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Tutorial: the Magnetic Connection Between the Sun and the Heliosphere

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Tutorial: the Magnetic Connection Between the Sun and the Heliosphere Tutorial: The magnetic Connection between the Sun and the Heliosphere Karel Schrijver The connection between Sun and Earth … TheThe problem:problem: Focus of this presentation 2 12/11/2007 Overview z FromFrom idealideal toto realreal …… z FiveFive piecespieces ofof thethe puzzle:puzzle: 1) The “streamer belt” of a model Sun 2) Evolution of the Sun-heliosphere coupling 3) Source regions of the solar wind 4) Forecasting the quiescent solar wind 5) Powering the solar wind (and the corona) z ConclusionsConclusions andand somesome questionsquestions 3 12/11/2007 An ideal world: solar/heliospheric model 2.5 R 200 R • The surface magnetic field is dispersed and advected to a good approximation as a scalar (1964). • The large-scale coronal magnetic • The heliospheric/ecliptic magnetic configuration can be approximated by configuration can be reasonably a potential field below a “source approximated by the “Parker spiral” surface” (1969). (1958). 4 12/11/2007 Simulation of the solar cycle Visualizing the evolution of the solar wind source domains, as seen in a ‘corotating’ frame, over 1-1.5 magnetic cycles: Surface view Surface grid Source-surf. grid Equatorial Equatorial Equatorial 40° North 40° North 40° North 90° North 90° North 90° North Surface φ-θ map Streamer belt still: Streamer belt envelope and neutral line: From ‘Earth’: (27-d syn. Bartels frame): 5 12/11/2007 Simulating photospheric activity Flux emergence Random stepping Diff. Rot. & Merid. flow Flux frag- mentation Relatively recent essential additions: Collision & magneto-convective coupling cancelation magneto-chemistry: fragmentation and collisions ephemeral-region population 6 12/11/2007 Effects of large-scale flows Differential rotation and meridional flow only, as viewed from 40°N 7 12/11/2007 Large-scale solar field z Large-scale solar field depends on source function, dispersal, meridional flow, and differential rotation +90° Observations 0° Model -90° 0 11 22 Time (years) z Good approximation of large-scale flux patterns, including polar fields 8 12/11/2007 The Sun through the cycle Total flux Flux in activity belt Polar-cap flux (>60º ) Absolute Net Positive only 9 12/11/2007 PFSS model and coronal holes Mirror surface z The large-scale coronal field is mostly potential z It can be approximated remarkably well by an electrostatic model: – charge distribution on the solar photosphere Source surface – within a perfectly conducting sphere of ~5 R~. Solar surface 1 Rss Φ 2 Rss SOHO/EIT 284Å with overlay of open- −R Φ field boundaries from a PFSS model ss for different Rss (see other examples at www.lmsal.com/forecast). 10 12/11/2007 The “current sheet” for a model Sun z The neutral line drifts around a Intersections of 27-d synodic rate, as observed. neutral line and No magic needed! ecliptic, in 27-d z Model: reference frame – One neutral line 90% of the time. – One additional polarity island: 10% of the time – Only ~30 islands throughout a full magnetic cycle. – Islands commonly pinch off from, and re-merge with, the neutral line. – Very few islands form at cusp: the quiescent corona rarely blows bubbles. 11 12/11/2007 MHD sim. shows disconnected field in current sheet Flux emergence Courtesy in a dipolar field MHD simulations by Riley Pete Riley 12 12/11/2007 MHD sim. shows disconnected field in current sheet MHD simulations by Lionello et al. (2005; ApJ 625, 463). 13 12/11/2007 MHD sim. shows disconnected field in current sheet Red: initially closed ; Blue: opened field White areas: field is not connected to the Sun at 30 Black: initially open ; green/cyan/yellow: successive solar radii (Lionello et al., 2005; ApJ 625, 463). openings/closings Circled: foot point of field line that closes and reopens Boxed: foot point of field line that opens All Such regions are adjacent to the current sheet. 14 12/11/2007 Sunspot cycles: history and approximation Successive cycles often differ strongly: 15 12/11/2007 Total flux on the Sun: cycle-to-cycle modulation Consequently the total flux on the Sun is modulated: Mx) 22 (10 16 12/11/2007 Polar-cap (>60°) absolute flux And the polar-cap field “capacitor” does not simply alternate in strength or even polarity: Mx) 22 (10 No polar polarity inversion? 17 12/11/2007 What if flux “decayed” by, e.g., 3D transport? The polar-cap flux behavior signals something is missing from our understanding: 18 12/11/2007 What if flux transport were modified? With polar-cap behavior ‘regularized’*, the heliospheric and cosmic-ray fluxes are roughly anti-correlated: Mx) 22 (10 Scaled 10Be isotope concentration Model heliospheric flux * For example by introducing 3D flux transport (Schrijver & DeRosa, Baumann et al.) or by modulating flux transport (Wang et al., Schrijver et al.). 