V. B. Yurchyshyn

Scaling Behavior of Structure Functions of the Longitudinal Magnetic Field in Active Regions on the Sun

In the framework of a refined Kolmogorov hypothesis, the scaling behavior of the Bz-component of the photospheric magnetic field is analyzed and compared with flaring activity in solar active regions. We use Solar and Heliospheric Observatory Michelson Doppler Imager, Huairou (China), and Big Bear measurements of the Bz-component in the photosphere for nine active regions. We show that there is no universal behavior in the scaling of the Bz-structure functions for different active regions. Our previous study has shown that scaling for a given active region is caused by intermittency in the field, (B)(), describing the magnetic energy dissipation. When intermittency is weak, the Bz field behaves as a passive scalar in the turbulent flow, and the energy dissipation is largely determined by the dissipation of kinetic energy in the active regions with low flare productivity. However, when the field (B)() is highly intermittent, the structure functions behave as transverse structure functions of a fully developed turbulent vector field, and the scaling of the energy dissipation is mostly determined by the dissipation of the magnetic energy (active regions with strong flaring productivity). Based on this recent result, we find that the dissipation spectrum of the Bz-component is strongly related to the level of flare productivity in a solar active region. When the flare productivity is high, the corresponding spectrum is less steep. We also find that during the evolution of NOAA Active Region 9393, the Bz dissipation spectrum becomes less steep as the active regions flare activity increases. Our results suggest that the reorganization of the magnetic field at small scales is also relevant to flaring: the relative fraction of small-scale fluctuations of magnetic energy dissipation increases as an active region becomes prone to producing strong flares. Since these small-scale changes seem to begin long before the start of a solar flare, we suggest that the relation between scaling exponents, calculated by using only measurements of the Bz-component, and flare productivity of an active region can be used to monitor and forecast flare activity.

Magnetic Topology in 1998 November 5 Two-Ribbon Flare as Inferred from Ground-based Observations and Linear Force-free Field Modeling

We analyzed the three-dimensional structure of the linear force-free magnetic —eld. A longitudinal magnetogram of Active Region NOAA 8375 has been used as the photospheric boundary condition. The 1998 November 5 2B/M8.4 two-ribbon —are can be explained in the framework of quadrupolar recon- nection theory: the interaction of two closed magnetic loops that have a small spatial angle. The energy derived from soft X-ray telescope (SXT)/Y ohkoh data (3¨6 ) 1030 ergs) is 1 order of magnitude higher than the lower limit of —are energy predicted by Melroses model. The latter estimation was made using the linear force-free extrapolation. It was suggested that, taking into account the nonlinear character of the observed magnetic —eld, we can increase the lower limit of the magnetic energy stored in the studied magnetic con—guration. The revealed magnetic con—guration allows us to understand the observed loca- tion and evolution of the —are ribbons and the additional energy released during the gradual phase of the —are, as well. Besides, reconnection of closed magnetic loops can logically explain the connection between a two-ribbon —are and a giant X-ray post—are arch, which usually is observed after the —are onset. We emphasize that unlike the Kopp and Pneuman con—guration, the model discussed here does not necessarily require destabilization and opening of the magnetic —eld. Subject headings: Sun: —aresSun: magnetic —elds

OSCILLATORY BEHAVIOR IN THE QUIET SUN OBSERVED WITH THE NEW SOLAR TELESCOPE

Surface photometry of the quiet Sun has achieved an angular resolution of 01 with the New Solar Telescope at Big Bear Solar Observatory, revealing that a disproportionate fraction of the oscillatory events appear above observed bright point-like structures. During the tracking of these structures, we noted that the more powerful oscillatory events are cospatial with them, indicating that observed flux tubes may be the source of many observed oscillatory events.