Sigma-Zed in EFDC+ GVC in EFDC


I am pretty curious and interested in the Sigma-Zed which is used in EFDC+ to deal with pressure gradient error.

I haven’t got the chance to know more about Sigma-Zed and try it personally. Based on the introduction from the website, it seems that Sigma-Zed is pretty much the same as GVC. Can anyone tell me what’s the difference?



Here are some of the differences between Sigma-Zed (SGZ) that is implemented in EFDC+ and GVC model.

1. SGZ approach in EFDC+ is computationally more efficient. GVC computes values for every cell / layer, even if they are not used. SGZ approach skips layers that are not used which results in reduced run times.
2. SGZ approach computes buoyancy integrals at each cell face whereas GVC computes a single cell centroid buoyancy integral. SGZ approach results in less artificially induced buoyancy gradient forcing.
3. SGZ uses the cell face metrics to compute buoyancy component of the internal soluation for the UVW distribution.
4. SGZ implement openMP (shared memory) technology that results in significant reduction in run time.

I hope this helps.