que Vc-VA = VE-VA? EXERCICE 3 (5 points). En utilisant la loi de Biot et Savart, exprimer le champ magnétique créé, en son centre 0, par une. 2) Que permet de calculer la loi de Biot et Savart? Donner son Tous les exercices doivent être traités sur les présentes feuilles (1 à 5) qui seront agrafées à la.

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In this paper we report simulations of hydromagnetic dynamo action in the solar convection zone at unprecedented spatial resolution. The exerckce property, in particular, represents an important improvement over most previous spherical convection simulations in which the latitudinal angular velocity contrast was confined mainly to mid- and low latitudes, namely, outside of the inner tangent cylinder.

Index of /Exercices/Magnetostatique

Our primary objective is to gain a better understanding of magnetic field amplification and transport by turbulent convection in the solar exerice and the essential role that such processes play in the operation of the solar dynamo. The triangular truncation in spectral space precludes any simple distribution of the data and work load among the nodes.

The typical speeds in these meridional circulations are about 20 m s 1. The horizontal structure of the radial and longitudinal magnetic field is also shown in Figure 4. Examination of Figure 12 at high latitudes does not reveal a prominent baroclinic contribution, and this is exercuce with the bland variation of entropy for case AB Fig.

Jacques Le Bourlot Prof. ReidelGlatzmaier, G. However, even this path yields a turbulent solution case D whose D is still close to the helioseismic contrast, thus largely resolving issue 2.

First, strong toroidal field structures must be generated. L identification d un cycle de 11 ans des taches solaires, s accompagnant d un ren. Indeed, we consistently observe that the downflows are able to extend over the full depth of the unstable layer, appearing as twisted sheets of downflow near the top and more distinctive plumes deeper in the layer. The alternative is to reduce the fixed maximum scale by studying smaller localized domains within the full shell and utilizing the 3 orders of magnitude to encompass the dynamical range of turbulent scales.

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The helioseismic probing with ring diagram methods and explicit inversions is able to sense the meridional circulations only fairly close to the solar surface, typically extending to depths of about 20 Mm or to a radius of 0. Exwrcice such simulations have achieved higher resolution relative to Gilman and Glatzmaier s earlier work, they are still generally dominated by banana cells owing to the strong rotational influence.

Two models, designated as LAM in Miesch et al. Rather, we find that the Reynolds stresses are the main agents responsible for maintaining the rotation profiles in our simulations see x 5 AchievvinggSustained Dynamo Action We now consider the dynamo possibilities that such intricate convective patterns and execrice differential rotation can lead to. The more turbulent case C was evolved for about days 18 rotations after being initiated from case B, and a set of its angular velocity profiles are shown sampling the last days in Figure 6b.

Index of /Exercices/Magnetostatique

If the magnetic diffusivity is sufficiently small, the field will exrrcice to amplify until it reaches a nonlinear saturation level where production balances dissipation. They tend to align with the rotation axis and to tilt away from the meridional plane, leading to Reynolds stresses that are crucial ingredients in redistributing the angular momentum within the shell see x 5; see also Miesch et al.

The same color scale is used in bcand d. The tachocline has been one of the most surprising discoveries of helioseismology, especially since its strong rotational shear affords a promising site for the solar global dynamo.

These structures are created somewhere below the photosphere and rise upward, bending to pierce the photosphere in the form of curved tubes. In order to simplify comparison of our results with deductions drawn from helioseismology Fig.

Convection, Turbulence, Rotation et Magnétisme dans les Étoiles – PDF

We seek solutions with an emerging flux at the top that is invariant with latitude issue 2. We turn now to more complex states associated with the turbulent flows that can be resolved using the ASH code. However, the diffusivities in our simulations arise from unresolved convective motions, not microscopic processes, and the effective transport properties of such motions are thought to yield Prandtl and magnetic Prandtl numbers of order unity.


We have found that the Reynolds stresses are crucial in transporting angular momentum toward the equator. Shown are random streak lines whose length is proportional to flow speed, with arrowheads indicating flow sense.

A striking property shared by all these temperature fields is that the polar regions are consistently warmer than the lower latitudes, a feature that we will find to be consistent with a fast or prograde equatorial rotation Driving Strong Differential Rotation The differential rotation profiles with radius and latitude that result from the angular momentum redistribution by the vigorous convection in our five simulations are presented in Figure 4.

Highly turbulent but localized threedimensional portions of a convecting spherical shell are being studied to assess transport properties and topologies of dynamical structures e. The low amplitude of F v confirms that in our simulations inertia dominates over viscous effects, i. Esercice baroclinic term Fig. Helioseismology has shown that gradients in angular velocity are particularly strong in the tachocline, pointing to this interface region between the convection zone and the deeper radiative interior as the likely site for the generation of strong toroidal fields.

Positive values correspond to flow directed from north exrcice latitudes to south negative latitudes.

Case H exhibits a differential rotation profile that is in good agreement with the solar internal rotation profile inferred from helioseismology in the bulk of the convection zone Thompson et al. The downflow networks as well involve more frequent branching points and smaller horizontal scales for the convective patterns, especially at higher latitudes.

These general properties are shared by our five cases, all of which have achieved good overall flux balance with radius, as can be assessed by examining F t. Here and are effective eddy diffusivities for vorticity and entropy. The strong latitudinal variation of angular velocity observed near the surface, where the rotation is considerably faster at the equator than near the poles, extends through much of the convection zone depth about Mm with relatively little radial dependence.