Limitations of bin and bulk microphysics in reproducing the observed spatial structure of light precipitation

2021 ◽  
Author(s):  
Mikael K. Witte ◽  
Hugh Morrison ◽  
Anthony B. Davis ◽  
Joao Teixeira
Keyword(s):  
Spatial Structure ◽  
Spatial Scales ◽  
Distribution Functions ◽  
Mixing Ratios ◽  
Eddy Simulation ◽  
Fundamental Limitations ◽  
Scale Modeling ◽  
Large Eddy ◽  
Cloud Regimes

AbstractCoarse-gridded atmospheric models often account for subgrid-scale variability by specifying probability distribution functions (PDFs) of process rate inputs such as cloud and rain water mixing ratios (qc and qr, respectively). PDF parameters can be obtained from numerous sources: in situ observations, ground- or space-based remote sensing, or fine-scale modeling such as large eddy simulation (LES). LES is appealing to constrain PDFs because it generates large sample sizes, can simulate a variety of cloud regimes/case studies, and is not subject to the ambiguities of observations. However, despite the appeal of using model output for parameterization development, it has not been demonstrated that LES satisfactorily reproduces the observed spatial structure of microphysical fields. In this study, the structure of observed and modeled microphysical fields are compared by applying bifractal analysis, an approach that quantifies variability across spatial scales, to simulations of a drizzling stratocumulus field that span a range of domain sizes, drop concentrations (a proxy for mesoscale organization), and microphysics schemes (bulk and bin). Simulated qc closely matches observed estimates of bifractal parameters that measure smoothness and intermittency. There are major discrepancies between observed and simulated qr properties, though, with bulk simulated qr consistently displaying the bifractal properties of observed clouds (smooth, minimally intermittent) rather than rain while bin simulations produce qr that is appropriately intermittent but too smooth. These results suggest fundamental limitations of bulk and bin schemes to realistically represent higher-order statistics of the observed rain structure.

scholarly journals Implicit large eddy simulation of shock-driven material mixing

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120217 ◽  
Author(s):  
F. F. Grinstein ◽  
A. A. Gowardhan ◽  
J. R. Ristorcelli
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Mixing ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Late Time ◽  
Eddy Simulation ◽  
Geometrical Complexity ◽  
Planar Shock ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.

scholarly journals Interpolation of LES Cloud Surfaces for Use in Direct Calculations of Entrainment and Detrainment

2011 ◽  
Vol 139 (2) ◽  
pp. 444-456 ◽  
Author(s):  
Jordan T. Dawe ◽  
Philip H. Austin
Keyword(s):  
Numerical Model ◽  
Spatial Scales ◽  
Grid Cell ◽  
Time Step ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Temporal And Spatial ◽  
Les Model ◽  
Direct Calculations ◽  
Good Agreement

Abstract Direct calculations of the entrainment and detrainment of air into and out of clouds require knowledge of the relative velocity difference between the air and the cloud surface. However, a discrete numerical model grid forces the distance moved by a cloud surface over a time step to be either zero or the width of a model grid cell. Here a method for the subgrid interpolation of a cloud surface on a discrete numerical model grid is presented. This method is used to calculate entrainment and detrainment rates for a large-eddy simulation (LES) model, which are compared with rates calculated via the direct flux method of Romps. The comparison shows good agreement between the two methods as long as the model clouds are well resolved by the model grid spacing. This limitation of this technique is offset by the ability to resolve fluxes on much finer temporal and spatial scales, making it suitable for calculating entrainment and detrainment profiles for individual clouds.

MESOSCALE EXPERIMENTS HELP TO EVALUATE IN-SITU BURNING OF OIL SPILLS1

1993 ◽  
Vol 1993 (1) ◽  
pp. 755-760
Author(s):  
David D. Evans ◽  
William D. Walton ◽  
Howard R. Baum ◽  
Kathy A. Notarianni ◽  
Edward J. Tennyson ◽  
...  
Keyword(s):  
Crude Oil ◽  
Combustion Products ◽  
Coast Guard ◽  
Effective Diameter ◽  
Smoke Plume ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Particulate Deposition ◽  
Primary Combustion Products

ABSTRACT Burning of spilled oil has distinct advantages over other cleanup countermeasures. It offers the potential to convert rapidly large quantities of oil into its primary combustion products, carbon dioxide and water, with a small percentage of other unburned and residue byproducts. Disadvantages include the dispersal of the combustion products into the air. Mesoscale and laboratory experiments have been conducted to measure the burning characteristics of crude oil fires. Measurements on crude oil pool fires from 0.4 m to 17.2 m in effective diameter were made to obtain data on the rate of burning, heat release rate, composition of the combustion products, and downwind dispersion of the products. The smaller experiments were performed in laboratories at the National Institute of Standards and Technology and the Fire Research Institute in Japan; and the larger ones at the U. S. Coast Guard Fire Safety and Test Detachment in Mobile, Alabama. From these experiments, the value for surface regression rate of a burning crude oil spill was found to be 0.055 mm/s. A major concern for public safety is the content and extent of the smoke plume from the fires. Smoke yield, the fraction of the oil mass burned that is emitted as particulate, was found to be 13 percent. A large-eddy simulation calculation method for smoke plume trajectory and smoke particulate deposition developed by NIST showed that the smoke particulate deposition from a 114 m2 burn would occur in striations over a long, slender area 3.2 km wide and 258 km downwind of the burn.

scholarly journals The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

2015 ◽  
Vol 8 (4) ◽  
pp. 3481-3522 ◽  
Author(s):  
P. J. H. Volker ◽  
J. Badger ◽  
A. N. Hahmann ◽  
S. Ott
Keyword(s):  
Large Scale ◽  
Wind Farm ◽  
Mesoscale Model ◽  
Wind Farms ◽  
Simulation Models ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. We describe the theoretical basis, implementation and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP), uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

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