Coherent structures in large-eddy simulations of a nonprecipitating stratocumulus-topped boundary layer

Paolo Davini, Fabio D'Andrea, Seung Bu Park, Pierre Gentine

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

The properties of coherent convective structures are analyzed in a nonprecipitating marine nocturnal stratocumulus-topped boundary layer (STBL) with a series of high-resolution large-eddy simulations (LESs). A new classification method based on octant analysis-using vertical velocity and two passive scalars-is introduced to systematically define convective structures in both the cloudy and the cloud-free regions. It is therefore possible to detect and track updrafts, downdrafts, and their turbulent shells (both ascending and subsiding), together with the entraining air from the inversion layer or the free troposphere. The geometrical and thermodynamical characteristics (e.g., areal fraction, temperature, liquid and total water mixing ratio, buoyancy) of those structures are then accurately described, and particular attention is given to their respective contributions to the turbulent transport of mass, heat, and moisture. It is shown that updrafts, downdrafts, and entrainment are equally important to describe the STBL dynamics. Conversely, it is found that shells, although they partially contribute to the mass transport, have a negligible contribution to the turbulent fluxes of heat and moisture.

Original languageEnglish
Pages (from-to)4117-4137
Number of pages21
JournalJournals of the Atmospheric Sciences
Volume74
Issue number12
DOIs
StatePublished - 1 Dec 2017

Keywords

  • Boundary layer
  • Clouds
  • Large eddy simulations
  • Stratiform clouds

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