The new Sunspot Number 400 years of solar activity revisited
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1 ROB STCE The new Sunspot Number 400 years of solar activity revisited Frédéric Clette World Data Center SILSO Observatoire Royal de Belgique, Brussels
2 The pre-history of the Sunspot Number 1610: Galilée, Scheiner, Harriot, Fabricius 18/2/2016 Sterrenwacht Urania, Hove 2
3 The pre-history of the Sunspot Number 1610: Galilée, Scheiner, Harriot, Fabricius 18/2/2016 Sterrenwacht Urania, Hove 3
4 A brief history of the sunspot number R. Wolf: introduction of the Wolf number [1850]: W= 10 Ng + Ns The 2 standard instruments: Standard «Fraunhofer» refractor D= 83mm, F= 1320mm Mag= 64x Small travel refractor D= 43mm, F= 550mm, Mag= 29x Still in use now (Thomas K. Friedli, Rudolf Wolf Society, Zürich) 18/2/2016 Sterrenwacht Urania, Hove H.U. Keller and T. K. Friedli Mid-1980 s R. Wolf in 1855 ( ) 4
5 A brief history of the sunspot number Inclusion of past sunspot observers: Samuel Heinrich Schwabe [ ]: Sunspot observations S. H. Schwabe Zürich primary observers: Staudacher Flaugergues Schwabe Wolf Wolfer Brunner Waldmeier /2/2016 Sterrenwacht Urania, Hove 5
6 A brief history of the sunspot number 1857: adding Staudacher ( ) Zürich primary observers: Staudacher Flaugergues Schwabe Wolf Wolfer Brunner Waldmeier /2/2016 Sterrenwacht Urania, Hove 6
7 A brief history of the sunspot number 1861: magnetic needle corrections Staudacher data x 2 Diurnal variation of the E-W component of the geomagnetic declination (ry index): Ionospheric current system induced by daytime solar UV radiation Indirect measure of solar UV irradiance variations 18/2/2016 Sterrenwacht Urania, Hove 7
8 A brief history of the sunspot number 1874: adding new data (Flaugergues, etc.) 1880: Magnetic needle corrections data before 1849 x /2/2016 Sterrenwacht Urania, Hove 8
9 A brief history of the sunspot number 1902: Wolfer correction cycle 5 ( ) x 0.58 Wolf-Wolfer transition [ ] New counting method: All small spots included in count Multiple umbrae in common penumbra counted as separate spots 16 years of parallel Wolf-Wolfer counts R Z = 0.6 W ZU Alfred Wolfer ( ) 18/2/2016 Sterrenwacht Urania, Hove 9
10 A brief history of the sunspot number Zürich period: 3 directors Sunspot weighting: Starting date uncertain: 1930 s (W. Brunner) or ~1944 (M. Waldmeier) Alfred Wolfer ( ) William Brunner ( ) M. Waldmeier [ ] 18/2/2016 Sterrenwacht Urania, Hove 10
11 A brief history of the sunspot number Second base station [1957]: Specola Solare Locarno (Ticino, SW) Observer: S. Cortesi (still observing today!) Trained to the Zürich method 18/2/2016 Sterrenwacht Urania, Hove S. Cortesi and M. Waldmeier circa
12 A brief history of the sunspot number The Zürich SSN computation SSN = Wolf number of the Zürich station 1980: closing of the Zürich Observatory Continuation of the Sunspot Number is threatened! 1981: transfer of the WDC Sunspot to Brussels (SIDC) New pilot station: Specola Solare Ticinese, Locarno New global statistical determination of SSN using the full network = R i 18/2/2016 Sterrenwacht Urania, Hove 12
13 Meeting at the ROB: February 2011 Sergio Cortesi Specola Main Observer Marco Cagnotti Specola Director Michele Bianda IRSOL Director Well! By now, you should know that guy André Koeckelenbergh SIDC - ROB Founder and Director 18/2/2016 Sterrenwacht Urania, Hove 13
14 From the SIDC to SILSO (Sunspot Index and Long-term Solar Observations) The World Data Center Brussels today
15 Statistics over the last 35 years 280 contributing stations 30 countries 80 long-duration stations (> 15 years) At any time, ~ stations ~180 observations/year/obs. 530,000 observations 18/2/2016 Sterrenwacht Urania, Hove 15
16 The SILSO worldwide network Currently: 85 stations in 30 countries Over 35 years: 280 contributing stations 18/2/2016 Sterrenwacht Urania, Hove 16
