Solar Magnetic Activity Cycles, Coronal Potential Field Models and Eruption Rates

Petrie, Gordon

doi:10.1088/0004-637x/768/2/162

Cited by 66 publications

(53 citation statements)

References 52 publications

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“…Several solar observatories provide the spherical harmonic coefficients α lm , so that to obtain the radial distribution of solar magnetic field Br(θ, ϕ), one should use Equation (1). Alternatively, when solar observatories provide the distribution of Br(θ, ϕ), usually in the form of a bi-dimensional array stored in a fits file format, one can invert Equation (1) Sanderson et al 2003;Petrie 2013). It is straightforward to invert Equation (1), using the mathematical properties of the associated Legendre polynomials (e.g.…”

Section: Inversion Of the Magnetic Field Equationsmentioning

confidence: 99%

The magnetic field vector of the Sun-as-a-star

Vidotto

2016

Mon. Not. R. Astron. Soc.

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Direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, we present a method to filter out the smallscale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. Our approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well. For that, we self-consistently decompose the three-components of the vector field using spherical harmonics of different l degrees. By retaining the low l degrees in the decomposition, we are able to calculate the large-scale magnetic field vector. Using a synoptic map of the solar vector field at Carrington Rotation CR2109, we derive the solar magnetic field vector at a similar resolution level as that from stellar magnetic images. We demonstrate that the large-scale field of the Sun is not purely radial, as often assumed -at CR2109, 83% of the magnetic energy is in the radial component, while 10% is in the azimuthal and 7% is in the meridional components. By separating the vector field into poloidal and toroidal components, we show that the solar magnetic energy at CR2109 is mainly (> 90%) poloidal. Our description is entirely consistent with the description adopted in several stellar studies. Our formalism can also be used to confront synoptic maps synthesised in numerical simulations of dynamo and magnetic flux transport studies to those derived from stellar observations.

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Section: Inversion Of the Magnetic Field Equationsmentioning

confidence: 99%

The magnetic field vector of the Sun-as-a-star

Vidotto

2016

Mon. Not. R. Astron. Soc.

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“…This means that the relation between SSN and CME rate changed in cycle 24 (the daily CME rate per SSN is greater in cycle 24), which will be discussed in 'Coronal mass ejections and flares' section. There is ongoing debate to understand the reason for this difference: possible artifacts (Wang and Colaninno 2014;Lamy et al 2014), changing strength of the poloidal field (Petrie 2012(Petrie , 2013, or the altered state of the heliosphere (Gopalswamy et al 2014a). …”

Section: Long-term Behavior Of Cme Ratesmentioning

confidence: 99%

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

Gopalswamy

Tsurutani

Yan

2015

Prog. in Earth and Planet. Sci.

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This paper presents an overview of results obtained during the CAWSES-II period on the short-term variability of the Sun and how it affects the near-Earth space environment. CAWSES-II was planned to examine the behavior of the solar-terrestrial system as the solar activity climbed to its maximum phase in solar cycle 24. After a deep minimum following cycle 23, the Sun climbed to a very weak maximum in terms of the sunspot number in cycle 24 (MiniMax24), so many of the results presented here refer to this weak activity in comparison with cycle 23. The short-term variability that has immediate consequence to Earth and geospace manifests as solar eruptions from closed-field regions and high-speed streams from coronal holes. Both electromagnetic (flares) and mass emissions (coronal mass ejections -CMEs) are involved in solar eruptions, while coronal holes result in high-speed streams that collide with slow wind forming the so-called corotating interaction regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating energetic particles and creating large geomagnetic storms. CIRs and their trailing high-speed streams (HSSs), on the other hand, are responsible for recurrent small geomagnetic storms and extended days of auroral zone activity, respectively. The latter leads to the acceleration of relativistic magnetospheric 'killer' electrons. One of the major consequences of the weak solar activity is the altered physical state of the heliosphere that has serious implications for the shock-driving and storm-causing properties of CMEs. Finally, a discussion is presented on extreme space weather events prompted by the 23 July 2012 super storm event that occurred on the backside of the Sun. Many of these studies were enabled by the simultaneous availability of remote sensing and in situ observations from multiple vantage points with respect to the Sun-Earth line.

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“…Using Kitt Peak and WSO synoptic magnetograms, Petrie (2013) investigated the evolution of the observed photospheric magnetic field and the modeled global coronal magnetic field during the past 3 1/2 solar activity cycles observed since the mid-1970s. Polar field changes were found to be well correlated with the presence of active region fields over most of the period studied, except between 2003 and 2006 when the active fields did not produce significant polar field changes.…”

Section: Unusual Cycle 23 Minimummentioning

confidence: 99%

“…Luhmann et al (2011) suggested that the observed enhanced CME rate of cycle 24 may be connected to the weak polar fields allowing more ejections to escape into the heliosphere. Petrie (2013) analyzed the CME rates recorded in the Computer Aided CME Tracking (CACTus Robbrecht et al, 2009) and Solar Eruptive Event Detection System (SEEDS Olmedo et al, 2008) catalogs, both based on SOHO/LASCO coronagraph data, and found evidence that the CME rate itself may be dependent on the polar field strength. Whereas the CME rate as measured from coronagraph data collected by numerous satellites flown during cycle 21 and the rise of cycle 22 (1975 -1989) was very well correlated with the sunspot number (Webb and Howard, 1994), the CACTUS and SEEDS CME rates were much less well correlated with the sunspot number over cycle 23 and the rise of cycle 24 (1997 -2012).…”

Section: Prominence Eruptions and Coronal Mass Ejectionsmentioning

confidence: 99%

Solar Magnetism in the Polar Regions

Petrie

2015

Living Rev. Sol. Phys.

100

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This review describes observations of the polar magnetic fields, models for the cyclical formation and decay of these fields, and evidence of their great influence in the solar atmosphere. The polar field distribution dominates the global structure of the corona over most of the solar cycle, supplies the bulk of the interplanetary magnetic field via the polar coronal holes, and is believed to provide the seed for the creation of the activity cycle that follows. A broad observational knowledge and theoretical understanding of the polar fields is therefore an essential step towards a global view of solar and heliospheric magnetic fields. Analyses of both high-resolution and long-term synoptic observations of the polar fields are summarized. Models of global flux transport are reviewed, from the initial phenomenological and kinematic models of Babcock and Leighton to present-day attempts to produce time-dependent maps of the surface magnetic field and to explain polar field variations, including the weakness of the cycle 23 polar fields. The relevance of the polar fields to solar physics extends far beyond the surface layers from which the magnetic field measurements usually derive. As well as discussing the polar fields' role in the interior as seed fields for new solar cycles, the review follows their influence outward to the corona and heliosphere. The global coronal magnetic structure is determined by the surface magnetic flux distribution, and is dominated on large scales by the polar fields. We discuss the observed effects of the polar fields on the coronal hole structure, and the solar wind and ejections that travel through the atmosphere. The review concludes by identifying gaps in our knowledge, and by pointing out possible future sources of improved observational information and theoretical understanding of these fields. 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

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Solar Magnetic Activity Cycles, Coronal Potential Field Models and Eruption Rates

Cited by 66 publications

References 52 publications

The magnetic field vector of the Sun-as-a-star

The magnetic field vector of the Sun-as-a-star

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

Solar Magnetism in the Polar Regions

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