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1.
Ilídio P. Lopes Douglas Gough 《Monthly notices of the Royal Astronomical Society》2001,322(3):473-485
The outer layers of Sun-like stars are regions of rapid spatial variation which modulate the p-mode frequencies by partially reflecting the constituent acoustic waves. With the accuracy that has been achieved by current solar observations, and that is expected from imminent stellar observations, this modulation can be observed from the spectra of the low-degree modes. We present a new and simple theoretical calculation to determine the leading terms in an asymptotic expansion of the outer phase of these modes, which is determined by the structure of the surface layers of the star. Our procedure is to compare the stellar envelope with a plane-parallel polytropic envelope, which we regard as a smooth reference background state. Then we can isolate a seismic signature of the acoustic phase and relate it to the stratification of the outer layers of the convection zone. One can thereby constrain theories of convection that are used to construct the convection zones of the Sun and Sun-like stars. The accuracy of the diagnostic is tested in the solar case by comparing the predicted outer phase with an exact numerical calculation. 相似文献
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W. J. Chaplin G. Houdek Y. Elsworth D. O. Gough G. R. Isaak R. New 《Monthly notices of the Royal Astronomical Society》2005,360(3):859-868
We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect. 相似文献
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Bob Forsyth and Andy Breen report from the RAS G Discussion Meeting at the Geological Society on 11 January 2002. Presentations came from both the solar and heliospheric communities, on the 3-D structure and dynamics of the solar corona and heliosphere and their inter-relation during the present maximum in the solar activity cycle. 相似文献
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S. Klimov S. Romanov E. Amata J. Blecki J. Büchner J. Juchniewicz J. Rustenbach P. Triska L. J. C. Woolliscroft S. Savin Yu. Afanas’yev U. de Angelis U. Auster G. Bellucci A. Best F. Farnik V. Formisano P. Gough R. Grard V. Grushin G. Haerendel V. Ivchenko V. Korepanov H. Lehmann B. Nikutowski M. Nozdrachev S. Orsini M. Parrot A. Petrukovich J. L. Rauch K. Sauer A. Skalsky J. Slominski J. G. Trotignon J. Vojta R. Wronowski 《Annales Geophysicae》1997,15(5):514-527
The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and searchcoil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper. 相似文献
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Environmental justice is both a vocabulary for political opportunity, mobilization and action, and a policy principle to guide public decision making. It emerged initially in the US, and more recently in the UK, as a new vocabulary underpinning action by community organizations campaigning against environmental injustices. However, as the environmental justice discourse has matured, it has become increasingly evident that it should play a role in the wider agendas for sustainable development and social inclusion. The links between sustainability and environmental justice are becoming clearer and more widely understood in the UK by NGOs and government alike, and it is the potential synergy between these two discourses which is the focus of this paper. This paper argues that the concept of 'just sustainability' provides a discourse for policymakers and activists, which brings together the key dimensions of both environmental justice and sustainable development. 相似文献
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D. O. Gough 《Solar physics》2017,292(5):70
It has been argued (Gough and McIntyre in Nature 394, 755, 1998) that the only way for the radiative interior of the Sun to be rotating uniformly in the face of the differentially rotating convection zone is for it to be pervaded by a large-scale magnetic field, a field which is responsible also for the thinness of the tachocline. It is most likely that this field is the predominantly dipolar residual component of a tangled primordial field that was present in the interstellar medium from which the Sun condensed (Braithwaite and Spruit in Nature 431, 819, 2004), and that advection by the meridional flow in the tachocline has caused the dipole axis to be inclined from the axis of rotation by about \(60^{\circ}\) (Gough in Geophys. Astrophys. Fluid Dyn., 106, 429, 2012). It is suggested here that, notwithstanding its turbulent passage through the convection zone, a vestige of that field is transmitted by the solar wind to Earth, where it modulates the geomagnetic field in a periodic way. The field variation reflects the inner rotation of the Sun, and, unlike turbulent-dynamo-generated fields, must maintain phase. I report here a new look at an earlier analysis of the geomagnetic field by Svalgaard and Wilcox (Solar Phys. 41, 461, 1975), which reveals evidence for appropriate phase coherence, thereby adding support to the tachocline theory. 相似文献