### Abstract

A large eddy simulation (LES) is used to estimate a reliable horizontal turbulent diffusion coefficient, K_{h}, in a convective mixed layer (CML). The introduction of a passive scalar field with a fixed horizontal gradient at a given time enables K_{h} estimation as a function of height, based on the simulated turbulent horizontal scalar flux. Here K_{h} is found to be of the order of 100 m^{2} s^{-1} for a typical terrestrial atmospheric CML. It is shown to scale by the product of the CML convective velocity, w_{∗}, and its depth, h. Here K_{h} is characterized by a vertical profile in the CML: it is large near both the bottom and top of the CML, where horizontal flows associated with convection are large. The equation pertaining to the temporal rate of change of a horizontal scalar flux suggests that K_{h} is determined by a balance between production and pressure correlation at a fully developed stage. Pressure correlation near the bottom of the CML is localized in convergence zones near the boundaries of convective cells and becomes large within an eddy turnover time, h/w_{∗}, after the introduction of the passive scalar field.

Original language | English |
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Pages (from-to) | 553-564 |

Number of pages | 12 |

Journal | Journal of Fluid Mechanics |

Volume | 758 |

DOIs | |

Publication status | Published - 2014 Nov 10 |

Externally published | Yes |

### ASJC Scopus subject areas

- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering

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## Cite this

*Journal of Fluid Mechanics*,

*758*, 553-564. https://doi.org/10.1017/jfm.2014.545