scholarly journals TOMOGRAPHY OF THE SOLAR INTERIOR

2006 ◽  
Vol 21 (22) ◽  
pp. 1701-1715 ◽  
Author(s):  
L. GIZON
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Solar Surface ◽  
Three Dimensional ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Turbulent Convection ◽  
Convective Structures ◽  
Surface Gravity Waves ◽  
Rich Spectrum

Solar oscillations consist of a rich spectrum of internal acoustic waves and surface gravity waves, stochastically excited by turbulent convection. They have been monitored almost continuously over the last ten years with high-precision Doppler images of the solar surface. The purpose of helioseismology is to retrieve information about the structure and the dynamics of the solar interior from the frequencies, phases and amplitudes of solar waves. Methods of analysis are being developed to make three-dimensional images of subsurface motions and temperature inhomogeneities in order to study convective structures and regions of magnetic activity, like sunspots.

Acoustic radiation by ocean surface waves

2000 ◽  
Vol 415 ◽  
pp. 1-21 ◽  
Author(s):  
STEVE ARENDT ◽  
DAVID C. FRITTS
Keyword(s):  
Surface Waves ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Acoustic Radiation ◽  
Three Dimensional ◽  
Phase Speed ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Ocean Surface Waves ◽  
Surface Gravity Waves

We calculate the radiation of acoustic waves into the atmosphere by surface gravity waves on the ocean surface. We show that because of the phase speed mismatch between surface gravity waves and acoustic waves, a single surface wave radiates only evanescent acoustic waves. However, owing to nonlinear terms in the acoustic source, pairs of ocean surface waves can radiate propagating acoustic waves if the two surface waves propagate in almost equal and opposite directions. We derive an analytic expression for the acoustic radiation by a pair of ocean surface waves, and then extend the result to the case of an arbitrary spectrum of ocean surface waves. We present some examples for both the two-dimensional and three-dimensional regimes. Of particular note are the findings that the efficiency of acoustic radiation increases at higher wavenumbers, and the fact that the directionality of the acoustic radiation is often independent of the shape of the spectrum.

scholarly journals Cloaking of a vertical cylinder in waves using variable bathymetry

2014 ◽  
Vol 750 ◽  
pp. 124-143 ◽  
Author(s):  
R. Porter ◽  
J. N. Newman
Keyword(s):  
Gravity Waves ◽  
Wave Equations ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Dimensional Problem ◽  
Practical Application ◽  
Surface Gravity Waves ◽  
Dimensional Boundary ◽  
Drift Force ◽  
Numerical Optimisation

AbstractThe paper describes a process which allows a vertical circular cylinder subject to plane monochromatic surface gravity waves to appear invisible to the far-field observer. This is achieved by surrounding the cylinder with an annular region of variable bathymetry. Two approaches are taken to investigate this effect. First a mild-slope approximation is applied to the governing linearised three-dimensional water wave equations to formulate a depth-averaged two-dimensional wave equation with varying wavenumber over the variable bathmetry. This is then solved by formulating a domain integral equation, solved numerically by discretisation. For a given set of geometrical and wave parameters, the bathymetry is selected by a numerical optimisation process and it is shown that the scattering cross-section is reduced towards zero with increasing refinement of the bathymetry. A fully three-dimensional boundary-element method, based on the WAMIT solver (see www.wamit.com) but adapted here to allow for depressions in the bed, is used to assess the accuracy of the mild-slope results and then further numerically optimise the bathymetry towards a cloaking structure. Numerical results provide strong evidence that perfect cloaking is possible for the fully three-dimensional problem. One practical application of the results is that cloaking implies a reduced mean drift force on the cylinder.

scholarly journals Challenges to the theory of solar convection

2006 ◽  
Vol 2 (S239) ◽  
pp. 35-35
Author(s):  
F. Cattaneo
Keyword(s):  
Gravity Waves ◽  
Multiple Scale ◽  
Magnetic Activity ◽  
Solar Radius ◽  
Convective Transport ◽  
Turbulent Convection ◽  
Substantial Fraction ◽  
Spatial And Temporal Scales ◽  
Solar Convection ◽  
Highly Nonlinear

AbstractTurbulent convection carries most of the solar luminosity from the stable radiative interior to the visible surface over a substantial fraction of the solar radius. The turbulent motions are highly nonlinear displaying activity on several spatial and temporal scales. The effects of these motions are to redistribute angular momentum, mix light elements, excite gravity waves and power magnetic activity. In this talk, I shall review some of the recent efforts, mostly based on numerical simulations, to model turbulent convection spanning multiple scale heights. I will discuss what we have learnt about the nature of convective transport, and what the relevant timescales are on which convection operates.

scholarly journals TSUNAMI GENERATION BY EARTHQUAKES: SEABED TOPOGRAPHY AND INERTIAL EFFECTS

