[MITgcm-support] run speed unaffected by timestep, 'deltaT', in?

[Dimitris Menemenlis]

What horizontal grid spacing are you using?

To give you some idea of a typical spin-up progression for deltat,
for the 1/12-deg global (llc1080) simulation, I integrated for:
- 1 day with deltat = 30 s,
- 9 days with deltat = 90 s,
- 10 days with deltat = 120 s,
- 25 days with deltat = 180 s,
- then starting on day 45 set deltat = 240 s.

The key diagnostic to look at in STDOUT is adcfl*.
If they consistently fall below 0.5, then you can increase deltat.

Regarding integration times, as Liam suggested, the overall time
may be dominated by parts of code that do not depend on deltat.
So go to end of STDOUT and find out where your code is spending time.

On May 19, 2014, at 4:30 AM, Jonny Williams <Jonny.Williams at bristol.ac.uk> wrote:

> Hi again
> 
> Regarding this, it seems that I do actually get a speed up of approximately 10 times from a factor of 100 difference in the timestep. Is this roughly what people would expect?
> 
> Thanks again and sorry for the initial confusion!
> 
> Jonny
> 
> On 19 May 2014 12:17, Jonny Williams <Jonny.Williams at bristol.ac.uk> wrote:
> Hi there
> 
> I am currently running a regional version of the MIgcm with OBCS and EXF forcing packages turned on. For the initial few years of the run I am running with a very short timestep of 24s and then after that I am running with a much linger timestep, 2400s. 
> 
> I was expecting a significant increased in run speed but this has not happened. I am recompiling in between these run steps.

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