Evaluating R&amp;D Impacts: Methods and Practice.

Barker, Katharine

doi:10.1111/j.1467-9310.1994.tb00894.x

Cited by 11 publications

(15 citation statements)

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“…Parameter sensitivity maps for several surface geoelectric arrays were presented and used for interpretation at first by Barker (1979). The aim of systematic analogue model experiments (a technique, extensively used in the eighties) was in effect providing parameter sensitivity information about various arrays.…”

Section: Introductionmentioning

confidence: 99%

Parameter sensitivity maps of surface geoelectric arrays I. Linear arrays

Szalai

Szarka

2008

Acta Geodaetica et Geophysica Hungarica

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This paper presents the general features of parameter sensitivity maps and illustrates their practical use. We define parameter sensitivity maps as geoelectric responses in the measuring plane (at the surface) due to an elementary cube within the subsurface at three different depths. Responses of the three component as well as the total response of electrical dipoles formed on opposite cube surfaces are shown. In this paper we present such maps for 14 various linear electrode arrays. This paper is followed by an accompanying one about nonlinear and focussed arrays. Parameter sensitivity maps in these two papers provide a compact characterization of all known geoelectric arrays. We give several examples how to use them in planning and interpretation of field measurements.

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Section: Introductionmentioning

confidence: 99%

Parameter sensitivity maps of surface geoelectric arrays I. Linear arrays

Szalai

Szarka

2008

Acta Geodaetica et Geophysica Hungarica

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“…Although this is a natural consideration for close binaries (Moss et al 2002), nevertheless it is not a priori excluded that, say, the meridional circulation in the solar interior could deviate from axisymmetry. Barker & Moss (1994) and Moss et al (1995) considered active longitude excitation that is promoted to some extent by meridional circulation. As far as it is known however nonaxisymmetric dynamo models with nonaxisymmetric flows do not directly demonstrate phase mixing.…”

Section: Nonaxisymmetric Dynamo Modesmentioning

confidence: 99%

“…Rädler et al 1990;Moss et al 1991aMoss et al , 1995Barker & Moss 1994;Moss 2004Moss , 2005Bigazzi & Ruzmaikin 2004) and also in more solar-like models (see e.g. Moss 1999;also Elstner & Korhonen 2005).…”

Section: Introductionmentioning

confidence: 99%

Active longitudes, nonaxisymmetric dynamos and phase mixing

Berdyugina

Moss

Sokoloff

et al. 2005

A&A

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We discuss the problem of solar active longitudes from the viewpoint of dynamo theory. We start from a recent observational analysis of the problem undertaken by Berdyugina & Usoskin (2003, A&A, 405, 1121 and Usoskin et al. (2005, A&A, 441, 347) who demonstrated from a study of sunspot data that solar active longitudes rotate differentially, with a small but significant asynchrony between northern and southern hemispheres. We suggest two concepts by which the underlying magnetic structure could lead to the observed phenomenologythe true differential rotation of a nonaxisymmetric magnetic structure and a stroboscopic effect. In the latter case, a solid body rotation of nonaxisymmetric magnetic structure is illuminated by an activity wave propagating from middle latitudes to the solar equator, and so mimics a differential rotation. We then discuss several mechanisms which could in principle lead to the excitation of active longitudes. In particular, we consider dynamo excitation of nonaxisymmetric magnetic modes, nonaxisymmetric structures as a manifestation of a relic magnetic field in the solar core, nonaxisymmetric solar hydrodynamics and nonlinear instabilities that lack axial symmetry. We conclude that these mechanisms all provide ways to explain the phenomenology, provided the stroboscopic interpretation is accepted. Of course, a quantitative explanation in the framework of any scenario requires ultimately a detailed numerical simulation. The interpretation of the available observations as a true differential rotation appears to provide a much more severe challenge for theorists. We are unable to suggest a plausible mechanism of this kind; however we can not exclude in principle such an explanation. We relate the phenomenon of solar active longitudes to the information available concerning stellar active longitudes, and also consider evidence from other tracers of solar activity.

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“…They agreed that when an algebraic alpha-quenching is the only nonlinearity, then with rotation laws of the form Ω = Ω(r) rather artificial distributions of Ω and the dynamo coefficient α are required to maintain nonaxisymmetric fields. Later, Barker & Moss (1994) and Moss et al (1995) studied models in which the large-scale Lorentz force acting on, and so modifying, the underlying rotational velocity field Ω 0 (r) was the sole nonlinearity. They found that stable nonaxisymmetric fields were now more readily obtained, without prior tuning of the spatial dependence of α and Ω 0 .…”

Section: Introductionmentioning

confidence: 99%

Nonaxisymmetric magnetic field generation in rapidly rotating late-type stars

Moss¹

2005

A&A

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Abstract.Recently the discovery of the "flip-flop" phenomenon, by which a predominant "active" longitude jumps by about 180• , on several rapidly rotating late-type stars has directed attention to the issues surrounding the presence of large-scale nonaxisymmetric magnetic fields in these objects. Here we study nonlinear mean field dynamo models with quasi-cylindrical rotation laws, acting in spherical shells. Stable nonaxisymmetric magnetic fields are found to be generated for a range of parameters and, for certain of these models, jumps in a measure plausibly related to the position of active longitudes are found to occur. In general, nonaxisymmetric fields appear to be easier to generate in thinner dynamo-active regions. However, flip-flops appear to be stronger for intermediate thicknesses of the dynamo-active shells.

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Evaluating R&D Impacts: Methods and Practice.

Cited by 11 publications

References 0 publications

Parameter sensitivity maps of surface geoelectric arrays I. Linear arrays

Parameter sensitivity maps of surface geoelectric arrays I. Linear arrays

Active longitudes, nonaxisymmetric dynamos and phase mixing

Nonaxisymmetric magnetic field generation in rapidly rotating late-type stars

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