We present the results of a series numerical experiments that investigate transport magnetic fields by turbulent penetrative compressible convection. find flux is preferentially transported downward out convecting region and stored in stably stratified below. This pumping mechanism believed to be crucial component for operation large-scale solar interface dynamo since it may responsible from convection zone stable overshoot region. The high-resolution three-dimensional simulations show...

view Abstract Citations (249) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Turbulent Compressible Convection Cattaneo, Fausto ; Brummell, Nicholas H. Toomre, Juri Malagoli, Andrea Hurlburt, Neal E. Numerical simulations with high spatial resolution (up to 96-cubed gridpoints) are used study three-dimensional, compressible convection. A sequence of four models decreasing viscous dissipation is considered in studying the changes flow...

We present the results of a series high-resolution, three-dimensional numerical experiments that investigate nature turbulent compressible convective motions extending from convection zone into stable layer below. In such convection, converging flows in near-surface cellular convecting network create strong downflowing plumes can traverse multiple scale heights zone. Such structures continue their downward beyond region, piercing layer, where they are decelerated by buoyancy braking. If...

Regions of the ocean's thermocline unstable to salt fingering are often observed host thermohaline staircases, stacks deep well-mixed convective layers separated by thin stably-stratified interfaces. Decades after their discovery, however, origin remains controversial. In this paper we use 3D direct numerical simulations shed light on problem. We study evolution an analogous double-diffusive system, starting from initial statistically homogeneous state and find that it spontaneously...

Double-diffusive instabilities are often invoked to explain enhanced transport in stably-stratified fluids. The most-studied natural manifestation of this process, fingering convection, commonly occurs the ocean's thermocline and typically increases diapycnal mixing by two orders magnitude over molecular diffusion. Fingering convection is also associated with structures on much larger scales, such as thermohaline intrusions, gravity waves staircases. In paper, we present an exhaustive study...

Abstract The magnetic dynamo cycle of the Sun features a distinct pattern: propagating region sunspot emergence appears around 30° latitude and vanishes near equator every 11 years (ref. 1 ). Moreover, longitudinal flows called torsional oscillations closely shadow migration, undoubtedly sharing common cause 2 . Contrary to theories suggesting deep origins these phenomena, helioseismology pinpoints low-latitude outer 5–10% Sun, near-surface shear layer 3,4 Within this zone, inwardly...

A plausible scenario for solar dynamo action is that the large-scale organized toroidal magnetic field generated by of strong radial shear at base convection zone, whereas weaker poloidal regenerated cyclonic throughout zone. We show, using high-resolution three-dimensional numerical simulations, required transport from zone to overshoot region can be achieved on a convective rather than diffusive timescale pumping mechanism in turbulent penetrative compressible convection. layer initially...

The effects of rotation on turbulent, compressible convection within stellar envelopes are studied through three-dimensional numerical simulations conducted a local f-plane model. This work seeks to understand the types differential that can be established in convective stars like Sun, for which recent helioseismic observations suggest an angular velocity profile with depth and latitude at variance many theoretical predictions. paper analyzes mechanisms responsible mean (horizontally...

The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. physics is simplified by considering perfect gas occupying rectilinear domain placed tangentially to rotating sphere at various latitudes, through which destabilizing heat flux driven. resulting considered for range Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence rotation both...

This paper offers the first coherent picture of interactions between convection and magnetic fields that lead to formation complicated filamentary structure a sunspot penumbra. Recent observations have revealed intricate interlocking-comb penumbral field. Some field lines, with associated Evershed outflows, plunge below solar surface near edge spot. We claim these lines are pumped downward by small-scale granular outside sunspot. mechanism is demonstrated in numerical experiments. Magnetic...

The linear and nonlinear dynamo properties of a class periodically forced flows is considered. forcing functions are chosen to drive, in the absence magnetic effects (kinematic regime), time-dependent version ABC flow with A = B C 1. time-dependence consists harmonic displacement origin along line x y z 1 amplitude frequency Ω. finite-time Lyapunov exponents computed for several values It found that these parameters near unity chaotic streamlines occupy most volume. In this parameter range,...

We study the dynamics associated with extension of turbulent convective motions from a convection zone (CZ) into stable region (RZ) that lies below latter. For purpose, we have run series three-dimensional direct numerical simulations solving Navier-Stokes equations under Boussinesq approximation in spherical shell geometry. observe overshooting stably stratified depends on three different parameters: relative stability RZ, transition width between two, and intensity turbulence. In cases...

