Nudging Sea Surface Height (Zeta) to Climatology in ROMS

[hyc006]

Hi everyone,

I’m currently using ROMS and trying to figure out how to nudge the sea surface height (zeta) to a given climatology file. I've looked through the available nudging options in ocean.in, and I see:

LnudgeM2CLM — for nudging 2D momentum
LnudgeM3CLM — for nudging 3D momentum
LnudgeTCLM — for nudging tracers (typically temperature and salinity)
LnudgeTgeneric — for generic tracers
I’ve successfully used LnudgeTCLM to nudge temperature. However, I couldn't find a clear option for nudging zeta. Is there a way to directly nudge sea surface height to climatology in ROMS? Or would it be better to approach this indirectly (e.g., through barotropic momentum)?

Thanks in advance for your help!

Best,
Hsin-Yi

[wilkin]

Free surface variability is driven by the divergence of the depth integrated velocity in the 2D engine. Attempting to nudge to a zeta field will be overcome by this unless a kinematically consistent adjustment is also make to ubar,vbar.

[arango]

In addition, nudging 2D momentum is very tricky because it will affect the barotropic transport, which depends on the source and destination bathymetries. I won't recommend it since you can spend months tuning realistic applications. In such cases, I recommend examining the application grid and its appropriateness based on the region's dynamics.

[hyc006]

Thank you very much for your detailed explanations and guidance. I will spend more time thinking through these aspects carefully as I continue working on my setup.

I really appreciate your help and the time you took to respond to my questions.