[MITgcm-support] Layers and NLayers

[Madeline Miller]

Hi Ryan,

Thanks for the detailed reply -- just what I needed!

Best,

Madeline

On Mon, Aug 8, 2016 at 9:08 AM, Ryan Abernathey <ryan.abernathey at gmail.com>
wrote:

> Hi Madeline,
>
> Sorry for the delayed reply--you caught me just before a vacation.
>
> It would be nice to have some more quantitative information with which to
> answer your questions. For now, I can give you the rules of thumb that I go
> by.
>
> The vertical resolution of your model is fundamentally limited by the
> number of vertical levels (Nz). If the stratification in your domain is
> fairly uniform, such as in a regional model, Nlayers ~= Nz is a good
> choice. However, if your model spans regions with very different
> stratification (e.g. a global model), you will want Nlayers > Nz.
>
> As for the layer spacing, you can use either even or uneven spacing. If
> you are using potential density and are interested in the deep MOC, you
> probably want much closer spacing in the abyssal density ranges. For
> example, if using sigma0, most of the ocean is volume between 27 and 27.82,
> but near-surface densities can be as low as 20 in the tropics. I have used
> various strategies to devise layer spacing, the most complicated being
> constructing the density PDF and then spacing the layers such that each
> contains approximately equal volume.
>
> If you have an eddy-resolving model, you can get away with just using a
> very high number of layers, evenly spaced, since the model's internal
> variability will smooth out the distribution. (The downside is that it is
> more computationally expensive.) This won't work well with a
> coarse-resolution model, however, because if your layer spacing is too
> fine, you might end up "skipping" layers.
>
> I am slowly working on a paper about layers, which I hope will provide
> more detailed answers to your questions.
>
> Cheers,
> Ryan
>
>
>
>
>
>
>
> On Fri, Jul 22, 2016 at 5:26 PM, Madeline Miller <
> madelinemiller at fas.harvard.edu> wrote:
>
>> Hi Ryan and other Layers experts,
>>
>> Is there any rule-of-thumb for choosing Nlayers as a function of Nr? I
>> know this depends on the density variations in my experiment, but have you
>> run into any limitations on the high or low end?
>>
>> I'm trying out the Layers package for the first time, which makes my
>> Friday very exciting.
>>
>> Best,
>>
>> Madeline
>>
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