[MITgcm-support] unrealistic model results in a regional model

Sun Dec 14 21:15:48 EST 2025

Hi Martin

After carefully checked the daily diagnostics, I found that the 'EXFswnet' does not change with time. That means, EXFswnet at grid (i,j) remains unchanged with time (I checked the simulation of 170days), but all other diagnostics (for instance, EXFlwnet, EXFhl) changed with time. I guess this may be a cause of my lower temperature than CMEMS, since the initial 'Surface solar radiation downwards' is on 19930101. And I am sure that the model reads only the first time slot of my 'Surface solar radiation downwards', as if I modified the code as 'wrslice('ERA5_sw_3hrs_1993.bin',sw(:,:,2:end),1,'real*4'), that is, write the sw forcing  from the second time slot, the simulated temperature changed significantly. However, I am really pullzed why this occured, the sw forcing was downloaded and processed in the same way as lw forcing.

Best,

FL
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Fanglou Liao <fanglou.liao at unswalumni.com>
Sent: Saturday, December 13, 2025 6:00 PM
To: mitgcm-support at mitgcm.org <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Hi Martin
Thank you very much for your advices. After I applied the 'Surface solar radiation downwards', 'Surface thermal radiation downwards' from ERA5, the very unphysical temperature disappeard. However, it's very weird that the simulated temperature is much lower than the CMEMS reanalysis results(attached, espcially in the coastal region). I believe my external forcing of heat flux is ok (attached). So I am not sure what I can do to improve my simulation.
Thanks a lot for your consistent help.
Best,
FL
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Martin Losch <Martin.Losch at awi.de>
Sent: Thursday, December 11, 2025 3:10 PM
To: MITgcm Support <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Hi Fanglou,

I can’t be shure but I think your downward longwave radiation file may have a problem: the maximum values are 7.5 W/m^2, typical values should be: 50 < lwdown < 450, so one to two orders of magnitude larger. As a consequence your lwheat is between 315 and 460 W/m^2 (ocean loosing heat), which is clear much larger than expected (-20 to 170). Your swdown file is also small (<30W/m^2, should be up to 0-450 and sometimes even larger), so that there’s not enough heating by the sun. As a consequence your net heat flux (qnet) is way to large (upward positive) and cools your ocean.

You should check the radiation input files. I can only speculate what went wrong: I faintly remember that ECMWF provides the radiative fluxes as accumulated fluxes or somehting, and that there needs to be some stuff done in order cast them in the correct form, can remember what the details were, but plenty of places where one can go wrong. Or you uses the wrong fields from the download sites. For the model we need downward solar radiation (and not net) and downward longwave (thermal) radiation (again not net).

Hope that helps,
Martin

On 11. Dec 2025, at 02:26, Fanglou Liao <fanglou.liao at unswalumni.com> wrote:

Hi Matt

Thank you so  much for your quick response. Please find attached files (you can find my external forcing of a few time slots, and also some diagnostics of heat flux).

Best,

FL
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org<mailto:mitgcm-support-bounces at mitgcm.org>> on behalf of Martin Losch <Martin.Losch at awi.de<mailto:Martin.Losch at awi.de>>
Sent: Thursday, December 11, 2025 12:26 AM
To: MITgcm Support <mitgcm-support at mitgcm.org<mailto:mitgcm-support at mitgcm.org>>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Hi Fanglou,

please share you data.exf.

Martin

On 10. Dec 2025, at 15:56, Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>> wrote:

Dear MITgcm support

I have a new problem in the temperature simulation, which I guess is associated with my external heat flux forcing. When I used hfluxfile, the temperature value is within the normal range, but a few ℃ lower than it should be. When I used sw, lw, atemp and aqh, then temperature in the coastal area can go down to -20℃ (but the velocity is generally ok, as attached)，which is clearly wrong. My external forcing was downloaded from 3-hrs ERA5 data.

I checked the diagnostics, found that the latent heat flux is a few times larger than it should be;

Any help will be greatly appreciated.

