Solar Soft X-ray Flares Research Articles

The Periodic and Temporal Behaviors of Solar X-Ray Flares in Solar Cycles 23 and 24

Abstract The recent solar cycles 23 and 24 are thought to be unusually quiet with more prolonged periods. Both sunspot groups and solar soft X-ray (SXR) flares show a decline in numbers comparable to cycles 21 and 22. In order to understand the periodic variations and distributions of solar flares with the sunspot group numbers in these cycles, this study investigates the periodicities and distributions of the solar SXR flares, 36354 in total (B (13351) 36.7%, C (20699) 56.9%, M (2141) 5.9%, and X (163) 0.45%) between 1996 July and 2016 December. The continuous wavelet transforms and cross-correlation methods were used to carry out the study. First, we found that the B- class flare number is asynchronous and negatively correlated with the sunspot group numbers. The flare class exhibits deviation when sunspot group numbers rise or fall around 100. The other class flares are in phase, synchronous with the sunspot group numbers. The C-class flares show the highest level of correlation of 0.868 with sunspot group numbers. A different number of short and intermediate periodicities was also noticed among the flare classes. Notable 256-day periodicity is found for B flares, 7, 64, and 300 days for C, 32, 64, and 256 days for M flares, and 40, 32, and 25 days for X flares. The difference in periodic variations of the flare classes could be attributed to the magnetic flux system of sunspot groups producing them.

On the Frequency Distributions of Solar Soft X-ray Flares

By giving three different definitions of peak flux(original peak flux, corrected peak flux, and scaled peak flux), we analyze the frequency distributions of 14057 flares recorded by GOES from 2000 to 2005. We find a significant result that the frequency distribution of the scaled peak flux for all the sample flares can be approximated by a perfect power-law function with an index of 2.18, without any usually deviating from the power-law at the lower fluxes.

Integral energy spectra of solar soft x-ray flares in the three solar activity cycles (1972-2001)

The flare energy distribution of ultraviolet Ceti-type stars has a power-law spectrum $N \propto E^{-b}$ . Solar optical flares have an identical power energy spectrum with $b \approx 0.80$ . In a ...

Temporal aspects and frequency distributions of solar soft X-ray flares

A statistical analysis of almost 50 000 soft X-ray (SXR) flares observed by GOES during the period 1976–2000 is presented. On the basis of this extensive data set, statistics on temporal properties of soft X-ray flares, such as duration, rise and decay times with regard to the SXR flare classes is presented. Correlations among distinct flare parameters, i.e. SXR peak flux, fluence and characteristic times, and frequency distributions of flare occurrence as function of the peak flux, the fluence and the duration are derived. We discuss the results of the analysis with respect to statistical flare models, the idea of coronal heating by nanoflares, and elaborate on implications of the obtained results on the Neupert effect in solar flares.

Association between solar soft X-ray flares and microwave bursts: AAnS 34/2 (1993)263–269

The statistical analysis of the appropriate physical parameters of solar soft X-ray (SXR) flares and microwave bursts originating in four larger active regions (Boulder Nos. 5395, 5629, 5669 and 5680) in 1989 shows that their correlation coefficient R reach 0.9≤R1. This fact indicates that there is a close association between SXR flares and microwave bursts.Such result can be interpreted by the physical process that a strong enough nonthermal electron beam injected downward from the microwave source (at the top of a flare loop) into the chromosphere is able to cause the chromospheric evaporation due to collision heating, the evaporated chromospheric plasma with superhot temperature Te(≈107K) moves upwards along the flare loop and emits SXR radiation. As the flare loop is filled with superhot plasma, the SXR emission reaches the peak flux. Thus the peak flux of SXR emission appears often later than that of microwave burst.

On the rate of energy input in thermal solar flares

The rise phases of solar soft X-ray flares observed by X-ray crystal spectrometers on P78-1 are discussed in terms of the rate of change of X-ray flux as a function of time. It is shown that the flux increases exponentially over most of the rise time. The e-folding time (tau) has a cutoff at approximately 13 s. Soft X-ray flares with smaller values of tau are not observed. It is suggested that this phenomenon is due to the ability of the solar atmosphere to absorb the input energy and convert it into a typical soft X-ray flare, when the value of tau is greater than about 13 s. For energy input rates with tau greater than about 13 s, the temperature attained by the plasma is typically around 2 x 10 to the 7th K, but for values of tau less than 13 s, the gas is heated to much higher temperatures (about 10 to the 8th K), producing a certain class of hard X-ray flares.

Iron-Line Emission during Solar Flares

view Abstract Citations (41) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Iron-Line Emission during Solar Flares Doschek, G. A. ; Meekins, J. F. ; Kreplin, R. W. ; Chubb, T. A. ; Friedman, H. Abstract Iron-line emission 1.9 A recorded by NRL Bragg crystal spectrometers on 080-6 during intense solar soft X-ray flares is discussed. Individual emission features are resolved in second order, and variability in emission from Fe xxv relative to inner-shell emission from lower ionization stages is considered. A feature at 1.932 A is attributed to radiation from Fe ii in the photosphere. In the region of the secondorder iron spectra, the two fine-structure components of the first excited P state of hydrogenic argon are resolved. Publication: The Astrophysical Journal Pub Date: December 1971 DOI: 10.1086/151243 Bibcode: 1971ApJ...170..573D full text sources ADS |