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Large-Scale Inflows Around Active Regions: Consequences on Surface Magnetic Field Dispersal Marc DeRosa, Karel Schrijver Lockheed Martin Solar and Astrophysics Laboratory Palo Alto, CA 9 November 2006 LoHCo Meeting, Boulder, CO Solar Surface-Flux Evolution Appearance and evolution of surface-flux provides many All scales are important! For example, active regions MDI has enabled detailed studies of the evolution of surface flux (especially small-scale ephemeral population). constraints on (and many clues toward understanding) the solar dynamo. would evolve differently if magnetic carpet were absent. Can we build an idealized model based on their characteristics? What can we learn about the dynamo from such models? Evolving Surface-Flux Transport Model flux emergence Research areas: Dynamo, alpha effect 3D magnetoconvection Global field-flow coupling Sub-resolution dynamics 3D flux transport This model includes: random stepping diff. rot. & merid. flow flux fragmentation collision & cancellation Schrijver (2001) – active to ephemeral region flux, atomic description (no grid) – bipole strengths, emergence latitudes, tilts chosen from empirically determined statistical distribution functions – nonlinear magnetoconvective coupling: nesting, and flux-dependent dispersal coefficient Consistency Check cycle maximum cycle minimum (Mx cm-2) Histograms of model flux match histograms of flux observed from magnetograms very well. Schrijver (2001) model magnetogram Model Activity Cycles pure simulated Sun (from 40° corotating frame) Formation of polar caps occurs naturally, arising from the tilt of emergent bipoles, combined with the convective dispersal and poleward meridional flows. Schrijver (2001) Model Activity Cycles pure simulated Sun (from 40° corotating frame) for fun: simulated star that is 30 more active than sun Schrijver (2001) Schrijver (2001) Historical Sunspot Cycles Schrijver, DeRosa & Title (2002) (1022 Mx) Model Surface Flux Schrijver, DeRosa & Title (2002) (1022 Mx) Net Flux Poleward of North-60° Schrijver, DeRosa & Title (2002) No polar polarity inversion? (1022 Mx) What If Flux Decayed with a Half-Life Set to 5 yrs? Schrijver, DeRosa & Title (2002) Possible Solution to the Conundrum: Active Region Inflows Helioseismic inferences of subsurface and near-surface flows indicate that many active regions seem to be surrounded by horizontal inflows on the order of 20-50 m/s very near the surface. Additionally, there is evidence that the magnitude of the What effects do these inflows have on the transport and evolution of surface magnetic fields? Can these inflows help to solve the polar-flux paradox? inflow velocities scales with the amount of flux contained within the active region. Measurements of Active Region Inflows Below are shown surface flows inferred from f-mode timedistance analysis for part of CR1949 (in 1999), as an example of this phenomenon. Gizon (2004) Measurements of Active Region Inflows Inflows surrounding active regions are also found in ring-diagram analyses of active regions. Hindman et al. (2004) What effects can these active-region inflows have on surface fields? Inflows affect the appearance and evolution of active regions. Inflows affect the amount of flux transported poleward during each sunspot cycle. Polar-cap flux is the source of much of the heliospheric field (especially during solar minimum). Polar-cap flux might eventually be recycled into the convection zone, and appear as emergent flux during future sunspot cycles. MDI Assimilation Model Schrijver & DeRosa (2003) Adding Inflows to the Model Model inflows scale with the gradient in absolute flux density, after 15 smoothing: v = . Model inflows are time-invariant. Adding Inflows to the Model → |v| = 0 m/s → |v| = 30 m/s → |v| = 10 m/s DeRosa & Schrijver (2007) MDI assimilation model Concluding Remarks Inflows faster than 10 m/s are needed to resolve the polarflux conundrum. However, … Inflows faster than 10 m/s markedly affect the evolution of active-region flux. The flows are either not as fast, not as persistent, or not uniformly converging around the active region as modeled here (or some combination of all three). We have assumed that active-region inflows and magnetic fields couple as efficiently all other observed surface flows. We have also assumed that the inflows are not dependent on the evolutionary stage of the active region. (The time dependence of the measured inflows is not well known.) Maybe too there is a selection effect in the helioseismic analyses? Looking forward to results of forward modeling efforts…