FL

# m/s
 precipfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_tp_3hrs_1993.bin',
# W/m2, downward positive
 swdownfile  =  '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_sw_3hrs_1993.bin',
# W/m2, downward positive
 lwdownfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_lw_3hrs_1993.bin',
# K
 atempfile   = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_t2m_3hrs_1993.bin',
# kg/kg
 aqhfile    =   '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_spehum_3hrs_1993.bin',
# m/s
 uwindfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_U10_3hrs_1993.bin',
# m/s
 vwindfile   = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_V10_3hrs_1993.bin',

________________________________
From: Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>>
Sent: Wednesday, December 10, 2025 10:53 PM
To: MITgcm Support <mitgcm-support at mitgcm.org<mailto:mitgcm-support at mitgcm.org>>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Dear MITgcm support

I have a new problem in the temperature simulation, which I guess is associated with my external heat flux forcing. When I used hfluxfile, the temperature value is within the normal range, but a few ℃ lower than it should be. When I used sw, lw, atemp and aqh, then temperature in the coastal area can go down to -20℃ (but the velocity is generally ok, as attached)，which is clearly wrong. My external forcing was downloaded from 3-hrs ERA5 data.

I checked the diagnostics, found that the latent heat flux is a few times larger than it should be;

Any help will be greatly appreciated.

FL

# m/s
 precipfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_tp_3hrs_1993.bin',
# W/m2, downward positive
 swdownfile  =  '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_sw_3hrs_1993.bin',
# W/m2, downward positive
 lwdownfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_lw_3hrs_1993.bin',
# K
 atempfile   = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_t2m_3hrs_1993.bin',
# kg/kg
 aqhfile    =   '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_spehum_3hrs_1993.bin',
# m/s
 uwindfile  = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_U10_3hrs_1993.bin',
# m/s
 vwindfile   = '/mnt/disk_B/user/liaof/MITgcm/verification/NSCS_case_5/input/InputFiles/ERA5_V10_3hrs_1993.bin',
________________________________
From: Matthew Mazloff <mmazloff at ucsd.edu<mailto:mmazloff at ucsd.edu>>
Sent: Tuesday, December 2, 2025 5:46 AM
To: Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Very glad you figured it out

Matt

On Nov 29, 2025, at 4:30 PM, Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>> wrote:

Hi Matt

I've solved the unphysical noisy problem. Thank you very much,

FL
________________________________

From: MITgcm-support <mitgcm-support-bounces at mitgcm.org<mailto:mitgcm-support-bounces at mitgcm.org>> on behalf of Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>>
Sent: Wednesday, November 26, 2025 5:10 PM
To: mitgcm-support at mitgcm.org<mailto:mitgcm-support at mitgcm.org> <mitgcm-support at mitgcm.org<mailto:mitgcm-support at mitgcm.org>>
Subject: Re: [MITgcm-support] unrealistic model results in a regional model

Hi Matt

Thank you so much for your response. I've tried your advices, and found that  U, V boundary conditions caused the noisy patterns and leading to unphysical results. Keeping only normal velocity (i.e., v=0 along the east boundary and u=0 along the south one; T, S were kept) at the open boundaries does not solve the problem. I've also tried to "make the bathymetry flat in the normal direction for several (6) grid cells", but the noisy patterns still occured.

restoring sponge time was also tried as suggested.

Best,

FL
________________________________

From: MITgcm-support <mitgcm-support-bounces at mitgcm.org<mailto:mitgcm-support-bounces at mitgcm.org>> on behalf of Fanglou Liao <fanglou.liao at unswalumni.com<mailto:fanglou.liao at unswalumni.com>>
Sent: Tuesday, November 25, 2025 9:38 PM
To: MITgcm Support <mitgcm-support at mitgcm.org<mailto:mitgcm-support at mitgcm.org>>
Subject: [MITgcm-support] unrealistic model results in a regional model

Dear MITgcm support

I am a new MITgcm user. I am building a regional ocean model with mitgcm, and have some problems with the model results, which I guess are associated with the open boundaries (East and South).  This model is of 0.03 deg, with initial (T, S, U, V) and open boundary conditions are interpolated from CMEMS reanalysis (0.083 deg). The external forcing are from ERA5. The Δt = 45 seconds. The model results are unrealistic, with small-scale patterns appear (attached), and the SST even dropped below 0 after a few days. When I closed the east and south boundaries, these problems disappeard.  Could you please kindly help me check my files attached and give me some advices?

Thank you very much

FL
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