Physics of the relationship of ICMEs - PowerPoint Presentation

Slide1

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

Session topic:

W

hat

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:

Chip

Manchester

(

P

lenary

prior to

session)

Craig

D

eForest

(Scene-setting)Slide2

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 eruptionSlide3

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?Slide4

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:

C

an

they change magnetic

structure?

A

re

draping fields as important as the CME

itself?

H

ow

much “erosion” of the CME

occurs?

D

oes

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.Slide5

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.