17 The SILSO worldwide network Currently: 85 stations in 30 countries Over 35 years: 280 contributing stations Professionnals 34% N-America S-America 5% 9% Africa 3% Amateurs 66% Asia 12% E-Europe 14% W-Europe 57% 18/2/2016 Sterrenwacht Urania, Hove 17
18 Sunspots: a key amateur contribution 18/2/2016 Sterrenwacht Urania, Hove 18
19 Sunspots: a key amateur contribution 18/2/2016 Sterrenwacht Urania, Hove 19
20 SSN accuracy vs other indices Steady decrease of daily dispersion (Poisson statistics) High correlation with recent photospheric indices (R>95%): D. Hathaway, SSN workshop 2012 R A, R Boulder, Area, Mx, F 10.7cm Measure of the global emergence rate of solar magnetic flux 18/2/2016 Sterrenwacht Urania, Hove STARA catalog; F. Watson,
21 A wide range of applications Constraint for solar dynamo models Quantitative reference for solar processes: Solar irradiance and solar wind Cosmogenic isotopes Timebase for Sun-driven processes (geomagnetism, etc.) Tracer of the long-term solar influences on Earth: Climate change Atmospheric drag (spacecraft operations) Cumulative Ground effects on infrastructures > 100 scientific publications / year (e.g. Electrical grid, pipelines) Part of public culture and astronomy education > Google hits on sunspot number 18/2/2016 Sterrenwacht Urania, Hove 21
22 Is the solar cycle fully known?
23 Two incompatible sunspot records Only alternate series: Group Number (Hoyt & Schatten 1998) GN = Larger data set, back to 1610 Only groups: more immune to cruder early observations Large persistent discrepancies between the series (up to 40%) N i k i Ng i RGO photographic data 18/2/2016 Sterrenwacht Urania, Hove 23
24 A necessary revision: Sunspot Number Workshops 4 workshops: Sac. Peak 2011, Brussels 2012, Tucson 2013, Locarno 2014, + ISSI Solar Cycle Workshop (Bern, 2014) Multiple diagnosed problems in the SN and GN: Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E.W.: 2014, Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle. Space Sci. Rev. 186, Solar Physics topical issue (2016) 18/2/2016 Sterrenwacht Urania, Hove 24
25 Sunspot Number corrections: overview Schwabe - Wolf transition ( ) Waldmeier s spot weighting ( ) Locarno s variable drifts ( ) 18/2/2016 Sterrenwacht Urania, Hove 25
26 The 1947 «Waldmeier» jump (SN) Jump in the SN confirmed by different cross-comparisons: Madrid SSN long-duration stations (e.g. Madrid) (Vaquero 2012) Vaquero, SSN Workshop, 2012 RGO sunspot area Sunspot area (RGO) (Svalgaard 2012) Svalgaard, SSN Workshop, 2012 SSN - N G No indications of changes in the RGO data around Change in the SN scale 18/2/2016 Sterrenwacht Urania, Hove Svalgaard,
27 The Waldmeier jump: the cause Sunspot weighting: Large spots are counted >1 (up to 5) Uncertain date of introduction: = = 3x1+3x =3x1+3 9 = 3x3 Locarno station trained to the method (1955): still in use! W w Blind test ( ): double counting by Marco Cagnotti Ratio W w / W u = ~ /2/2016 Sterrenwacht Urania, Hove W u Svalgaard,
28 Locarno s variable drift ( ) Long reconstruction : exploitation of all 280 SILSO stations + additional recovered stations (SONNE, AAVSO). After correction by the k factor over : Constant ratio between the reconstructed series and the corrected original series Average ratio before and after 1981 are equal: Scale factor = / /2/2016 Sterrenwacht Urania, Hove 28
29 The «Specola» drifts All k coefficients vs time before correction 18/2/2016 Sterrenwacht Urania, Hove 29
30 The «Specola» drifts After correction based on a multi-station average reference 18/2/2016 Sterrenwacht Urania, Hove 30
31 Group Number correction: overview Revision of GN database ( ) Elimination of interpolated nulls ( ) Reconstruction: 5 backbone observers ( ) Svalgaard & Schatten (2015) Greenwich trend ( ) 18/2/2016 Sterrenwacht Urania, Hove 31
