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Title: Extended Subadiabatic Layer in Simulations of Overshooting Convection

Abstract

We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. We find that a substantial fraction of the lower part of the convection zone (CZ) is stably stratified according to the Schwarzschild criterion while the enthalpy flux is outward directed. This occurs when the heat conduction profile at the bottom of the CZ is smoothly varying, based either on a Kramers-like opacity prescription as a function of temperature and density or a static profile of a similar shape. We show that the subadiabatic layer arises due to nonlocal energy transport by buoyantly driven downflows in the upper parts of the CZ. Analysis of the force balance of the upflows and downflows confirms that convection is driven by cooling at the surface. We find that the commonly used prescription for the convective enthalpy flux being proportional to the negative entropy gradient does not hold in the stably stratified layers where the flux is positive. We demonstrate the existence of a non-gradient contribution to the enthalpy flux, which is estimated to be important throughout the convective layer. A quantitative analysis of downflows indicates a transition from a tree-like structure where smaller downdrafts merge into larger ones in the upper partsmore » to a structure in the deeper parts where a height-independent number of strong downdrafts persist. This change of flow topology occurs when a substantial subadiabatic layer is present in the lower part of the CZ.« less

Authors:
;  [1]; ; ;  [2];  [3]; ;  [4]
  1. Leibniz-Institut für Astrophysik, An der Sternwarte 16, D-14482 Potsdam (Germany)
  2. ReSoLVE Centre of Excellence, Department of Computer Science, P.O. Box 15400, FI-00076 Aalto (Finland)
  3. NORDITA, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)
  4. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany)
Publication Date:
OSTI Identifier:
22654405
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 845; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; CONVECTION; COOLING; COSMOLOGY; DENSITY; ENTHALPY; ENTROPY; HYDRODYNAMICS; LAYERS; OPACITY; POWER TRANSMISSION; SCHWARZSCHILD METRIC; SURFACES; TEMPERATURE DEPENDENCE; THERMAL CONDUCTION; TURBULENCE

Citation Formats

Käpylä, Petri J., Arlt, Rainer, Rheinhardt, Matthias, Käpylä, Maarit J., Olspert, Nigul, Brandenburg, Axel, Lagg, Andreas, and Warnecke, Jörn. Extended Subadiabatic Layer in Simulations of Overshooting Convection. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA83AB.
Käpylä, Petri J., Arlt, Rainer, Rheinhardt, Matthias, Käpylä, Maarit J., Olspert, Nigul, Brandenburg, Axel, Lagg, Andreas, & Warnecke, Jörn. Extended Subadiabatic Layer in Simulations of Overshooting Convection. United States. doi:10.3847/2041-8213/AA83AB.
Käpylä, Petri J., Arlt, Rainer, Rheinhardt, Matthias, Käpylä, Maarit J., Olspert, Nigul, Brandenburg, Axel, Lagg, Andreas, and Warnecke, Jörn. 2017. "Extended Subadiabatic Layer in Simulations of Overshooting Convection". United States. doi:10.3847/2041-8213/AA83AB.
@article{osti_22654405,
title = {Extended Subadiabatic Layer in Simulations of Overshooting Convection},
author = {Käpylä, Petri J. and Arlt, Rainer and Rheinhardt, Matthias and Käpylä, Maarit J. and Olspert, Nigul and Brandenburg, Axel and Lagg, Andreas and Warnecke, Jörn},
abstractNote = {We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. We find that a substantial fraction of the lower part of the convection zone (CZ) is stably stratified according to the Schwarzschild criterion while the enthalpy flux is outward directed. This occurs when the heat conduction profile at the bottom of the CZ is smoothly varying, based either on a Kramers-like opacity prescription as a function of temperature and density or a static profile of a similar shape. We show that the subadiabatic layer arises due to nonlocal energy transport by buoyantly driven downflows in the upper parts of the CZ. Analysis of the force balance of the upflows and downflows confirms that convection is driven by cooling at the surface. We find that the commonly used prescription for the convective enthalpy flux being proportional to the negative entropy gradient does not hold in the stably stratified layers where the flux is positive. We demonstrate the existence of a non-gradient contribution to the enthalpy flux, which is estimated to be important throughout the convective layer. A quantitative analysis of downflows indicates a transition from a tree-like structure where smaller downdrafts merge into larger ones in the upper parts to a structure in the deeper parts where a height-independent number of strong downdrafts persist. This change of flow topology occurs when a substantial subadiabatic layer is present in the lower part of the CZ.},
doi = {10.3847/2041-8213/AA83AB},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 845,
place = {United States},
year = 2017,
month = 8
}
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