 2 -8 -10

dD'

Jan

1840-1849

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec rD Year 15

Wolf got Declination Ranges for Milan from Schiaparelli and it became clear that the pre-1849 SSNs were too low

Justification for Adjustment to 1874 List

160 140 120 100 80 60 40 20 0 4

R Wolf Wolf = 1.23 Schwabe '1861 List' 1849-1860

5

Wolf

6 7 8

'1874 List' 1836-1873

9

'1861 List' 1836-1848 Schwabe

10 11

rD' Milan

12 13 The ‘1874’ list included the 25% [Wolf said 1/4] increase of the pre-1849 SSN 16

The Wholesale Update of SSNs before 1849 is Clearly Seen in the Distribution of Daily SSNs The smallest non-zero SSN is 11, but there are no 11s before 1849 11 * 5/4 = 14 17

Wolf’s SSN was consistent with his many-station compilation of the diurnal variation of Declination 1781-1880 First cycle of Dalton Minimum It is important to note that the relationship is

linear

for calculating averages 18

Wolf used 4’ Fraunhofer telescopes with aperture 80 mm [Magn. X64]

Still in use today [by T. Friedli] continuing the Swiss tradition [under the auspices of the Rudolf Wolf Gesellshaft] This is the ‘Norm’ Telescope 19

Wolf occasionally [and eventually – from 1870s on exclusively] used much smaller handheld, portable telescopes [due to frequent travel], leaving the 80mm for his assistants or when he was home These telescopes also still exist and are still in use today to safeguard the stability of the series Wolf estimated that to scale the count using the small telescopes to the 80mm Standard telescope, the count should be multiplied by 1.5

20

At some point during the 1940s the Zürich observers began to weight sunspots in their count Weights [from 1 to 5] were assigned according to the size of a spot. Here is an example where the three spots present were counted as 9, inflating the sunspot number by 18% [(3*10+9)/(3*10+3)=1.18] The weighting scheme is not generally known. One of those things that we have all forgotten.

21

What Do the Observers at Locarno Say About the Weighting Scheme:

Sergio Cortesi started in 1957, still at it, and in a sense is the

real

SSN, as SIDC normalizes everybody’s count to match Sergio’s keeper of the “For sure the main goal of the former directors of the observatory in Zurich was to maintain the coherence and stability of the Wolf number, and changes in the method were not done just as fun. I can figure out that they gave a lot of importance to verify their method of counting. Nevertheless the decision to maintain as “ secret " the true way to count is for sure source of problems now!” (email 6-22-2011 from Michele Bianda, IRSOL, Locarno) 22

Corroborating Indications of the ‘Waldmeier Discontinuity’ ~1946

• SSN for Given Sunspot Area increased 21% • SSN for Given Ca II K-line index up 19% • SSN for Given Diurnal Variation of Day-side Geomagnetic Field increased by 20% • Ionospheric Critical Frequency

foF2

depends strongly on solar activity. The slope of the correlation changed 20% between sunspot cycle 17 and 18 23

Illustrating that Observed Rz after 1945 is Higher than Deduced from Sunspot Areas 24

Ca II K-line Data Scaled to Rz shows similar Jump in Rz Sunspot Number after 1945 From ~40,000 CaK spectroheliograms from the 60-foot tower at Mount Wilson between 1915 and 1985, a daily index of the fractional area of the visible solar disk occupied by plages and active network has been constructed [Bertello et al., 2008]. Monthly averages of this index is strongly correlated with the sunspot number SSN = 27235 CaK – 67.14 [before 1946].

