[MITgcm-support] [EXTERNAL] Warm start and cold start yielding same results

[kunal madkaiker]

Thank you Dimitris and Martin.

@Martin, I went through the documentation and tried setting each boundary
(E,W,S) OB_balance as -1, so that it would balance the net flow at
individual boundaries.
What the OBCS_balanceFac* should be set? Could you please advise me?

Thanks
Kunal


On Tue, Oct 19, 2021 at 11:47 PM Dimitris Menemenlis <
menemenlis at jpl.nasa.gov> wrote:

> Just for fun, this cold/warm start exercise is one of the very first study
> that I carried out using the MITgcm:
>
> https://journals.ametsoc.org/view/journals/atot/14/6/1520-0426_1997_014_1420_loaogc_2_0_co_2.xml
>
> Dimitris
>
>
> On Oct 19, 2021, at 5:58 AM, Martin Losch <Martin.Losch at awi.de> wrote:
>
> Kunal,
>
> basic ocean circulation theory tells us that density gradients drive the
> flow and that the dominant large scale mode is geostrophic. So it is not
> surprising that your initial hydrography immediately leads to a geostrophic
> balance, which is more or less independent of the initial conditions.
>
> As for obcs balancing, please refer to the documentation. You options do
> not appear useful for the problem at hand.
>
> Martin
>
> On 12. Oct 2021, at 14:02, kunal madkaiker <kunal.madkaiker02 at gmail.com>
> wrote:
>
> Dear All,
>
> I am trying to setup the physical model in north Indian Ocean in order to
> study the mesoscale eddies, using warm start as well as cold start.
>
> In warm start, Initial conditions of T,S come from WOA18 and U,V from
> SODA. Boundary conditions of T,S,U,V are from SODA and ext. forcing from
> ERA5.
> For cold start, setup is same except initial velocities are zero. Timestep
> is 120s and spatial resolution is ~5km. I am running model for 30 days as
> of now (doing monthly climatological simulations). Lateral boundary is from
> west, east and south.
>
> Both the simulations: warm and cold start is yielding the same results in
> terms of current, temperature etc. and I am not seeing any significant
> effect of the initial velocities in the warm start simulation. My
> understanding is that somehow the boundary conditions are nullifying the
> effect of initial velocities, but I am not understanding why that might
> happen.
>
> Kindly provide some suggestions. Let me know if anything is wrong from my
> end.
>
> Also, I would appreciate some help in setting the OBCS balance values.
> Currently, I am balancing individual boundaries by giving value as -1. The
> flow pattern in my domain is such that, during summer monsoon (JJAS) water
> flows from Arabian sea to bay of bengal (west to east) and vice versa
> during winter monsoon (OND).
>
> Attaching some plots and my namelists. Apologies for the long email.
>
> Thanks and Regards
> Kunal
>
> <Cold_UV.png><Comp_warm_coldstart_SST.png><Warm_UV.png><data><data.exf><data.obcs>_______________________________________________
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