Observations on Current Sheet and Magnetic

Reconnection in Solar Flares

Haimin Wang and

Jiong QiuBBSO/NJIT

Background

Magnetic reconnection at low corona is the drive of flares. Recent observations have provided indirect evidence of magnetic reconnection as depicted by the standard (eruptive) flare model.

The rate of magnetic reconnection may be derived from flare observations using sound assumptions and approximations.

Current sheet is the most important structure in the magnetic reconnection process.

How do scientists “observe” magnetic Reconnection and Current Sheet, the driver of solar flares?

“observe” magnetic reconnection in a standard flare configuration

(Courtesy of Terry Forbes )

flare loop arcade and two ribbons in EUV

TRACE Fe 19.5nm

two-ribbon flare observed in different wavelengths

Yohkoh SoHO RHESSILoop-top hard X-ray source (Masuda et al. 1994) and super-hot source (Tsuneta 1997)

High-temperature structure indicative of current sheet (Ko et al. 2003)

Hard X-ray sources at two ends of RCS (Sui et al. 2003).

High temperature ridges along outer loops (Tsuneta 1996)

Evidence of chromospheric evaporation (Czaykowska et al. 1999)

Soft X-ray jets (Shimizu 1994, 1995)

Signatures of magnetic reconnection and Current sheet in the corona: satellite observations

Here put a couple of figures from satelliteObservations.

Masuda flare: hard X-ray source above the loop top(Masuda et al. 1994)

YOHKOH

soft X-ray jet as indication ofreconnection outflow

(Shimizu 1994)

soft X-ray high temperature ridges along outer or newly formed loops

(Tsuneta 1996)

YOHKOH

high temperature structure indicative of current sheet (Ko et al. 2003)

X-ray sources at two ends of current sheet (Sui et al. 2003)

SOHO

RHESSI

The rate of magnetic reconnection

can be inferred from some sorts of

observations using sound

assumptions and approximations.

Magnetic reconnection

is the driver of

solar flares.

Magnetic reconnection rate

is deduced by measuring

expansion of flare ribbons

across magnetic fields.

E field

corona

surface

Physical approach : Forbes & Lin (2000)

Ec: electric field along the reconnecting current sheet (RCS) at the corona

V11

l

M1.0 flare on 2000 September 12

Ribbon 1

Ribbon 2

electric field(V/cm)

voltage drop (Mx/s)

magnetic reconnection rate and flare emission

11 12 13 14 hr

.8

.6

.4

.2

.0

4

3

2

1

0

flare soft X-ray emission rate

E field (V/cm)

flux rate(1e+18 Mx/s)

X1.6 flare on 2001 October 19

Electric field(v/cm) Voltage drop

(Mx/s)

Ribbon 1

Ribbon 2

flux rate (1e+18 Mx/s)

16:20 16:30 16:40 16:50 17:00

E field (V/cm)

flare microwave emission at 10 GHz

6

4

2

0

7.5

5.0

2.5

0.0

Magnetic reconnection rate and flare non-thermal emission

rate of total magnetic

flux reconnected

rate of total magnetic

flux reconnected

E field

E field

flare

flare

flux rate

flux rate E field

E field

flare

flareEither way, it

evolves along with

flare high-energy

emission.

two ways to measure

the magnetic

reconnection rate 11 12 13

14

16:10 16:20 16:30 16:40 16:50 17:00

event 1

event 27.5

5.0

2.5

0.0

0.8

0.4

0.0

They are all driven

magnetically.

Coronal mass ejections

are often accompanied by

filament eruptions and flares.

correlation

between

mass flight

and

flare emission

(Zhang et al. 2001)

CME

flare

In some flare-CME events, acceleration of CMEs and magnetic reconnection that drives flares are closely related.

(Lin et al. 2004)

CME

filament

two-ribbon flare

A schematic flux rope model for CME and flare

mass acceleratio

n

magnetic reconnection

flare emission

Strong Correlation Between Magnetic Reconnection Rate and Filament Acceleration

(Jing et al., 2004, Ap.J. to be submitted)

Weaker Correlation Between Magnetic Reconnection Rate and CME Acceleration (Jing et al., 2004, Ap.J. to be submitted)

The derived magnetic reconnection rate is temporally correlated with flare non-thermal emission and mass acceleration of core flux rope ejection.

SUMMARY

Indirect Evidence of Current Sheets and Magnetic Reconnection

• High temperature region in Helmet Structure

• Plasma outflow above flare loop• Loop top HXR source • Organized separation of flare ribbons