Waldmeier’s Sunspot Number 19% higher than Brunner’s from Ca II K-line 25

The Amplitude of the Diurnal Variation,

rY

, [from many stations] shows the same Change in Rz ~1945 26

The Ratio Group/Zurich SSN has Two Significant Discontinuities

At ~1946 (After Max Waldmeier took over) and at ~1885 27

Removing the Recent one [+20%] by Multiplying Rz before 1946 by 1.20, Yields Leaving one significant discrepancy ~1885 28

70 65 60 55 50 45 40 35 30 25 Scaling to 9-station chain

rY '9-station Chain' y = 1.1254x + 4.5545

30

R 2 = 0.9669

35 1884-1908 40 45 1953-2008

Helsinki , Nurmij ä rvi

50 55 Helsinki Nurmijärvi Diurnal Variation Helsinki and its replacement station Numijärvi scales the same way towards our composite of nine long-running observatories and can therefore be used to check the calibration of the sunspot number (or more correctly to reconstruct the F10.7 radio flux – see next slide)

Range of Diurnal Variation of East Component

70 65 60 55 50 45 40 35 30 1840 rY nT 1850

Helsinki

1860 1870

9-station Chain Nurmij ä rvi

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 29

The HLS-NUR data show that the Group Sunspot Number before 1880 must be Increased by a factor 1.64

±0.15 to match

rY

(F10.7) This conclusion is independent of the calibration of the Zürich SSN, Rz 30

Removing the Early one by multiplying

Rg

by 1.47, Yields

There is still some ‘fine structure’, but only TWO adjustments remove most of the disagreement 31

• • • •

The Sunspot Number Series

The Zürich Sunspot Number, Rz, and the Group Sunspot Number, Rg, can be reconciled by making only TWO adjustments: The first adjustment [20%] is to Rz ~1945 The second adjustment [~50%] is to Rg ~1885 No justification for secular trend Of note is that there is no Modern Grand Maximum 32

That was the Past. How about the Future?

From 2001 to 2011 Livingston and Penn have measured field strength and brightness at the darkest position in umbrae of 1843 spots using the Zeeman splitting of the Fe 1564.8 nm line. Most observations are made in the morning [7h MST] when seeing is best. Livingston measures the absolute [true?] field strength averaged over his [small: 2.5″x2.5″] spectrograph aperture, and not the Line-of-Sight [LOS] field. 33

0.2

In spite of large scatter the magnetic

0.6

0.4

0.8

1.0

field has decreased 500 G since 2000

Umbral Intensity

Livingston also measures the intensity of

Intensity

the umbra compared to the continuum and finds that [in the infrared] that for all spots he can see [i.e. intensity < 1] the field is greater than ~1450 G. Another 500 G to go...

0.0

2000 2005 2010

Umbral Magnetic Field

Year Hence his statement that if [when?] the decline of the field continues, spots will effectively ‘disappear’ or at least be much less visible.

4000 3500

B Gauss

Intensity 1 cycle 24 3000 0.8

2500 2000 1500 1000 2000 2005 2010 Year 0.6

cycle 23 0.4

1000 1500 2000 2500 3000 B Gauss 3500 4000 34

The Distribution of Field Strengths has Shifted with Time

Distribution of Sunspot Magnetic Field Strengths 2005-2008 2009-2011 2001-2004

1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 Gauss Is this just a sunspot cycle dependence?

35

Other indications of fewer spots?

250

R

200

Sunspot Number vs. F10.7 Flux Monthly Averages

y = -1.4940E-11x 6 + 1.6779E-08x 5 - 7.4743E-06x 4 + 1.7030E-03x 3 - 2.1083E-01x 2 + 1.4616E+01x - 4.1029E+02

R 2 = 0.9759

150

1951-1990

100

1996-2011

50

F10.7 sfu

0 0 50 100 150 200 250 300 Since ~1996 there have been fewer visible sunspots for a given F10.7 flux 36

The Observed Sunspot Number vs. that Calculated from the ‘old’ Relationship is too low Recently Since the Sunspot Number is dominated by the number of small spots, the loss of visibility of small spots might be a natural explanation.

Was the Maunder Minimum just an example of an extreme L&P effect?

Is this happening again?

37

Similar effect seen in SSN compared to sunspot areas

38

Livingston, Penn, and Svalgaard:

Extrapolating the behavior from the past 13 years into the next 13 years suggests the Sun may enter a new Grand Minimum.

If true, we shall learn a lot about ‘The Forgotten Sun’ that nobody alive today has ever seen, with obvious implications for the climate debate and environmental issues generally.

