scholarly journals Evaluating Low-Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part III: Tropical and Subtropical Cloud Transitions over the Northern Pacific

2013 ◽  
Vol 26 (16) ◽  
pp. 5761-5781 ◽  
Author(s):  
Anning Cheng ◽  
Kuan-Man Xu
Keyword(s):  
Precipitable Water ◽  
Modeling Framework ◽  
Radiative Fluxes ◽  
Northern Summer ◽  
Community Atmosphere Model ◽  
Low Cloud ◽  
The Mean ◽  
Cloud Parameterization ◽  
Boundary Layer Cloud ◽  
Multiscale Modeling Framework

Abstract An analysis of simulated cloud regime transitions along a transect from the subtropical California coast to the tropics for the northern summer season (June–August) is presented in this study. The Community Atmosphere Model, version 5 (CAM5), superparameterized CAM (SPCAM), and an upgraded SPCAM with intermediately prognostic higher-order closure (SPCAM-IPHOC) are used to perform global simulations by imposing climatological sea surface temperature and sea ice distributions. The seasonal-mean properties are compared with recent observations of clouds, radiation, and precipitation and with multimodel intercomparison results. There are qualitative agreements in the characteristics of cloud regimes along the transect among the three models. CAM5 simulates precipitation and shortwave radiative fluxes well but the stratocumulus-to-cumulus transition occurs too close to the coast of California. SPCAM-IPHOC simulates longwave radiative fluxes and precipitable water well, but with systematic biases in shortwave radiative fluxes. The broad, stronger ascending band in SPCAM is related to the large biases in the convective region but the characteristics of the stratocumulus region are still more realistic and the transition occurs slightly farther away from the coast than in CAM5. Even though SPCAM-IPHOC produces the most realistic seasonal-mean transition, it underestimates the mean gradient in low-cloud cover (LCC) across the mean transition location because of an overestimate of LCC in the transition and convective regions that shifts the transition locations farther from the coast. Analysis of two decoupling measures shows consistency in the mean location and the histogram of decoupling locations with those of LCC transition. CAM5, however, lacks such a consistency, suggesting a need for further refinement of its boundary layer cloud parameterization.

scholarly journals Regional Assessments of Low Clouds against Large-Scale Stability in CAM5 and CAM-CLUBB Using MODIS and ERA-Interim Reanalysis Data

2015 ◽  
Vol 28 (4) ◽  
pp. 1685-1706 ◽  
Author(s):  
Terence L. Kubar ◽  
Graeme L. Stephens ◽  
Matthew Lebsock ◽  
Vincent E. Larson ◽  
Peter A. Bogenschutz
Keyword(s):  
Large Scale ◽  
Reanalysis Data ◽  
Smooth Transition ◽  
Cloud Data ◽  
Low Clouds ◽  
Community Atmosphere Model ◽  
Northeastern Pacific ◽  
Low Cloud ◽  
Cloud Parameterization ◽  
Static Energy

Abstract Daily gridded cloud data from MODIS and ERA-Interim reanalysis have been assessed to examine variations of low cloud fraction (CF) and cloud-top height and their dependence on large-scale dynamics and a measure of stability. To assess the stratocumulus (Sc) to cumulus (Cu) transition (STCT), the observations are used to evaluate two versions of the NCAR Community Atmosphere Model version 5 (CAM5), both the base model and a version that has implemented a new subgrid low cloud parameterization, Cloud Layers Unified by Binormals (CLUBB). The ratio of moist static energy (MSE) at 700–1000 hPa (MSEtotal) is a skillful predictor of median CF of screened low cloud grids. Values of MSEtotal less than 1.00 represent either conditionally or absolutely unstable layers, and probability density functions of CF suggest a preponderance of either trade Cu (median CF < 0.4) or transitional Sc clouds (0.4 < CF < 0.9). With increased stability (MSEtotal > 1.00), an abundance of overcast or nearly overcast low clouds exists. While both MODIS and ERA-Interim indicate a fairly smooth transition between the low cloud regimes, CAM5-Base simulates an abrupt shift from trade Cu to Sc, with trade Cu covering both too much area and occurring over excessively strong stabilities. In contrast, CAM-CLUBB simulates a smoother trade Cu to Sc transition (CTST) as a function of MSEtotal, albeit with too extensive coverage of overcast Sc in the primary northeastern Pacific subsidence region. While the overall CF distribution in CAM-CLUBB is more realistic, too few transitional clouds are simulated for intermediate MSEtotal compared to observations.

