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Register a new userOn the Distinct Periodicities of Sunspot Counts in Flaring and Non-flaring Active Regions
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Stefano Sello
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In a recent work, Kilcik et al. (2017), have detected the temporal and periodic behavior of sunspot counts (SSC) in flaring (i.e. C, M, or X class flares), and non-flaring active regions for the last two solar cycles, covering the period: 1996 - 2016. The main results obtained are: 1) The temporal behavior of monthly means of daily total SSC in flaring and non-flaring active regions are different and these differences are also varying from cycle to cycle; 2) The periodicities detected in SSC of flaring and non-flaring active regions are quite different and these variations are also different from one cycle to another; the highest detected period in the flaring active regions is 113 days, while there are much higher periodicities (327, 312, and 256 days) in non-flaring regions. The detection of typical different periodicities in flaring and non-flaring regions can suggests both important differences and physical interpretation in the magneto-hydrodynamic behavior of the Sun. For this reason in the present paper we show a further periodicity analysis of the sunspot counts in flaring and in non-flaring active regions using the same data source of that used by the above cited authors and applying a powerful wavelet analysis tool which is particularly useful to detect multiscale features of complex unsteady and unevenly sampled time series. In order to futher support the differences and similarities found in the time behavior of SSC in flaring and non-flaring regions, we also computed the behavior of the wavelet entropy, a proper time function which allow us to measure the degree of complexity in the dynamics of the related time series.
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We analyzed temporal and periodic behavior of sunspot counts (SSCs) in flaring (C, M, or X class flares), and non-flaring active regions (ARs) for the almost two solar cycles (1996 through 2016). Our main findings are as follows: i) The temporal variation of monthly means of daily total SSCs in flaring and non-flaring ARs are different and these differences are also varying from cycle to cycle; temporal profile of non-flaring ARs are wider than the flaring ones during the solar cycle 23, while they are almost the same during the current cycle 24. The second peak (second maximum) of flaring ARs are strongly dominate during current cycle 24, while this difference is not such a remarkable during cycle 23. The amplitude of SSCs in the non-flaring ARs are comparable during the first and second peaks (maxima) of the current solar cycle, while the first peak is almost not existent in case of the flaring ARs. ii) Periodic variations observed in SSCs of flaring and non-flaring ARs are quite different in both MTM spectrum and wavelet scalograms and these variations are also different from one cycle to another; the largest detected period in the flaring ARs is 113 days, while there are much higher periodicities (327, 312, and 256 days) in non-flaring ARs. There are no meaningful periodicities in MTM spectrum of flaring ARs exceeding 45 days during solar cycle 24, while a 113 days periodicity detected from flaring ARs of solar cycle 23. For the non-flaring ARs the largest period is 72 days during solar cycle 24, while the largest period is 327 days during current cycle.
The evolution of magnetic helicity has a close relationship with solar eruptions and is of interest as a predictive diagnostic. In this case study, we analyse the evolution of the normalised emergence, shearing and total magnetic helicity components in the case of three flaring and three non-flaring active regions (ARs) using SHARPs (Spaceweather Helioseismic Magnetic Imager Active Region Patches) vector magnetic field data. The evolution of the three magnetic helicity components is analysed with wavelet transforms, revealing significant common periodicities of the normalised emergence, shearing and total helicity fluxes before flares in the flaring ARs. The three non-flaring ARs do not show such common periodic behaviour. This case study suggests that the presence of significant periodicities in the power spectrum of magnetic helicity components could serve as a valuable precursor for flares.
With machine learning entering into the awareness of the heliophysics community, solar flare prediction has become a topic of increased interest. Although machine learning models have advanced with each successive publication, the input data has remained largely fixed on magnetic features. Despite this increased model complexity, results seem to indicate that photospheric magnetic field data alone may not be a wholly sufficient source of data for flare prediction. For the first time we have extended the study of flare prediction to spectral data. In this work, we use Deep Neural Networks to monitor the changes of several features derived from the strong resonant Mg II h&k lines observed by IRIS. The features in descending order of predictive capability are: The triplet emission at 2798.77 $text{AA}$, line core intensity, total continuum emission between the h&k line cores, the k/h ratio, line-width, followed by several other line features such as asymmetry and line center. Regions that are about to flare generate spectra which are distinguishable from non-flaring active region spectra. Our algorithm can correctly identify pre-flare spectra approximately 35 minutes before the start of the flare, with an AUC of 86 % and an accuracy, precision and recall of 80 %. The accuracy and AUC monotonically increases to 90 % and 97 % respectively as we move closer in time to the start of the flare. Our study indicates that spectral data alone can lead to good predictive models and should be considered as an additional source of information alongside photospheric magnetograms.
It is widely assumed that the most probable sites of flare occurrences are the locations of high horizontal magnetic field gradients in the active regions. Instead of magnetograms the present work checks this assumption by using sunspot data, the targeted phenomenon is the pre-flare behaviour of the strong horizontal gradients of the magnetic field at the location of the flare. The empirical basis of the work is the SDD (SOHO/MDI-Debrecen sunspot Data) sunspot catalogue. Case studies of two active regions and five X-flares have been carried out to find possible candidates for pre-flare signatures. It has been found that the following properties of the temporal variations of horizontal magnetic field gradient are promising for flare forecast: the speed of its growth, its maximal value, its decrease after the maximum until the flare and the rate of its fluctuation.
Context. QPPs are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun. Aims. We combine imaging and spectroscopic measurements of available space missions, and investigate the properties of non-damping oscillations at flaring loops. Methods. We used the IRIS to measure the spectrum over a narrow slit. The double-component Gaussian fitting method was used to extract the line profile of Fe XXI 1354.08 A at O I window. The quasi-periodicity of loop oscillations were identified in the Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while a phase shift of about Pi/2 is detected between the Doppler velocity and peak intensity. The amplitudes of Doppler velocity and line width oscillation are about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period of about 155 s is identified in the Doppler velocity and peak intensity of Fe XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are not damped significantly during the observation, it might be linked to the global kink modes of flaring loops. The periodicity at about 155 s is most likely a signature of recurring downflows after chromospheric evaporation along flaring loops. The magnetic field strengths of the flaring loops are estimated to be about 120-170 G using the MHD seismology diagnostics, which are consistent with the magnetic field modeling results using the flux rope insertion method.
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