19 12/11/2007 Source regions of the solar wind Perspective changes over the past few years: z Much of the IMF is rooted in active regions (even sunspots). – Luhmann et al., 2002, JGR 107, 10.1029 – Neugebauer et al., 2002, JGR 107, A12, 13-1 – Schrijver and DeRosa, 2003, SPh 212, 165 – Wang and Sheeley, 2003, ApJ 587, 818 z Heliospheric field from up to a dozen source regions at cycle maximum (may be connected by thin channels). z Much of the slow wind originates in the ARs whose fields generally lie near the cusp at low (i.e., IMF) latitudes. 20 12/11/2007 Data assimilation into a global model Assimilating (“inserting”) magnetograms into the model: 21 12/11/2007 “Sources” of heliospheric field Magnetic plage regions Heliospheric field foot points 9 Heliospheric field originates in coronal holes 9AND in active regions! 22 12/11/2007 “Sources” of the IMF Magnetic plage regions IMF foot points 9 IMF originates in coronal holes over unipolar network AND in young and mature active regions! 23 12/11/2007 Sources of heliospheric field At solar maximum, 30-50% of the interplanetary magnetic field connects directly to active regions (incl. sunspots) Model: field open to the heliosphere SOHO TRACE 24 12/11/2007 Sources of heliospheric field At solar maximum, 30-50% of the interplanetary magnetic field connects directly to active regions (incl. sunspots) Model: field open to the heliosphere e Closed field SOHO Open TRACE field 25 12/11/2007 Sources of heliospheric field (all directions from the Sun) • Latitudes above 30 degrees contribute 20 to 80% of the total heliospheric flux. 26 12/11/2007 IMF: plage vs. activity belt Non-plage • Latitudes above 30 degrees contribute no more than 40% of the IMF •Some 30-50% of the IMF at cycle maximum Plage originates in magnetic plages. 27 12/11/2007 Streamers and the solar wind 28 12/11/2007 How important is the small stuff (I) ? z Quiet-Sun “magnetic carpet”: – Large-scale patterns survive for months or more – Network flux concentration survive for at most a few days, and magnetic connections much less than a day, owing to emergence of many small bipoles (“ephemeral regions”) 29 12/11/2007 How important is the small stuff (II) ? z A “magnetic canopy” was thought to separate the strong network field from essentially field-free regions around the network in a closed-vault geometry. But then: z “Weak field” away from the network discovered in the mid 70s z Maybe “weak field,” but lots of flux: ~5 ⎯ 50 Mx/cm2 , on average ~20 Mx/cm2 z Maybe not “weak,” but merely “small”: 1016-17Mx compared to 1018-19Mx? 30 12/11/2007 Photosphere-corona connection Potential field above unipolar network and mixed-polarity intranetwork; side and top view z The “intranetwork field” steals flux from the network, so that z the field geometry is inconsistent with the classical canopy concept, while Oh, and much of the quiet- z the connectivity into corona & heliosphere changes on minute-to-hours time scale! Sun corona is not low-β! (Schrijver and van Ballegooijen, 2005; also Hansteen …) 31 12/11/2007 Photosphere-corona connection Potential field above unipolar network and mixed-polarity intranetwork; side and top view z The “intranetwork field” steals flux from the network, so that z the field geometry is inconsistent with the classical canopy concept. 32 12/11/2007 ‘Incomplete knowledge’ : Having observations of only ¼- 1/3 of the solar surface introduces substantial uncertainties (2nd half of the movie) not seen in a model with perfect knowledge (1st half of the movie). Note the substantial field deflections from the sub-solar point to the photosphere! 33 12/11/2007 Forecast accuracy: wind speeds / base field strength The polarity pattern of Around spot maximum, the heliospheric field is the source strength of forecast accurately the source-surface more than a month into heliospheric field can the future. be forecast accurately only a few days ahead of time, because (a) Not surprising: this active regions evolve pattern is dominated quickly, and (b) active by the largest scales, regions are seen too which evolve slowly. late. 34 12/11/2007 Forecast accuracy:polarity of the IMF The polarity pattern of the heliospheric field is forecast accurately more than a month into the future. Not surprising: this pattern is dominated Correlation coefficient by the largest scales, vs. forecast interval which evolve slowly. 35 12/11/2007 Forecast accuracy: wind speeds / base field strength Around spot maximum, the source strength of the heliospheric field can be forecast rms(t0) accurately only a few days ahead of time, because (a) active regions evolve quickly, and (b) active regions are “seen too late.” 36 12/11/2007 The extended stellar atmosphere 37 12/11/2007 PFSS – MHD modeling and solar-wind models z Cycle maximum: 30-50% of the IMF from ARs, z significantly non-potential ~10-30% of the regions on the surface, z with the wind perturbed by wide-angle CMEs ~15-20% of the time (during non-potential phases of ARs), and z inadequate knowledge of much of the solar surface: z PFSS source-region mapping must fail ~20% of the time.
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