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What do sunspots tell us about recent and past trends in solar activity ?Frdric Clette & Laure Lefvre Royal Observatory of BelgiumWDC - SILSOESWW11 Nov 20141SN and GN recalibration: early preview21/11/2014ESWW11 Nov. 20142

Ongoing revision of inhomogeneities in the Sunspot Number (WDC-SILSO) and Group Number series (Hoyt & Schatten 1994, 1998)

SN Workshops, 2011-2015

SN and GN recalibration: early preview21/11/2014ESWW11 Nov. 20143RGO trendSN weighting RGO/SOONSpecola driftClette, Svalgaard, Vaquero, Cliver, 2014Space Science Reviews, Aug. 2014, Springer Online First , 69 pagesDOI 10.1007/s11214-014-0074-2Arxiv: http://arxiv.org/abs/1407.32314 main corrections10 to 40%Obtained independentlyBased only on sunspot data

SN and GN agree within uncertainties back to the Dalton MinimumImplications: low secular trends21/11/2014ESWW11 Nov. 20144Corrected SN & GN series agreeSecular trend is largely eliminated < 5% / century

Trend +15%/centuryTrend +40%/centurySN correction: SN /1.20 after 1947 GN correction: GN * 1.37 before 1880

Soon after the Maunder Minimum, solar activity was similar to present levels21/11/2014ESWW11 Nov. 20145

Open solar flux (geomagnetic indices) Similar conclusions: recent open magnetic field reconstructions show only a weak trend over last 180 years (Lockwood, Living Reviews SP, 9/2013)

New SN series (red):correction of SN scale drifts due to the Locarno pilot station

Changes in cycle 22 Implications: recent cycles21/11/2014ESWW11 Nov. 20146Cycle 22Slightly decreased (- 5 to10%)Maximum 22 second peak is higher, almost equal to first peak

Changes in cycle 23Implications: recent cycles21/11/2014ESWW11 Nov. 20147Cycle 23Slightly increased (+ 5 to 10%)Maximum 23 second peak becomes higher than the first peak. Cycle 23 decline raised by about 20%New maximum in 2002 instead of 2000Implications: recent cycles

Still significant disagreement during the decline of cycle 23Indication of a real solar change21/11/2014ESWW11 Nov. 20148New SN series (red):correction of SN scale drifts due to the Locarno pilot station

Deviation between Ri and F10.7 in cycle 23

Implications: a variable number of spots/group (SN/GN ratio)Reconstructed GN series (SILSO, SONNE):Both indices SN and GN calculated from the same data setChanging SN/GN ratio :Stable over cycles 19 to 22Decline in cycle 23 and 24Decrease of the average number of spots per group by ~30%

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SONNE SSNLocarno SSN SN and GN contain a different information about the solar cycleA probe for past changes in the solar dynamo ?Implications: a variable number of spots/group (SN/GN ratio)1021/11/2014ESWW11 Nov. 2014

Tlatov 2013Apparent secular variations of the ratio SN/GN (Tlatov 2013): NS/NG increase for stronger cycles ?Ratio of the original SN/GN series: different sets of observations. 10Vanishing small spots21/11/2014ESWW11 Nov. 20141111Cycle 23 small-spot deficitExploitation of detailed sunspot catalogs: DPD, Debrecen; NOAA/SOON (Lefvre & Clette 2011, 2012, 2013)Scale-dependent small-spot deficit in cycle 23:Deficit of small groups (A & B types): Ratio cycle 23 / cycle 22 ~ 50%Deficit of small spots inside all groups: Ratio cycle 23 / cycle 22 < 75%Starts in 1998, significant only after 2000

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Small vs Large groupsClette & Lefvre 201212Small vs Large spots12Cycle 23 small-spot deficit

ESWW11 Nov. 2014Similar size-dependent trends found by Kilcik et al. 2013: Upgrade of Kilcik et al. 2011 resultsBased on Learmonth data

Small spots A,B types: factor ~2 deficit Intermediate C type: moderate decreaseLarge D,E,F,H groups: no difference between SC23 and 24.A,BCD,E,FH_____ Sunspot counts--------- Sunspot group counts_____ International SN Ri21/11/20141313Similar results from Nagovitsyn et al. 20134 classes based on their area (multimodal distribution)Only the smallest spots (A5/pixel).Smallest spots 0.95): RG, RA, RBoulder, Area, Mx(Bachmann et al. 2004, Rybansky et al. 2005, Wilson and Hathaway 2006, Tapping et al. 2007, Bertello et al. 2010, Hempelmann and Weber 2012)Measure of the global emergence rate of (toroidal) magnetic flux (Petrovay 2010, Stenflo 2012)

Chromospheric and mixed indices (TSI, CaII-K, MgII):Good but lower correlations:Non-linear relationTime lags (magn. flux dispersion)Different physics !

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Mean mag. fluxSunspot Nb.Stenflo, 2012Solanki & Fligge 1999Sunspot number versus other solar indices and fluxesBlind Source Separation applied solar radio and UV indices:Method: Bayesian positive source separation (Moussaoui et al. 2006)

21/11/2014ESWW11 Nov. 2014353 clusters of indices, each dominated by one of 3 sources :Photosphere (SN, GN)Chromospheric (DSA, MgII, Ly, radio > 10cm)Coronal (radio < 10cm)

T. Dudok de Wit, SSN2 Workshop, 2012CoronaChromosphereChromospherePhotosphereNetwork, plagesRadio gyroresonanceActive regions35

Cycle 24 in the long-term SN perspectiveCycle 24 is among the late cyclesTie-point (Ri=13) at the end of preceding cycle2 main cycle families:Steep strong (max > 130)Slow weak (max < 80)

Best fit with cycles 12, 14, 15, 16 Tie-point (Ri=40) in the rising phase of the cyclesReturn to an average activity regime like in the late 19th and early 20th century

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Cycle 24 best matches:

Cycle 14 [1902-1913]: Rmax = 64.2

Cycle 15 [1913-1923]: Rmax = 105.4 !3 features of moderate cycles:Plateau (duration up to 3 years)Multiple sharp peaksLate maximum (~highest random peak)

Cycle decline by mid-2015Next minimum in 2019-202021/11/2014ESWW11 Nov. 2014Cycle 1537

Cycle 14Cycle 24 in the long-term SN perspective