Coherent Structures in Large-Eddy Simulations of a Nonprecipitating Stratocumulus-Topped Boundary Layer

Coherent Structures in Large-Eddy Simulations of a Nonprecipitating Stratocumulus-Topped Boundary... AbstractThe 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Coherent Structures in Large-Eddy Simulations of a Nonprecipitating Stratocumulus-Topped Boundary Layer

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0050.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe 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.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Dec 17, 2017

References

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