Round table discussion The Sun during solar cycles 23-24

1. Round table discussionThe Sun during solar cycles 23-24 Presenters: Schmutz, Lockwood, Richardson, Mursula, Charbonneau, Abreu

2. Are we living in special solar times? • Last 50-60 years have seen particularly strong activity cycles - the strongest during the last 400 years and in general the Sun has spent only a few % of the time in the last 10000 years at such high levels of activity. • We are now in a particularly long and weak minimum: • open flux is very low • irradiance is very low • solar wind is exceptionally weak • What does this mean for the future of solar activity?

3. Do the irradiance data agree?

4. Do the irradiance data agree?

5. Cycle 23 computed TSI Reconstruction of TSI from PSPT data with SRPM model by I. Ermolli (Rome). Note good fit during declining phase of cycle 23 to VIRGO Figure kindly provided by I. Ermolli Looks very promising, but unfortunately, no PSPT data for previous minimum

6. Predicting the next cycle

7. Predicted next cycle: how does it compare with reality? Avge SN for 2009 = 1

12. Modelling the variation of solar total and spectral irradiance Sami K. Solanki with major contributions from: L. Balmaceda, N.A. Krivova, Y.C. Unruh, L. Vieira, T. Wenzler

13. Topics covered by this talk • Models of total and spectral solar irradiance for different time intervals: • the satellite era • the period since the Maunder minimum • the holocene (if time permits) • In general: the longer the timescale, the simpler and less reliable the model becomes (although some short-term models are also pretty simple)

14. Satellite era Different model philosophies: • Correlation between TSI/SSI and proxies (spot area, Mg II index or similar). 2 free parameters per wavelength • Models employing model atmospheres to compute TSI and spectral irradiance • SRPM (Fontenla et al.): divide, e.g., Ca II images into 5-7 categories depending on brightness. Different model atmosphere for each category • SATIRE (Krivova et al.): use magnetograms & only distinguish between spots, QS and bright magnetic features

15. SATIRE: Spectral And Total Irradiance REconstruction Semi-empirical model with main assumption: B-field at solar surface causes TSI + SSI variations in UV,vis,IR Components: Spots (contin. images), faculae + network (magnetograms), quiet Sun Model atmospheres 1 free parameter

16. SATIRE TSI vs. PMOD composite >90% of solar irradiance variations on time scales days – solar cycle caused by surface magnetism. Caveat: There is a free parameter in the model Wenzler et al. 2006, A&A

17. What about other composites? • PMOD composite is best-off compared to the data. • Scafetta and Willson (2009) used the wrong reconstruction... PMOD ACRIM DIARAD What about the current minimum? Unfortunately, MDI continuum images are corrupted since 2004. We are currently redoing the processing of the MDI data set. Plan to be finished by summer Wenzler et al. 2009

18. SUSIM data Model Spectral irradiance with SATIRE Spectral irradiance variations modelled by SATIRE, compared with observations (Krivova et al. ’06, ’08; Unruh et al. 99, 08), and variation of spectral lines over solar cycle (Danilovic et al. 2009) with same value of free parameter as derived from TSI. See talk by Krivova

19. Next step: use MHD simulations to remove last free parameter 0 G Vögler et al. 2005 6000x6000x1400 km box 20km grid 50 G 200 G 400 G Radiation MHD simulations of solar surface layers. Open lower boundary with fixed value of entropy for bottom inflow (i.e. assume irradiance changes in surface layers)

20. Facular spectra from MHD simulations • Spectra at μ=1 from MURAM: • lines: different 200G snapshots • green shading: 50G snapshots • blue shading: 400 G • Black line: SATIRE μ=1 spectrum with α= 0.2 Unruh et al. in prep.

21. Measured Reconstructed Sunspots Evidence for Secular Change: Interplanetary Magnetic Field • Reconstructed fromgeomagnetic aa index • Sun’s open flux nearly doubled during the last century What produced this doubling? What are implications for solar irradiance? Lockwood et al. 1999 Rouillard & Lockwood 2007

22. Secular Change of the Sun's Magnetic Flux: a Mechanism • Underlying concept: overlapping solar cycles. The overlap can be produced by • emergence of flux from new cycle (e.g. in form of ephemeral regions) before end of previous cycle (Harvey 1993, etc.) • long lifetime (decay time) of open (and closed) flux (e.g. Schrijver, Baumann) Solanki et al. 2000, 2002

23. Open flux: different computations Very different methods of computing open flux give similar results: flux transport models (Wang et al. 2005; Baumann et al. 2004; Schüssler & Baumann 2008; Schrijver & DeRosa 2004) confirm simpler model of Solanki et al. (2000) Lockwood et al. 1999 Solanki et al. 2000 Wang et al. 2005 Models require SN as input

24. Constraining the model Vieira et al. in prep Model must reproduce all available data sets

25. Solar Irradiance Since 1610 Based on Magnetic Field Reconstruction Estimates of secular rise in total solar irradiance since Maunder minimum ≈0.8-1.5 W/m2 Value depends on whether we use open flux due to Lockwood et al. or Rouillard et al. (latter gives lower value) A secular variation of total solar irradiance > 1.5 W/m2 cannot be ruled out, but is not likely to be based on variations of solar surface magnetic flux Recent reconstructions of irradiance since Maunder min.: Foster (2004): 0.5-1.5 Wm-2, Wang et al. (2005): 0.8-1.2 Wm-2, Krivova et al. (2007): 1.3-1.5 Wm-2, Tapping et al. (2007): 1±0.4 Wm-2, Preminger & Walton: no long-term trend (shorter reconstructions: Shoell et al. 07, Crouch et al. 2008) Krivova et al. 2007, Vieira et al. in prep.

26. Long term spectral irradiance Preliminary reconstruction of spectral irradiance between Lyαand 160 μm from Maunder minimum to now

27. Sunspot Number for Last 11400 Years • 14C from tree rings  cycle averaged SN for past 11400 years • Reconstruction depends on evolution of geomagnetic field & mixing in oceans • Alternative data set: 10Be from ice cores. Depends on mixing in atmosphere, etc. Solanki et al. 2004 Usoskin et al. 2006a,b, 2007

28. Preliminary: irradiance over 11 kyr • Only cycle averages can be reconstructed with 14C data • Make use of relationship between 10-year avges. of SN and of reconstructed irradiance since Maunder minimum • Apply to SN reconstructed over last 11 millennia from 14C (same can also be done for SN from 10Be, etc.) • Uncertainty is larger than for last 400 years since uncertainty in SN reconstruction enters directly into irradiance

31. Can we determine cycle amplitudes in previous millennia? • Possibly in a statistical sense: assume statistical relations found in last 400 years hold also for earlier times • Consider, e.g., relationship between cycle maxima and minima of the 2-year mean, with the 10-year mean

32. Cycle amplitudes in previous millennia • Maxima of irradiance envelope, as well as maxima & minima of 2-year means are linearly correlated with 10-year mean • Since the 10-year mean is available, these relations give a chance to estimate in a statistical sense the other quantities

33. Preliminary variability envelopes prior to 1610 AD

34. Preliminary irradiance reconstruction through Holocene

37. Modulation parameter

38. Ti-44 activity: measurement vs. model /kg)