scholarly journals Rossby Waves and Jets in Two-Dimensional Decaying Turbulence on a Rotating Sphere

2007 ◽  
Vol 64 (12) ◽  
pp. 4246-4269 ◽  
Author(s):  
Yoshi-Yuki Hayashi ◽  
Seiya Nishizawa ◽  
Shin-ichi Takehiro ◽  
Michio Yamada ◽  
Keiichi Ishioka ◽  
...  
Keyword(s):  
Rossby Waves ◽  
Momentum Transport ◽  
Two Dimensional ◽  
Mean Flow ◽  
Jet Formation ◽  
Rotating Sphere ◽  
Angular Momentum Transport ◽  
Flow Generation ◽  
Flow Directions ◽  
Decaying Turbulence

Abstract Jet formation in decaying two-dimensional turbulence on a rotating sphere is reviewed from the viewpoint of Rossby waves. A series of calculations are performed to confirm the behavior of zonal mean flow generation on the parameter space of the rotation rate Ω and Froude number Fr. When the flow is nondivergent and Ω is large, intense easterly circumpolar jets tend to emerge in addition to the appearance of a banded structure of zonal mean flows with alternating flow directions. When the system allows surface elevation, circumpolar jets disappear and an equatorial easterly jet emerges with increasing Fr. The appearance of the intense easterly jets can be understood by the angular-momentum transport associated with the generation, propagation, and absorption of Rossby waves. When the flow is nondivergent, long Rossby waves tend to be absorbed near the poles. In contrast, when Fr is large, Rossby waves can hardly propagate poleward and tend to be absorbed near the equator.

scholarly journals Angular Momentum Transport and Dynamo Effect in Kepler Disks

2001 ◽  
Vol 200 ◽  
pp. 410-414
Author(s):  
Günther Rüdiger ◽  
Udo Ziegler
Keyword(s):  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Spherical Model ◽  
Momentum Transport ◽  
Rotational Instability ◽  
Jet Formation ◽  
Angular Momentum Transport ◽  
Dynamo Effect ◽  
Background Shear

Properties have been demonstrated of the magneto-rotational instability for two different applications, i.e. for a global spherical model and a box simulation with Keplerian background shear flow. In both nonlinear cases a dynamo operates with a negative (positive) α-effect in the northern (southern) disk hemisphere and in both cases the angular momentum transport is outwards. Keplerian accretion disks should therefore exhibit large-scale magnetic fields with a dipolar geometry of the poloidal components favoring jet formation.

Circumpolar jets emerging in two-dimensional non-divergent decaying turbulence on a rapidly rotating sphere

2007 ◽  
Vol 39 (1-3) ◽  
pp. 209-220 ◽  
Author(s):  
Shin-Ichi Takehiro ◽  
Michio Yamada ◽  
Yoshi-Yuki Hayashi
Keyword(s):  
Two Dimensional ◽  
Rotating Sphere ◽  
Decaying Turbulence

scholarly journals Mean flow generation in rotating anelastic two-dimensional convection

2016 ◽  
Vol 28 (1) ◽  
pp. 017101 ◽  
Author(s):  
Laura K. Currie ◽  
Steven M. Tobias
Keyword(s):  
Two Dimensional ◽  
Mean Flow ◽  
Flow Generation

scholarly journals Convective Generation of Equatorial Superrotation in Planetary Atmospheres

2011 ◽  
Vol 68 (11) ◽  
pp. 2742-2756 ◽  
Author(s):  
Junjun Liu ◽  
Tapio Schneider
Keyword(s):  
Angular Momentum ◽  
General Circulation ◽  
Rossby Waves ◽  
Giant Planet ◽  
Circulation Model ◽  
Planetary Atmospheres ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Heating From Below ◽  
Equatorial Rossby Waves

