Living in a Star Sarah Gibson High Altitude Observatory / NCAR

3D real-time astronomy We are observing a stellar system from within What we see may impact us in near-real time Unescapably three-dimensional Fundamentally magnetic Talk outline: –Coupled sun-earth system/space weather –3D models for understanding/predicting solar eruptions Solar eruption (CME)

Weather as we usually think of it

All Weather Originates at the Sun Solar Structure: Core Where the energy is created. Nuclear reactions burn every second about 700 million tons of hydrogen into helium. Radiation Zone Where energy is transported by radiation. Although the photons travel at the speed of light, they bounce so many times through the dense material that they use about a million years to escape the Sun. Convection Zone Energy transported by convection (just like boiling soup) where heat is transported to the photosphere.

The Solar Corona Million Degrees Magnetically Dominated Expands to fill interplanetary space

EIT 195 Angstroms May 2, 1998TRACE 171 Angstroms The Magnetic Sun Magnetic fields organize solar structures, and drive solar dynamics

Solar Activity - Flares

Space Weather - Flares Flares represent transfer of magnetic energy to thermal/radiative energy. Flares affect the ionosphere and radio communication at the Earth. Flares also release energetic particles into space. Flares are not the whole story, though!

Solar Activity - Mass Ejections Not just hot stuff involved in solar dynamics (Relatively) cool/dense “prominence” mass may erupt Coronal mass ejections: CMEs

Space Weather - CMEs CMEs represent transfer of magnetic energy into kinetic energy The interaction of CME and Earth magnetic fields may drive geomagnetic storms CMEs drive shock waves where energetic particles are accelerated CMEs are often associated with flares -- double whammy!

Propagate through Solar System

Impact Earth’s Magnetic Field

Negative Space Weather Impacts Radiation hazards for astronauts Damage to and/or disabling of satellites Communication blackouts Power grid damage Introduction of errors in GPS systems

Frequency of Large Events Between 1978 through May 2005, (which includes the last 3 solar maxima) there were 41 severe storms (DsT < -200) Severe Storm Rates: Activity maximum ~ 4 per year Activity minimum ~ 0.2 per year CME Rates: Activity maximum: ~ 4 per day (avg.) Activity minimum: ~ 0.4 per day (avg.) Expect only a small percentage (~10%) of CMEs to intercept earth and only a small percentage of those will cause severe activity

Magnetic Fields are Key!

(Illing and Hundhausen, 1986) plasma and field are “frozen together” plasma structures trace out field Most importantly - magnetic energy the driver of eruptions understanding the magnetic structure key to understanding what makes the CME go Modeling Magnetic Fields A range of observations suggest a “twisted flux rope” configuration for the CME

Magnetic Flux Ropes What’s a magnetic flux rope? Suggested definition: A set of magnetic field lines that winds about an axial field line Roussev (2003) (after Titov and Demoulin (1999)) After Gibson and Low (1998) Amari et al. (2003) Loosely wound Tightly wound Spheromak-based

Magnetic Flux Ropes: Magnetic Clouds Are there flux ropes in interplanetary space? Widely used as models for magnetic clouds (interplanetary manifestation of CMEs) Lepping et al. (1995) Manchester et al. (2004a; 2004b)

Magnetic Flux Ropes: CMEs Are there flux ropes in the corona during the eruption of a coronal mass ejection (CME)? Also quite well accepted Amari et al., (2003 ) Examples of models where rope forms during eruption Antiochos et al. (1999); Lynch et al. (2004); MacNeice et al. (2004)Tokman and Bellan (2002)

Do flux ropes exist quiescently in the corona prior to the CME, or are they formed in eruption? Controversial! Erupting flux rope model Gibson and Fan (2006) A pre-CME equilibrium coronal magnetic flux rope Can store magnetic energy sufficient to drive a CME Can trigger the CME by its loss of equilibrium (Lin et al. 1998; Amari et al, 2000; 2003, 2004, 2005; Linker et al., 2003; Toeroek and Kliem, 2003; Fan 2005) Equilibrium flux rope model Fan and Gibson(2006) Magnetic Flux Ropes: Pre-CME

Fan and Gibson (2006) Simulation 1: Flux Rope Emerges and Finds Equilibrium

Simulation 2: Loss of Equilibrium and Eruption of Flux Rope Fan (2005) Alternatively, if the rope changes its axis orientation it can “rupture” through the overlying arcade (e.g., Sturrock et al., 2001). This can occur if the twist threshold for the kink instability is crossed.

Simulation 3: Partial Ejection of a Magnetic Flux Rope Gibson and Fan (2006)

Simulation 3: Partial Ejection of a Magnetic Flux Rope Gibson, S. E., and Y. Fan, The partial expulsion of a magnetic flux rope, Astrophys. Journ. Lett., 637L, 65, 2006.

Partially-Ejected Flux Rope: Partial-Mass Eruption CME partial eruption of prominence and cavity: HAO/MLSO Mk4 coronagraph, November 19, 1999 CME partial eruption of prominence and cavity. Isocontours show density; cool, dense prominence mass in brown. Part of the flux rope is carried away, part remains behind. Part of the (prominence) mass is carried away, part remains behind. Magnetic twist (and energy) also remains behind — likely to erupt again.

End state: X-ray cusp over reformed sigmoid with non-erupting prominence below Partially-Ejected Flux Rope: Flares

Partially-ejected flux rope: change in topology

Writhing Motion During Eruption

Partially-Ejected Flux Fope: Forming Tori Writhing plus reconnection -- created toroidal topology Grey field lines -- poloidal axes Red field lines -- many times toroidally winding

Implications for Magnetic Clouds Need to get topology right.

Conclusions "If the sun didn't have a magnetic field, then it would be as boring a star as most astronomers think it is.” (Leighton) “Magnetic fields are to astrophysics what sex is to psychoanalysis” (van de Hulst) We live in the outer atmosphere of a 3D, magnetic star The sun uniquely affects us, but we have unique views (up-close and 3D) of it Magnetic fields are the key to understanding, predicting, and mitigating space weather We need coronal magnetic field observations!

The Sun at different temperatures

Activity Maximum 1980 Activity Minimum year cycle changes in the corona

Solar cycle evolution of corona

Writhing prominence

Reconnected Field Lines Over Surviving Part of the Prominence Mass

Create the Aurora