Magnetic instability of filaments in different solar regions

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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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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Super-active regions in solar cycle 24

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316000223 ◽

2015 ◽

Vol 11 (S320) ◽

pp. 309-314 ◽

Cited By ~ 1

Author(s):

Anqin Chen ◽

Jingxiu Wang

Keyword(s):

Solar Cycle ◽

Active Regions ◽

Total Solar Irradiance ◽

Flare Activity ◽

Solar Cycles ◽

Solar Cycle 24 ◽

Satisfactory Account ◽

Current Cycle ◽

Flare Index ◽

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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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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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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Solar cycle variation of helicity characteristics indicated by SP/Hinode

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300238x ◽

2012 ◽

Vol 8 (S294) ◽

pp. 149-150

Author(s):

Juan Hao ◽

Mei Zhang

Keyword(s):

Solar Cycle ◽

Active Regions ◽

Field Measurements ◽

Second Phase ◽

Solar Cycle Variation ◽

Cycle Variation ◽

Phase Cycle ◽

Solar Cycle 24 ◽

Cycle 24 ◽

Weak Fields

AbstractHelicity characteristics in active regions (ARs) are studied, using so far the most accurate vector magnetic field measurements obtained with SP/Hinode. Our sample includes all ARs observed by SP/Hinode, up to June 2012. The sample is divided into three sub-samples: Cycle 23 (from 2006.11 to 2008.06), Cycle 24a (from 2008.10 to 2010.09) and Cycle 24b (from 2010.10 to 2012.06). We confirm our previous findings that the usual hemispheric helicity sign rule is not obeyed in the descending phase of solar cycle 23 and is obeyed in the ascending phase of solar cycle 24. And we find that the second phase of the solar cycle 24 (Cycle 24b) shows an even stronger evidence of the usual hemispheric helicity sign rule than its first phase (Cycle 24a). It is also found that our previous finding that the strong and weak fields possess the opposite helicity signs is not followed in Cycle 24b, whereas it is weakly followed in Cycle 24a and strongly followed in the descending phase of Cycle 23. This means that this rule also has a solar cycle variation, in addition to the solar cycle variation of the usual hemispheric helicity sign rule, and there is a roughly 2-years time delay between the two.

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Low frequency radio observations of the ‘background’ corona during the declining phase of solar cycle 24

2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) ◽

10.23919/ursiap-rasc.2019.8738381 ◽

2019 ◽

Author(s):

M. Vrunda ◽

R. Ramesh ◽

C. Kathiravan ◽

M. Rajesh

Keyword(s):

Solar Cycle ◽

Low Frequency ◽

Radio Observations ◽

Solar Cycle 24 ◽

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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