Physics of the relationship of ICMEs to their CME progenitors (Wed AM) Two major efforts are under way to address the structure of CMEs that hit the Earth, and B z in particular, with the long-term goal of better forecasting geomagnetic storms: - AFOSR Basic Research Initiative - NASA LWS Focus Science Topic Physics Session topic: What is the Physics that determines (1) How much of the original CME at the Sun makes up the ICME that hits the Earth? (2) What are the most important physical processes that control this? e.g., Overlying coronal fields. Solar wind draping fields. Background solar wind. Reconnection processes. Internal versus external processes. CME interactions Invited speakers: 1.Chip Manchester (Plenary prior to session) 2.Craig DeForest (Scene-setting)

Scene-setting: Craig DeForest Event study from “cradle to grave” to illustrate all aspects of the problem from low in the corona out to 1 AU Long argument about whether we need the concept of an ICME as distinct from a CME Most CMEs expand self-similarly Most twisting is observed low down during eruption Understanding 3D structure requires multiple lines of view When do CMEs disconnect? Models and data both show flattening of the CME as it propagates Discussion of separation of background solar wind from swept- up solar wind in the data: mass can increase by factor of 4 from onset in both data and models Flux ropes can both form in eruption and precede eruption

Magnetic structure of ICMEs at Earth: Questions Does the photospheric field morphology tell us anything about B z ? Gopal: Yes! Neutral line orientation foretells flux rope orientation 80% of the time Does the coronal field morphology tell us anything about B z ? If so, do we need NLFF fields or will potential fields suffice? Does every eruption launch a flux rope in the lower corona? Assertion: all ICMEs are flux ropes, based on sample of head-on events Hugh: don’t forget flares! EVE data show that the coronal material that launches is cool (lower charge states) If so, does the flux rope maintain integrity or can it be pushed around in the lower corona as it erupts? Untwists? Chip: reconnection can produce twisting in flux rope Gopal: Coronal holes can deflect CMEs. Does the apparent “chaos” we see in CME launches mean that coronal observations low down aren’t useful?

Magnetic structure of ICMEs at Earth: Questions Do the overlying strapping fields affect B in e.g., the tether-cutting model? Bellan/Ha: Lab experiment suggests for moderate strapping fields you get solar-like take-off and acceleration, some evidence that strapping fields were dragged along in eruption Jackson: solar wind B z consistent with leakage of small amount of closed field lines through the source surface How important are solar wind interactions: -Can they change magnetic structure? -Are draping fields as important as the CME itself? -How much “erosion” of the CME occurs? -Does solar wind turbulence matter to the CME? Discussed whether swept-up material has a simpler magnetic structure than following CME: no! See very turbulent B in sheath data, models agree, possible role for Alfven waves.

Magnetic structure of ICMEs at Earth: Questions Do interactions with other CMEs alter the magnetic structure? Gopal: clear examples of CMEs overtaking others, see radio enhancements when this happens Does this affect magnetic structure? Yes: two flux ropes can merge via reconnection, depending on orientation Strong shocks overtaking a weak CME can enhance its geoeffectiveness, more common than thought Colaninno: poster on shock overtaking a CME, no change in magnetic structure Multiple topics were not covered Over 20 people contributed to the discussion.