What we can learn from active region flux emergence David Alexander Rice University Collaborators: Lirong Tian (Rice) Yuhong Fan (HAO)

INFERENCES FROM OBSERVATIONS OF ACTIVE REGION FLUX  Key Observations:  Evolution of flux emergence  Distribution, evolution and transport of surface flux  Distribution of twist (currents, helicity, free energy)  Magnetic connectivity (3D current distribution, …)  Energy release (sigmoids, CMEs, flares, …)  mass flow into corona (prominences etc.)  …  What they tell us:  complex surface flux distribution related to 3D complexity in corona (storage and release of free energy) and to nature of emerging structure which in turn is related to survival/evolution of flux passing through convection zone e.g. non Hale-icity related to sub-surface kinking, large flare production, sunspot rotation, sigmoid formation …  evolution of twist to/from writhe (helicity) related to destabilization of corona  asymmetric and fragmented flux related to evolution of fluxrope through convection zone (last 10 Mm?) and to complex coronal current distributions  …

ASYMMETRIC FLUX EMERGENCE OBSERVATIONS Tian and Alexander 2009 NOAA 0656 (and its recurrent AR ) The leading polarity with negative flux is more compact, emerges strongly, and moves fast, while the following polarity, with positive flux, is dispersed and fragmented.

ASYMMETRIC HELICITY INJECTION FROM OBSERVATIONS Tian and Alexander 2009 a: Total radial magnetic flux (x10 22 Mx) of positive and negative polarities; d: total helicity flux (x10 42 Mx 2 ) over 5 days for the positive and negative polarities c: helicity injection rate (x10 40 Mx 2 per hr) the positive and the negative polarities b: leading (positive) flux vs following (negative) flux. HELICITY IS ASYMMETRIC FOLLOWING POLARITY (*) SHOWS MORE FLUCTUATION AR 8214

ASYMMETRIC HELICITY INJECTION FROM OBSERVATIONS Tian and Alexander 2009 AR 10656

ASYMMETRIC FLUX EMERGENCE SIMULATION (a)Selected field lines threading through the coherent apex cross-section of the Ω-tube that approaches to the top boundary, for the low latitude case; (b)Values of the magnetic field strength B along the field lines in (a) as a function of depth for the leading (black diamond points) and the following (red crosses) sides, and the field- line averaged mean B as a function of depth for the leading (blue line) and following (yellow line) side. (c)Values of α ≡ J·B/B 2 computed along each of the selected field lines in (a) as a function of depth for the leading (black diamond points) and the following (red crosses) sides. The field-line averaged mean α as a function of depth is shown as solid lines for the leading (blue) and the following (yellow) side. (d)(e), and (f ) are the same as (a), (b), and (c) respective, except that they are for the high latitude case. Fan 2008 ; Fan, Alexander and Tian 2009

ASYMMETRIC HELICITY INJECTION SIMULATION Fan 2008 ; Fan, Alexander and Tian 2009 (a)The computed helicity fluxes through the leading and the following polarity areas of each radial cross-sections of radius r, for r ranging from the middle of the convection zone to a depth below the apex of the Ω- tube. The black curves show (dH R /dt) l (solid) and (dH R /dt) f (dash-dotted) respectively. The blue curves show contributions to (dH R /dt) l (solid) and and (dH R /dt) f (dash- dotted) due to horizontal vortical motions of the field line footpoints, and the red curves show contributions to (dH R /dt) l (solid) and (dH R /dt) f (dash- dotted) due to the vertical rise of the tubes. (b) is the same as (a) except for the high latitude case.

DISTRIBUTION OF TWIST AT SURFACE Following polarity is fragmented with individual flux elements showing mixed sign of the twist.

CORONAL CONSEQUENCES Coronal field can be oriented in a number of ways

CORONAL CURRENT SYSTEM I Following polarity comprised of small scale mixed polarity mixed twist field: conditions for distributed reconnection in corona -ve +ve

CORONAL CONSEQUENCES Twist gradient along field line: conditions for equilibriation of twist via torsional Alfven waves Longcope and Welsch, ve +ve  A ~ 1 day

QUESTIONS  How does the corona respond to asymmetric and mixed surface currents?  Is an equilibrium state even attainable and what does it look like?  Spontaneous and ubiquitous tangential continuities? (Low 2006 – 2009)  Continuous and ubiquitous reconnection? Transients/heating?  How is the helicity manifested in the corona? (propagation of twist)  What is the connection to the large scale ‘pre-existing’ corona? Coronal consequences of asymmetric current systems

QUESTIONS General consequences of emergence process  Is the corona, its topology and evolution consistent with the dynamics and evolution of the sub-surface expectations?  Can we infer gross properties of the near sub-surface region from surface observations? e.g. can the observations usefully inform the models?  Nature or nurture? Is solar activity (flares/CMEs etc.) a result of genetics (properties defined at birth) or environmental conditions (evolution of AR atmosphere, interaction with large scale corona, …)

HELICITY OBSERVATIONS Pariat et al. (2005, 2006) Jeong & Chae (2007) Berger & Field (1984) Demoulin & Berger (2003)

HELICITY SIMULATION