V.I. Abramenko, V.B. Yurchyshyn, H. Wang , T.R. Spirock, P.R. Goode

Big Bear Solar Observatory, NJITCrimean Astrophysical Observatory, Ukraine

Email: avi@bbso.njit.edu

34th Meeting of SPD

16-29 June 2003

INTRODUCTION

Analysis of the non-thermal broadening of soft X-ray spectral lines

in solar flares observed with Yohkoh (Alexander et al. 1998, Harra et al. 2001) showed that the non-thermal velocity begins to rise before the flare onset and peaks often before the Hard X-ray emission.

There are changes in the turbulent state of an active region, leading to the

flare onset, in other words, there is a preflare turbulent phase.

The non-thermal velocity COES X-ray flux

= 11 min - the growth time

of the non-thermal

velocity

INTRODUCTION

Due to the magnetic coupling between the corona and the photosphere (Parker 1979, 1996), preflare turbulent phase may involve the photosphere, too.

Photospheric plasma is in a state of highly developed turbulence, where

the vertical component of the magnetic field, Bz, diffuses in the same way

as a passive scalar in a turbulent flow (Parker 1979, Petrovay and Szakaly 1993).

Thus, we can apply methods of the theory of turbulence

to the longitudinal magnetic field of an active region

measured near the center of the solar disk.

OBSERVATIONAL DATA

from Big Bear Solar

observatory :

Video (upper penal)

and Digital (lower penal)

Magnetograph

Systems

BLongitudinal magnetic field

Pixel sise:

0.6 x 0.6 arcsec

The X9.4 flare The M8.4 flare

The X1.6 flare The M8.7 flare

Measurements covered

the time periods before,

during and after a major

flare with an appropriate

time cadence.

METHOD

A. The degree of intermittency of the magnetic field

An increase in the turbulence implies that the turbulence becomes more intermittent.

Intermittency characterizes a tendency of a turbulent field to concentrate into

widely spaced very intense small-scale features.

Frisch, 1995:

An example of highly

intermittent structure:

METHOD

A. The degree of intermittency of the magnetic field

The degree of intermittency may be estimated by determining

structure functions of high statistical orders:

Non-intermittent

turbulence

Here, q is the order of a statistical moment, r is a separation vector,

x is the current point on a magnetogram. <…> denotes the averaging

over a magnetogram. q is a slope within the inertial range of scales.

The routine was

proposed by

Abramenko et al.

ApJ 577, 2002

METHOD

A. The degree of intermittency of the magnetic field

Non-intermittent

turbulence

Highly intermittent

turbulence

-1

METHOD B. Correlation length of the magnetic energy dissipation field

For the longitudinal component of the photospheric magnetic field

the energy dissipation, per unit mass in a unit of time, can be written (Monin & Yaglom 1975):

For every magnetogram

we calculated the magnetic energy

dissipation structure, x,y.

The correlation length

of these these clusters, , was

determined using the method

of the turbulence theory

(Monin and Yaglom 1975).

RESULTS

CONCLUSIONS

Our results

- support the existence of the preflare turbulent phase in an active region (Alexander et al. 1998, Harra et al. 2001)

- are in agreement with the concept that a solar flare is the collective energy released by an avalanche of reconnection events at small-scale discontinuities

of the magnetic field (the self-organized criticality concept )

(Parker 1987; Longcope and Noonan 2000 ; Charbonneau, McIntosh,

Liu and Bogdan 2001)

- show that statistical properties of a flare-related nonlinear dissipative

process in an active region can be studied by using the photospheric longitudinal magnetic field.

The X9.4 flareThe X9.4 flare

The X1.6 flareThe X1.6 flare

The M8.7 flareThe M8.7 flare

First, we calculated the correlation function:

We have to normalize B(r) by the variance of dissipation:

b(r) = B(r) / B(0)

B(r ) = ((x+r) - )·((x)- )

By integrating b(r), over all scales r, we obtain a correlation

length of the energy dissipation structure:

= b(r) drmax

r

Correlation length of the

magnetic energy dissipation

cluster

The M8.4 flare on Nov 5, 1998 in active region NOAA 8375The M8.4 flare on Nov 5, 1998 in active region NOAA 8375

GOES

H

Flux

c

The M8.7 flare on July 26, 2002 in active region NOAA 0039The M8.7 flare on July 26, 2002 in active region NOAA 0039

H

GOES

c

Flux

The X1.6 flare on October 19, 2001 in active region NOAA The X1.6 flare on October 19, 2001 in active region NOAA 96619661

GOES

H

Flux

c

The X9.4 flare on March 22, 1991 in active region NOAA The X9.4 flare on March 22, 1991 in active region NOAA 65556555

GOES

Flux

c

Table 1.Table 1.

Table 2.Table 2.

1.In all of the cases we found a peak in , which was followed by a peak in . During the time interval between them, , a rapid growth of the soft X-ray and H flux occurred.

2.The peak in beta was preceded by a period of gradual growth of , . Maximum in occurred earlier than the peak of the hard X-ray emission.

3. The maximum of tends to follow or to occur nearly simultaneously (with the accuracy of about 2-5 min) with the maximum of the Hard X-ray emission.

4. Based on limited examples, we conclude that the

time intervals and are inversely proportional to impulsivity and intensity of flares.

CONCLUSIONS