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Title: TRANSPORT BY MERIDIONAL CIRCULATIONS IN SOLAR-TYPE STARS

Abstract

Transport by meridional flows has significant consequences for stellar evolution, but is difficult to capture in global-scale numerical simulations because of the wide range of timescales involved. Stellar evolution models therefore usually adopt parameterizations for such transport based on idealized laminar or mean-field models. Unfortunately, recent attempts to model this transport in global simulations have produced results that are not consistent with any of these idealized models. In an effort to explain the discrepancies between global simulations and idealized models, here we use three-dimensional local Cartesian simulations of compressible convection to study the efficiency of transport by meridional flows below a convection zone in several parameter regimes of relevance to the Sun and solar-type stars. In these local simulations we are able to establish the correct ordering of dynamical timescales, although the separation of the timescales remains unrealistic. We find that, even though the generation of internal waves by convective overshoot produces a high degree of time dependence in the meridional flow field, the mean flow has the qualitative behavior predicted by laminar, 'balanced' models. In particular, we observe a progressive deepening, or 'burrowing', of the mean circulation if the local Eddington-Sweet timescale is shorter than the viscous diffusion timescale.more » Such burrowing is a robust prediction of laminar models in this parameter regime, but has never been observed in any previous numerical simulation. We argue that previous simulations therefore underestimate the transport by meridional flows.« less

Authors:
Publication Date:
OSTI Identifier:
22039101
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 755; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CAPTURE; COMPUTERIZED SIMULATION; CONVECTION; DIFFUSION; EFFICIENCY; INTERNAL WAVES; MEAN-FIELD THEORY; ROTATION; STAR EVOLUTION; SUN; THREE-DIMENSIONAL CALCULATIONS; TIME DEPENDENCE

Citation Formats

Wood, T S, and Brummell, N. H., E-mail: tsw25@soe.ucsc.edu. TRANSPORT BY MERIDIONAL CIRCULATIONS IN SOLAR-TYPE STARS. United States: N. p., 2012. Web. doi:10.1088/0004-637X/755/2/99.
Wood, T S, & Brummell, N. H., E-mail: tsw25@soe.ucsc.edu. TRANSPORT BY MERIDIONAL CIRCULATIONS IN SOLAR-TYPE STARS. United States. https://doi.org/10.1088/0004-637X/755/2/99
Wood, T S, and Brummell, N. H., E-mail: tsw25@soe.ucsc.edu. 2012. "TRANSPORT BY MERIDIONAL CIRCULATIONS IN SOLAR-TYPE STARS". United States. https://doi.org/10.1088/0004-637X/755/2/99.
@article{osti_22039101,
title = {TRANSPORT BY MERIDIONAL CIRCULATIONS IN SOLAR-TYPE STARS},
author = {Wood, T S and Brummell, N. H., E-mail: tsw25@soe.ucsc.edu},
abstractNote = {Transport by meridional flows has significant consequences for stellar evolution, but is difficult to capture in global-scale numerical simulations because of the wide range of timescales involved. Stellar evolution models therefore usually adopt parameterizations for such transport based on idealized laminar or mean-field models. Unfortunately, recent attempts to model this transport in global simulations have produced results that are not consistent with any of these idealized models. In an effort to explain the discrepancies between global simulations and idealized models, here we use three-dimensional local Cartesian simulations of compressible convection to study the efficiency of transport by meridional flows below a convection zone in several parameter regimes of relevance to the Sun and solar-type stars. In these local simulations we are able to establish the correct ordering of dynamical timescales, although the separation of the timescales remains unrealistic. We find that, even though the generation of internal waves by convective overshoot produces a high degree of time dependence in the meridional flow field, the mean flow has the qualitative behavior predicted by laminar, 'balanced' models. In particular, we observe a progressive deepening, or 'burrowing', of the mean circulation if the local Eddington-Sweet timescale is shorter than the viscous diffusion timescale. Such burrowing is a robust prediction of laminar models in this parameter regime, but has never been observed in any previous numerical simulation. We argue that previous simulations therefore underestimate the transport by meridional flows.},
doi = {10.1088/0004-637X/755/2/99},
url = {https://www.osti.gov/biblio/22039101}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 755,
place = {United States},
year = {Mon Aug 20 00:00:00 EDT 2012},
month = {Mon Aug 20 00:00:00 EDT 2012}
}