scholarly journals LOW-POWER SOLAR FLARES OF OPTICAL AND X-RAY WAVELENGTHS FOR SOLAR CYCLES 21–24

2020 ◽  
Vol 6 (3) ◽  
pp. 16-22
Author(s):  
Aleksandr Borovik ◽  
Anton Zhdanov
Keyword(s):  
Solar Activity ◽  
Low Power ◽  
Solar Flares ◽  
Optical Emission ◽  
Flare Activity ◽  
X Rays ◽  
Solar Cycles ◽  
X Ray ◽  
Cycle 24 ◽  
Using Data

Using data obtained in optical and X-ray wavelengths, we have analyzed solar flare activity for cycles 21–24. Over the last three cycles, solar activity is shown to decrease significantly. As compared to solar cycle 21 (the most active over the last 50 years), in cycle 24 2–4-class large optical flares are 4.4 times rarer; 1-class flares, 8.2 times; and S-class small flares, 4.1 times. The number of X-class flares decreased 3.7 times; M-class flares, 3.2 times. This confirms that secular solar activity trends affect peak values of 11-year cycles. It is shown that optical low-power flares can be accompanied by proton fluxes and X-ray bursts of different intensity, including X-class ones. Ranges of small flare emission in soft X-rays largely overlap with emission ranges of flares of high optical classes. We have confirmed that X-ray emission from solar flares appears on average 2 min before the optical emission. The X-ray maximum for small optical flares and 1-class flares occurs approximately 1 min later; for 2–4-class flares, 2 min.

scholarly journals LOW-POWER SOLAR FLARES OF OPTICAL AND X-RAY WAVELENGTHS FOR SOLAR CYCLES 21–24

2020 ◽  
Vol 6 (3) ◽  
pp. 18-25
Author(s):  
Aleksandr Borovik ◽  
Anton Zhdanov
Keyword(s):  
Solar Activity ◽  
Low Power ◽  
Solar Flares ◽  
Optical Emission ◽  
Flare Activity ◽  
X Rays ◽  
Solar Cycles ◽  
X Ray ◽  
Cycle 24 ◽  
Using Data

Using data obtained in optical and X-ray wavelengths, we have analyzed solar flare activity for cycles 21–24. Over the last three cycles, solar activity is shown to decrease significantly. As compared to solar cycle 21 (the most active over the last 50 years), in cycle 24 2–4-class large optical flares are 4.4 times rarer; 1-class flares, 8.2 times; and S-class small flares, 4.1 times. The number of X-class flares decreased 3.7 times; M-class flares, 3.2 times. This confirms that secular solar activity trends affect peak values of 11-year cycles. It is shown that optical low-power flares can be accompanied by proton fluxes and X-ray bursts of different intensity, including X-class ones. Ranges of small flare emission in soft X-rays largely overlap with emission ranges of flares of high optical classes. We have confirmed that X-ray emission from solar flares appears on average 2 min before the optical emission. The X-ray maximum for small optical flares and 1-class flares occurs approximately 1 min later; for 2–4-class flares, 2 min.

scholarly journals Electrons and X-Ray Emission of Solar Flares

1990 ◽  
Vol 142 ◽  
pp. 409-413
Author(s):  
V. G. Kurt
Keyword(s):  
Solar Activity ◽  
Statistical Analysis ◽  
Solar Flare ◽  
Frequency Dependence ◽  
Power Law ◽  
Solar Flares ◽  
X Rays ◽  
Fast Electrons ◽  
X Ray ◽  
Flare Frequency

A statistical analysis of solar flare X-rays and interplanetary particle fluxes, measured onboard VENERA-13, 14 Spacecraft, was performed. The correlation of fluences for different manifestations of solar flares is strong, especially for fast electrons and hard and soft X-ray emissions. Frequency dependence on fluence value ϵi for practically all Kinds of solar flare emission can be described by power law ν (ϵ > ϵO) ∼ ϵ−0.45±0.15 which does not change significantly with solar activity. For different Hα flare importances the values of ϵi were obtained. It is proposed that appearance of certain energy flare frequency is strongly dependent on some scale factor.

scholarly journals Extreme Space Weather Events during the First Cycles of Epochs with Decreased Solar Activity

2021 ◽  
Vol 61 (6) ◽  
pp. 801-809
Author(s):  
V. N. Ishkov
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Flare Activity ◽  
Solar Cycles ◽  
Geomagnetic Index ◽  
Near Earth Space ◽  
Weather Events ◽  
Solar Cyclicity ◽  
Cycle 24 ◽  
Extreme Space Weather Events

Abstract The problem of the distribution of extreme and very strong magnetic storms with intensities (G5, G4) in the first cycles (12 and 24) of epochs of lowered solar activity was considered based on homogeneous series of the geomagnetic index Aa with allowance for the modern scale of the intensity of disturbances in the near-Earth space and the scenario of solar cyclicity. The significant decrease in the number of such events and active solar phenomena in the last cycle may indicate that the sunspot and flare activity in solar cycle 12 was significantly higher than that in cycle 24, but it was significantly lower than in solar cycles of the epoch of increased solar activity.

scholarly journals Statistical Study of North-South Asymmetry during Solar Cycles 21, 22, 23 and 24

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Raj Kumar ◽  
Mahesh Chandra Mathpal ◽  
Bimal Pande ◽  
Seema Pande
Keyword(s):  
Statistical Study ◽  
Flare Activity ◽  
Solar Cycles ◽  
X Ray ◽  
The North ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Class Flare ◽  
South Asymmetry ◽  
Northern And Southern Hemispheres