Abstract In rapidly rotating planetary atmospheres that are heated from below, equatorial superrotation can occur through convective generation of equatorial Rossby waves. If the heating from below is sufficiently strong that convection penetrates into the upper troposphere, then the convection generates equatorial Rossby waves, which can induce the equatorward angular momentum transport necessary for superrotation. This paper investigates the conditions under which the convective generation of equatorial Rossby waves and their angular momentum transport lead to superrotation. It also addresses how the strength and width of superrotating equatorial jets are controlled. In simulations with an idealized general circulation model (GCM), the relative roles of baroclinicity, heating from below, and bottom drag are explored systematically. Equatorial superrotation generally occurs when the heating from below is sufficiently strong. However, the threshold heating at which the transition to superrotation occurs increases as the baroclinicity or the bottom drag increases. The greater the baroclinicity is, the stronger the angular momentum transport out of low latitudes by baroclinic eddies of extratropical origin. This competes with the angular momentum transport toward the equator by convectively generated Rossby waves and thus can inhibit a transition to superrotation. Equatorial bottom drag damps both the mean zonal flow and convectively generated Rossby waves, weakening the equatorward angular momentum transport as the drag increases; this can also inhibit a transition to superrotation. The strength of superrotating equatorial jets scales approximately with the square of their width. When they are sufficiently strong, their width, in turn, scales with the equatorial Rossby radius and thus depends on the thermal stratification of the equatorial atmosphere. The results have broad implications for planetary atmospheres, particularly for how superrotation can be generated in giant planet atmospheres and in terrestrial atmospheres in warm climates.

Jet formation in decaying two-dimensional turbulence on a rotating sphere

2010 ◽  
pp. 253-263
Author(s):  
Shigeo Yoden ◽  
Yoshi-Yuki Hayashi ◽  
Keiichi Ishioka ◽  
Yuji Kitamura ◽  
Seiya Nishizawa ◽  
...  
Keyword(s):  
Two Dimensional ◽  
Jet Formation ◽  
Rotating Sphere

scholarly journals Energy Accumulation in Easterly Circumpolar Jets Generated by Two-Dimensional Barotropic Decaying Turbulence on a Rapidly Rotating Sphere

2007 ◽  
Vol 64 (11) ◽  
pp. 4084-4097 ◽  
Author(s):  
Shin Takehiro ◽  
Michio Yamada ◽  
Yoshi-Yuki Hayashi
Keyword(s):  
Kinetic Energy ◽  
Rotation Rate ◽  
Flux Analysis ◽  
Two Dimensional ◽  
Banded Structure ◽  
Zonal Flows ◽  
Rotating Sphere ◽  
Zonal Component ◽  
The Mean ◽  
Decaying Turbulence

Abstract A series of numerical experiments on two-dimensional decaying turbulence is performed for a barotropic fluid on a rotating sphere. Numerical calculations have confirmed two important asymptotic features: emergence of the banded structure of zonal flows and their extreme latitudinal inhomogeneities in which kinetic energy is accumulated into the easterly circumpolar jets. The banded structure of zonal flows is established relatively early on in the initial stage. Later, after extended periods of time integration, only the circumpolar jets are intensified gradually, while there is no further evolution in the banded structure in the low and midlatitudes. Wave activity flux analysis illustrates that the initial vortices in the low and midlatitudes propagate poleward as Rossby waves and converge to produce easterly circumpolar flows. In association with this convergence, accumulation of the mean zonal component of kinetic energy proceeds. The tendency for the accumulation becomes strong as the rotation rate is increased, and nearly all of the kinetic energy is concentrated to the circumpolar flows in cases of rapid rotation. A theoretical model is constructed under the assumption that a circumpolar jet emerges around the latitude where the local Rhines scale is equal to the distance from the Pole, and that initial vortices at the lower latitudes contribute to the generation of the jets. The model describes the mean zonal component of kinetic energy and the averaged speed and width of the circumpolar jets as functions of the rotation rate, which agree satisfactorily with the numerical results.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

scholarly journals Fokker-Planck Models for Rotating Stellar Systems

1996 ◽  
Vol 174 ◽  
pp. 363-364 ◽  
Author(s):  
Christian Einsel ◽  
Rainer Spurzem
Keyword(s):  
Initial Conditions ◽  
Planck Equation ◽  
Rotational Energy ◽  
Momentum Transport ◽  
Core Collapse ◽  
Initial Model ◽  
Fundamental Parameters ◽  
Angular Momentum Transport ◽  
Collapse Phase ◽  
Fokker Planck

Observations of Globular Cluster ellipticity distributions related to some fundamental parameters give strong evidence for a decay of rotational energy in these systems with time. In order to study the effectiveness of angular momentum transport (or loss, resp.) a code has been written which solves the Fokker-Planck equation in (E, Jz)-space and follows the evolution from some initial conditions through core collapse (and possibly gravothermal oscillations) up to the post-collapse phase. For the purpose of comparability with N-body simulations rotating initial model configurations according to the prescriptions of Lupton & Gunn (1987) have been constructed. These models are intended to continue previous work by Goodman (1983, Fokker-Planck) and Akiyama & Sugimoto (1989, N-Body). In this contribution the derivation of the flux coefficients is given.

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