Super-active regions in solar cycle 24

AbstractComparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. So far, there have been only five SARs and 45 X class flares. The monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. In this contribution, we present new studies on SARs in Cycle 24. The SARs in the current cycle have relatively smaller flare index (Iflare) and composite vector field index (Icom) comparing with the SARs in cycles 22 and 23. There is a clearly linear relationship between Iflare and Icom. The emphasis of this contribution is put on the similarity and different behaviors of vector magnetic fields of the SARs in the current solar cycle and the previous ones. We try to get a satisfactory account for the general characteristics and relatively lower level of solar flare activity in Cycle 24.

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Regression Analysis of Sunspot Numbers for the Solar Cycle 24 in Comparison to Previous Three Cycles

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v4i2.2030 ◽

2014 ◽

Vol 4 (2) ◽

pp. 477-483

Author(s):

Debojyoti Halder

Keyword(s):

Regression Analysis ◽

Solar Cycle ◽

Sunspot Number ◽

The Sun ◽

Sunspot Numbers ◽

Solar Cycle 24 ◽

Current Cycle ◽

Cycle 24

Sunspots are temporary phenomena on the photosphere of the Sun which appear visibly as dark spots compared to surrounding regions. Sunspot populations usually rise fast but fall more slowly when observed for any particular solar cycle. The sunspot numbers for the current cycle 24 and the previous three cycles have been plotted for duration of first four years for each of them. It appears that the value of peak sunspot number for solar cycle 24 is smaller than the three preceding cycles. When regression analysis is made it exhibits a trend of slow rising phase of the cycle 24 compared to previous three cycles. Our analysis further shows that cycle 24 is approaching to a longer-period but with smaller occurrences of sunspot number.

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Source-region characteristics of anemone active regions in the ascending phase of solar cycle 24

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038927 ◽

2020 ◽

Vol 642 ◽

pp. A233

Author(s):

R. Sharma ◽

C. Cid

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Minimum Distance ◽

Source Region ◽

Coronal Holes ◽

Active Regions ◽

Yearly Average ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Rise Phase

Context. Active regions in close proximity to coronal holes, also known as anemone regions, are the best candidates for studying the interaction between closed and open magnetic field topologies at the Sun. Statistical investigation of their source-region characteristics can provide vital clues regarding their possible association with energetic events, relevant from space weather perspectives. Aims. The main goal of our study is to understand the distinct properties of flaring and non-flaring anemone active regions and their host coronal holes, by examining spatial and magnetic field distributions during the rise phase of the solar cycle, in the years 2011–2014. Methods. Anemone regions were identified from the minimum-distance threshold, estimated using the data available in the online catalogs for on-disk active regions and coronal holes. Along with the source-region area and magnetic field characteristics, associated filament and flare cases were also located. Regions with and without flare events were further selected for a detailed statistical examination to understand the major properties of the energetic events, both eruptive and confined, at the anemone-type active regions. Results. Identified anemone regions showed weak asymmetry in their spatial distribution over the solar disk, with yearly average independent from mean sunspot number trend, during the rise phase of solar cycle 24. With the progression in solar cycle, the area and minimum-distance parameters indicated a decreasing trend in their magnitudes, while the magnetic field characteristics indicated an increase in their estimated magnitudes. More than half of the regions in our database had an association with a filament structure, and nearly a third were linked with a magnetic reconnection (flare) event. Anemone regions with and without flares had clear distinctions in their source-region characteristics evident from the distribution of their properties and density analysis. The key differences included larger area and magnetic field magnitudes for flaring anemone regions, along with smaller distances between the centers of the active region and its host coronal hole.

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Magnetic instability of filaments in different solar regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001806 ◽

2016 ◽

Vol 12 (S327) ◽

pp. 71-76

Author(s):

J. Palacios ◽

A. Guerrero ◽

C. Cid ◽

E. Saiz ◽

Y. Cerrato

Keyword(s):

Solar Cycle ◽

Potential Field ◽

Active Regions ◽

Magnetic Instability ◽

Field Modelling ◽

Decay Index ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Potential Field Modelling ◽

3D Evaluation

AbstractMagnetic instability is a key consideration for filament eruptions and subsequent CMEs. In this contribution we are considering different magnetic conditions for active and non-active regions, such as coronal hole regions and quiet sun, and also active regions of a simple magnetic configuration. The aim is to assess magnetic instability through potential and non-potential field modelling and 3D evaluation of the magnetic decay index. Some eruptive examples from solar cycle 24 using HMI/SDO data are presented, complemented with observations of AIA/SDO.

