[MITgcm-support] changing rSphere

[Alistair Adcroft]

Halving the radius has halved all grid lengths and so you now have to 
consider changes in CFL and stability numbers (as Ed suggested): 
horizontal advection and waves will require that you halve the 
time-step. If I recall correctly, the diffusive terms may involve a 
time-scale; this expt uses a Shapiro filter and you'll need to figure 
out whether it scales with time-step or not.

A.

Jonathan Mitchell wrote:
> Hi Ed-
> 
> I am still getting my mind around the architecture having picked up the 
> model just a week or two ago, and I'm still unsure what I should be 
> asking when problems arise.  So even though the cubesphere grid is 
> mentioned in the introduction of the documentation, I hadn't run across 
> it yet.  Thanks for your patience.
> I'm using normal spherical polar coordinates; in my "data" namelist, 
> "usingSphericalPolarGrid" is set to "true".  I'm trying to set up the 
> Held-Suarez benchmark example to run Titan-like conditions; I've started 
> with the setup found in "verification/hs94.1x64x5" and changed planetary 
> parameters as well as the relaxation temperature profile.  As I said 
> previously, I'm able to change the rotation rate, surface gravity, 
> surface pressure, etc to mimic Titan, but I wasn't able to set the 
> planetary radius below 3500 km (Titan is 2575 km) without the model 
> blowing up.
> I guess I originally wanted to know if reducing the planetary radius by 
> 1/2 or more causes problems in general.  I gather this is not the case, 
> so I'll have to look more carefully at stability criteria, initial 
> conditions, etc. as you suggested.
> 
> Best,
> Jonathan
> 
> On Apr 15, 2005, at 10:24 AM, Ed Hill wrote:
> 
>> On Thu, 2005-04-14 at 21:17 -0500, Jonathan Mitchell wrote:
>>
>>> Hmm, this is something I haven't learned about yet.  Is there
>>> documentation on these "tile*.mitgrid" files?
>>
>>
>> Hi Jonathan,
>>
>> In all sincerity, the amount of useful help folks get on this list is
>> roughly proportional to the useful info they provide *us*.
>>
>> So, again, are you using a cubesphere grid?  If so, I'll point you
>> towards tools that you can use to scale the grid quantities (that is,
>> the pre-computed lengths and areas) with the planetary radius.
>>
>> And if you're not using a cubesphere grid, then you should look for
>> other reasons why the model blows up.  Perhaps one or more of the
>> stability criteria scale with the planetary radius?  Or perhaps your
>> initial conditions become increasingly unreasonable (violate the CFL
>> limit) as you change the radius?
>>
>> Ed
>>
>> -- 
>> Edward H. Hill III, PhD
>> office:  MIT Dept. of EAPS;  Rm 54-1424;  77 Massachusetts Ave.
>>              Cambridge, MA 02139-4307
>> emails:  eh3 at mit.edu                ed at eh3.com
>> URLs:    http://web.mit.edu/eh3/    http://eh3.com/
>> phone:   617-253-0098
>> fax:     617-253-4464
>>
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>>
> ----------------------------------------------
> Jonathan Mitchell
> Dept. of Astronomy & Astrophysics
> University of Chicago
> 773.834.2160 (w)
> 773.702.8212 (fax)
> ----------------------------------------------
> 
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-- 
Dr Alistair Adcroft            http://www.mit.edu/~adcroft
MIT Climate Modeling Initiative        tel: (617) 253-5938
EAPS 54-1624,  77 Massachusetts Ave,  Cambridge,  MA,  USA