Regarding the Nudging-Relaxation Timescales

[yadusharma]

Hi Forum,

I want to set the salinity relaxation for 10 Days and boundary nudging for different timescale say 30 Days. I understand from the forum and documentations that TNUDG is used common for both the cases(If i am not wrong ). So how can I solve this ?. I would be grateful for any suggestions or hints.

Thanking you.

[kate]

I used to have things like "#ifdef ARCTIC" in set_vbc.F where the surface salinity nudging happened, adjusting the timescale there. Then someone sent me a version in which there is a new variable with the timescale for surface salinity nudging which is read from the input file. Either approach works.

Beware that TNUDG is not used for the boundary nudging timescale if you also have a nudging to climatology. I actually want to use the boundary timescale on the boundary - the boundary files are updated more frequently than the climatology fields in my runs.

[yadusharma]

Hi Kate Thanks for the suggestions, I understand from one of your earlier post also that, I can set the values in set_vbc.F as follows,



# elif defined SRELAXATION
stflx(i,j,isalt)=-Tnudg(isalt,ng)*Hz(i,j,N(ng))* &

# if defined SALTEXPT
& 36.0_r8*
endif
& (t(i,j,N(ng),nrhs,isalt)-sss(i,j))
# endif

Am I correct

I have one more doubt (maybe I didn't understand the trick),
Should I change the TNUDG value according to the SSS field frequency (Monthly or daily) in my netcdf file?

ie,if I provide netcdf file with daily SSS field (say from HYCOM) for SRELAXATION and keep the TNUDG value say 360, then how ROMS is using my daily field?

[kate]

The nudging timescale doesn't have to be related to the update frequency. The surface salinity nudging in our runs is meant to be a slowish nudging to a climatology - we have a global field that's a monthly climatology (without interannual variability). Therefore we nudge to it more slowly than to the incoming boundary values. Still, we want it to be stronger than the 360 day timescale of the outflow boundary conditions. If you use strong nudging to daily HYCOM values, then it won't be as free to diverge from HYCOM.

Why does everyone say "I have a doubt" when really you all have questions?