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Descriptive study of X-class flares released in the year 2014, during the double peak of SC-24

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316000405 ◽

2015 ◽

Vol 11 (S320) ◽

pp. 330-332

Author(s):

Ahmed A. Hady ◽

Marwa H. Mostafa ◽

Susan W. Samwel

Keyword(s):

Data Analysis ◽

Solar Cycle ◽

Solar Flares ◽

Descriptive Study ◽

Energetic Particles ◽

Main Peak ◽

Solar Cycles ◽

Double Peak ◽

Solar Cycle 24 ◽

Cycle 24

AbstractDuring the declining phase of the Solar cycle 24, a new peak appeared on January 7, 2014. The release of x-class flares, with the high energetic particles, were found to be more intense than that occurred during the main peak of the same cycle. Few X-class flares were released, lately, during the year 2014. We note that during the last 5 solar cycles, a new peak has appeared, releasing high energetic particles and X-class solar flares, which are called the secondary peak or the double peak of solar cycle. The aim of this descriptive study is to follow the morphological and magnetic changes of the active region before, during, and after the production of X-class flares according to data analysis. Furthermore, the causes of the release of such eruptive storms have been discussed for the period, year 2014, during the double peak of the solar cycle 24.

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

Geomagnetism and Aeronomy ◽

10.1134/s0016793221060074 ◽

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.

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Characteristics of Sunquake Events Observed in Solar Cycle 24

10.5194/egusphere-egu21-1461 ◽

2021 ◽

Author(s):

Alexander Kosovichev ◽

Ivan Sharykin

Keyword(s):

Solar Cycle ◽

Solar Flares ◽

Active Regions ◽

Impulsive Phase ◽

High Energy ◽

Lower Atmosphere ◽

Solar Dynamics Observatory ◽

X Ray ◽

Solar Cycle 24 ◽

Cycle 24

<p>Helioseismic response to solar flares ("sunquakes") occurs due to localized force or/and momentum impacts observed during the flare impulsive phase in the lower atmosphere. Such impacts may be caused by precipitation of high-energy particles, downward shocks, or magnetic Lorentz force. Understanding the mechanism of sunquakes is a key problem of the flare energy release and transport. Our statistical analysis of M-X class flares observed by the Solar Dynamics Observatory during Solar Cycle 24 has shown that contrary to expectations, many relatively weak M-class flares produced strong sunquakes, while for some powerful X-class flares, helioseismic waves were not observed or were weak. The analysis also revealed that there were active regions characterized by the most efficient generation of sunquakes during the solar cycle. We found that the sunquake power correlates with maximal values of the X-ray flux derivative better than with the X-ray class. The sunquake data challenge the current theories of solar flares.</p>

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Probable Value for the Next Sunspot Minimum

Advances in Astronomy ◽

10.1155/2014/815065 ◽

2014 ◽

Vol 2014 ◽

pp. 1-4

Author(s):

Virginia Mabel Silbergleit

Keyword(s):

Solar Cycle ◽

Solar Minimum ◽

The Sun ◽

Solar Cycles ◽

Additional Insight ◽

Sunspot Minimum ◽

Sunspot Numbers ◽

Solar Cycle 24 ◽

Cycle 24

Gumbel’s first distribution is applied to smoothed monthly mean sunspot numbers for solar cycles 10 to 24. According to that, the next minimum for solar cycle 24-25 transition would be the deepest solar minimum of the last 150 years. This study provides an additional insight about changes in the Sun which are currently happening.

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The Statistical Analysis of Characteristics of Coronal Mass Ejection During the Descending Phase of Solar Cycle 23 and 24

Journal of Mountain Research ◽

10.51220/jmr.v16i2.9 ◽

2021 ◽

Vol 16 (2) ◽

Author(s):

Hemlata Dharmashaktu ◽

N.K. Lohani

Keyword(s):

