"Межпятенные микроволновые источники"
Radio-observations allow us to reveal the long-lived (2–5 days) intersunspot sources (ISS), whose centers are often located above the neutral line of the magnetic field separating leading and following parts of a whole active region (the first type of ISS (ISS-I)) or above the neutral line separating magnetic polarities into complex sunspots (the second type of ISS (ISS-II)). ISS-I and ISS-II demonstrate gyrocyclotron or gyrosynchrotron spectra, more dynamic pre-flare behavior than ISS-III with bremsstrahlung in the quiet active regions. The qualitative model of “three magnetic fluxes” explaining the origin of accelerated particles in ISS and their long-lasting existence and spectral features is proposed.
In this paper, we describe the spatial structure and time characteristics of the microwave emission of active region AR 12673 during the rapid changes in the magnetic flux on September 4, 2017 using Nobeyama Radioheliograph observations. It is shown that the microwave emission of the active region exhibits extremely dynamic behavior of its spatial brightness distribution as well as a very non-stationary, impulsive, emission from the specific position where М1.2 class flare happens later. It is shown from comparison of microwave and EUV maps that the strong non-stationary microwave flare happens at the position where a system of intersecting compact EUV loops appears.
Results: The first M-class flare occurred on September 4, 2017 at 05:36-06:05 UT. We found that 100-minute oscillations were observed on September 4 during a few hours before M1.2 flare. At the same time, there were no noticeable oscillations on September 3. The observed effect is similar to the previously detected effect for 3-minute and 10-minute oscillations, namely, before radio burst there was increase of the power of oscillations. The effect can be interpreted as a relationship between MHD waves propagating along the magnetic flux tube of sunspot and beginning of the flares.
Methods: We used the Nobeyama Radioheliograph (NoRH) daily observations. The radio maps of the whole solar disk were synthesized in non-standard mode with a cadence of ten seconds and ten seconds averaging. We computed the time series of maximum brightness temperature and total flux over selected field-of-view (FOV) and used spectral wavelet analysis of the time series.
Context: We continue research the oscillation parameters in solar active regions (ARs) in connection with their flare activity.
Aims: The aim of this paper is to study oscillations of microwave emission of AR NOAA 12673 before first M-class flare in September 2017.
Radiation of microwave sources above sunspots at a frequency of 17 GHz gives information on parameters of solar plasma in the regions of magnetic field B ~ 200 G in the transition region between chromosphere and corona. Short period (with periods in several minutes) oscillations of microwave emission of solar active regions (ARs) reflect wave processes in the magnetic flux tubes of the sunspots. We present an analysis of short period oscillations of microwave emission of AR NOAA 12242 before two flares on December 17, 2014. The analysis is based on solar radio images, obtained using the Nobeyama Radio Heliograph. The radio maps of the whole solar disk were synthesized in non-standard mode with a cadence of 10s and 10s averaging. The spatial resolution of the radio maps is about 10ʹ–15ʺ. We found that about 40–50 min before the M1.5 flare (01:00 UT) the power of about ten-minute oscillations is increased. At the same day the power of ten-minute oscillations increased about 60 min before the M8.7 flare (04:42 UT). The observed effect is similar to the previously detected independently by two authors effect for 3-minute oscillations, namely, for 15–20 min before radio burst there was increase of the power of 3-minute oscillations. The effect can be interpreted as a relationship between MHD waves, propagating along the magnetic flux tube of sunspot, and beginning of the flare.
We define, calculate and analyze irregularity indices λISSN of daily series of the International Sunspot Number ISSN as a function of increasing smoothing from N = 162 to 648 days. The irregularity indices λ are computed within 4-year sliding windows, with embedding dimensions m = 1 and 2. λISSN displays Schwabe cycles with ~5.5-year variations ("half Schwabe variations" HSV). The mean of λISSN undergoes a downward step and the amplitude of its variations strongly decreases around 1930. We observe changes in the ratio R of the mean amplitude of λ peaks at solar cycle minima with respect to peaks at solar maxima as a function of date, embedding dimension and, importantly, smoothing parameter N. We identify two distinct regimes, called Q1 and Q2, defined mainly by the evolution of R as a function of N: Q1, with increasing HSV behavior and R value as N is increased, occurs before 1915–1930; and Q2, with decreasing HSV behavior and R value as N is increased, occurs after ~1975. We attempt to account for these observations with an autoregressive (order 1) model with Poissonian noise and a mean modulated by two sine waves of periods T1 and T2 (T1 = 11 years, and intermediate T2 is tuned to mimic quasi-biennial oscillations QBO). The model can generate both Q1 and Q2 regimes. When m = 1, HSV appears in the absence of T2 variations. When m = 2, Q1 occurs when T2 variations are present, whereas Q2 occurs when T2 variations are suppressed. We propose that the HSV behavior of the irregularity index of ISSN may be linked to the presence of strong QBO before 1915–1930, a transition and their disappearance around 1975, corresponding to a change in regime of solar activity.
We have recently introduced an irregularity index λ for daily sunspot numbers ISSN, derived from the well-known Lyapunov exponent, that attempts to reflect irregularities in the chaotic process of solar activity. Like the Lyapunov exponent, the irregularity index is computed from the data for different embedding dimensions m (2-32). When m = 2, λ maxima match ISSN maxima of the Schwabe cycle, whereas when m = 3, λ maxima occur at ISSN minima. The patterns of λ as a function of time remain similar from m = 4 to 16: the dynamics of λ change between 1915 and 1935, separating two regimes, one from 1850 to 1915 and the other from 1935 to 2005, in which λ retains a similar structure. A sharp peak occurs at the time of the ISSN minimum between cycles 23 and 24, possibly a precursor of unusual cycle 24 and maybe a new regime change. λ is significantly smaller during the ascending and descending phases of solar cycles. Differences in values of the irregularity index observed for different cycles reflect differences in correlations in sunspot series at a scale much less than the 4-yr sliding window used in computing them; the lifetime of sunspots provides a source of correlation at that time scale. The burst of short-term irregularity evidenced by the strong l-peak at the minimum of cycle 23-24 would reflect a decrease in correlation at the time scale of several days rather than a change in the shape of the cycle.