Hot answers tagged

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....
user avatar
  • 4,935
18 votes

Great Pacific Garbage Patch Equilibrium Points

Theoretically, I agree that there should be one instable equilibrium point between the two stable equilibrium points when we have a 2D current field. However, there are some additional components of ...
user avatar
18 votes
Accepted

Great Pacific Garbage Patch Equilibrium Points

Yes, you're right, there should be (at least one) saddle point in the middle of the loop. And indeed, if you search for illustrations of Pacific ocean circulation, you can see the saddle point in ...
user avatar
17 votes
Accepted

Why is WRF most often configured at 3:1 nesting ratio?

To understand why the nesting ratio of 3 is preferred to the nesting ratio of 2, it is important to understand the following two features of WRF: 1) Grids are Arakawa C-staggered: mass points are at ...
user avatar
  • 4,935
16 votes
Accepted

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 ...
user avatar
  • 13.9k
16 votes
Accepted

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 ...
user avatar
  • 4,935
15 votes
Accepted

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 ...
user avatar
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 ...
user avatar
  • 4,935
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 ...
user avatar
13 votes
Accepted

Why can't wave models model storm surge?

Yes. Spectral wave models cannot model storm surge because the wave energy balance equation that they integrate does not describe the physical processes associated with storm surge. Wave models solve ...
user avatar
  • 4,935
12 votes
Accepted

Similarities between grand circulation solvers and mantle convection solvers

Disclaimer: This is a partial answer given that my background is modeling of the ocean. I hope that some mantle convection modelers can complement this answer. The question is good but the answer is ...
user avatar
12 votes
Accepted

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 ...
user avatar
  • 4,935
12 votes
Accepted

Predicting rainfall with governing equations

The Barotropic vorticity equation is insufficient to model rain. Part of this is due to the word 'Barotropic,' which indicates a lack of thermal gradient. The other reason is that while vorticity is a ...
user avatar
11 votes

Is there value in using a model that fails at validation against measurements?

The late George Box famously said: All models are wrong. Some models are useful All models are wrong. That's important. All models are wrong. In any real-world system that we're interested in, ...
user avatar
  • 4,090
11 votes
Accepted

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'...
user avatar
  • 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 ...
user avatar
  • 4,090
11 votes
Accepted

Converting grid resolution from degrees to kilometers

Assuming spherical shape, Earth's circumference is about $40,000\mathrm{km}$. These are split into $360^\circ$, so one degree is a bit more than $100\mathrm{km}$. This is true for latitudes. For ...
user avatar
  • 994
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. ...
user avatar
  • 12.7k
10 votes

Software for sediment transport modeling

I think the best option for sediment transport modeling is the Community Sediment Transport Modeling System (CSTMS) package that was developed for ROMS. CSTMS was created by a group of sediment ...
user avatar
  • 14.7k
10 votes
Accepted

How to calculate w-wind?

Omega, ω is closely related to w in meteorology. It can be moved towards w using the chain (this reminder from Watkins at SJSU helped)... ...
user avatar
10 votes

What is the difference between GFS analysis and GFS forecast data?

I'm no expert at this, I've just been working with a variety of gfs gribs for a while now. The only thing I know about them is what I've read and I'll cite them here. I don't know where you got ...
user avatar
  • 291
9 votes

What determines the differences in results between various weather models?

Everything. Parametrizations Spatial (horizontal and vertical) and temporal resolution Initialization Dynamical core Handling of some complex non-linear physical processes (i.e. snow) Topography ...
user avatar
  • 439
9 votes
Accepted

Is there value in using a model that fails at validation against measurements?

The answer depends very much on where the model fails. If it is very accurate in some regimes but very inaccurate in others, that model can still be used in those regimes where it is known to be very ...
user avatar
  • 20.5k
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 ...
user avatar
  • 6,277
9 votes
Accepted

References for moving and nested grids in models

Book: Shyy W, Udaykumar HS, Rao MM, Smith RW. Computational Fluid Dynamics with Moving Boundaries. Taylor& Francis: London, 1996. Some relevant papers: Jin C, Xu K. A unified moving grid gas-...
user avatar
9 votes

Why do deviated wells show poor correlation to seismic data?

Two-way time to depth calibration is a vertical problem. How you handle deviated wells probably depends a bit on how you are tying the wells. Here are two things to watch out for: You should be ...
user avatar
  • 10.8k
9 votes
Accepted

Long-term Wind Speed Forecasting: reality or wishful thinking?

Warning: "long-term wind-speed forecasting for generation" has (at least) two very different meanings. One refers to forecasting a distribution of wind speeds; the other refers to hour-by-hour (or ...
user avatar
  • 4,090
9 votes

Does finer input data lead to a better model accuracy?

My experience with the WRF is in tropical cyclone simulation, but here are some things to consider: Smaller scale information might already be resolved in your higher resolution initial conditions, ...
user avatar
  • 315
9 votes
Accepted

How to run earth system, land surface and climate models?

As alluded to in some of the comments, all of the CMIP5 models will have been run on supercomputers, and it takes a lot of effort to get one of them running on a new platform, even for a team who know ...
user avatar
  • 3,303
8 votes

Is there value in using a model that fails at validation against measurements?

Yes there is value. 1)Often times we use models to check our own understanding of a process. If the model is built with all known factors included, it might still fail to produce results that can ...
user avatar
  • 12.7k

Only top scored, non community-wiki answers of a minimum length are eligible