Long-period oscillations of active region patterns: least-squares mapping on second-order curves

Abstract

Context. Active regions (ARs) are the main sources of variety in solar dynamic events. Automated detection and identification tools need to be developed for solar features for a deeper understanding of the solar cycle. Of particular interest here are the dynamical properties of the ARs, regardless of their internal structure and sunspot distribution. Aims. We studied the oscillatory dynamics of two ARs: NOAA 11327 and NOAA 11726 using two different methods of pattern recognition. Methods. We developed a novel method of automated AR border detection and compared it to an existing method for the proofof-concept. The first method uses least-squares fitting on the smallest ellipse enclosing the AR, while the second method applies regression on the convex hull. Results. After processing the data, we found that the axes and the inclination angle of the ellipse and the convex hull oscillate in time. These oscillations are interpreted as the second harmonic of the standing long-period kink oscillations (with the node at the apex) of the magnetic flux tube connecting the two main sunspots of the ARs. We also found that the inclination angles oscillate with characteristic periods of 4.9 h in AR 11726 and 4.6 h in AR 11327. In addition, we discovered that the lengths of the pattern axes in the ARs oscillate with similar characteristic periods and these oscillations might be ascribed to standing global flute modes. Conclusions. In both ARs we have estimated the distribution of the phase speed magnitude along the magnetic tubes (along the two main spots) by interpreting the obtained oscillation of the inclination angle as the standing second harmonic kink mode. After comparing the obtained results for fast and slow kink modes, we conclude that both of these modes are good candidates to explain the observed oscillations of the AR inclination angles, as in the high plasma β regime the phase speeds of these modes are comparable and on the order of the Alfvén speed. Based on the properties of the observed oscillations, we detected the appropriate depth of the sunspot patterns, which coincides with estimations made by helioseismic methods. The latter analysis can be used as a basis for developing a magneto-seismological tool for ARs.

Case study on the identification and classification of small-scale flow patterns in flaring active region

“…An example case study of such oscillations is discussed in Philishvili et al (2017), where oscillatory flows in the active region AR11429 are interpreted as standing longitudinal (acoustic) modes with periods within the range of 116 − 147 sec. The nature of these oscillations drastically differs from those with long periods (> 1 hour) reported by Dumbadze et al (2017) and references therein. As to the aperiodic motions of the observed intensity blobs in the same active region (AR11429), these are the main objective of the present study.…”

Astronomical Research and Outreach in Georgia

“…Dynamics of active regions on the Sun during solar flares and eruptions are studied and long-period oscillations are revieled (Dumbadze et al 2017). Spectrosopic inversions of Ca line during various classes of solar flares are investigated (Kuridze et al 2017).…”

Long period fluctuations of solar active regions

“…The ARs show complex morphology and dynamics that determine the different types of waves and oscillatory motions. The study of these oscillations can be divided into some branches: umbral chromospheric oscillations with a typical period of three minutes (Centeno et al, 2006, Chorley et al, 2010; umbral photospheric oscillations with a typical period of five minutes (Shergelashvili & Poedts, 2005, Thomas et al, 1984; long-period oscillations with a typical period of several hours (Dumbadze et al, 2017, Efremov et al, 2007; and ultra-long-period oscillations of sunspot umbrae, with typical periods of several days (Gopasyuk, 2004, Khutsishvili et al, 1998.…”