I noticed that the BBC experiment runs the HadCM3 experiment. IIRC, that was run as a spin-up test. What\'s the difference from HadSM3? Why isn\'t HadCM3 run here too? Could you share why HadCM3 was chosen for this gig with BBC?

Thanks.

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The difference is in the way that the ocean and ocean/atmosphere interaction is handled. In hadsm3, the ocean is simplified (s in hadsm3 stands for slab). In hadcm3 the ocean and atmosphere are coupled (the c in hadcm3) and the interaction between the atmosphere and ocean are more realistic. It is also computationally more intensive.

The initial experiments using hadsm3 were/are needed to test various parameters and the range of values that give reasonable climates. The results from that are then used to choose parameters for the hadcm3 runs. The hadcm3 should be coming here within the next month or so.

It is sensible to use a simplified slab model to investigate equilibrium climate sensitivity (change in temp to a doubling of CO2) because it reaches equilibrium much faster because there is no slow reacting ocean.

When trying to do a realistic hindcast/forecast you need a realistic ocean.

You may want to read more about the different models at http://boinc-doc.net/boinc-wiki/index.php?title=Climateprediction_Model and links from there.


Hope this helps

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The answers were quite enlightening. But why was HadCM3 chose for this gig with BBC? I suspect that it was just the opportunity to attract lots of participants for a more computationally-intensive model...

Thank you.

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HadCM3 was chosen because it was a good model to choose for the purpose. This means

a) Good/useful in scientific quality terms.

see graph 2b at
http://boinc-doc.net/boinc-wiki/index.php?title=Explanation_of_the_Nature_Journal_-_First_CPDN_Results#What_about_the_effects_of_Parameters.3F

This isn\'t a cut down model for educational use only - the models are generally better than the CMIP II models.

and

b) suitable for distributing to PCs\'. All climate models of a similar useful quality are complicated beasts and some would be easier to transfer to 32bit computers than others.

For sure the partnership with the BBC was to attract more participants. However the strategy page in Sept 2003 was more or less the same and mentioned that they were planning to do experiments 2 and 3 with a coupled ocean and experiment 1 used a simplified slab ocean. So it was clear that it was going to get more complicated even back then. I doubt that this Meltdown programme (Monday 20th Feb BBC 9PM-10pm) was planned back then.

I think the BBC has insisted on having some things, but this is more like some usability testing than changing the scientists plans.

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1. Anyone know about the expected run time of the BBC app?

Is it likely to be about as long as a slab, about as long as a sulphur, or somewhere between?

This matters to me as I cannot conveniently run the sulphurs on many of my boxes and would prefer a shorter app.

2. Does the BBC app show up as a separate project in stats (eg BOINC stats) or as part of the CPDN stats?

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1. Anyone know about the expected run time of the BBC app? Is it likely to be about as long as a slab, about as long as a sulfur, or somewhere between?

It takes about 20% longer than sulfur-cycle.

2. Does the BBC app show up as a separate project in stats (eg BOINC stats) or as part of the CPDN stats?

It shows up as a separate project.

HTH

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... It takes about 20% longer than sulfur-cycle. ...

20% or 2.3 * as long? (i.e, 230%!)

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Mike is close to the mark.

The bbc.cpdn Run is a sulphur cycle plus an ocean cycle, not for SC\'s 75 years but for 160 years. That\'s right, 160 years.

There is another difference. The TCM uses less disk space but the tradeoff is more data uploaded, and more often.

[Edited for typo. As usual.]

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20% or 2.3 * as long? (i.e, 230%!)

You\'re right. I was comparing disparate machines.

I\'m running the BBC CPDN on this machine and it completed a sulfur-cycle WU in about 45 days. The BBC CPDN WUs are estimated to take 135 days!

HTH

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thanks everyone for the replies re run length of the BBC WU.

Sadly this puts the BBC expt right out of my reach, but I\'d like to thank all you folks with modern machines for doing this work, the planet needs you!

River~~

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