scholarly journals Evaluating Low-Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part I: Sensitivity to Spatial Resolution and Climatology

2013 ◽  
Vol 26 (16) ◽  
pp. 5717-5740 ◽  
Author(s):  
Kuan-Man Xu ◽  
Anning Cheng
Keyword(s):  
Multiscale Modeling ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Energy Budget ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Vertical Resolution ◽  
Modeling Framework ◽  
Low Cloud ◽  
Multiscale Modeling Framework

Abstract The multiscale modeling framework, which replaces traditional cloud parameterizations with a 2D cloud-resolving model (CRM) in each atmospheric column, is a promising approach to climate modeling. The CRM component contains an advanced third-order turbulence closure, helping it to better simulate low-level clouds. In this study, two simulations are performed with 1.9° × 2.5° grid spacing but they differ in the vertical resolution. The number of model layers below 700 hPa increases from 6 in one simulation (IP-6L) to 12 in another (IP-12L) to better resolve the boundary layer. The low-cloud horizontal distribution and vertical structures in IP-12L are more realistic and its global mean is higher than in IP-6L and closer to that of CloudSat/Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations. The spatial patterns of tropical precipitation are significantly improved; for example, a single intertropical convergence zone (ITCZ) in the Pacific, instead of double ITCZs in an earlier study that used coarser horizontal resolution and a different dynamical core in its host general circulation model (GCM), and the intensity of the South Pacific convergence zone (SPCZ), and the ITCZ in the Atlantic is more realistic. Many aspects of the global seasonal climatology agree well with observations except for excessive precipitation in the tropics. In terms of spatial correlations and patterns in the tropical/subtropical regions, most surface/vertically integrated properties show greater improvement over the earlier simulation than that with lower vertical resolution. The relationships between low-cloud amount and several large-scale properties are consistent with those observed in five low-cloud regions. There is an imbalance in the surface energy budget, which is an aspect of the model that needs to be improved in the future.

scholarly journals Mean Structure and Diurnal Cycle of Southeast Atlantic Boundary Layer Clouds: Insights from Satellite Observations and Multiscale Modeling Framework Simulations

2014 ◽  
Vol 28 (1) ◽  
pp. 324-341 ◽  
Author(s):  
David Painemal ◽  
Kuan-Man Xu ◽  
Anning Cheng ◽  
Patrick Minnis ◽  
Rabindra Palikonda
Keyword(s):  
Boundary Layer ◽  
Multiscale Modeling ◽  
Diurnal Cycle ◽  
Cloud Cover ◽  
Satellite Observations ◽  
Modeling Framework ◽  
Boundary Layer Clouds ◽  
Mean Structure ◽  
The Mean ◽  
Multiscale Modeling Framework

Abstract The mean structure and diurnal cycle of southeast (SE) Atlantic boundary layer clouds are described with satellite observations and multiscale modeling framework (MMF) simulations during austral spring (September–November). Hourly resolution cloud fraction (CF) and cloud-top height (HT) are retrieved from Meteosat-9 radiances using modified Clouds and the Earth’s Radiant Energy System (CERES) Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms, whereas liquid water path (LWP) is from the University of Wisconsin microwave satellite climatology. The MMF simulations use a 2D cloud-resolving model (CRM) that contains an advanced third-order turbulence closure to explicitly simulate cloud physical processes in every grid column of a general circulation model. The model accurately reproduces the marine stratocumulus spatial extent and cloud cover. The mean cloud cover spatial variability in the model is primarily explained by the boundary layer decoupling strength, whereas a boundary layer shoaling accounts for a coastal decrease in CF. Moreover, the core of the stratocumulus cloud deck is concomitant with the location of the strongest temperature inversion. Although the model reproduces the observed westward boundary layer deepening and the spatial variability of LWP, it overestimates LWP by 50%. Diurnal cycles of HT, CF, and LWP from satellites and the model have the same phase, with maxima during the early morning and minima near 1500 local solar time, which suggests that the diurnal cycle is driven primarily by solar heating. Comparisons with the SE Pacific cloud deck indicate that the observed amplitude of the diurnal cycle is modest over the SE Atlantic, with a shallower boundary layer as well. The model qualitatively reproduces these interregime differences.

scholarly journals Marine boundary layer cloud regimes and POC formation in a CRM coupled to a bulk aerosol scheme

2013 ◽  
Vol 13 (24) ◽  
pp. 12549-12572 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood ◽  
A. Muhlbauer
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Three Dimensional ◽  
Two Dimensional ◽  
State Variables ◽  
Liquid Water Path ◽  
Modeling Framework ◽  
Boundary Layer Cloud ◽  
Cloud Regimes ◽  
Layer Cloud

