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STELLAR MIXING LENGTH THEORY with ENTROPY RAIN
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.ORCID iD: 0000-0002-7304-021X
2016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 832, no 1, 6Article in journal (Refereed) Published
Abstract [en]

The effects of a non-gradient flux term originating from the motion of convective elements with entropy perturbations of either sign are investigated and incorporated into a modified version of stellar mixing length theory (MLT). Such a term, first studied by Deardorff in the meteorological context, might represent the effects of cold intense downdrafts caused by the rapid cooling in the granulation layer at the top of the convection zone of late-type stars. These intense downdrafts were first seen in the strongly stratified simulations of Stein & Nordlund in the late 1980s. These downdrafts transport heat nonlocally, a phenomenon referred to as entropy rain. Moreover, the Deardorff term can cause upward enthalpy transport even in a weakly Schwarzschild-stably stratified layer. In that case, no giant cell convection would be excited. This is interesting in view of recent observations, which could be explained if the dominant flow structures were of small scale even at larger depths. To study this possibility, three distinct flow structures are examined: one in which convective structures have similar size and mutual separation at all depths, one in which the separation increases with depth, but their size is still unchanged, and one in which both size and separation increase with depth, which is the standard flow structure. It is concluded that the third possibility with fewer and thicker downdrafts in deeper layers remains the most plausible, but it may be unable to explain the suspected absence of large-scale flows with speeds and scales expected from MLT.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016. Vol. 832, no 1, 6
Keyword [en]
convection, Sun: granulation, turbulence
National Category
Fluid Mechanics and Acoustics Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:kth:diva-202128DOI: 10.3847/0004-637X/832/1/6ISI: 000393043300001Scopus ID: 2-s2.0-84996569789OAI: oai:DiVA.org:kth-202128DiVA: diva2:1079402
Note

QC 20170308

Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-06-16Bibliographically approved

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