[MITgcm-support] [EXTERNAL] topography with OBCS

Sun Jun 21 05:56:21 EDT 2020

Hi Martin,
I do what you do and extrapolate my boundary fields into land, and there is no salinity < 33 in any of the boundary files (including all masked areas) which is why I am so confused that such low values show up in the output. The same is true for the temperature fields. So independently of any mistakes I make in the masking, there should be no values in the salinity < 33. It seems like something must introduce zero salinities independently of the boundary files I use...and this happens, as you can see in the attached figure, at every ocean-land transition along the boundary. I guess I could only create open boundaries where I actually have ocean, but I would have thought this shouldn't make a difference... What do you think?
Andreas

________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Martin Losch <Martin.Losch at awi.de>
Sent: Friday, 19 June 2020 3:50 PM
To: MITgcm Support <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] [EXTERNAL] topography with OBCS

Hi Andreas,

check the masks.
You should be able to specify salinity everywhere and the masks should take care of this, i.e. if you specify salinity over land points, they will be masked.
In your case it looks like your mask and obcs file disagree and a land point is not masked but interpreted as zero salinity (but you knew that). I usually extrapolate my boundary field into land to avoid this.

Martin

> On 19. Jun 2020, at 05:12, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:
>
> Hi Andreas, are you sure that you are extracting your boundary conditions at the correct location?
> You could be off by one grid cell, which could cause this problem. Dimitris
>
>
>> On Jun 18, 2020, at 6:21 PM, Andreas Klocker <andreas.klocker at utas.edu.au> wrote:
>>
>> Hi,
>>
>> I am trying to set up a regional model configuration with OBCS. For some reason the model seems to introduce salinities where I actually have bathymetry (see attached figure; bathymetry left, salinities right). Salinities this low definitely do not exist in the files containing the bounday conditions. Is it necessary to set the open boundary exactly to where I have ocean, or should the bathymetry file take care of this by telling the model there should be nothing happening in case of zero water depth?
>>
>> Here's my data.obcs file:
>>
>> # Open-boundaries
>> &OBCS_PARM01
>>
>> OB_Iwest = 600*1,
>> OB_Ieast = 600*-1,
>> OB_Jsouth = 2600*1,
>> OB_Jnorth = 2600*-1,
>>
>> useOBCSsponge = .TRUE.,
>> useOBCSbalance = .TRUE.,
>> useOBCSprescribe = .TRUE.,
>>
>> useOrlanskiWest = .FALSE.,
>> useOrlanskiEast = .FALSE.,
>> useOrlanskiSouth = .FALSE.,
>> useOrlanskiNorth = .FALSE.,
>>
>> OBWuFile = 'OWU',
>> OBWvFile = 'OWV',
>> OBWtFile = 'OWT',
>> OBWsFile = 'OWS',
>>
>> OBEuFile = 'OEU',
>> OBEvFile = 'OEV',
>> OBEtFile = 'OET',
>> OBEsFile = 'OES',
>>
>> OBSuFile = 'OSU',
>> OBSvFile = 'OSV',
>> OBStFile = 'OST',
>> OBSsFile = 'OSS',
>>
>> OBNuFile = 'ONU',
>> OBNvFile = 'ONV',
>> OBNtFile = 'ONT',
>> OBNsFile = 'ONS',
>>
>> # OBCS_monitorFreq= 86400.,
>> # OBCS_monSelect = 1,
>> &
>>
>> # Orlanski parameters
>> &OBCS_PARM02
>> # Cmax=0.45,
>> # cVelTimeScale=1000.,
>> &
>>
>> &OBCS_PARM03
>> Urelaxobcsinner=864000.,
>> Urelaxobcsbound=86400.,
>> Vrelaxobcsinner=864000.,
>> Vrelaxobcsbound=86400.,
>> spongeThickness=40.,
>> &
>>
>> Thanks in advance!
>> Andreas
>>
>>
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