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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi Terry,<br>
There is not wetting and drying implemented in the MITgcm, i.e. a "wet" column will remain wet with all 28 levels wet.<br>
With a linear free surface approximation, you will find that the free surface can be lower than the top level or even the full depth (which is an unphysical regime obviously). There is the possibility to use a non-linear free surface with the z* coordinate,
in this case there is a rescaling of the z level thicknesses with the movements of the free surface. But there is a limit to this. It won't get dry and the scaled depth might not go lower than 10-20% of the initial depth without blowing up.<br>
cheers,<br>
david<br>
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<div style="direction: ltr;" id="divRpF884611"><font face="Tahoma" color="#000000" size="2"><b>From:</b> MITgcm-support [mitgcm-support-bounces@mitgcm.org] on behalf of Terry Chen [505883357@qq.com]<br>
<b>Sent:</b> Monday, January 08, 2018 3:11 AM<br>
<b>To:</b> mitgcm-support@mitgcm.org<br>
<b>Subject:</b> [MITgcm-support] Simple problems about the output of salinity and eta<br>
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<div>Hello everyone,</div>
<div> Since I am a beginner of the z-coordinate model, these questions form me may be a little bit silly.</div>
<div> I am using MITgcm in a coastal region, and I find some confusing problems about the eta.</div>
<div> I have divided 28 layers vertically, and start my modeling with the force of tide. From the manual I learn that k=1 is for the surface layer, and k=28 is for the bottom. Then I find that during the tide period, all of the salinity and velocity outputs
was for all 28 layers, while actually the total depth at that time was less than the sum thickness of the 28 layers. In other words, I can't see any changes resulted from the decline of water level in the outputs of the salinity and velocity. </div>
<div> At the ebb tide, some eta output near the land is even lower than my model depth, which may mean this point is dry or with a depth set by the hFacMin, but I can still find that the output here is more than 1 layer.</div>
<div> Is that mean the z-coordinate is actually moving up and down or some extrapolation exist here ? How should I understand the eta can be lower than my depth?</div>
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<div>Best,</div>
<div>Terry</div>
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<div><span style="line-height:36px"><b><font size="4">Thank you for your reading！</font></b></span></div>
<div><font size="4">Terry Chen</font></div>
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<div><font size="2"><font size="2">Physical Oceanography</font></font>
<div><font size="2">School Of Marine Science</font></div>
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<div><font size="2">Sun Yat-sen University<br>
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