scholarly journals Magnetic Structures of Solar Active Regions, Full‐Halo Coronal Mass Ejections, and Geomagnetic Storms

2006 ◽  
Vol 646 (2) ◽  
pp. 1335-1348 ◽  
Author(s):  
Y. Liu ◽  
D. F. Webb ◽  
X. P. Zhao
Keyword(s):  
Coronal Mass Ejections ◽  
Geomagnetic Storms ◽  
Active Regions ◽  
Magnetic Structures ◽  
Solar Active Regions

scholarly journals The spatial relationship between active regions and coronal holes and the occurrence of intense geomagnetic storms throughout the solar activity cycle

1998 ◽  
Vol 16 (1) ◽  
pp. 49-54 ◽  
Author(s):  
S. Bravo ◽  
J. A. L. Cruz-Abeyro ◽  
D. Rojas
Keyword(s):  
Solar Activity ◽  
Coronal Mass Ejections ◽  
Geomagnetic Storms ◽  
Coronal Holes ◽  
Spatial Relationship ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Frequency Of Occurrence ◽  
Sunspot Maximum

Abstract. We study the annual frequency of occurrence of intense geomagnetic storms (Dst < –100 nT) throughout the solar activity cycle for the last three cycles and find that it shows different structures. In cycles 20 and 22 it peaks during the ascending phase, near sunspot maximum. During cycle 21, however, there is one peak in the ascending phase and a second, higher, peak in the descending phase separated by a minimum of storm occurrence during 1980, the sunspot maximum. We compare the solar cycle distribution of storms with the corresponding evolution of coronal mass ejections and flares. We find that, as the frequency of occurrence of coronal mass ejections seems to follow very closely the evolution of the sunspot number, it does not reproduce the storm profiles. The temporal distribution of flares varies from that of sunspots and is more in agreement with the distribution of intense geomagnetic storms, but flares show a maximum at every sunspot maximum and cannot then explain the small number of intense storms in 1980. In a previous study we demonstrated that, in most cases, the occurrence of intense geomagnetic storms is associated with a flaring event in an active region located near a coronal hole. In this work we study the spatial relationship between active regions and coronal holes for solar cycles 21 and 22 and find that it also shows different temporal evolution in each cycle in accordance with the occurrence of strong geomagnetic storms; although there were many active regions during 1980, most of the time they were far from coronal holes. We analyse in detail the situation for the intense geomagnetic storms in 1980 and show that, in every case, they were associated with a flare in one of the few active regions adjacent to a coronal hole.

Cluster of solar active regions and onset of coronal mass ejections

2015 ◽  
Vol 58 (9) ◽  
Author(s):  
JingXiu Wang ◽  
YuZong Zhang ◽  
Han He ◽  
AnQin Chen ◽  
ChunLan Jin ◽  
...  
Keyword(s):  
Coronal Mass Ejections ◽  
Active Regions ◽  
Solar Active Regions

scholarly journals Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and Implications for CME–CME Interactions

2021 ◽  
Author(s):  
Jenny Marcela Rodriguez Gomez ◽  
Tatiana Podlachikova ◽  
Astrid Veronig ◽  
Alexander Ruzmaikin ◽  
Joan Feynman ◽  
...  
Keyword(s):  
Space Weather ◽  
Coronal Mass Ejections ◽  
Solar Minimum ◽  
Geomagnetic Storms ◽  
Active Regions ◽  
Solar Cycles ◽  
Characteristic Energy ◽  
Time Index ◽  
Threshold Time ◽  
Large Flare

&lt;p&gt;Coronal Mass Ejections (CMEs) and their interplanetary counterparts (ICMEs) are the major sources for strong space weather disturbances. We present a study of statistical properties of fast CMEs (v&amp;#8805;1000 km/s) that occurred during solar cycles 23 and 24. We apply the Max Spectrum and the declustering threshold time methods. The Max Spectrum can detect the predominant clusters, and the declustering threshold time method provides details on the typical clustering properties and timescales. Our analysis shows that during the different phases of solar cycles 23 and 24, fast CMEs preferentially occur as isolated events and in clusters with, on average, two members. However, clusters with more members appear, particularly during the maximum phases of the solar cycles. During different solar cycle phases, the typical declustering timescales of fast CMEs are&amp;#160;&amp;#964;&lt;sub&gt;c&lt;/sub&gt; =28-32 hrs, irrespective of the very different occurrence frequencies of CMEs during a solar minimum and maximum. These findings suggest that &amp;#160;&amp;#964;&lt;sub&gt;c&lt;/sub&gt; &amp;#160; for extreme events may reflect the characteristic energy build-up time for large flare and CME-prolific active regions. Statistically associating the clustering properties of fast CMEs with the disturbance storm time index at Earth suggests that fast CMEs occurring in clusters tend to produce larger geomagnetic storms than isolated fast CMEs. Our results highlight the importance of CME-CME interaction and their impact on Space Weather.&lt;/p&gt;

scholarly journals Understanding the Origins of Problem Geomagnetic Storms Associated with “Stealth” Coronal Mass Ejections

