Properties and emergence patterns of bipolar active regions

Harvey, K. L.; Zwaan, C.

doi:10.1007/bf00675537

Cited by 171 publications

(148 citation statements)

References 15 publications

Supporting

Mentioning

130

Contrasting

Unclassified

Order By: Relevance

“…However, there exists a clustering tendency of magnetic activity, first noted by Cassini (1729), i.e., ARs tend to emerge in the immediate vicinity or within the boundaries of an existing AR (Bumba and Howard, 1965). Liggett and Zirin (1985) and later Harvey and Zwaan (1993) showed that there is a 10 to 22-fold higher emergence rate within existing ARs than in the quiet sun. Repeated episodes of major flux emergence within an evolving active region leads to increased magnetic complexity, cancellation rate, leading to magnetic activity.…”

Section: Main Laws and Intrinsic Characteristics Of Large-scale Magnementioning

confidence: 91%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

View full text Add to dashboard Cite

The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

show abstract

Section: Main Laws and Intrinsic Characteristics Of Large-scale Magnementioning

confidence: 91%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

265

131

View full text Add to dashboard Cite

show abstract

“…The frequency of their occurrence is regulated by the solar cycle. Observations have shown that active regions have a tendency to cluster, i.e., new magnetic fluxes preferably emerge in the vicinity of old ones [Gaizauskas et al, 1983;Harvey and Zwaan, 1993]. The clusters may last for as many as six solar rotations and there are indications that the fastest CMEs preferably originate from them [Ruzmaikin and Feynman, 1998].…”

Section: Introductionmentioning

confidence: 99%

Distribution and clustering of fast coronal mass ejections

2011

View full text Add to dashboard Cite

[1] The purpose of this paper is to investigate the statistical properties of high-speed coronal mass ejections (fast CMEs), which play a major role in Space Weather. We study the cumulative distribution of the initial CME speeds applying a new, advanced statistical method based on the scaling properties of averages of maximal speeds selected in time intervals of fixed sizes. This method allows us for the first time to obtain a systematic statistical description of the fast CME speeds. Using this method, we identify a self-similar (power law) high-speed portion of the spectrum of the speed maxima in the range of speeds from about 700 km/s to 2000 km/s. This self-similar range of the speed distribution provides a meaningful definition of "the fast" CMEs and indicates that these CMEs are produced by a process that is the same across the range of scales. The investigation of the temporal behavior of the fast CME events indicates that the time intervals between fast CMEs are not independent, i.e., fast CMEs arrive in clusters. We characterize the fast CMEs clustering by the exponent called the extremal index, which is the inverse of the averaged number of CMEs per cluster. An independent correlation analysis of the tail of the CME distribution confirms and further quantifies the temporal dependence among the fast CME events. To illustrate the predictive capabilities of the method, we identify clusters in the time series of CMEs with speeds greater than 1000 km/s and calculate their statistical characteristics such as the size and duration of the clusters. The method used in this paper can be applied to many other extreme geophysical events.

show abstract

“…However, the open magnetic flux that threads the coronal source surface is, at most, a few percent of the total flux threading the photosphere: most of the flux that has emerged through the photosphere (Harvey & Zwaan 1993) closes in loops in the corona below the source surface (Wang et al 2000a(Wang et al , 2000b. Furthermore, the dependence of contrast on flux tube radius means that how the photospheric flux is distributed spatially is also crucial to the net effect on I TS .…”

Section: Introductionmentioning

confidence: 99%

An evaluation of the correlation between open solar flux and total solar irradiance

Lockwood

2002

A&A

View full text Add to dashboard Cite

Abstract. The correlation between the coronal source flux FS and the total solar irradiance ITS is re-evaluated in the light of an additional 5 years' data from the rising phase of solar cycle 23 and also by using cosmic ray fluxes detected at Earth. Tests on monthly averages show that the correlation with FS deduced from the interplanetary magnetic field (correlation coefficient, r = 0.62) is highly significant (99.999%), but that there is insufficient data for the higher correlation with annual means (r = 0.80) to be considered significant. Anti-correlations between ITS and cosmic ray fluxes are found in monthly data for all stations and geomagnetic rigidity cut-offs (r ranging from −0.63 to −0.74) and these have significance levels between 85% and 98%. In all cases, the fit is poorest for the earliest data (i.e., prior to 1982). Excluding these data improves the anticorrelation with cosmic rays to r = −0.93 for one-year running means. Both the interplanetary magnetic field data and the cosmic ray fluxes indicate that the total solar irradiance lags behind the open solar flux with a delay that is estimated to have an optimum value of 2.8 months (and is within the uncertainty range 0.8-8.0 months at the 90% level).

show abstract

Properties and emergence patterns of bipolar active regions

Cited by 171 publications

References 15 publications

Evolution of Active Regions

Evolution of Active Regions

Distribution and clustering of fast coronal mass ejections

An evaluation of the correlation between open solar flux and total solar irradiance

Contact Info

Product

Resources

About