Solar-B 5, Tokyo, November 2003 J. Sánchez Almeida Instituto de Astrofísica de Canarias, Spain

Solar-B 5, Tokyo, November 2003  What is quiet Sun? Why is it important?  Main observational properties Surface coverage Degree of tangling Magnetic field strengths Magnetic flux and energy Variations with the solar cycle  Influence on the corona  Origin of the QS magnetism (hints from theory)  Conclusions  Connection with Solar-B

Solar-B 5, Tokyo, November 2003 Network Inter-Network

Solar-B 5, Tokyo, November ”x1” Domínguez Cerdeña et al. (03)) Inter-Network Quiet Sun  angular resolution mag.  0.5”  sensitivity  20 G  VTT (obs. Teide), speckle reconstructed  Unsigned flux density  20 G

Solar-B 5, Tokyo, November ”x1” Domínguez Cerdeña et al. (03)) Inter-Network Quiet Sun  angular resolution mag.  0.5”  sensitivity  20 G  VTT (obs. Teide), speckle reconstructed  Unsigned flux density  20 G

Solar-B 5, Tokyo, November 2003 Magnetogram of the Sun at maximum Kitt Peak magnetogram

Solar-B 5, Tokyo, November 2003  Most of the (unsigned) magnetic flux and energy existing on the solar surface at any given time is in the quiet Sun.  It may play a significant role in all the physical processes pertaining to the global solar magnetic properties (dynamo, coronal heating, sources of the solar wind,…).  This role has been neglected so far.  Easy target for the new spectro-polarimeters.

Solar-B 5, Tokyo, November 2003 Between 90% at solar maximum and 99% at solar minimum (e.g., Harvery 1994) Surface Coverage

Solar-B 5, Tokyo, November 2003 Degree of tangling The magnetic structures of the quiet Sun are not spatially resolved. Actually, the magnetic field vector varies within scales smaller than the smallest that we can resolve 350 km  0.5” observer 100 km line of sight Resolution Element magnetic field vector

Solar-B 5, Tokyo, November 2003 IR spectral linesVisible spectral lines SA et al. 2003b

Solar-B 5, Tokyo, November 2003 Stokes Profiles

Solar-B 5, Tokyo, November 2003 Stokes V profiles observed in the Quiet Sun (SA & Lites, 2000) Usual hypothesis

Solar-B 5, Tokyo, November 2003 polarization signals in complex (tangled) magnetic fields cancel out Q 2 = -Q 1  Q 1 +Q 2 = Q obs = 0  V 2 = -V 1  V 1 +V 2 = V obs = 0

Solar-B 5, Tokyo, November 2003 SA et al. (2003) The symbols correspond to observations of IN Quiet Sun Magnetic fields

Solar-B 5, Tokyo, November 2003 In short, due to the complex topology of the QS magnetic fields, The measure of the magnetic field properties is a non-trivial issue. It involves a big deal of modeling and assumptions on the underlying atmosphere: Inversion Codes. All measurements are bound to underestimate the magnetic flux content of the QS fields.

Solar-B 5, Tokyo, November 2003 Magnetic Field Strengths Sunspots: Plage & Network regions: Inter-Network quiet Sun:

Solar-B 5, Tokyo, November 2003 SA et al. 2003b

Solar-B 5, Tokyo, November 2003 SA et al. 2003b; Socas Navarro & SA 2003 PDF: probability of finding a given field strength (per unit field strength). from Hanle effect from Zeeman effect

Solar-B 5, Tokyo, November 2003

 Most of the quiet Sun (IN) surface is covered by weak magnetic fields. more than 95% of the surface has  Magnetic flux density in the form of weak and strong magnetic field strengths. Flux (B < 500 G) = 55 G = 75 % of the flux Flux (B < 100 G ; Hanle signals) = 50 G = 60 % of the flux Flux (B > 500 G) = 20 G = 25 % of the flux All the present observations showing quiet Sun magnetic fields underestimate the existing flux density: 75 G < B < 120 G

Solar-B 5, Tokyo, November 2003 Network AR + Network Quiet Sun (visible + IR) AR+N data from Schrijver & Harvey, 94, SPh, 150, 1 Quiet Sun (Hanle)

Solar-B 5, Tokyo, November 2003  Energy density in the form of weak and strong magnetic field strengths. Energy (B < 500 G) = 24 % of the mag. energy Energy (B < 100 G ; Hanle signals) = 19 % of the mag. energy Energy (B > 500 G) = 76 % of the mag. energy

Solar-B 5, Tokyo, November 2003 Variation along the solar cycle Unknown, but it is one of the clear observational targets. To be achieved thanks to the new synoptic magnetograms (e.g., SOLIS ). Claims on the the variation: No flux density variation along the cycle within 40% (SA 2003c). Refers to the tail of kG of the PDF Variation of some 100% (Faurobert et al. 2001). Refers to the weakest fields, deduced from Hanle signals. No variation of hanle signals (Trujillo-Bueno & Shukina 2003). If existing, the variations are negligible as compared to the variation observed in active regions.