North-south asymmetry has been a significant aspect exhibited by various solar activity parameters of the Sun. In this work we have statistically analyzed soft X-ray (SXR) flares during the period Jan 1981 to Dec 2016 for four different solar cycles (SCs) covering cycles 21, 22, 23 and 24. We have presented the class wise (B, C, M & X) variation of SXR flares for these SCs. SXR flare activity is lowest in solar cycle 24 as compared to cycles 22 and 23. It is shown that M class activity continuously decreased from SC 21 to 24. X and C class flares show higher activity in SC 22 and 23 as compared to SC 24, whereas B class flare activity is higher for SC 23. We have also studied the north-south (N-S) asymmetry of SXR flares for SCs 21, 22, 23 and 24. Our study revealed that during SCs 21, 22 and 23 the flare activity was more pronounced in the Southern hemisphere. However, the flare activity was equally distributed between the northern and southern hemispheres for SC 24

scholarly journals Statistical Study of North-South Asymmetry during Solar Cycles 21, 22, 23 and 24

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Raj Kumar ◽  
Mahesh Chandra Mathpal ◽  
Bimal Pande ◽  
Seema Pande
Keyword(s):  
Statistical Study ◽  
Flare Activity ◽  
Solar Cycles ◽  
X Ray ◽  
The North ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Class Flare ◽  
South Asymmetry ◽  
Northern And Southern Hemispheres

North-south asymmetry has been a significant aspect exhibited by various solar activity parameters of the Sun. In this work we have statistically analyzed soft X-ray (SXR) flares during the period Jan 1981 to Dec 2016 for four different solar cycles (SCs) covering cycles 21, 22, 23 and 24. We have presented the class wise (B, C, M & X) variation of SXR flares for these SCs. SXR flare activity is lowest in solar cycle 24 as compared to cycles 22 and 23. It is shown that M class activity continuously decreased from SC 21 to 24. X and C class flares show higher activity in SC 22 and 23 as compared to SC 24, whereas B class flare activity is higher for SC 23. We have also studied the north-south (N-S) asymmetry of SXR flares for SCs 21, 22, 23 and 24. Our study revealed that during SCs 21, 22 and 23 the flare activity was more pronounced in the Southern hemisphere. However, the flare activity was equally distributed between the northern and southern hemispheres for SC 24

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

Statistical analysis of soft X-ray solar flares during solar cycles 22, 23, and 24

2021 ◽  
Vol 366 (1) ◽  
Author(s):  
Bo Xiong ◽  
Ting Wang ◽  
Xiaolin Li ◽  
Yunxing Yin
Keyword(s):  
Statistical Analysis ◽  
Solar Flares ◽  
Solar Cycles ◽  
X Ray

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24

2021 ◽  
Vol 55 (2) ◽  
pp. 169-182
Author(s):  
Amrita Prasad ◽  
Soumya Roy ◽  
Koushik Ghosh ◽  
Subhash Chandra Panja ◽  
Sankar Narayan Patra
Keyword(s):  
Solar Flares ◽  
Solar Cycles ◽  
X Ray

scholarly journals Statistical studies of duration of low-power solar flares

2018 ◽  
Vol 4 (2) ◽  
pp. 8-16
Author(s):  
Александр Боровик ◽  
Aleksandr Borovik ◽  
Антон Жданов ◽  
Anton Zhdanov
Keyword(s):  
Low Power ◽  
Solar Flares ◽  
Flare Region ◽  
Statistical Studies ◽  
Time Parameters ◽  
The Mean ◽  
Using Data

This paper is a sequel to papers dealing with time parameters of solar flares in the Hα line. Using data from the international flare patrol for 1972–2010, we have determined the mean duration of flares of different importance and classes of area. We have established that 94.6 % of flares last more than 60 min. The duration of 90 % of flares with min is 2.1–3.3 hrs. In rare cases, flares can last about 12 hrs. The duration of powerful solar flares does not exceed 8.3 hrs. We have found that the duration of solar flares depends on features of their development. Flares with one brilliant point in the flare region have the shortest duration; two-ribbon flares and flares exhibiting several intensity maxima have the longest duration. We have confirmed that the duration of flares increases with increasing classes of area and brightness.

scholarly journals Constraining Soft and Hard X-Ray Irradiation in Ultraluminous X-Ray Sources

2021 ◽  
Vol 922 (2) ◽  
pp. 91
Author(s):  
Yanli Qiu ◽  
Hua Feng
Keyword(s):  
Optical Emission ◽  
Current Data ◽  
Compact Objects ◽  
X Rays ◽  
Optical Counterpart ◽  
X Ray ◽  
Outer Disk ◽  
Stringent Constraint ◽  
Supercritical Accretion ◽  
Key Questions

Abstract Most ultraluminous X-ray sources (ULXs) are argued to be powered by supercritical accretion onto compact objects. One of the key questions regarding these objects is whether or not the hard X-rays are geometrically beamed toward the symmetric axis. We propose testing the scenario using disk irradiation to see how much the outer accretion disk sees the central hard X-rays. We collect a sample of 11 bright ULXs with an identification of a unique optical counterpart, and model their optical fluxes considering two irradiating sources: soft X-rays from the photosphere of the optically thick wind driven by supercritical accretion, and if needed in addition, hard X-rays from the Comptonization component. Our results indicate that the soft X-ray irradiation can account for the optical emission in the majority of ULXs, and the fraction of hard X-rays reprocessed on the outer disk is constrained to be no more than ∼10−2 in general. Such an upper limit is well consistent with the irradiation fraction expected in the case of no beaming. Therefore, no stringent constraint on the beaming effect can be placed according to the current data quality.

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