[MITgcm-support] ECCOv4 Configurations: R-Star Coordinate Error with Modified Wind Forcing

[Yohei Takano - BAS]

Hi Martin,

Thank you for your advice, and yes, I am using the ECCOv4-r2 sea ice parameters (from Gael's
setup). It could be the sea ice (thinking of what I wrote in the previous e-mail) so I will try setting
the SEAICEpressReplFac = 0., and rerun the model from the beginning.

Regarding the sea ice related diffusivities, are you talking about this part in the parameters?
'SEAICEdiffKhHeff = 400., SEAICEdiffKhArea = 400., SEAICEdiffKhSnow = 400.,'. Just to confirm so
should I also turn these off after turning on the SEAICEpressReplFac = 0.,? (please let me know if
I misunderstand something).

I am also curious about Gael's thoughts behind this setting.

Thank you again, I appreciate your input.

Regards,

Yohei

________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Martin Losch <Martin.Losch at awi.de>
Sent: 12 February 2024 06:28
To: MITgcm Support <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] ECCOv4 Configurations: R-Star Coordinate Error with Modified Wind Forcing

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Hi Yohei,

if this is related to sea ice and if you are using the ECCOv4-r2 sea ice parameters (thi is what I found: https://github.com/gaelforget/ECCOv4/blob/master/input/data.seaice), then you could try to set
 SEAICEpressReplFac = 0.,
and rerun (from the beginning). I have also tried to get rid of landpoints where wind forcing “pushes” ice into corners where it cannot escape. The eccov4-r2 data.seaice contains large (400) diffusivities for seaice variables, which probably were used to alleviate this problem (@Gael, correct me if I’m wrong). In my experience, this is no longer necessary with SEAICEpressReplFac = 0.,

Martin


On 11. Feb 2024, at 18:00, Yohei Takano - BAS <yokano at bas.ac.uk> wrote:

Dear all,

   I am working on setting up a simulation with the ECCOv4-r2 configuration. The first step is to
run (spin-up) the model with this configuration, except I detrended the atmospheric wind forcing
(including zonal, meridional wind stress and surface wind speed). The model ran for a while (~ 10 years)
but stops after that with "STOP ABNORMAL END: S/R CALC_R_STAR", which is related to the r* coordinate
from my understanding. More specifically it is "too SMALL rStarFac[C,W,S]" and I see very small
hFactorC (from diagnostics) at a grid point near the continent (or perhaps sea ice related since it is in the Southern Ocean).

   The reason behind the error is this modified atmospheric wind forcing but I am a bit stuck on how I can
fix this issue (i.e. how can I further modify the forcing to prevent this error) and would like to ask for advice on dealing with
this issue. I saw comments in the previous question (in this list) lowering deltaT but I don't think that will solve the issue in this case.

    rStarFac error actually happens quite often in my case modifying the atmospheric forcing and for those
who have experienced similar challenge, I would like to ask for some advice how to deal with this.
Thank you in advance.

Regards,

Yohei


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