About the Maximum magnitudes for diffusivity terms

Hi, all

I have a question about setting the vertical eddy viscosities& diffusivities.

For the “background or constant eddy viscosity & diffusivity” and “Maximum magnitudes for diffusivity terms” settings, “use constant” and “use maximums” can be chose respectively. But neither was checked for the default setting in EE (see attached). I’m confused whether the default setting means a constant eddy viscosity & diffusivity was used? I also found that the “use constant” and “use maximums” can be both checked, but i have no idea about the meaning.

Could any one give me some explanations? Thank you very much!

Best wish!

Bin Attached files

Hi Bin,

In EFDC Model, horizontal and vertical eddy viscosities are represented by AH and AV. AHO (Backgroud / Constant horizontal Eddy viscosity) and AVO (Background vertical eddy viscosity) can be used to assign initial values for the computation of AH and AV. So, when the constant option is used, then AH and AV won’t change with time i.e., AH = AH) and AV = AVO. However, if the constant option is not checked, then AH and AV change with time and it won’t be constant. AV is computed using Mellor and Yamada scheme.

If maximum is checked then AV and AB are checked at each time step and if calculated AB is greater than ABMX , then AB is set to ABMX. So, when maximum is checked, then AV and AB maximum values cannot exceed AVMX and ABMX respectively. You can check calavb.f90 for more details.

I hope this helps.

Janesh Devkota