Impact of Local Grid Refinements of Spherical Centroidal Voronoi Tessellations for Global Atmospheric Models

2017 ◽  
Vol 21 (5) ◽  
pp. 1310-1324 ◽  
Author(s):  
Yudi Liu ◽  
Taojin Yang
Keyword(s):  
Model Simulation ◽  
Horizontal Resolution ◽  
Global Model ◽  
Test Cases ◽  
Atmospheric Models ◽  
Voronoi Tessellations ◽  
Local Refinement ◽  
Reflected Waves ◽  
Centroidal Voronoi Tessellations ◽  
Local Grid

AbstractIn order to study the local refinement issue of the horizontal resolution for a global model with Spherical Centroidal Voronoi Tessellations (SCVTs), the SCVTs are set to 10242 cells and 40962 cells respectively using the density function. The ratio between the grid resolutions in the high and low resolution regions (hereafter RHL) is set to 1:2, 1:3 and 1:4 for 10242 cells and 40962 cells, and the width of the grid transition zone (for simplicity, WTZ) is set to 18° and 9° to investigate their impacts on the model simulation. The ideal test cases, i.e. the cosine bell and global steady-state nonlinear zonal geostrophic flow, are carried out with the above settings. Simulation results showthat the larger the RHL is, the larger the resulting error is. It is obvious that the 1:4 ratio gives rise to much larger errors than the 1:2 or 1:3 ratio; the errors resulting from the WTZ is much smaller than that from the RHL. No significant wave distortion or reflected waves are found when the fluctuation passes through the refinement region, and the error is significantly small in the refinement region. Therefore,when designing a local refinement scheme in the global model with SCVT, the RHL should be less than 1:4, i.e., the error is acceptable when the RHL is 1:2 or 1:3.

scholarly journals Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream–aquifer exchanges

2015 ◽  
Vol 19 (11) ◽  
pp. 4531-4545 ◽  
Author(s):  
J. Zhu ◽  
C. L. Winter ◽  
Z. Wang
Keyword(s):  
Groundwater Flow ◽  
Effective Conductivity ◽  
Model Simulation ◽  
Three Dimensional ◽  
Small Scale ◽  
Heihe River ◽  
Effective Parameters ◽  
Aquifer Systems ◽  
Basin Scale ◽  
Local Grid

Abstract. Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream–aquifer exchanges, and (H3) the biases result from slow paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream–aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop lognormally distributed conductivity (K) fields on local grid scales. Stream–aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model. Although aquifer heterogeneities are uncorrelated at local scales, they appear to induce coherent slow paths in groundwater fluxes that in turn reduce aquifer–stream exchanges. Since surface water–groundwater exchanges are critical hydrologic processes in basin-scale water budgets, these results also have implications for water resources management.

Climate impacts of land-use change in China and its uncertainty in a global model simulation

2008 ◽  
Vol 32 (4) ◽  
pp. 473-494 ◽  
Author(s):  
Huqiang Zhang ◽  
Xuejie Gao ◽  
Yaohui Li
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Model Simulation ◽  
Climate Impacts ◽  
Global Model

scholarly journals An Intercomparison of T-REX Mountain-Wave Simulations and Implications for Mesoscale Predictability

2011 ◽  
Vol 139 (9) ◽  
pp. 2811-2831 ◽  
Author(s):  
James D. Doyle ◽  
Saša Gaberšek ◽  
Qingfang Jiang ◽  
Ligia Bernardet ◽  
John M. Brown ◽  
...  
Keyword(s):  
Wave Breaking ◽  
Numerical Models ◽  
Lower Boundary ◽  
Horizontal Resolution ◽  
Test Cases ◽  
Mountain Wave ◽  
Initial State ◽  
Wave Characteristics ◽  
Rotor Experiment ◽  
Ensemble Systems

Numerical simulations of flow over steep terrain using 11 different nonhydrostatic numerical models are compared and analyzed. A basic benchmark and five other test cases are simulated in a two-dimensional framework using the same initial state, which is based on conditions during Intensive Observation Period (IOP) 6 of the Terrain-Induced Rotor Experiment (T-REX), in which intense mountain-wave activity was observed. All of the models use an identical horizontal resolution of 1 km and the same vertical resolution. The six simulated test cases use various terrain heights: a 100-m bell-shaped hill, a 1000-m idealized ridge that is steeper on the lee slope, a 2500-m ridge with the same terrain shape, and a cross-Sierra terrain profile. The models are tested with both free-slip and no-slip lower boundary conditions. The results indicate a surprisingly diverse spectrum of simulated mountain-wave characteristics including lee waves, hydraulic-like jump features, and gravity wave breaking. The vertical velocity standard deviation is twice as large in the free-slip experiments relative to the no-slip simulations. Nevertheless, the no-slip simulations also exhibit considerable variations in the wave characteristics. The results imply relatively low predictability of key characteristics of topographically forced flows such as the strength of downslope winds and stratospheric wave breaking. The vertical flux of horizontal momentum, which is a domain-integrated quantity, exhibits considerable spread among the models, particularly for the experiments with the 2500-m ridge and Sierra terrain. The differences among the various model simulations, all initialized with identical initial states, suggest that model dynamical cores may be an important component of diversity for the design of mesoscale ensemble systems for topographically forced flows. The intermodel differences are significantly larger than sensitivity experiments within a single modeling system.

Mahalanobis centroidal Voronoi tessellations

2015 ◽  
Vol 46 ◽  
pp. 48-54 ◽  
Author(s):  
Ronald Richter ◽  
Marc Alexa
Keyword(s):  
Voronoi Tessellations ◽  
Centroidal Voronoi Tessellations
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