SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

““Reconnection along a streamer Reconnection along a streamer Current Sheet induced by Current Sheet induced by

a CME expansion”a CME expansion”

A. Bemporad1, G. Poletto1, F. Landini2, M. Romoli2

1INAF – Arcetri Astrophysical Observatory2University of Florence, Astronomy Department

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad The January 10-11, 2005 CME

(LASCO/C2 images)

(LA

SC

O/C

2 di

ffer

ence

mov

ie)

Before the event:• Streamer complex in the West limbThe event:• CME first appear.: 10/12, 18:36 UT• Slow CME: v(20 Rʘ)=320 km/s• Accelerating: a ~ 4.5 m/s2

During/after the event:• Outflows along two lateral streamers

UVCS slit UVCS slit UVCS slit

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

Outline

• Coronal background magnetic configuration

• LASCO data: post-CME evolution of a streamer CS

• UVCS data: evolution of CS physical parameters during reconnection

• Conclusions

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

(from http://ccmc.gsfc.nasa.gov/ )

The magnetic configuration

East limb West limb

CME

outflow

outflow

• On December 10-11 a system of ARs is crossing the West limb (GOES/SXI)• Photospheric fields show a quadrupolar configura-tion at the West limb• Visible also in extrapolated magnetic fields (PFSS)

Outflows along streamers possibily induced by the CME propagation.

…through which physical processes?

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad Streamer CS reconnection

(from Zhang, Wang & Hu, ApJ 2006)

• Some CME models (as the magnetic breakout model by Antiochos, Lynch, MacNeice et al.) requires a quadru-polar magnetic configuration.• The two CS reconnection model (Zhang, Wang, Hu) considers a flux rope coexisting with two CS, a vertical one below it and a transverse one above it.

(from Barta, Vrsnak & Karlicky, 2007)

• Elongated CS becomes unstable via CS tearing

The CME propagation may induce reconnection in the lateral streamer CS → outflows!

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad CS seen in LASCO

(from M. Aschwanden, Springer 2004)Basic 2D models for magnetic reconnection:1) Sweet-Parker: , SLOW; 2) Petschek: , FAST (3 orders of mag. faster)

)(/)(2/tan)(/)(/ innoutninnoutnvvvvMvv eeeeoutinAininoutoutinin

For both models:

By measuring densities and geometrical propertiesof CSs from WL the rec. rate Min can be estimated

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

2) From LASCO/C2 images we measured various CS geometrical properties

The CS reconnection rate

down

up

1) From daily LASCO/C2 pB images we computed densities ne along different radials inside and outside coronal structures → average ne(in) / ne(out) ~ 2

What happened at earlier times?

• At earlier times CS reconnection is Petscheck-tipe with• Reconnection rate decreases with time; reconn. region elongates towards a Sweet-Parker-tipe.

1tan inM

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“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad UVCS observations

UVCS slit

Slit center: 35°S (latitude interval: 3°N – 64°S) Spatial resolution: ~ 3·104 kmTime interval: 10/12, 08:29 → 11/12, 07:33 UT (23 hours)Time resolution: 2 minDetected spectral lines: Ly-, Ly- and lines from OVI, SiXII, AlXI ions. • SiXII and AlXI lines due only to collisional ex. →• OVI and H lines due both to radiative and collisional excitation → (Doppler dimming)

),,(, 22 LnTInI eelineeline

),,,(,)(,)( 2 LnTvInradInradI eerlineelineeline

• Line intensities show mainly the south- ward streamer: apparently no significant intensity variations.

Slit center

• Average subtracted line intensities reveal a much more complicate evolution

What is their interpretation?

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

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“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad UV line intensity evolution

CME front

CME core?

Two convergingfeatures

From OVI line intensity we identify:1) CME front 2) CME core (?) 3) Two converging features inside the southward streamer

UV

CS

slit

field

of

view

Interpretation: during the CME transit in the UVCS field of view we observe inflows towards the reconnecting streamer CS

First direct observation in UVCS!

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

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“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad CS properties at UVCS

From the inclination of OVI converging features: vin = 3 – 4 km/s

INFLOW INFLOW

CS thickness

From the width of the post-reconne-ction feature = 105 km

From the h vs t curve of the X point extrapolated at UVCS vout= 16 km/s

• The CS reconnection rate is

111043 inCS v m2s-1

• The CS magnetic diffusivity is

25.019.0/ outin vvM

For comparison: 1262/11312122/39 102.3106.1;110 smnsmsmT eancl

Related to turbulence in the tearing CS (hyperresistivity)? (J. Lin 2007)anclCS

,

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad CS physical parameters

From UV line intensities we estimatene using the ratio technique: from whereeradcol nOVIIOVIIR )(/)(

),,,( LvnTRR outee

Knowing vout, L, Robs we computedne = ne(Te) curves.

Given ne(Te), we derive Te that better reproduce the observed

I(SIXII) and I(AlXI)

ne (cm-3) Te (K)

Corona 4·106 1.2·106

Pre-rec 6.5·106 1.8·106

Rec 7.2·106 2.2·106

Main 7.6·106 2.5·106

Pre

-re

c

Re

c

Ma

in

OVI

10·AlxiSixii

OVI

AlxiSixii

• Density in pre-reconnection CS is ~ 2 larger than in the surrounding corona • CS density increases with time by a factor ~2.6 during reconnection• Temperature increases by ~50%

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

Summary

• The December 10, 2005 CME occurred in a quadrupolar background corona: outflows are associated along north- and southward streamers.

• We interpreted outflows as a consequence of reconnection along the streamer CS induced by the CME.

• From LASCO data: evolution of reconnection rate, transition from Petschek to Sweet-Parker regime.

• From UVCS data: first detection of magnetic reconnection in UVCS; CS diffusivity much larger than expected (hyperresistivity?).

• During reconnection the CS to corona density contrast increases by ~2.6, temperature increases by 50%.

SOHO-20 “Transient events on the Sun andIn the Heliosphere” – August 28, 2008, GhentSOHO-20 “Transient events on the Sun and

In the Heliosphere” – August 28, 2008, Ghent

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

“Reconnection along a streamer CS induced by a CME expansion” – A. Bemporad

This interpretation is confirmed by extrapolatingLASCO h vs t curves down to UVCS altitudes