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Solar radiative variability Solar activity and the magnetic cycle

Recent progress in modelling solar radiative variability on centennial timescales Paul Charbonneau Département de Physique, Université de Montréal. Solar radiative variability Solar activity and the magnetic cycle Long-term reconstructions of TSI/SSI Simulated magnetic cycles

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Solar radiative variability Solar activity and the magnetic cycle

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  1. Recent progress in modelling solar radiative variability on centennial timescales Paul Charbonneau Département de Physique, Université de Montréal • Solar radiative variability • Solar activity and the magnetic cycle • Long-term reconstructions of TSI/SSI • Simulated magnetic cycles • Magnetic modulation of convection • What is next… Collaborators: Piotr Smolarkiewicz, Mihai Ghizaru, Dario Passos, Antoine Strugarek, Jean-François Cossette, Patrice Beaudoin, Cassandra Bolduc, Amélie Bouchat, Caroline Dubé, Nicolas Lawson, Étienne Racine, Corinne Simard, Gustavo Guerrero, Roxane Barnabé, Zbigniew Piotrowski McGill AOS 19/01/2015

  2. The ones who did the real work Jean-François Cossette PhD granted November 2014 Now Hale postdoctoral Fellow at the University of Colorado/Boulder, U.S.A. Cassandra Bolduc PhD turned in November 2014 Co-Advisor Michel Bourqui, ex. McGill/AOS Now postdoc at PMOD/Davos, Switzerland McGill AOS 19/01/2015

  3. 19/11/2014, along HWY 40 into Montréal Solar/stellar magnetism McGill AOS 19/01/2015

  4. The solar constant (1) Definition: Wavelength-integrated electromagnetic energy illuminating one square meter of Earth’s upper atmosphere, at a Sun-Earth distance of one astronomical unit (149598500 km). Now called Total Solar Irradiance (TSI) TSI = 1362 +/- 4 Watt / m2 McGill AOS 19/01/2015

  5. The solar constant (2) 1838: IST ~ 690 W/m2 John Herschel (1792-1871) Claude Pouillet (1790-1868) McGill AOS 19/01/2015

  6. The solar constant (3) 1881, Mt Whitney, CA: TSI=2903 W/m2 !! Samuel PierpontLangley (1834-1906) (Invented the bolometer) McGill AOS 19/01/2015

  7. The total solar irradiance (1) http://spot.colorado.edu/~koppg/TSI/ (Invented the bolometer) McGill AOS 19/01/2015

  8. The total solar irradiance (2) Min/max change in Earth’s equilibrium temperature: 0.04oC http://spot.colorado.edu/~koppg/TSI/ McGill AOS 19/01/2015

  9. The solar spectral irradiance Plot by J. Lean, NRL, courtesy NASA From UV to X-Rays, variability increases a lot with decreasing wavelength; However, the bulk of electromagnetic energy at these wavelengths is absorbed very high in the Earth’s atmosphere (stratosphere and higher). The UV (120-400nm) accounts for 1% of the TSI, but 14% of its variability. McGill AOS 19/01/2015

  10. Solar/stellar magnetism « If the sun did not have a magnetic field, it would be as boring a star as most astronomers believe it to be » (Attributed to R.B. Leighton) McGill AOS 19/01/2015

  11. Solar ac SoHO/LASCO C-3 tivity SoHO/EIT 19.5 nm McGill AOS 19/01/2015

  12. Solar activity SoHO/LASCO C-3 McGill AOS 19/01/2015

  13. Sunspots (1) SDO / HMI Continuum McGill AOS 19/01/2015

  14. Harriot, Fabricius, Galileo, Scheiner… McGill AOS 19/01/2015

  15. The sunspot cycle (1) Heinrich Schwabe Discovered in 1843 by an amateur astronomer, after 17 years of nearlycontinuoussunspot observations. The sunspot cycle has a period of approximately 11 years, and its amplitude shows large cycle-to-cycle fluctuations, as well as extendedepisodes of apparent halt.. Rudolf Wolf McGill AOS 19/01/2015

  16. Sunspots (2) G.E. Hale, F. Ellerman, S.B. Nicholson, and A.H. Joy, The Astrophysical Journal, 49,153-178, (1919) McGill AOS 19/01/2015