2018 ◽  
pp. 58
Author(s):  
Robert A. Dalrymple ◽  
Morteza Derakhti
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Smooth Particle Hydrodynamic ◽  
Far Field ◽  
Relative Importance ◽  
Inertial Effects ◽  
Tsunami Generation ◽  
Moving Bed ◽  
Surface Gravity Waves ◽  
Seabed Topography

In this presentation, we examine the effects of the shape and height of a moving bed on the generated surface gravity waves using the 3-D Smooth Particle Hydrodynamic model, GPUSPH (Hérault et al., 2010). Further, we investigate the relative importance of the inertial effects on the general characteristics of the generated Tsunami in the near- and far-field for various rates of the bed displacement, ranging from creeping to impulsive regimes. The sensitivity of the inertial effects on the shape of the moving bed is also discussed. Finally, the characteristics of the acoustic waves generated during the various bed displacement scenarios are examined.

scholarly journals Seismic Tomography of the Near Solar Surface

2000 ◽  
Vol 179 ◽  
pp. 339-342
Author(s):  
L. Gizon ◽  
T. L. Duvall ◽  
R. M. Larsen
Keyword(s):  
Gravity Waves ◽  
Seismic Tomography ◽  
Solar Surface ◽  
Surface Gravity ◽  
Surface Gravity Waves ◽  
Time Distance ◽  
Sunspot Penumbra

AbstractSurface gravity waves have been used to probe flows in the two megameters beneath the photosphere using the techniques of time-distance helioseismology. The results suggest that supergranule velocities are smaller than at the surface. The outward flow outside a sunspot penumbra (the moat) is observed, as is an inward flow in the region beyond the moat.

scholarly journals Lost and found sunquake in the 6 September 2011 flare caused by beam electrons

2018 ◽  
Vol 619 ◽  
pp. A65 ◽  
Author(s):  
Connor Macrae ◽  
Sergei Zharkov ◽  
Valentina Zharkova ◽  
Malcolm Druett ◽  
Sarah Matthews ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
White Light ◽  
Hydrodynamic Model ◽  
Acoustic Waves ◽  
Solar Surface ◽  
Statistical Significance ◽  
Onset Time ◽  
Solar Interior ◽  
Shock Propagation ◽  
X Rays

The active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second flare of 7 September 2011. In this paper we present the first observation of a sunquake for the 6 September 2011 flare detected via statistical significance analysis of egression power and verified via directional holography and time–distance diagram. The surface wavefront exhibits directional preference in the north-west direction We interpret this sunquake and the associated flare emission with a combination of a radiative hydrodynamic model of a flaring atmosphere heated by electron beam and a hydrodynamic model of acoustic wave generation in the solar interior generated by a supersonic shock. The hydrodynamic model of the flaring atmosphere produces a hydrodynamic shock travelling with supersonic velocities toward the photosphere and beneath. For the first time we derive velocities (up to 140 km s−1) and onset time (about 50 s after flare onset) of the shock deposition at given depths of the interior. The shock parameters are confirmed by the radiative signatures in hard X-rays and white light emission observed from this flare. The shock propagation in the interior beneath the flare is found to generate acoustic waves elongated in the direction of shock propagation, that results in an anisotropic wavefront seen on the solar surface. Matching the detected seismic signatures on the solar surface with the acoustic wave front model derived for the simulated shock velocities, we infer that the shock has to be deposited under an angle of about 30° to the local solar vertical. Hence, the improved seismic detection technique combined with the double hydrodynamic model reported in this study opens new perspectives for observation and interpretation of seismic signatures in solar flares.

scholarly journals Solar Differential Rotation Revealed by Helioseismology and Simulations of Deep Shells of Turbulent Convection

2004 ◽  
Vol 215 ◽  
pp. 326-331
Author(s):  
Juri Toomre ◽  
Allan Sacha Brun
Keyword(s):  
Differential Rotation ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Turbulent Convection ◽  
Theoretical Modelling ◽  
Dynamo Action ◽  
Diverse Range ◽  
Dynamical Coupling ◽  
Weak Winds ◽  
Distinguishing Features

The sun is supposedly a very simple star, halfway along its long and possibly boring life on the main sequence. Yet it has some distinguishing features. Since we live close to it, our existence is probably blessed by this star having only modest cycles of magnetic activity and weak winds. By being so close, we can observe many aspects of the diverse range of motions and magnetic fields linked to turbulent convection in its convection zone. And this turns out to be anything but simple as we consider the dynamical coupling of convection, rotation and magnetism within this modest star. The lessons that have emerged from recent helioseismic probing of the solar interior and from 3–D numerical simulations of turbulent convection have bearing on differential rotation and magnetic dynamo action also occurring within more complex stars. We consider recent findings from both helioseismology and theoretical modelling on the operation of the deep shell of vigorous convection within our nearest star.

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