1
The Spots That Won’t Form
Leif SvalgaardStanford University
3rd SSN Workshop, Tucson, AZ, Jan. 2013
2
Is the SSN Always a Good
Measure of Solar Activity?
F = 0.9325 R + 55.0
r2 = 0.9938
F = 1.0731 R + 59.2
r2 = 0.9497
60
80
100
120
140
160
180
200
220
240
0 20 40 60 80 100 120 140 160 180 200
F10.7 sfu
R SSN
Waldmeier 1947-1970
SIDC 1996-2012
Relationship between Solar Radio Flux and Sunspot Number
y = -0.0000114x3 + 0.0038145x2 + 0.5439367x + 63.6304010
R2 = 0.9931340
0
50
100
150
200
250
0 20 40 60 80 100 120 140 160 180 200
F10.7
SSN 1952-1990
Canonical Relationship SSN and F10.7
Since ~1990 we record progressively fewer sunspots than expected from observations of F10.7 microwave flux
3
For a given F10.7 flux there are too few sunspots after 2000
4
We see fewer sunspots for given MPSI
MWO Plage Strength Index
Calibration Change
Same result if Ca II or Mg II index is used
MPSI is the sum the absolute values of the magnetic field strengths for all pixels where that value is between 10 and 100 gauss. The sum is then divided by the total of number of pixels in the magnetogram.
SSN = 55 MPSI
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015
SSN* = 54.18 MPSI 1.0046
SSN obs / SSN*
5-month running average
Year
?
Cycle variation on Downwards Trend
5
For a given CA II K-line index there are too few sunspots after 2000
The rising phase seems to be slightly higher than the declining, but the overall trend is a decline of sunspot numbers compared to the CA II emission index.
6
Sunspots per Area
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
RZ / SA0.732
Wolfer Brunner Waldmeier SIDC
Monthly Means>1000
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010
Rz (corr) / Observed Sunspot Area 0.732
Monthly Means >1000
7
The Sunspot Number is ‘too low’ compared to TSI
0
10
20
30
40
50
60
70
80
90
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
1360.8
1360.9
1361.0
1361.1
1361.2
1361.3
1361.4
1361.5
1361.6
Ri TSI SORCE
TSI no longer following the sunspot number?
The Total Solar Irradiance used to track the Sunspot Number quite nicely, but with fewer spots compared to faculae, TSI is increasing compared to that expected by the Sunspot Number.
8
The Livingston & Penn Data
From 1998 through 2012 Livingston and Penn have measured field strength and brightness at the darkest position in umbrae of 3548 spots using the large Zeeman splitting of the infrared Fe 1564.8 nm line..
Temp.
9
Spot Umbral Intensity
[Temperature] and Magnetic
Field Changing
0.4
0.6
0.8
1
1000 1500 2000 2500 3000 3500 4000
Intensity
B Gauss
cycle 24
cycle 23
10
Evolution of Distribution of Magnetic
Field Strengths
1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750
2009-2011
2005-2008
1998-2004
Gauss
Distribution of Sunspot Magnetic Field Strengths
Sunspots form by assembly of smaller patches of magnetic flux. As more and more magnetic patches fall below 1500 G because of the shift of the distribution, fewer and fewer visible spots will form, as observed
Normalized to same maximum
Normalized to same area
11
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 observersWe are losing the small spots
What could be the cause of that?0
5
10
15
20
25
30
35
40
45
2009 2009.5 2010 2010.5 2011 2011.5 2012 2012.5 2013
0
1
2
3
4
5
6
7
Cagnotti
Cortesi
Spots Weighted Groups
12
Confirmation Using the SOON Data
Giuliana de Toma reports the number of spots per group recorded by the SOON network. At solar minimum the noise is large (ovals). The result is similar to the decrease seen by the SONNE network. The same decrease is seen in the number of spots per group for very small groups.
SOON
13
The Zürich Classification
a: no penumbra, no bipolar structure
b: no penumbra, but clear bipolar structure
h: with penumbra, but no clear bipolar structure
But large spots
Evolution
Pore: A feature in the photosphere, 1 to 3 arc seconds in extent, usually not much darker than the dark spaces between photospheric granules. It is distinguished from a sunspot by its short lifetime, 10 to 100 minutes.
14
Declining Occurrence of Small Spot Groups [Zürich Class A and B]
Data from Waldmeier, McIntosh, and Locarno
0
10
20
30
40
50
60
1950 1960 1970 1980 1990 2000 2010 2020
A
B
A+B
S/G
Percentage Frequency of Small Groups
When Yearly Number of Groups > 100
G
15
New Solar Activity ‘Regime’
• Can we use the statistical properties of past solar cycles to say something about future cycles?
• If the Maunder Minimum was qualitatively different the answer seems to be ‘No’
• If the Sun is now entering a qualitatively new regime the same conclusion may hold
• ‘Rear guard’ struggle to deny such a possibility seems to miss a chance for exciting new solar physics
16
Cosmic Ray Proxy [Berggren et al.]
Climate?
GSNM.M.
17
NGRIP is better than Dye-3
NGRIP
Dye-3
Note scale difference by factor of 5. Dye-3 has problems between 1680-1770.
The Figures show the Flux of the 10Be atoms, not the Concentration.
Unreliable
18
The Problem with Dye-3In Dye-3, differences between concentration and flux exist mainly around 1490–1530 AD and partly during 1680–1770 AD. In order to investigate how these periods and differences correspond to solar activity, we compare NGRIP and Dye-3 concentration and flux with frequencies found in the sunspot number record (Figure 2). We note that NGRIP 10Be concentration and flux both have a negative relationship to solar activity, although there are occasional leads and lags before 1820 AD and during 1880–1910 AD in both 10Be parameters relative to the solar data. In Dye-3, there are phase differences until around 1780 AD, after which 10Be is well synchronized with the sunspots. This indicates that there is either some dating uncertainty in the older part of the cores, where Dye-3 dating was established by a different method than in the newer part, or there was a slower response in the 10Be deposition to changes in solar activity. It should be stressed that the good agreement between NGRIP and Dye-3 fluxes suggest that remaining dating inaccuracies are small. In the period around 1800 AD when NGRIP 10Be is slightly out of phase with the sunspot cycle, Dye-3 concentration is in phase, underlining the importance of having data from at least two high resolution cores for an accurate solar activity reconstruction. In addition, we reconfirm earlier findings [Beer et al., 1998] of a cyclically active sun during [grand] solar minima; a clear Schwabe cycle is present in both cores during the Maunder minimum, especially so in NGRIP.
19
‘Burning Prairie’ => Magnetism
Foukal & Eddy, Solar Phys. 2007, 245, 247-249
20
My Working Hypothesis
• The Maunder Minimum was not a serious deficit of magnetic flux, but
• A lessening of the efficiency of the process that compacts magnetic fields into visible spots
• This may now be happening again
• If so, there is new solar physics to be learned, let us not shy away from that!