working with AESTUS

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The model I'm using to look at internal wave dynamics was created by Daniel Bourgault and Dan Kelley (see Aestus on Daniel Bourgault's website, or Bourgault and Kelley 2004). It is a laterally averaged non-hydrostatic model. This means two things:
  1. In a laterally averaged model, we assume that advection perpendicular to the primary flow is minimally significant. This allows us to reduce the number of dimensions in the model and reduce the time necessary to complete each run (i.e. more experiments in the same amount of time).
  2. A Non-hydrostatic model does not hold the hydrostatic assumption as true. This means the system does not have to be in hydrostatic balance, where the pressure gradient is balanced by the buoyancy forces,Istantanea 2009-02-24 22-14-56.jpg.  Generally, this makes sense: the deeper you go the denser the water and the greater the pressure. But when you want to investigate the dynamics of water that is being mixed, by internal waves for example, the denser water mass is not always deeper. This makes the math for solving the model more complicated and a non-hydrostatic model is capable of handling that.
A big part of running any model is setting up initial conditions that will accurately recreate your system. This is something I'm still fine tuning, and perhaps I'll talk more about that in a later post.

For now, here's what a sample output looks like:
plattsIW.jpg


The figure above shows an internal wave traveling from left to right aross Platts Bank (43°10'N  69°40'W). The colorbar on the right shows density (sigma). Red = less dense water and Blue = denser water. The leading packet of waves (right-most dip of red) is relatively organized in comparison with the trailing wave, especially near the left edge of the bank. This is not only aesthetically pleasing (at least to the author), but it's interesting in terms of what it means for energy dissapation, mixing, and advection. The isobaths 4 km before Platts and 2 km after were artificially created in order to look at the dynamics of the internal waves with the bank not the bathymetric features before and after.

Next time, I'll talk about how we populate the model with krill-like particles to examine the interactions between krill (euphausiidae) and the waves.

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This page contains a single entry by Peter Stetson published on February 25, 2009 3:09 AM.

First unofficial forecast was the previous entry in this blog.

First Forecast w/ Assimilation is the next entry in this blog.

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