We present direct numerical simulations based on the full MHD equations of dynamo action in a nonrotating, convectively stable layer containing forced, localized velocity shear. The operates by interaction two processes: production toroidal magnetic field from poloidal shear, and regeneration loops due to combined buoyancy Kelvin-Helmholtz instabilities. nature process is such that it can occur only if initial fields exceed critical value typically depends Reynolds number. As such, this does...

Meridional flows with velocities of a few meters per second are observed in the uppermost regions solar convection zone. The amplitude and pattern deeper interior, particular near top radiative region, crucial importance to wide range magnetohydrodynamical processes. In this paper, we provide systematic study penetration large-scale meridional from zone into particular, effects assumed boundary conditions applied at convective-radiative interface on flows. Using simplified analytical models...

Observations of the sun reveal highly complex flows and magnetic structures that must result from turbulent convection in solar envelope. A remarkable degree large-scale coherence emerges small-scale dynamics, as seen cycles activity differential rotation profile this star. High-performance computing now permits numerical simulations compressible turbulence magnetohydrodynamics with sufficient resolution to show compact vorticity fields can coexist larger scales. Such structured is yielding...

Abstract High resolution numerical simulations of thermal convection in a rapidly rotating channel with gravity perpendicular to the rotation vector are described. The convecting columns subject β-effect resulting from topographic vortex stretching. symmetries problem allow many invariant wavenumber sets, and this property is associated existence stable multiple-equilibria at modest supercriticality. transition chaotic behavior involves production intermittent unstable orbits off two-torus...

We investigate the dynamo properties of Boussinesq, penetrative convection in presence rotation and large-scale velocity shear flows. Several numerical experiments are conducted a local Cartesian computational domain which relative stability lower stable layer, rate, supercriticality convection, strength imposed flow varied. Once statistically steady hydrodynamic state is achieved for any set parameters, weak seed magnetic field added subsequent evolution followed. In all cases studied,...

We discuss a series of high-resolution fully nonlinear MHD numerical simulations relevant to processes that are expected operate in the solar tachocline. study generation strong toroidal magnetic field by stretching action velocity shear on weak background poloidal field, process often referred dynamo theory as Ω-effect. Here we specifically layer horizontal vertical subadiabatically stratified atmosphere, and examine buoyancy properties resulting configurations. find layers can indeed be...

view Abstract Citations (71) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Turbulent Supersonic Convection in Three Dimensions Malagoli, Andrea ; Cattaneo, Fausto Brummell, Nicholas H. Previous numerical calculations of two-dimensional, compressible convection are extended to three dimensions, using a higher order Godunov scheme. The results show that the flow readily becomes supersonic upper boundary layer, where shock structures form...

In a recent paper addressing the solar Ω-effect, we found that action of forced vertical (radial) shear on component poloidal magnetic field could induce buoyancy produced rising, undulating tubular structures, as often envisaged arising from tachocline. However, such dynamics were only to exist under extreme circumstances (extremely large forcing). Here, analytically examine reasons underpinning difficulties in obtaining this type system. Specifically, various assumptions about maintenance...

Motivated by the problem of origin astrophysical magnetic fields, we introduce two concepts. The first is that a "system-scale dynamo", i.e., dynamo can organize fields on scale object. second an "essentially nonlinear dynamo". This which relies velocity driven forces and/or instabilities. We construct simple framework be used to study such dynamos and give examples in evolution generate system-scale field. argue this provides valuable complementary approach more conventional studies based...

Fingering convection (otherwise known as thermohaline convection) is an instability that occurs in stellar radiative interiors the presence of unstable compositional gradients. Numerical simulations have been used order to estimate efficiency mixing induced by this instability. However, fully three-dimensional (3D) computations parameter regime appropriate for astrophysics (i.e. low Prandtl number) are prohibitively expensive. This raises question whether two-dimensional (2D) could be...

The filamentary structure of a sunspot penumbra is believed to be magnetoconvective in origin. In the outer there difference inclination up 30°-40° between magnetic fields associated with bright and dark filaments, latter plunge downward below surface toward edge spot. We have proposed that these are dragged by pumping caused external granular convection. this paper we model process more elaborate idealized configuration includes curvature force exerted an arched field addition buoyancy,...