[MITgcm-support] the meaning of ETAN

[Martin Losch]

EtaN can have different meanings depending on the coordinate system (pressure or z-level), and the free-surface options, that’s why EtaN has this general but a little unintuitive description: “perturbation of surface” 

For the free surface version (which probably all use by now) in z-levels (also the default), EtaN is the dynamic sea surface height. For ridgid lid, it is pressure (skaled to height units), for pressure coordinates, it is the bottom pressure perturbation. ( I hope I got that right )

Martin

On Nov 12, 2014, at 1:18 PM, 刘成彦 <killy at nuist.edu.cn> wrote:

> 
> Dear all
> 
> Recently, I have focused on the output of the ETAN in data.diagnostics. In my experiment, I could know the meaning of ETAN clearly. In the
> manual, it writes that ETAN means “Perturbation of Surface”, and in the code of the diagnostics_main_init.F, it is expressed as ‘Sea Surface
> Elevation’;
> 
> Could I interpreted the ETAN as follows:
> 
> At first, the ocean is resting, and the ETAN is zero at every points. Then, when the energy is transfuse into the ocean by surface boundary
> conditions, the first layer of the ocean starts rippling, and the ETAN is the value of the deviation of the surface to the resting ocean.
> 
> Cheers
> 
> Liu
> 
> 
> ----------------
> *********************************************
> Dr. Chengyan Liu
> Nanjing University of Information
> Science & Technology
> No.219, Ningliu Road, Nanjing, Jiangsu,
> China(Postcode: 210044)
> Phone: 18251854735
> E-Mail: killy at nuist.edu.cn
> 
> *********************************************
>  
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