18 votes

How important is understanding linear algebra in groundwater modeling?

Relatively important, depending on the basic principles of the modeling you are interested in, and to what extent you want to get yourself involved in it. In many areas of computational geophysics, e....
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  • 4,925
16 votes
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How to get cell indices from latitude and longitude in WRF model grids?

I've been a WRF user for almost 5 years now, and contributed code to a recent public release. I am not aware that WPS (WRF Preprocessing System) has such a tool that takes in the grid and point ...
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  • 4,925
16 votes
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What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction?

The hydrostatic approximation begins with the full 3-D momentum equation (Navier-Stokes) and through scale analysis the vertical momentum equation reduces to: $$\dfrac{\partial p}{\partial z} = -\rho ...
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15 votes
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What are the differences between an LES-SGS model and a RANS based turbulence model?

The biggest difference between LES and RANS is that, contrary to LES, RANS assumes that $\overline{u'_i} = 0$ (see the Reynolds-averaged Navier–Stokes equations). In LES the filter is spatially based ...
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14 votes

Resources for learning the technical parts of atmospheric modeling

For fundamentals on numerical methods applied in atmosphere and ocean modeling, see the GARP publication by Mesinger and Arakawa: Numerical Methods Used in Atmospheric Models. This old, but certainly ...
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  • 4,925
13 votes
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What is the force imposed by underwater currents?

You are looking for the drag force imposed by the fluid flow on an object: $$F = \dfrac{1}{2} \rho v^{2} C_D A$$ where $\rho$ is the density of the fluid, $v$ is the speed of the flow, $C_D$ is the ...
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  • 4,925
13 votes

What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction?

This is my favorite example of the difference between a hydrostatic and a non-hydrostatic code. The simulation depicts a lock exchange which you can picture as opening your window if you live in a ...
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12 votes
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Stability correction factor in the Wavewatch III wave model

The stability correction factor ASF is related to the effects of atmospheric stability (function of buoyancy and shear) on wave growth, and has been implemented in ...
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  • 4,925
11 votes
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Confusion about grid registration concepts and their relevance in modelling

Yes, it makes a difference. In this case the grid-registered dataset is higher fidelity. However, the cell-registered is easier to handle. As you see, both types of data are available on the dataset'...
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  • 10.8k
11 votes

What exactly is a model grid?

A model is a simplified representation of a system. Rather than try to model everything down to the microscopic level, or as vectors, we often aggregate phenomena across geographic areas, to simplify ...
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  • 4,060
10 votes

How to get cell indices from latitude and longitude in WRF model grids?

This question might be better suited for GIS stack exchange... but I'll take a shot: dx and dy are the distance per grid cell in the projected grid units, which is part of your grid definition. ...
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  • 12.7k
10 votes
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Are there any general-purpose climate-model coupling projects?

Yes, there were many model coupling projects in the past, as well as many ongoing coupling projects in the present and near future. The main motivation behind model coupling is the need for the ...
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  • 4,925
10 votes

Are there any general-purpose climate-model coupling projects?

Coupler software (e.g. OASIS, MCT, C-Coupler) is frequently used to combine these different components of earth system models. Of course interfacing models with each other using these couplers or ...
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  • 1,662
9 votes

How to get cell indices from latitude and longitude in WRF model grids?

I am posting my code that calculates i_parent_start and j_parent_start. It is in Java and as people are aware Java does not have ...
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  • 6,208
8 votes
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What are the differences between implicit and explicit methods when applied to modelling Earth systems?

The answer by @IsopycnalOscillation explains some implications of using explicit and implicit schemes and in what applications one is preferred over the other. Here, I describe how these two methods ...
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  • 4,925
8 votes
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Meaning of Coupling in Modelling

In Earth-system models, the term "coupling" is often used in two ways. The first is "offline" coupling, where output from one model is passed to another model for computation of some variable. The ...
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  • 12.7k
8 votes

How do spectral methods work in the context of numerical weather prediction models?

Presume that the atmosphere can be modeled with waves of different frequencies. Therefore, the atmosphere can be written as a series of sine and cosine functions with different frequencies and ...
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7 votes

How to get cell indices from latitude and longitude in WRF model grids?

Try NCL. It has a package for WRF-related functions, including the bidirectional grid-coordinates conversion routine. To convert coordinate pairs to grid indices, follow the documentation here: ...
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  • 181
7 votes

Meaning of Coupling in Modelling

Coupling refers to communication and interchange of information between models. For example a typical standalone atmospheric model may be initialized with information about sea surface temperature. ...
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  • 13.9k
7 votes

What are the differences between implicit and explicit methods when applied to modelling Earth systems?

Implicit and explicit methods have the same differences no matter what context. The building blocks from which these methods are constructed are the same, they all use Taylor series expansion of a ...
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7 votes
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How to install ESMF and ESMFPy in Ubuntu using gfortran, gcc, python?

First download the esmf tar file from http://www.earthsystemmodeling.org/esmf_releases/public/ESMF_7_1_0r/reg/ESMF_Framework_Down.html Then install netcdf library and gfortran compiler using ...
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6 votes
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How to estimate dispersion in stratified flows

There are lots of studies considering Lagrangian dispersion. One critical aspect is the addition of random displacement to the deterministic particle track in order to consider subgrid-scale processes....
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  • 14.7k
6 votes
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Optimal vertical coordinate for complex topography

This is a big question, but there are benefits and difficulties with all representations, and the efficacy of any coordinate will also depend upon other numerical choices such as the calculation of ...
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6 votes
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How are boundary conditions considered in PDEs?

In any solution to a PDE, whether analytical or numerical, you will always need as many BCs as the number of derivative steps. For examples: $$dY/dt = k Y$$ needs one BC while $$\partial Y/\partial t =...
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5 votes

What exactly is a model grid?

Specifically the term the values are archived on 2.5° grid means that the values that are being reported are being saved and are available at that resolution for historical values. The higher ...
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  • 508
5 votes

What exactly is a model grid?

To add a bit more mathematical conception to the idea of a grid: think about a 2-D grid(X,Y) as a matrix: this matrix represents a solution to the system of equations you are trying to solve at grid ...
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  • 6,356
5 votes
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How do academics/institutions run large climate simulations given the computing challenges?

This question is a little vague, with multiple aspects, but I shall do my best. Computing resources Some universities have their own clusters or supercomputers. But many countries also have regional ...
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4 votes

Meaning of Coupling in Modelling

Coupling is used in the context of feedback between various processes. It can be weak or strong. E.g, if you heat a rod it expands mechanically due to thermoelastic effects (strong coupling) but when ...
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  • 2,361
4 votes
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Does hydroxyl radical chemistry in air quality models create numerical stability problems?

The hydroxyl radical chemistry is not modeled explicitly in air quality models, so numerical stability is not an issue. Instead, OH is held in pseudo-steady-state. For instance, see CMAQ's ...
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  • 12.7k
4 votes

Effect of urbanization on weather events

I did my undergraduate capstone on observational moisture changes around cities. It's an interesting field, though it certainly seems fairly challenging to draw out and explain changes given the ...
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