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Magnetic Reconnection Across the HCS

Magnetic Reconnection Across the HCS. Mark Moldwin UM and Megan Cartwright UC-Berkeley. Isradynamics April 2010. With thanks to Mark Linton at NRL Linton and Moldwin, JGR, 2009. Cambridge Univ Press, 2009. Goal of Talk.

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Magnetic Reconnection Across the HCS

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  1. Magnetic Reconnection Across the HCS Mark Moldwin UM and Megan Cartwright UC-Berkeley Isradynamics April 2010 With thanks to Mark Linton at NRL Linton and Moldwin, JGR, 2009 Cambridge Univ Press, 2009

  2. Goal of Talk • Flux Tubes and Current Sheets are the “quanta”-structures of plasma physics • These are universal structures that span all scales and tell us about universal processes that create them. • Reconnection happens at thin current sheets including in the Solar Wind

  3. Universal Magnetic Structures • Magnetized plasmas form a FINITE set of structures seen over wide range of scales • For this talk, I posit that there are only three groups – flux tubes, cavities, current sheets. • What does this tell us about magnetized plasmas? Why only three?

  4. Examples of Three Groups • Cavities: Magnetospheres, heliospheres • Current Sheets: Heliospheric Current Sheet, magnetospheric current sheets • Flux Tubes: the smallest fundamental plasma structure

  5. What is a Flux Tube? • Ideal MHD’s frozen-in flux condition • Equation of motion has the pressure gradient and Lorentz term on RHS • Magnetic force has two components - magnetic pressure term acting perpendicular to field and a tension term along field. • Can think of flux tubes as mutually repulsive rubber bands • They are the “elementary particles” of MHD

  6. What are Flux Ropes, and what do they tell us about RXN? • Field aligned currents cause the field to twist – hence the term “rope” • Some are created by magnetic reconnection and can have sharp and clear boundaries. Due to topology change allow exchange of Energy/momentum/mass between flux tubes

  7. Flux Ropes • The center of the rope is the core field • Edges of rope often have current sheets to separate it from surrounding plasma

  8. Coronal Mass Ejections are the primary driver of major Geomagnetic storms Their structure determines their geomagnetic effectiveness The are magnetic flux ropes created by magnetic reconnection

  9. CME 3D Structure

  10. Formation of Coronal Mass Ejection • Breakout CME: reconnection in front of CME allows it to erupt • Most models: reconnection behind CME, cuts fieldlines connecting it to the Sun, and causes flaring and particle acceleration • In some models, reconnection below CME is main driver of eruption MacNeice et al. 2004

  11. Observation of Coronal Mass Ejection • Eruption from Corona of magnetic field and plasma • Magnetic field bulges out, then pinches together behind eruption, leading to post-CME reconnection • Coronograph and in-situ measurements both consistent with twisted flux rope magnetic structure LASCO C2 Coronagraph

  12. 1 2 4 3 How to transform CMEs into ICMEs? The majority of CMEs has a clearly discernible multi-part structure. But most ICMEs exhibit a very different two-part structure: a shock-compressed sheath layer followed by a rather homogeneous low beta plasma, with several other characteristic signatures. ? ? From Schwenn

  13. Bidirectional electron event occurring over same time period as Moldwin et al., [1995] small-scale (duration ~ 4 hr) flux rope.

  14. Reconnection across HCS • Gosling, Phan et al. have presented numerous observations of signatures in the solar wind consistent with classic Petschek-like reconnection jets

  15. Multiple Reconnection across HCS? • New class of flux ropes discovered in solar wind (Moldwin et al., 2001) • Scale order of an hour (Cartwright and Moldwin, 2008; 2010)

  16. Double Helix Nebule • IR image • Near center of Milky Way • About 80 LY long Morris et al. Nature, 2007

  17. Take Home Message • Flux Ropes are formed by reconnection or strong shearing of magnetic fields • Observed throughout space • Guide field is often present – creates twisted flux rope, with twist field wrapped around an axis of guide field • Play significant role in energy, mass, and momentum transfer in Sun-Earth relationship (CMEs and storms, role of RXN across HCS) • Universal Magnetic Structure is due to formation by magnetic reconnection. • Want to understand Heliosphere – need to understand magnetic reconnection

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