  17. The sunspot cycle (2) 2001, cycle peak Magnetogram McGill AOS 19/01/2015

  18. The solar magnetic cycle The solar magnetic cycle has a period of ~22 yr, but solar activity does not care about magnetic polarity, so that solar activity cycles on a ~11 yr period McGill AOS 19/01/2015

  19. Solar activity McGill AOS 19/01/2015

  20. Solar internal structure McGill AOS 19/01/2015

  21. Two schools of thoughts • All TSI variation on all relevant timescales are due to varying surface coverage of magnetic features (spots, faculae, network, etc.). Strongest evidence: reconstructions based on photospheric data can reproduce 95% of observed variance. • Some TSI variations on timescales decadal and longer originate from deep inside the sun (changes in solar radius, photospheric temperature gradient, magnetic modulation of convective energy flux, etc.). Strongest evidence: cyclic modulation of p-mode frequencies. McGill AOS 19/01/2015

  22. Semi-empirical reconstructions of total and spectral solar irradiances [ with C. Bolduc, and a lot of other people…] McGill AOS 19/01/2015

  23. Fragmentation … McGill AOS 19/01/2015

  24. … and erosion McGill AOS 19/01/2015

  25. A fragmentation-based model[ Crouch et al. 2008, ApJ, 677, 723 ] • A Monte Carlo simulation of surface magnetic flux evolution: • Spots of surface area A are injected on a computational • « solar disk » (data from Royal Greenwich Obs.) • Emergences on backside treated statistically • Spots fragment randomly, and erode at their perimeter • These processes of fragmentation/erosion continue until • only elementary magnetic flux tubes are left; • these disappear randomly • The resulting distribution of surface features N(A;t) • is convolved with a contrast function, including limb • darkening, to yield a TSI time series. McGill AOS 19/01/2015

  26. From surface magnetism to TSI[ Crouch et al. 2008, ApJ, 677, 723; Bolduc et al. 2015, ApJ, submitted ] A four-component model: quiet sun, spots, faculae, network: Irradiance deficit due to « spots  » : (Lean et al. 1998; Brandt et al. 1994) Irradiance excess due to « faculae » and « network » : (Chapman & Meyer 1986) Quiet Sun modulation from F10.7 radio flux : (Tappinget al. 2007) McGill AOS 19/01/2015

  27. Genetic algorithms A class of optimizationmethodsinspired by biologialevolution, particularly appropriate for complex, partlystochastic multimodal optimizationtasks. Initialisation: construct a population of random solution; computetheir fitness Select best members of the population Breed new generationfromselected best Compute fitness of new population members Fittest solution good enough? END! YES NO McGill AOS 19/01/2015

  28. TSI reconstructions (1)[ Bolduc et al. 2015, ApJ, submitted ] McGill AOS 19/01/2015

  29. TSI reconstructions (2)[ Bolduc et al. 2015, ApJ, submitted ] McGill AOS 19/01/2015

  30. TSI reconstructions (3)[ Bolduc et al. 2015, ApJ, submitted ] Reconstructions going back centuries or millennia take the models far out of their calibration regimes : extrapolation is dangerous ! McGill AOS 19/01/2015

  31. Magnetically-mediated cyclic modulation of convective energy transport [ with J.-F. Cossette, P. Smolarkiewicz, M. Ghizaru ] McGill AOS 19/01/2015

  32. The MHD equations McGill AOS 19/01/2015

  33. EULAG-MHD[ Smolarkiewicz & Charbonneau, J. Comput. Phys. 236, 608-623 (2013) ] EULAG: a robust, general solver for multiscale geophysical flows EULAG-MHD: MHD generalization of above; developed mostly at UdeM in close collaboration with Piotr Smolarkiewicz Core advection scheme: MPDATA, a minimally dissipative iterative upwind NFT scheme; equivalent to a dynamical, adaptive subgrid model. Thermal forcing of convection via volumetric Newtonian cooling term in energy equation, pushing reference adiabatic profile towards a very slightly superadiabatic ambiant profile Strongly stable stratification in fluid layers underlying convecting layers. Model can operate as LES or ILES McGill AOS 19/01/2015

