A Grid-Refinement-Based Approach for Modeling the Convective Boundary Layer in the Gray Zone: A Pilot Study

A Grid-Refinement-Based Approach for Modeling the Convective Boundary Layer in the Gray Zone: A... AbstractThe model gray zone refers to the range of grid spacings comparable to the dominant length scale of the flow. In the gray zone, the flow is partially resolved and partially subgrid-scale (SGS). Neither ensemble-averaging-based parameterizations nor turbulence closures are appropriate for parameterizing the effects of SGS motions on the resolved flow. The gray zone of the convective boundary layer (CBL) is in the range of CBL depth, typically of O(1 km). A new approach that seeks explicit resolution of the unstable surface layer through a nest layer of fine grid spacing is proposed to improve CBL parameterization in the gray zone. To provide the theoretical basis for the approach, a linear analytic model is presented and one-way nested simulations are performed to investigate the dynamical coupling between the surface layer and the mixed layer. The analytic model shows that at the onset of thermal instability, the vertical and the horizontal structures of the mixed layer are set by surface layer forcings. The nested 3D simulations extend the findings from the analytic model, and further reveal potential improvements in highorder statistics, resolved convective structures both including and extending above the nest region, compared to the stand-alone gray zone simulations. This study suggests that when the most energetic scales of CBL convection is resolved in the surface layer, the overall simulation of the CBL improves at gray zone resolutions. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

A Grid-Refinement-Based Approach for Modeling the Convective Boundary Layer in the Gray Zone: A Pilot Study

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-16-0376.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe model gray zone refers to the range of grid spacings comparable to the dominant length scale of the flow. In the gray zone, the flow is partially resolved and partially subgrid-scale (SGS). Neither ensemble-averaging-based parameterizations nor turbulence closures are appropriate for parameterizing the effects of SGS motions on the resolved flow. The gray zone of the convective boundary layer (CBL) is in the range of CBL depth, typically of O(1 km). A new approach that seeks explicit resolution of the unstable surface layer through a nest layer of fine grid spacing is proposed to improve CBL parameterization in the gray zone. To provide the theoretical basis for the approach, a linear analytic model is presented and one-way nested simulations are performed to investigate the dynamical coupling between the surface layer and the mixed layer. The analytic model shows that at the onset of thermal instability, the vertical and the horizontal structures of the mixed layer are set by surface layer forcings. The nested 3D simulations extend the findings from the analytic model, and further reveal potential improvements in highorder statistics, resolved convective structures both including and extending above the nest region, compared to the stand-alone gray zone simulations. This study suggests that when the most energetic scales of CBL convection is resolved in the surface layer, the overall simulation of the CBL improves at gray zone resolutions.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Aug 9, 2017

References

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