Evaluation of Large-Eddy Simulations via Observations of Nocturnal Marine Stratocumulus

By Bjorn Stevens, C. Moeng, A. Ackerman, Chris Bretherton, A. Chlond, S. Roode, J. Edwards, J. Golaz, Hongli Jiang, M. Khairoutdinov and 7 more. 2005

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Data from the first research flight (RF01) of the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study are used to evaluate the fidelity with which large-eddy simulations (LESs) can represent the turbulent structure of stratocumulus-topped boundary layers. The initial data and forcings for this case placed it in an interesting part of parameter space, near the boundary where cloud-top mixing is thought to render the cloud layer unstable on the one hand, or tending toward a decoupled structure on the other hand. The basis of this evaluation consists of sixteen 4-h simulations from 10 modeling centers over grids whose vertical spacing wa s5ma t thecloud-top interface and whose horizontal spacing was 35 m. Extensive sensitivity studies of both the configuration of the case and the numerical setup also enhanced the analysis. Overall it was found that (i) if efforts are made to reduce spurious mixing at cloud top, either by refining the vertical grid or limiting the effects of the subgrid model in this region, then the observed turbulent and thermodynamic structure of the layer can be reproduced with some fidelity; (ii) the base, or native configuration of most simulations greatly overestimated mixing at cloud top, tending toward a decoupled layer in which cloud liquid water path and turbulent intensities were grossly underestimated; (iii) the sensitivity of the simulations to the representation of mixing at cloud top is, to a certain extent, amplified by particulars of this case. Overall the results suggest that the use of LESs to map out the behavior of the stratocumulus-topped boundary layer in this interesting region of parameter space requires a more compelling representation of processes at cloud top. In the absence of significant leaps in the understanding of subgrid-scale (SGS) physics, such a representation can only be achieved by a significant refinement in resolution—a refinement that, while conceivable given existing resources, is probably still beyond the reach of most centers.

Subfields: Atmospheric Science, Environmental Engineering, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/58477d83b56e67f24ae36f767d40b4501c68abef

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Citations in the corpus

Notes on state-of-the-art investigations of aerosol effects on precipitation: a critical review (2009, background): “At the same time, the problem of adequate description of turbulent mixing and entrainment is not yet solved (see, e.g., Stevens et al 2005).”
Impacts of cloud microphysics on trade wind cumulus: which cloud microphysics processes contribute to the diversity in a large eddy simulation? (2015, methodology): “For this sensitivity test, the experimental setup of the second Dynamics and Chemistry of Marine Stratocumulus Research Flight 1 (DYCOMS-II RF01) (Stevens et al. 2005) was used.”
Formulation of the Dutch Atmospheric Large-Eddy Simulation (DALES) and overview of its applications (2010, background): “The GCSS looks at different aspects of boundary layer clouds, mainly shallow cumulus and stratocumulus clouds (Bretherton et al., 1999a,b; Duynkerke et al., 1999, 2004; Brown et al., 2002; Siebesma et al., 2003; Stevens et al., 2001, 2005; Ackerman et al., 2009; van Zanten et al., 2010).”
Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer (2009, methodology): “The cloud field sampled on that flight was bimodal, with pockets of heavily drizzling open cells amid a deck of closed-cell stratocumulus that was drizzling lightly (vanZanten and Stevens 2005; Stevens et al. 2005a).”
MicroHH 1.0: a computational fluid dynamics code for direct numerical simulation and large-eddy simulation of atmospheric boundary layer flows (2017, background): “(Heus et al., 2010), UCLA-LES (Stevens et al., 2005), and PALM (Maronga et al., 2015), deserve a reference as MicroHH could not have been possible without those.”
A New Moist Turbulence Parameterization in the Community Atmosphere Model (2009, methodology): “The case specifications are given by Stevens et al. (2005) and only key aspects will be summarized here.”
The Influence of Entrainment and Mixing Assumption on Aerosol–Cloud Interactions in Marine Stratocumulus (2009, background): “…cloudy air can play an important role in the evolution of climatologically significant marine stratocumulus (Sc) (e.g., Lilly 1968; Deardorff 1980; Randall 1980; MacVean and Mason 1990; Wang and Albrecht 1994; Moeng et al. 1995; Gerber et al. 2005; Stevens et al. 2005; Burnet and Brenguier 2007).”
Mechanisms of marine low cloud sensitivity to idealized climate perturbations: A single‐LES exploration extending the CGILS cases (2013, background): “Stevens (2012), The influence of wind speed on shallow marine cumulus convection, J.”
Droplet growth in warm turbulent clouds (2012, background): “This has led Stevens et al. (2005) to suggest that the entrainment rate may not only be sensitive to the energy-containing eddies but also to the small-scale (subgrid) eddies which are not explicitly resolved in LES, either directly or indirectly through the impact of the small-scale (subgrid)…”
The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics (2014, methodology): “a. Model description and experimental setup Simulations were performed using the University of California, Los Angeles (UCLA) large-eddy simulation (LES) model [see Stevens et al. (2005)].”
The Parallelized Large-Eddy Simulation Model (PALM) version 4.0 for atmospheric and oceanic flows: model formulation, recent developments, and future perspectives (2015, background): “The optimization and scalability of PALM and future developments like the vertical self-nesting of PALM or the multiple GPU adaptation that will be available in the near future will support the usage of PALM for such applications.”