[MITgcm-support] rSphere definition when using 'deepAtmosphere' option for ocean modelling - quick question

[Flynn Ames]

Hi Jean-Michel,

Many thanks for this clarification, this makes sense and has cleared up all confusion.

Thanks again,
Flynn
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Jean-Michel Campin <jmc at mit.edu>
Sent: 28 February 2023 2:26 PM
To: mitgcm-support at mitgcm.org <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] rSphere definition when using 'deepAtmosphere' option for ocean modelling - quick question

Hi Flynn,

I will try to clarify how the deepAtmosphere (deepAtmosphere=TRUE) scaling is computed:

It really depends what vertical coordinate you are using:
1) using Z-cordinate:
   scaling fct (i.e., distance from center of the sphere) is "rSphere+rF" (level interface)
   or "rSphere+rC" (level center), and since rF(1) = seaLev_Z
  (with default seaLev_Z value =0)), it means the "rSphere" value correspond to the top
  of the model (where the free-surface is).
2) using P-coordinate:
   scaling fct (i.e., distance from center of the sphere) is "rSphere+phiRef/gravity"
  which means that:
  a) for Ocean in P-coord, since at the top phiRef = seaLev_Z*gravity (but this time
   the top is at rF(Nr+1)), the "rSphere" value correspond also to the top of the model
   (assuming we are using the default seaLev_Z=0 value).
  b) for Atmosphere in P-coord,
   since phiRef = seaLev_Z*gravity at the bottom (i.e., at rF(1)), the "rSphere" value
   correspond to the bottom of the model.

Cheers,
Jean-Michel

On Mon, Feb 27, 2023 at 04:39:26PM +0000, Flynn Ames wrote:
> Dear MITgcm community,
>
> Hello - I'm hoping to sanity check my interpretation of the 'rsphere' parameter in the MITgcm.
>
> I've been interpreting rsphere as the distance to the top of the model domain (surface of the ocean).
> However, it was recently pointed out to me that rSphere could instead potentially refer to the distance to the bottom of the model domain (bottom of the ocean).
>
> In the code, in the file 'set_grid_factors.F', it appears the computation of the deepAtmosphere adjustments to the grid cell size assume the radius is defined at the top of the domain (the adjustment factor appears to create a smaller cell for increasing Nr). So it seems my initial interpretation could be correct. Though I was wondering if someone else could confirm this?
>
> My ocean model has the 'deepAtmosphere' option turned on (with an ocean depth comparable to the radius of the sphere), so this interpretation will have significant effects upon my results.
>
>
> Thanks for your time!
> Flynn
>

> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.mitgcm.org%2Fmailman%2Flistinfo%2Fmitgcm-support&data=05%7C01%7Cf.ames%40pgr.reading.ac.uk%7C2c2ad23488fe400f3c1808db1997d744%7C4ffa3bc4ecfc48c09080f5e43ff90e5f%7C0%7C0%7C638131912159161562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=gOOMFlpvZ8QGkkGCUWNLkAETc9ThjknCtBcV6gYgOF0%3D&reserved=0

_______________________________________________
MITgcm-support mailing list
MITgcm-support at mitgcm.org
https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.mitgcm.org%2Fmailman%2Flistinfo%2Fmitgcm-support&data=05%7C01%7Cf.ames%40pgr.reading.ac.uk%7C2c2ad23488fe400f3c1808db1997d744%7C4ffa3bc4ecfc48c09080f5e43ff90e5f%7C0%7C0%7C638131912159161562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=gOOMFlpvZ8QGkkGCUWNLkAETc9ThjknCtBcV6gYgOF0%3D&reserved=0
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20230228/4ea894c7/attachment-0001.html>