Solar Cycle ◽

Angular Width ◽

Maximum Speed ◽

Solar Cycles ◽

Linear Speed ◽

23Rd Solar Cycle ◽

23Rd Cycle ◽

Solar Cycle 23 ◽

Solar Cycle 24 ◽

Cycle 24

The characteristics of CMEs we studied are angular width, linear speed, and acceleration for all categories of CMEs such as narrow (W ≤20°), intermediate (20°< W<200°), wide (W ≥ 200°) and linear speed <500 km/s during the descending phase of solar cycle 23 and 24 and compared them. We have found that there are 1951 narrow CMEs during solar cycle 23 that is 1.9 times greater than in solar cycle 24 (1047). On the other side, the number of intermediate CMEs during solar cycle 24 (1571) is 1.14 times more than solar cycle 23 (1162). We observed no noticeable difference between the number of wide CMEs of solar cycle 23 (29) and 24 (36). The angular width of CMEs during the descending phase of solar cycle 23 and solar cycle 24, predominately distributed around 100-600. The fascinating result is that the angular width distributions for the descending phase of solar cycles are approximately identical. On comparing the results of linear speed of both solar cycle, we can say that, (i) 93.7% (1729) and 87.7% (908) of narrow CMEs, (ii) 97% (1328) and 94% (1479) of intermediate CMEs and (iii) 44% (13) and 42% (15) of wide CMEs have speed of <500 km s-1, respectively. Mostly the fractions of narrow and intermediate CMEs decline sharply at the speeds greater than 500 km s-1. The maximum speed observed during the 23rd cycle is 1994 km/s (wide CME) and the 24th cycle is 3163 km/s (wide CME) respectively. It was noticed that the speed of the 24th solar cycle CME is higher than the 23rd solar cycle CME. The major fraction of CMEs has acceleration in the range of -20 to 20 km s-2, all types of CMEs. The narrow and intermediate CMEs mostly show acceleration while wide CMEs show deceleration.

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Solar Flare Build-Up and Release

Solar Physics ◽

10.1007/s11207-020-01698-w ◽

2020 ◽

Vol 295 (10) ◽

Author(s):

Hugh S. Hudson

Keyword(s):

Magnetic Field ◽

Solar Cycle ◽

Waiting Times ◽

Active Regions ◽

Coronal Magnetic Field ◽

Sunspot Area ◽

Observational Evidence ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Event Magnitude

Abstract Flares and coronal mass ejections should follow a pattern of build-up and release, with the build-up phase understood as the gradual addition of stress to the coronal magnetic field. Recently Hudson (Mon. Not. Roy. Astron. Soc.491, 4435, 2020) presented observational evidence for this pattern in two isolated active regions from 1997 and 2006, finding a correlation between the waiting time after the event, and the event magnitude. In this article we systematically search for related evidence in the largest 14 active regions of Solar Cycle 24, chosen as those with peak sunspot area exceeding 1000 millionths of the solar hemisphere (MSH). The smallest of these regions, NOAA 12673, produced the exceptional flares SOL2017-09-06 and SOL2017-09-10. None of these regions showed significant correlations of waiting times and flare magnitudes, although two hinted at such an interval-size relationship. Correlations thus appear to be non-existent or intermittent, depending on presently unknown conditions.

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Periodic Variation of Solar Flare Index for the Last Solar Cycle (Cycle 24)

Advances in Astronomy ◽

10.1155/2021/5391091 ◽

2021 ◽

Vol 2021 ◽

pp. 1-8

Author(s):

Atila Ozguc ◽

Ali Kilcik ◽

Volkan Sarp ◽

Hülya Yeşilyaprak ◽

Rıza Pektaş

Keyword(s):

Solar Cycle ◽

Southern Hemisphere ◽

Northern Hemisphere ◽

Wavelet Transforms ◽

Data Sets ◽

Flare Activity ◽

Data Set ◽

Analysis Methods ◽

Flare Index ◽

Cycle 24

In this study, we used the flare index (FI) data taken from Kandilli Observatory for the period of 2009–2020. The data sets are analyzed in three categories as Northern Hemisphere, Southern Hemisphere, and total FI data sets. Total FI data set is obtained from the sum of Northern and Southern Hemispheric values. In this study, the periodic variations of abovementioned three categories FI data sets were investigated by using the MTM and Morlet wavelet analysis methods. The wavelet coherence (XWT) and cross wavelet (WTC) analysis methods were also performed between these data sets. As a result of our analysis, the following results were found: (1) long- and short-term periodicities ( 2048 ± 512 day and periodicities smaller than 62 days) exist in all data sets without any exception at least with 95 % confidence level; (2) all periodic variations were detected maximum during the solar cycle, while during the minima, no meaningful period is detected; (3) some periodicities have data preference that about 150 days Rieger period appears only in the whole data set and 682-, 204-, and 76.6-day periods appear only in the Northern Hemisphere data sets; (4) During the Solar Cycle 24, more flare activity is seen at the Southern Hemisphere, so the whole disk data periodicities are dominated by this hemisphere; (5) in general, there is a phase mixing between Northern and Southern Hemisphere FI data, except about 1024-day periodicity, and the best phase coherency is obtained between the Southern Hemisphere and total flare index data sets; (6) in case of the Northern and Southern Hemisphere FI data sets, there is no significant correlation between two continuous wavelet transforms, but the strongest correlation is obtained for the total FI and Southern Hemisphere data sets.

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