  34. Simulation design Simulate anelastic convection in thick, rotating and unstably stratified fluid shell of electrically conducting fluid, overlaying a stably stratified fluid shell. Recent such simulations manage to reach Re, Rm ~102-103, at best; a long way from the solar/stellar parameter regime. Throughout the bulk of the convecting layers, convection is influenced by rotation, leading to alignment of convective cells parallel to the rotation axis. Stratification leads to downward pumping of the magnetic field throughout the convecting layers. McGill AOS 19/01/2015

  35. Rotation and differential rotation (1) No rotation Rotation at solar rate This is stratified, rotating turbulence ! Vertical (radial) flow velocity, in Mollweide projection [ from Guerrero et al. 2013, Astrophys. J., 779, 176 ] McGill AOS 19/01/2015

  36. MHD simulation of global dynamos [ Ghizaru et al. 2010, ApJL, 715, L133 ] Temperature perturbation Radial flow component Radial magnetic field component http://www.astro.umontreal.ca/~paulchar/grps> Que faisons nous > Simulations MHD Electromagnetic induction by internal flows is the engine powering the solar magnetic cycle. The challenge is to produce a magnetic field well-structured on spatial and temporal scales much larger/longer than those associated with convection itself. This is the magnetic self-organisation problem. McGill AOS 19/01/2015

  37. Simulated magnetic cycles (1) Large-scale organisation of the magnetic field takes place primarily at and immediately below the base of the convecting fluid layers McGill AOS 19/01/2015

  38. Magnetic modulation of convective energy transport in EULAG-MHD simulation[ Cossette et al. 2013, ApJL, 777, L29 ] The simulation is more « luminous » at magnetic cycle maximum, by a solar-like 0.2% Lsol ! McGill AOS 19/01/2015

  39. How to modulate convective energy transport Vertical flow speed Temperature deviation from horizontal mean • Lorentz force modulates convective velocity ur; • Change in magnitude of temperature perturbations; • Change in degree of correlation between the two; • Change in latitudinal distribution of F . • All of above ? And/or something else … ? McGill AOS 19/01/2015

  40. Spatiotemporal variabilityof the convective flux[ Cossette et al. 2013, ApJL, 777, L29 ] Zonally-averaged toroidal field and convective flux at r/R=0.87 McGill AOS 19/01/2015

  41. Convective entrainment and « hot spots » McGill AOS 19/01/2015

  42. Pinning it down…[ Cossette et al. 2013, ApJL, 777, L29 ] Differences are in the tails of the flux distributions: hot spots are enhanced, turbulent entrainment is suppressed. The strongest (anti)correlations with the magnetic cycle are for the negative convective fluxes. McGill AOS 19/01/2015

  43. Small (multi)periodic signal in temperature[ Beaudoin et al. 2015, in prep. ] 95% confidence Foukal et al. 2006, Nature443, 161-166: this cannot produce TSI variations ! McGill AOS 19/01/2015

  44. Convection is NOT diffusion ! • The Newtonian diffusive heat flux is proportional to the temperature gradient; the heat flux is entirely determined by local conditions. • The convective heat flux is proportional to temperature at point of origin of upflows and downflows; for strongly turbulent convection, these flow structures can cross many scale heights; the heat flux is strongly non-local. McGill AOS 19/01/2015

  45. Convection is NOT diffusion ! McGill AOS 19/01/2015

  46. The least you should remember from this talk The solar magnetic cycle drives all of solar activity, including radiative variability at all wavelengths. Solar radiative variability is strongly wavelength-dependent. Radiative variability on short timescales is dominated by the surface coverage of various magnetic features. On long timescales (decadal and up), deep-seated, magnetically-driven modulation of heat transport may play a significant role in TSI variations. Global MHD numerical simulations now allow quantitative investigations of these effects; but need to get closer to the surface to allow detailed comparison to observations There is much more to solar impacts on Earth’s atmosphere than TSI variations. McGill AOS 19/01/2015

  47. One crazy correlation… Lightning data from Stringfellow 1974, Nature, 249, 332 McGill AOS 19/01/2015

  48. FIN McGill AOS 19/01/2015

  49. The « millenium simulation »[ Passos & Charbonneau 2014, A&A, in press ] Define a SSN proxy, measure cycle characteristics (period, amplitude…) and compare to observational record. McGill AOS 19/01/2015

  50. Zonally-averaged Bphi at r/R =0.718 Magnetic cycles (1) Zonally-averaged Bphi at -58o latitude McGill AOS 19/01/2015

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