## How to compute the energy dissipation in the model

General scientific issues regarding ROMS

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FEEL2020
Posts: 4
Joined: Mon Mar 09, 2020 3:12 pm
Location: Beijing Jiaotong University

### How to compute the energy dissipation in the model

Hello everyone;

As a beginner of ROMS,i meet a question? How to compute the energy dissipation in the model? At present, I use vertical eddy viscosity coefficient（Km）, bottom friction and horizontal viscosity as dissipation. Is this method reasonable？Is there a way to output energy dissipation？

FEEL2020
Posts: 4
Joined: Mon Mar 09, 2020 3:12 pm
Location: Beijing Jiaotong University

### Re: How to compute the energy dissipation in the model

Or use the diagnostic files（Diagnostic momentum terms） to calculate the energy of dissipation ？

SivaHeramb
Posts: 5
Joined: Mon Aug 05, 2019 1:39 pm
Location: Indian Institute of Technology Delhi

### Re: How to compute the energy dissipation in the model

Hi Feel,

Did you find any way to calculate the dissipation?

Thanks

FEEL2020
Posts: 4
Joined: Mon Mar 09, 2020 3:12 pm
Location: Beijing Jiaotong University

### Re: How to compute the energy dissipation in the model

Now I calculate the dissipation by Diagnostic momentum terms

pmaccc
Posts: 56
Joined: Wed Oct 22, 2003 6:59 pm
Location: U. Wash., USA

### Re: How to compute the energy dissipation in the model

We give some details about using the ROMS diagnostics to calculate terms in energy budgets in this paper. Email me if you want a copy. pmacc@uw.edu

MacCready, P., and S. N. Giddings, 2016: The Mechanical Energy Budget of a Regional Ocean Model. J. Phys. Oceanogr., 46, JPO-D-16-0086.1, doi:10.1175/JPO-D-16-0086.1.

SivaHeramb
Posts: 5
Joined: Mon Aug 05, 2019 1:39 pm
Location: Indian Institute of Technology Delhi

### Re: How to compute the energy dissipation in the model

Hi pmaccc,

I calculated terms according to the budget equations based on your paper (MacCready 2016).

In my case, kinetic energy clearly decreases with time, but the KE_storage term in the budget comes out to be a positive value. I was not clear how could this happen.

Also, I was wondering how does the Coriolis term comes into these equations, as it should not be contributing to the kinetic energy.

Could you please give some insight on these two questions?

Siva

pmaccc
Posts: 56
Joined: Wed Oct 22, 2003 6:59 pm
Location: U. Wash., USA

### Re: How to compute the energy dissipation in the model

Siva - that is a perplexing result. How do you know that KE decreases with time?

SivaHeramb
Posts: 5
Joined: Mon Aug 05, 2019 1:39 pm
Location: Indian Institute of Technology Delhi

### Re: How to compute the energy dissipation in the model

I calculated the kinetic energy from u and v velocities. It decreases with time.

And, I calculated the KE storage term (in the budget equation) using huon and u_accel.

pmaccc
Posts: 56
Joined: Wed Oct 22, 2003 6:59 pm
Location: U. Wash., USA

### Re: How to compute the energy dissipation in the model

Siva,

Budgets can be surprisingly difficult to calculate, and are easy to make coding errors in. When you make a budget term from the diagnostics, try to make the same budget term from scratch using the history files, and then plot the two on the same graph vs. time. In most cases they should be reasonably similar. The most important thing is to start with simpler fields. First, construct a budget of volume. If this cannot be done with reasonably small error then there is no point on going on to more complicated budgets (salt or temp would be next). The volume budget error should be near machine precision when using fields from the averages.