The variations of the scaling parameters of the structure functions in solar active regions at the pre-flare stage

Abstract

A series of subflares in active region NOAA 9077 (July 2000) and in the activity complex NOAA 0039 + NOAA 0050 were investigated. The structure functions and their characteristics for sets of images of active regions in the hydrogen-alpha line (Hα-line) were calculated. The ranges of the spatial scales of different scaling behavior of the structure functions were revealed. The existence of intermittent turbulence (multi-fractal structure) in active regions of the chromosphere is shown. Peculiarities of the scaling parameters variations of the structure functions at pre-flare stage are investigated. It was found that on average 20 min before a subflare onset considerable deviation of these variations from the mean occurs, which may be of importance for predictions. It was discovered that maximum variations of scaling parameters with an accuracy to 15 min (on average), in a number of cases coincide with variations of the elongated chromospheric structures in an active-region area. We used H α filtergrams obtained with the chromospheric telescope of the Baikal observatory operated by ISTP SD RAS. The telescope is coupled with a Halle birefringent filter with a 0.05 nm bandpass, and a Princeton Instruments 2048 × 2048 pixel CCD camera with 16-bit amplitude resolution.

Multifractal spectrum of solar active region NOAA 10960 in the Hα spectral line

“…The medium is in the state of intermittent turbulence, strongly different from the classic Kolmogorov's turbulence. The difference is observed not only for larger moments of structure functions, but also for smaller ones (Salakhutdinova and Golovko (2004)). Magnetic fields of the solar chromosphere are frozen into plasma.…”

“…Some publications were devoted to research about existence of scale invariant solar magnetic field at a level of photosphere (Abramenko et al (2002), Lawrence et al (1993), Salakhutdinova and Golovko (2004), Stark et al (1997)). They emphasized the following.…”

Fractal properties of active regions

“…To study the dynamic regimes of possible turbulence in solar active regions, a fractal analysis of narrow-band images of the chromosphere and transition layer was carried out in [1][2][3][4]. This approach was motivated by the opportunity of obtaining fundamentally new information based on state-of-theart digital images of the solar atmosphere with high spatial and temporal resolution.…”

“…These techniques include the use of structure * E-mail: golovko@iszf.irk.ru functions [1,13], Detrended Fluctuation Analysis (DFA), which involves the development of a onedimensional random-walk model [14], the Wavelet Transform Modulus Maxima (WTMM) technique, which is based on the wavelet transform [15], the use of moments of the partitioning function, and the micro-canonical technique of multi-fractal segmentation [16][17][18][19].…”

“…In our earlier papers [1][2][3][4], we investigated the fractal properties of the intensities in some spectral lines of the solar chromosphere and of the magnetic fields of solar active regions using structure functions, multi-fractal spectra, and the multi-fractal segmentation. The general scheme for each of these methods is the same.…”