Are there other indications that this might happen?

39

Where is the Extended Cycle?

Altrock, 2011

CYCLE 18 CYCLE 19 CYCLE 20 CYCLE 24

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.

TO: Hill, 2011

40

Fold South unto North

Sunspot, NM

The Extended Cycle [if any] is not very clear

Arosa, Switzerland

41

Our ‘Understanding’ of the Extended Cycle

Robbrecht et al. ApJ, 2010: “We conclude that the so-called extended cycle in coronal emission is a manifestation not of early new-cycle activity, but of poleward concentration of old-cycle trailing-polarity flux by meridional flow” The red contours computed from PFSS coronal field (MWO) 42

Waldmeier also Interpreted The Green Line Emission as Marking the Boundary of the Polar Cap, ‘Rushing to the Pole’ when the New Cycle Started 43

The angle between B and Br seems to show an ‘extended cycle’

44

The average signed magnetic field shows a large scale structure without any hint of extended cycles Solving the Enigma of the ‘Extended Cycle’ is a worthy Goal of SC24 Research 45

The Polar Fields are as Mysterious as Ever, perhaps Reversing Early

46

The HCS is Approaching Typical Solar ‘Maximum’ Inclinations Unexpected early for a small solar cycle 47

-4000

Scattered Light Decreases Measured Magnetic Fields

SN 706 vs. 705

1500

M agne tic fie ld re duction factor

1.0

13% uT 1000 y = 0.5409x - 8.7224

0.8

500 R 2 = 0.8956

0.6

0 0.4

-3000 -2000 -1000 0 1000 2000 y = -0.0239x + 0.8792

R 2 = 0.744

-500 0.2

-1000 y = 0.5424x

R 2 = 0.8942

-1500 0.0

16 Sept 1978 0 2 4 6 8 10 12 -2000

% Scatte re d Light

14 -1000

SN 9641 vs. 9640

600 8.81% uT 400 y = 0.6107x - 1.088

R 2 = 0.9519

200 -500 0 -200 0 -400 16 May 2009 500 y = 0.6102x

R 2 = 0.9516

1000 -600 16 Compare magnetograms taken with clean and dirty coelostat mirror 48

What a Mess!

Our time series of solar activity indicators are inconsistent and poorly calibrated.

People pick the ones they like in support of their pet theories.

We cannot provide other disciplines with properly vetted solar data What to do about this?

49

Sunspot Workshop in 2011

We view the September workshop as the first step in an effort to provide the solar community with a vetted long-term sunspot number and the tools to keep it on track.

Ed Cliver (Co-Organizer), Leif Svalgaard (Co-organizer), Rainer Arlt, K.S. Balasubramaniam, Luca Bertello, Tom Bogdan or Doug Biesecker, Frederic Clette, Ingrid Cnossen, Thierry Dudok de Wit, Peter Foukal, Thomas Friedli, David Hathaway, Carl Henney, Phil Judge, Ali Kilcik, Laure Lefevre, Bill Livingston, Jeff Morrill, Kalevi Mursula, Alexei Pevtsov, Art Richmond, Aaron Ridley, Alexis Rouillard, Ken Schatten, Ken Tapping, Jose Vaquero, Stephen White 50

An ISSI Workshop in 2012

The Team proposal that you have submitted in response to the 2011 Call was evaluated by the Science Committee and the ISSI Directorate and considered to be of high scientific value and relevance . The proposal is thus approved for implementation.

International Teams in Space Science Proposal 2011 Title: Long-term reconstruction of Solar and Solar Wind Parameters Co Organizers: Leif Svalgaard (USA), Mike Lockwood (UK), Jürg Beer (Switzerland) Team members: Andre Balogh (UK), Paul Charbonneau (Canada), Ed Cliver (USA), Nancy Crooker (USA), Marc DeRosa (USA), Ken McCracken (Australia), Matt Owens (UK), Pete Riley (USA), George Siscoe (USA), Sami Solanki (Germany), Friedhelm Steinhilber (Switzerland), Ilya Usoskin (Finland), Yi-Ming Wang (USA) 51