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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For instance, is the behavior of case AB with noticeably slow rotation at high latitudes an example of one class of behavior and our other cases that of another family? This transport is established by correlations in velocity components arising from convective structures that are tilted toward the rotation axis and depart from the local radial direction and away from the meridional plane.

The computational domain extends from 0: Given the computational resources available, we prefer to concentrate our effort on processes that establish the primary differential lol in the bulk of the convection zone and in future studies will seek to incorporate the bot regions.

We seek solutions with an emerging flux at the top that is invariant with latitude issue 2. The poleward flow in both hemispheres peaks at about 20 latitude and then decreases rapidly, changing to weak equatorward flow bior 30, which attains about one-third that peak amplitude.

Convection, Turbulence, Rotation et Magnétisme dans les Étoiles

This diverse range of activity is most likely generated by two conceptually distinct magnetic dynamos e. Fluids, 7, Takehiro, S. We have shown that the strong D results from the role of the Reynolds stresses in redistributing the angular momentum.

We may assess the transport of angular momentum within these systems by considering the mean radial F r and latitudinal F h angular momentum fluxes. There was a tendency for D to diminish in some of the turbulent solutions that also required the emerging energy biit to be invariant with latitude. Since the meridional circulation kinetic energy MCKE is typically about 2 orders of magnitude smaller than the differential rotation kinetic energy DRKEas we will detail in x 3.

The angular velocity profile in such simulations is generally sensitive to the parameters of the problem, and fe solar-like profiles such as case H can be achieved by varying the Reynolds and Prandtl numbers in particular Elliott et al.

There is further melding and shearing of particular downflow lanes as the convection cells evolve over a broad range of timescales, some of which are comparable to the rotation period.

We then investigate the intricate structure and evolution of the dynamo-generated fields in x 4 and their back-reaction on mean flows in x 5. The ASH code is extremely flexible and has demonstrated excellent scalability on massively parallel supercomputers such as the Cray T3E, IBM SP-3, and Origin As boundary conditions, we impose impenetrable and stress-free conditions for the velocity field and constant flux i. The Reynolds stresses above are associated with correlations of the velocity components such as the v d0 rv 0 correlation, which arise from organized tilts within the convective structures, especially in the downflow plumes see, e.


Helioseismology has revealed that the rotation profiles obtained by inversion of frequency splittings of the p modes e. Absent those features, T2 yielded profiles with a small D and even a slightly slower equatorial rotation rate than that in the midlatitudes.

The solid curves represent the total fluxes and serve to indicate the quality of stationarity achieved. Temporal and longitudinal averages of the meridional flows achieved in the cases A, AB, B, C, and D, deduced from sampling in, and 35 days, respectively.

Thus, we are concerned only with the central portion of the convection zone, dealing with neither the penetrative convection below that zone nor the two shear layers present at the top and bottom of it. Strong vertical fields of mixed polarity still correlate well with downflow lanes and plumes. There is a clear difference in the size and structure of the convective patterns at low and high latitudes. We do not fully understand why in case AB such a strikingly different profile results compared to that in our other solutions and of the progenitor simulations biof which the contrast D is mainly achieved in the lower latitudes.

They often tend to produce mean fields of a dipolar nature, although quadrupolar configurations are preferred in some parameter regimes, generally characterized by high Rayleigh numbers and low magnetic Prandtl numbers Grote et al.

Case H is well evolved, with a complex convective structure and a solar-like differential rotation profile x 3. It may be that in parameter space there only exists a small basin of attraction for such behavior, although we think it more likely that several solution states may coexist for the same control parameters, one of which exhibits the gradual rotational slowing at high latitudes and others having most variations confined to low and midlatitudes.

First, strong toroidal field structures must be generated. The simulations reported here resolve nonlinear interactions among a larger range of scales than any previous MHD model of global-scale solar convection, but motions still must exist in the Sun on scales smaller than our grid resolution.

Others believe that the poloidal field is regenerated by the cumulative action of many small-scale cyclonic turbulent motions on the field throughout the convection zone, rather than just close to the surface e. In case AB, two circulation cells are present with radius at low latitudes and only weak circulations at latitudes above Here and are effective eddy diffusivities for vorticity and entropy. It is evident that baroclinicity yields a fair semblance of a balance over much of the deeper layer, with the baroclinic term Fig.


As viewed near the top, the tendency of the convection in our laminar case A to be organized into banana cells nearly aligned with the rotation axis at low latitudes is progressively disrupted by increasing the level of complexity in going in turn to cases AB, B, C, and D.

Index of /Exercices/Magnetostatique

This subsurface region is now being intensively probed using local domain helioseismic methods, revealing the presence of remarkable large-scale meandering flow fields much like jet streams, banded zonal flows, and evolving meridional circulations, all of which contribute to what is called solar subsurface weather SSW; Haber et al.

The ASH code solves the three-dimensional anelastic equations of motion in a rotating spherical shell geometry using a pseudospectral semi-implicit approach Clune et al.

Second, an inverse process is required to complete the cycle, regenerating the poloidal field from the toroidal field.

As the level of turbulence is increased in going from case A to case C, F r, V reduces in amplitude and the transport of angular momentum by the Reynolds stresses and by the meridional circulation change accordingly to maintain equilibrium. The behavior at higher latitudes that involves retrograde displacement of the downflow networks is somewhat more intricate, partly because the convection cells are of smaller scale and exhibit the frequent formation of new downflow lanes as in feature 4 that can serve to cleave existing cells.

The ME in case M2 is still too small 0. The effect of closed as opposed to open boundary conditions seems to be that in the former the magnetic energy amplification is more efficient, with potentially a lower dynamo threshold. Our next challenge is to satisfy issue 1 simultaneously with issue 2 in the more turbulent solutions, which may also lead to being more nearly constant on radial lines at mid- to high latitudes. The single-cell behavior there for case AB appears to enable more effective extraction of angular momentum by Reynolds stresses from the high to the low latitudes, thereby yielding a distinctive rotational slowing of the high latitudes.

All cases exhibit a prograde equatorial rotation and a strong contrast D from equator to pole.