32 The «Greenwich» trend (GN) Ratio of the RGO group count relative to parallel visual observers Ratio increases by ~40% over Indications of changes in the early RGO data set (Willis et al, 2013): Photographic plate type Measuring method the R Z -R g discrepancy is due to an underestimate of R g before /2/2016 Sterrenwacht Urania, Hove Vaquero, SSN Workshop,
33 The backbone Group Number ( ) New approach for linking the scale of observers over centuries (Svalgaard 2012, Clette et al. 2014, Svalgaard & Schatten 2015): Backbone provided by 5 longduration observers to which other observers are normalized. Only visual sunspot observers are used, including in the 20 th century Backbone observer Main interval Full interval Staudacher Schwabe Wolfer Koyama Locarno Nb Obsev. 18/2/2016 Sterrenwacht Urania, Hove 33
34 The backbone Group Number ( ) Final composite backbone: Base reference: A. Wolfer (standard counts, standard refractor) (reference) 1.00 Svalgaard 2013, /2/2016 Sterrenwacht Urania, Hove 34
35 Combining all corrections: matching SN and GN Original series: SN / 0.6 GN x /2/2016 Sterrenwacht Urania, Hove 35
36 Combining all corrections: matching SN and GN Close agreement over the entire interval Still significant differences before 1826: (10% 20%): Target for next upgrade! 18/2/2016 Sterrenwacht Urania, Hove 36
37 Upgraded data distribution and production New SILSO Web site (since early 2014) Operational transition to the new SN: July 1 st, 2015 Adaptation of entire software for all SILSO products: hemispheric numbers, daily estimated SN (EISN), 12-month predictions Unchanged base method for the total SN but: Pilot station: Specola, Locarno un-weighted counts (original Wolf formula) New scale convention: Zürich factor 0.6 set to 1.0 New reference: A. Wolfer ( ) 18/2/2016 Sterrenwacht Urania, Hove 37
38 Lessons learned The problem is not in the subjectivity of individual observers: Errors = equivalent to shot noise in CCD detectors! Robustness provided by the multiplicity of simultaneous observers All problems associated with mistakes or changes in the processing method: Use of a single standard station (Zürich, Locarno, RGO) Mixing with other techniques: RGO photographic data (fast technological evolution) Change in sunspot counting method (sunspot weighting, group splitting) 18/2/2016 Sterrenwacht Urania, Hove 38
39 Comparison with other solar series
40 Better agreement with modern solar indices Original SN too low versus the F 10.7 radio flux after 2000 Reconstructed SN and the backbone GN over no more anomaly after 2000 F 10.7 is too high by 10% after 1983! 18/2/2016 Sterrenwacht Urania, Hove 40
41 Better agreement with modern solar indices Mismatch between original SN and solar irradiances (TSI, MgII, Lyα, total sunspot magnetic flux) Second peak in cycle 23 (November 2001) now higher than first peak (July 2000) Yeo et al Main unexplained discrepancies are eliminated. 18/2/2016 Clette & Lefèvre 2015 Sterrenwacht Urania, Hove 41
42 Secular trends: a new picture
43 Uniform peak cycle amplitudes over last 3 centuries Soon after the Maunder Minimum, solar activity returned to high levels equivalent to recent cycles of the 20 th century 18/2/2016 Sterrenwacht Urania, Hove 43
44 Comparison with indirect indices of solar activity Geomagnetic indices: reconstructed open magnetic flux over the last 180 years (Lockwood et al, 2013) Recent reconstructions show identical cycle amplitudes between the mid-19 th century and the 20 th century 18/2/2016 Lockwood 2013 Sterrenwacht Urania, Hove 44
45 Long-term tracers of solar activity Cosmogenic isotopes ( 10 Be, 14 C): Polar ice cores Tree rings, sediments Calibrated on the sunspot cycle Allow extrapolations over millennia. Restrictions: Complex intermediate processes Influence of the secular geomagnetic field variations Steinhilber et al., PNAS 109/16,, 2012) 18/2/2016 Sterrenwacht Urania, Hove 45
