[ecco-support] Budgets in ECv4, release 3

[Menemenlis, Dimitris (329C)]

Hi Martha, single precision is 32-bit base-2, or approximately ~10^6 decimal.
So no surprise that you get noise at the 10^-7 level.
What application requires that budgets be closed at the 10^-7 level?
>From an engineering perspective, the ECCO budgets are so uncertain
that anything past the second decimal point is almost
certainly without much meaning.

Dimitris

On Nov 4, 2017, at 6:39 PM, Martha Buckley <marthabuckley at gmail.com<mailto:marthabuckley at gmail.com>> wrote:

Hi Ou,
It may be possible to close the budgets for the global ocean with single precision output, but this is not the case for regional budgets.  For these we really do need to have double precision outputs. Attached are a couple of plots that show this.

I am looking at mass and heat budgets over the top 1000m. What I did was take the r3/iter3 output, which has double precision, and after loading each file (e.g., UVELMASS, etc.), I converted to single precision (the back to double so the gcmfaces programs work). When I use the double precision output, (tend-ocean convergence - forcing)./ tend < 1e-7 for both mass and heat (see budgetM1000m_errorDouble.eps and budgetHC1000m_errorDouble.eps).  However, when the outputs are converted to single precision the errors are much, much larger, (see budgetM1000m_errorSingle.eps and budgetHC1000m_errorSingle.eps).

One of the touted advantages of ECCO is the ability to do budgets, so we need outputs that allow us to do budget over any arbitrary regions, not just simple ones, like the global average. So can we get the new outputs in double precision please?!
thanks,
Martha


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