Abstract. A cloud-resolving model (CRM) coupled to a new intermediate-complexity bulk aerosol scheme is used to study aerosol–boundary-layer–cloud–precipitation interactions and the development of pockets of open cells (POCs) in subtropical stratocumulus cloud layers. The aerosol scheme prognoses mass and number concentration of a single lognormal accumulation mode with surface and entrainment sources, evolving subject to processing of activated aerosol and scavenging of dry aerosol by clouds and rain. The CRM with the aerosol scheme is applied to a range of steadily forced cases idealized from a well-observed POC. The long-term system evolution is explored with extended two-dimensional (2-D) simulations of up to 20 days, mostly with diurnally averaged insolation and 24 km wide domains, and one 10 day three-dimensional (3-D) simulation. Both 2-D and 3-D simulations support the Baker–Charlson hypothesis of two distinct aerosol–cloud "regimes" (deep/high-aerosol/non-drizzling and shallow/low-aerosol/drizzling) that persist for days; transitions between these regimes, driven by either precipitation scavenging or aerosol entrainment from the free-troposphere (FT), occur on a timescale of ten hours. The system is analyzed using a two-dimensional phase plane with inversion height and boundary layer average aerosol concentrations as state variables; depending on the specified subsidence rate and availability of FT aerosol, these regimes are either stable equilibria or distinct legs of a slow limit cycle. The same steadily forced modeling framework is applied to the coupled development and evolution of a POC and the surrounding overcast boundary layer in a larger 192 km wide domain. An initial 50% aerosol reduction is applied to half of the model domain. This has little effect until the stratocumulus thickens enough to drizzle, at which time the low-aerosol portion transitions into open-cell convection, forming a POC. Reduced entrainment in the POC induces a negative feedback between the areal fraction covered by the POC and boundary layer depth changes. This stabilizes the system by controlling liquid water path and precipitation sinks of aerosol number in the overcast region, while also preventing boundary layer collapse within the POC, allowing the POC and overcast to coexist indefinitely in a quasi-steady equilibrium.

STOCHASTICALLY SCALABLE FLOW CONTROL

2009 ◽  
Vol 23 (4) ◽  
pp. 675-698 ◽  
Author(s):  
Thomas Voice
Keyword(s):  
Flow Control ◽  
Probabilistic Models ◽  
Mean Field ◽  
Parameter Choice ◽  
Modeling Framework ◽  
Flow Rates ◽  
Coefficients Of Variation ◽  
Scalable Tcp ◽  
Exponential Red ◽  
The Mean

Recent advances in the mathematical analysis of flow control have prompted the creation of the Scalable TCP (STCP) and Exponential RED (E-RED) algorithms. These are designed to be scalable under the popular deterministic delay stability modeling framework. In this article, we analyze stochastic models of STCP and STCP combined with E-RED link behavior. We find that under certain plausible network conditions, these probabilistic models also exhibit scalable behavior. In particular, we derive parameter choice schemes for which the equilibrium coefficients of variation of flow rates are bounded, however large, fast, or complex the network. Our model is shown to exhibit behavior similar to the mean field convergence that has recently been observed in TCP.

Material Characterization of Additively Manufactured Part via Multi-Level Stochastic Upscaling Method

2015 ◽  
Author(s):  
Recep M. Gorguluarslan ◽  
Sang-In Park ◽  
David W. Rosen ◽  
Seung-Kyum Choi
Keyword(s):  
Material Characterization ◽  
Modeling Framework ◽  
Upscaling Technique ◽  
Simulation Based ◽  
Scale Models ◽  
Multiple Levels ◽  
Multiscale Modeling Framework ◽  
Input Uncertainties

An integrated multiscale modeling framework that incorporates a simulation-based upscaling technique is developed and implemented for the material characterization of additively manufactured cellular structures in this paper. The proposed upscaling procedure enables the determination of homogenized parameters at multiple levels by matching the probabilistic performances between fine and coarse scale models. Polynomial chaos expansion is employed in upscaling procedure to handle the computational burden caused by the input uncertainties. Efficient uncertainty quantification is achieved at the mesocale level by utilizing the developed upscaling technique. The homogenized parameters of mesostructures are utilized again at the macroscale level in the upscaling procedure to accurately obtain the overall material properties of the target cellular structure. Actual experimental results of additively manufactured parts are integrated into the developed procedure to demonstrate the efficacy of the method.

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