[MITgcm-support] cell size variation

[Patrick Rosendahl]

Thank you, I get much better results!

Next thing I was wandering, if that equation has to be fulfilled for 
zero-level (no waves) only? I have ~6cm waves in a 5cm upper layer (the 
wave reduces it to 5-3=2cm and enlarges it to 5+3=8cm).
Is there a rule-of-thumb for the maximum streching of the upper most layer?

Best,
Patrick

Martin Losch wrote:
> the rule of thumb is:
> abs(delz(k+1)/delz(k)) < 1.4
> In your case: 0.03/0.005 = 6
> 
> Martin
> 
> On 9 Apr 2008, at 10:34, Patrick Rosendahl wrote:
> 
>> Hello all,
>>
>> I get unstable results with the following configuration in free- 
>> surface and non-hydrostatic mode:
>>
>> delZ=1*0.03,100*0.005,
>>
>> The depth is 0.5m, divided into a 3cm upper layer (that will  contain 
>> the free surface), and the rest is divided into 5mm layers.
>>
>>
>> In the mail "Re: [MITgcm-support] z coordinate" from Baylor Fox- Kemper:
>> >Hi Rima,
>> >  The MITgcm is not accurate when you change the delZ so rapidly.   You
>> >are much better off using the 20 levels, if you can afford to run it
>> >that way.  If not, you can make a few levels of delz=30m, then
>> >gradually increase until you reach bottom.  The grid size shouldn't
>> >increase too rapidly from level to level, approximately 20% at most.
>> >This will be even more important in nonhydrostatic mode.
>> >   -Baylor
>>
>>
>> Is there a guide for the cell thickness? Is 20% really necessary?
>>
>> Best,
>> Patrick
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> 
> 
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