46 Grands minima and mini-glaciations Medieval Maximum Spörer Maunder Dalton Fröhlich & Lean /2/2016 Sterrenwacht Urania, Hove 46
47 Revisiting the Maunder Minimum Sunspots did not vanish entirely during the MM: Weak solar cycle still present (short 9-year period) 18/2/2016 Sterrenwacht Urania, Hove 47
48 Temperature Climat forcings over 4 centuries Solar forcing CO 2 Volcanic eruptions (dust) 18/2/2016 Sterrenwacht Urania, Hove 48
49 Tendances récentes: CO 2 ou Soleil? Robert A. Rohde / Global Warming Art The temperature evolution over the last 50 years does not match the trends in solar activity 18/2/2016 Sterrenwacht Urania, Hove 49
50 Cycle 24 and beyond
51 Categories of solar cycles Strong cycles: Early rise: short shallow minimum steep short rise to the maximum Sharp maximum (single peak) Weak cycles: Late rise: long deep minimum progressive and slower rise Flat maximum with multiple peaks 18/2/2016 Sterrenwacht Urania, Hove 51
52 Which cycles were most similar? Cycles 12, 14 and 24: Similar characteristics Long plateau at maximum Multiple maxima of similar amplitude (activity surges) 18/2/2016 Sterrenwacht Urania, Hove 52
53 Similar cycles: monthly means Cycle 12 Cycle 14 Multiple short surges of activity Similar amplitudes «Random» time of maximum over a wide interval 18/2/2016 Sterrenwacht Urania, Hove 53
54 Roles of hemispheres Strong phase difference North-South Not a new feature: same delay since last inversion in cycle 20 Longer delay: due to slower equatorward migration of active belts in cycle 24 18/2/2016 Sterrenwacht Urania, Hove 54
55 Similar cycles: preceding and following cycles No clear correlation pattern in neighboring cycles Preceding & following cycles can be high or low Lower cycles do not imply the onset of a Grand Minimum 18/2/2016 Sterrenwacht Urania, Hove 55
56 Time of next minimum? = = Cycle 24 has entered its declining phase Next minimum: to (mid-value: ) 18/2/2016 Sterrenwacht Urania, Hove 56
57 Looking ahead
58 Future prospects: beyond the sunspot counts New needs: Hemispheric SN before 1950 (N/S asymmetries) Global distributions: latitude, size Magnetic dipole (width, tilt) The information exists! Dispersed, paper documents Need for digitization Feature extraction software (standardization) Prospects for advanced multisecular sunspot-based proxies Hevelius Digitized Carrington drawing, Tlatov 2012 Staudacher Schwabe butterfly diagram (Arlt 2010) DigiSun software, ROB, Brussels E. Spee, 1895, ROB, Brussels 18/2/2016 Sterrenwacht Urania, Hove 58
59 Future prospects: image-based indices Can a proxy of the SN be created in the future, based on images data? require long cross-calibration (whole range of activity more than one cycle) complex visibility of smallest spots vs seeing, contrast. No replacement soon. New indices can be created but are distinct from the SN: parallel proxy series. R W 10 1 g f g R C W g Af g f g (Zharkova et al. EGSO, 2003) 18/2/2016 Sterrenwacht Urania, Hove 59
60 Conclusions Epochal revision of the sunspot record (1 st since Wolf) From a static heritage to a living data series: long overdue! Cultural shock for the scientific community Multiple implications opening new research paths Renewed interest for the long-term sunspot record: Recent wave of new publications Topical issue of Solar Physics (> 40 papers) Base for a new Sunspot Number production 18/2/2016 Sterrenwacht Urania, Hove 60
61 Stay tuned. World Data Center SILSO Sunspot Index and Long-term Solar Observations SN workshops: 18/2/2016 Sterrenwacht Urania, Hove 61
62 USET ROB Brussels 17/08/2002 9:25UT 18/2/2016 Sterrenwacht Urania, Hove 62
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