Flare Activity of the Sun and Variations in its UV Emission During Cycle 24

Abstract

Abstract. The flare activity and the ultraviolet emission of the sun during its 24-th cycle are analysed. As compared to cycles 21-23, where the most powerful flares were observed during the decay phase, in cycle 24 the greatest number of powerful flares (>X2.7) occurred in the rising phase and at the maximum with the exception of the two largest flares of cycle 24 X9.3 and X8.2 in September 2017. We showed that regression fits of solar UV indices to the overall radiation level from the sun are substantially different for cycle 24 compared to cycles 21-23. It is found that for the flare of August 9, 2011 (SDO and GOES-15 observations), the flare propagates in a direction from the upper corona to the transition region and to the chromosphere. A study of the N-S asymmetry in the distribution of the flares in cycle 24 reveals a strong predominance of flares in the N-hemisphere in 2011 and in the S-hemisphere in 2014. It is also found that during cycles 23 and 24, the delays in the onset of proton events relative to the onset of the flares that cause them have a distribution with a distinct maximum corresponding to a delay of 2 hours for protons with energies >10 MeV, as well as for those with energies >100 MeV.

North-South Distribution and Asymmetry of GOES SXR Flares during Solar Cycle 24

“…It appears from Figure 1 that the activity peak in 2011 was due to NH excess activity (number of SXR flares in NH is higher than the SH), whereas the second peak in 2014 was due to SH excess activity (number of SXR flares in SH is higher than NH). Recently, Bruevich and Yakunina (2017) have studied the N-S distribution of large (≥ M1) solar flares in solar cycle 24. They have also found a strong predominance of flares in the NH in 2011 and in the SH in 2014.…”

“…The solar N-S asymmetry is considered as one of the most interesting properties of solar activity and studied in many manifestations of solar activity such as flares, prominences, sunspots, filaments, etc. (Howard 1974;Roy 1977;Yadav et al 1980;Swinson et al 1986;Ballester 1987, 1990;Carbonell et al 1993;Oliver and Ballester 1994;Joshi 1995;Javaraiah and Gokhale 1997;Verma 2000;Ataç and Özgüç 2001;Temmer et al 2002;Joshi and Joshi 2004;Ballester et al 2005;Javaraiah and Ulrich 2006;Zaatri et al 2006;Temmer et al 2006;Carbonell et al 2007;Li et al 2009a,b;Gigolashvili et al 2011;Chowdhury et al 2013;Chandra et al 2013;Obridko et al 2014;Joshi et al 2015;Zhang et al 2015;Javaraiah 2016;Bruevich and Yakunina 2017;Deng et al 2017;Gurgenashvili et al 2017;Xie et al 2018;El-Borie et al 2019;Li et al 2019).…”

Powerful Solar Flares in September 2017. Comparison with the Largest Flares in Cycle 24

“…The time of onset and maximum of a flare in the 30.4 nm and 9.4 nm lines and in the interval 0.1-0.8 nmAs opposed to cycles 21-23, weak flare activity was observed in cycle 24: a total of 133 X-class >M5.0 flares, of which 49 were X-class >X1. The largest number of these flares was observed near the first and second maxima of the cycle (of the 10 largest flares, only two took place on the falling branch: these are the largest flares in cycle 24 which occurred on September 6 and September 10, 2017)[5,6]. By comparison with cycles 21-23, the largest X-class x-ray flares >X15 were observed on the falling branches of cycles 21 and 23, as well as in the maximum of cycle 22[7][8][9].…”

Magnetic Helicity Flux across Solar Active Region Photospheres: II. Association of Hemispheric Sign Preference with Flaring Activity during Solar Cycle 24

“…We explore the north-south hemispheric asymmetry of solar activity during solar cycle 24. The north-south asymmetry has been studied with respect to various solar activity indices for cycle 24, including the total number of flares for a given GOES class (e.g., Bruevich & Yakunina 2017;Joshi & Chandra 2019), and sunspot areas (e.g., Li et al 2019). The scatter plots in Figure 5 are used to examine any notable asymmetry in the distributions of the HSP, the average Φ and the average F idx between the HRs in northern (stars) and southern (circles) hemispheres.…”