Solar structures related to coronal holes

Molodenskii, M. M.; Starkova, L. I.

doi:10.1134/s1063772907120074

Cited by 5 publications

(8 citation statements)

References 2 publications

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“…One possibility to improve the compatibility between the force-free assumption (that is used in extrapolation methods) and the nonforce-free nature of the measurements (that are used as boundary conditions) is to modify the measurements. This operation, called preprocessing, changes the local values of the vector magnetogram in order to better fulfill some global, necessary constraints that a force-free field must obey (Molodenskii, 1969;Aly, 1989). The preprocessing method that we used (Fuhrmann, Seehafer, and Valori, 2007;Fuhrmann et al, 2011) keeps the modifications of measured values within given limits, ideally of the order of local measurements' errors.…”

Section: Instrumentation and Data Handlingmentioning

confidence: 99%

Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures

Valori

Green²,

Démoulin

et al. 2011

Sol Phys

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We study the flux emergence process in NOAA active region 11024, between 29 June and 7 July 2009, by means of multi-wavelength observations and nonlinear force-free extrapolation. The main aim is to extend previous investigations by combining, as much as possible, high spatial resolution observations to test our present understanding of small-scale (undulatory) flux emergence, while putting these small-scale events in the context of the global evolution of the active region. The combination of these techniques allows us to follow the whole process, from the first appearance of the bipolar axial field on the east limb, until the buoyancy instability could set in and raise the main body of the twisted flux tube through the photosphere, forming magnetic tongues and signatures of serpentine field, until the simplification of the magnetic structure into a main bipole by the time the active region reaches the west limb. At the crucial time of the main emergence phase high spatial resolution spectropolarimetric measurements of the photospheric field are employed to reconstruct the three-dimensional structure of the nonlinear force-free coronal field, which is then used to test the current understanding of flux emergence processes. In particular, the knowledge of the coronal connectivity confirms the identity of the magnetic tongues as seen in their photospheric signatures, and exemplifies how the twisted flux, that is emerging on small scales in the form of a sea-serpent, is subsequently rearranged by reconnection into the large-scale field of the active region. In this way, the multi-wavelength observations combined with a nonlinear force-free extrapolation provide a coherent picture of the emergence process of small-scale magnetic bipoles, which subsequently reconnect to form a large scale structure in the corona.

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Section: Instrumentation and Data Handlingmentioning

confidence: 99%

Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures

Valori

Green²,

Démoulin

et al. 2011

Sol Phys

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“…A form of the virial theorem taking into account the possibility of non-zero Lorentz forces is (Molodenskii 1969)…”

Section: The Origin Dependence Of the Virial Integralmentioning

confidence: 99%

“…are the net horizontal Lorentz forces on the volume (Molodenskii 1969;Aly 1984). Hence for non-zero F x or F y there is no unique virial energy estimate.…”

Section: Introductionmentioning

confidence: 99%

An Improved Virial Estimate of Solar Active Region Energy

Wheatland

Metcalf

2006

ApJ

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The MHD virial theorem may be used to estimate the magnetic energy of active regions based on vector magnetic fields measured at the photosphere or chromosphere. However, the virial estimate depends on the measured vector magnetic field being force-free. Departure from force-freeness leads to an unknown systematic error in the virial energy estimate, and an origin dependence of the result. We present a method for estimating the systematic error by assuming that magnetic forces are confined to a thin layer near the photosphere. If vector magnetic field measurements are available at two levels in the low atmosphere (e.g. the photosphere and the chromosphere), the systematic error may be directly calculated using the observed horizontal and vertical field gradients, resulting in an energy estimate which is independent of the choice of origin. If (as is generally the case) measurements are available at only one level, the systematic error may be approximated using the observed horizontal field gradients together with a simple linear force-free model for the vertical field gradients. The resulting `improved' virial energy estimate is independent of the choice of origin, but depends on the choice of the model for the vertical field gradients, i.e. the value of the linear force-free parameter $\alpha$. This procedure is demonstrated for five vector magnetograms, including a chromospheric magnetogram.Comment: 17 pages, 1 figur

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“…A few years later, Molodenskii & Starkova (2007) justified theoretically formation of such partings and performed their computer simulation. They also concluded that these partings are the inevitable and natural component of the magnetized solar atmosphere, representing the "sign-reversal lines for the normal component of the curvature vector of the magnetic lines".…”

Section: Introductionmentioning

confidence: 99%

Coronal partings

Nikulin

Dumin

2016

Advances in Space Research

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The basic observational properties of “coronal partings”—the special type of quasi-one-dimensional magnetic structures, identified by a comparison of the coronal X-ray and EUV images with solar magnetograms—are investigated. They represent the channels of opposite polarity inside the unipolar large-scale magnetic fields, formed by the rows of magnetic arcs directed to the neighboring sources of the background polarity. The most important characteristics of the partings are discussed. It can be naturally assumed that—from the evolutionary and spatial points of view—the partings can transform into the coronal holes and visa versa. The classes of global, intersecting, and complex partings are identified

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Solar structures related to coronal holes

Cited by 5 publications

References 2 publications

Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures

Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures

An Improved Virial Estimate of Solar Active Region Energy

Coronal partings

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