2021 ◽  
Vol 217 (8) ◽  
Author(s):  
Nariaki V. Nitta ◽  
Tamitha Mulligan ◽  
Emilia K. J. Kilpua ◽  
Benjamin J. Lynch ◽  
Marilena Mierla ◽  
...  
Keyword(s):  
Solar Activity ◽  
Coronal Mass Ejections ◽  
Geomagnetic Storms ◽  
Active Regions ◽  
The Sun ◽  
Interplanetary Coronal Mass Ejections ◽  
Source Regions ◽  
Solar Eruptions ◽  
Cycle 24 ◽  
Mass Ejection

AbstractGeomagnetic storms are an important aspect of space weather and can result in significant impacts on space- and ground-based assets. The majority of strong storms are associated with the passage of interplanetary coronal mass ejections (ICMEs) in the near-Earth environment. In many cases, these ICMEs can be traced back unambiguously to a specific coronal mass ejection (CME) and solar activity on the frontside of the Sun. Hence, predicting the arrival of ICMEs at Earth from routine observations of CMEs and solar activity currently makes a major contribution to the forecasting of geomagnetic storms. However, it is clear that some ICMEs, which may also cause enhanced geomagnetic activity, cannot be traced back to an observed CME, or, if the CME is identified, its origin may be elusive or ambiguous in coronal images. Such CMEs have been termed “stealth CMEs”. In this review, we focus on these “problem” geomagnetic storms in the sense that the solar/CME precursors are enigmatic and stealthy. We start by reviewing evidence for stealth CMEs discussed in past studies. We then identify several moderate to strong geomagnetic storms (minimum Dst $< -50$ < − 50  nT) in solar cycle 24 for which the related solar sources and/or CMEs are unclear and apparently stealthy. We discuss the solar and in situ circumstances of these events and identify several scenarios that may account for their elusive solar signatures. These range from observational limitations (e.g., a coronagraph near Earth may not detect an incoming CME if it is diffuse and not wide enough) to the possibility that there is a class of mass ejections from the Sun that have only weak or hard-to-observe coronal signatures. In particular, some of these sources are only clearly revealed by considering the evolution of coronal structures over longer time intervals than is usually considered. We also review a variety of numerical modelling approaches that attempt to advance our understanding of the origins and consequences of stealthy solar eruptions with geoeffective potential. Specifically, we discuss magnetofrictional modelling of the energisation of stealth CME source regions and magnetohydrodynamic modelling of the physical processes that generate stealth CME or CME-like eruptions, typically from higher altitudes in the solar corona than CMEs from active regions or extended filament channels.

scholarly journals CMEs and Prominences and their Evolution Over the Solar Cycle

1998 ◽  
Vol 167 ◽  
pp. 463-474 ◽  
Author(s):  
David F. Webb
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Coronal Mass Ejections ◽  
Energetic Particle ◽  
Geomagnetic Storms ◽  
The Sun ◽  
Interplanetary Shocks ◽  
X Ray ◽  
Magnetic Structures ◽  
Source Regions

AbstractCoronal mass ejections (CMEs) are an important aspect of coronal and interplanetary dynamics. They cause large geomagnetic storms and can drive transient interplanetary shocks, which in turn are a key source of energetic particle events. However, our knowledge of the origins and early development of CMEs at the Sun is limited. CMEs are most frequently associated with erupting prominences and long-enduring soft X-ray arcades, but sometimes with no observed surface activity. I review some of the well determined coronal properties of CMEs and what we know about their source regions, with emphasis on the characteristics of the associated prominences and helmet streamers. One of these characteristics is that many CMEs seem to arise from multipolar magnetic structures with multiple or kinked inversion lines. I also discuss the solar-cycle dependencies of these structures, including the role that erupting prominences and CMEs may play in the ejection of magnetic flux and helicity from the Sun.

scholarly journals The Source Locations of Major Flares and CMEs in the Emerging Active Regions

2021 ◽  
Author(s):  
Lijuan Liu ◽  
Yuming Wang ◽  
Zhenjuan Zhou ◽  
Jun Cui
Keyword(s):  
Coronal Mass Ejections ◽  
Active Regions ◽  
The Self ◽  
Flux Emergence ◽  
Polarity Inversion ◽  
Common Process ◽  
Solar Active Regions

&lt;p&gt;Major flares and coronal mass ejections (CMEs) tend to originate from the compact&amp;#160;polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as &amp;#8220;collisional shearing&amp;#8221; is proposed by Chintzoglou et al. (2019) to explain the&amp;#160;phenomenon, which suggests that the collision between different emerging bipoles is able&amp;#160;to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs,&amp;#160;we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of &amp;#8220;collisional shearing&amp;#8221;. We find that none of the active PILs is the self PIL&amp;#160;(sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional&amp;#160;PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined&amp;#160;systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external&amp;#160;&amp;#160;PIL between the AR and the nearby preexisting polarities). Collision accompanied by&amp;#160;shearing and flux cancellation is found developing at all PILs prior to the eruptions,&amp;#160;with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we&amp;#160;find that the magnitude of the flares is positively correlated with the collisional length&amp;#160;of the active PILs, indicating that the intenser activities tend to originate from the&amp;#160;PILs with severer collision. The results suggest that the &amp;#8220;collisional shearing&amp;#8221;, i.e.,&amp;#160;bipole-bipole interaction during the flux emergence is a common process in driving the&amp;#160;major activities in emerging ARs.&lt;/p&gt;

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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