Solar-B 5, Tokyo, November 2003 Options for the origin of the quiet Sun magnetic structures Debris from active regions produced by the global solar dynamo Turbulent local dynamo driven by granulation. (Petrovay & Szakaly 1993, Cattaneo 1999,…) Turbulent global dynamo (Stein & Nordlund 2001, Schussler et al. 2003, etc.)

Solar-B 5, Tokyo, November 2003 Debris from Active Regions: Unlikely ARs emerge (and so decay) at a rate of 6 x Mx day -1 IN magnetic flux > 1.2 x Mx then IN cannot decay in less than 200 days, (200 days = 1.2 x Mx / 6 x Mx day -1 ) otherwise they would be gone before fresh AR flux replenishes it. 200 days is too long since the IN fields vary in timescales of min … Lifetimes found in the literature are hours.

Solar-B 5, Tokyo, November 2003 BzBz Temperature 1” Turbulent local dynamo Cattaneo & Emonet, 2001

Solar-B 5, Tokyo, November 2003 SA et al. (2003)

Solar-B 5, Tokyo, November ” seeing original Effects of insufficient angular resolution the intrinsic polarization is largely reduced a residual is left the structures becomes large (seeing-size) all structures have sub-resolution mixed polarities

Solar-B 5, Tokyo, November 2003 Turbulent global dynamo Unclear how to distinguish this mechanism from the local dynamo. complex topology no variation along the cycle tight coupling with granular motions Stein & Nordlund 2001

Solar-B 5, Tokyo, November 2003

Traditionally, the influence of the IN fields on the coronal magnetic field is neglected. Argument: the magnetic field is so complex that most of the field lines close in very low loops and never reach the corona. However: The base of the corona is very low: 2500 km (VALC) Cancellation is often non-local (e.g., Schrijver & Title, 2002) so a fraction actually makes it to the corona. The IN flux is so large that a small fraction makes a significant absolute contribution

Solar-B 5, Tokyo, November 2003 Hoffman et al force free extrapolations loop height < 500 km 1000 km < height < 2000 km

Solar-B 5, Tokyo, November 2003 magnetic energy equals thermal energy density Hoffman et al prominences

Solar-B 5, Tokyo, November 2003 The topology of the network fields reaching the corona is significantly modified (in a non-trivial way) by the presence of IN fields. Schrijver & Title (2003)

Solar-B 5, Tokyo, November ”  Solar B resolution IN fields would be routinely detected with normal mapping of the spectropolarimeter of SOT. (however, only the tail of kG IN fields)

Solar-B 5, Tokyo, November 2003 Studying the IN magnetism is appealing, since it allows to address basic problems of solar physics (solar dynamo, coronal structure and heating, sources of the solar wind, magnetic decay, …) Because of the complications of the magnetic field, non-trivial magnetic field measurements are needed. Stokes profiles are needed for this task (provided complex magnetic fields are allowed for by the inversion techniques).

Solar-B 5, Tokyo, November 2003  The quiet Sun is a component of the solar magnetism whose role has been neglected so far, but whose true role is not understood yet.  Quantitatively important in terms of the global magnetic properties (e.g., carries more unsigned flux than all active regions at the solar max.) It occupies most of the solar surface.  Complex magnetic topology. The diagnostic of their properties based on the observed polarization is a non- trivial issue. Stokes profiles + inversion techniques needed! It is not possible to describe the magnetic field of a IN pixel with a single magnetic field vector.

Solar-B 5, Tokyo, November 2003 è (?) fairly easy to detect with high angular resolution (easy to achieve by the new generation of ground based 1m-class + Adaptive Optics or space-borne magnetometers, line SOLAR-B.) è (??) No strong variation along the cycle. Refers to the tail of kG fields detected in visible magnetograms.  (?) Magnetic Flux and magnetic energy dominated by the tail of kG fields.  Distribution of magnetic field strengths: from 0 to 1.5 kG.

Solar-B 5, Tokyo, November 2003 è (??) Does it reach coronal heights? Probably it does in the quiet Corona è (??) Relationship with the origin and acceleration of the solar wind? è (??) Coronal heating due to nano-flares? è (??) Role within the global solar dynamo responsible for the 22 years solar cycle: passive, leading role … è (??) Responsible for the chromospheric basal flux.

Solar-B 5, Tokyo, November 2003

V 2 = -V 1