Re: [asa] NASA - Climate Simulation Computer Becomes More Powerful

Dave:

I worked for over 20 years in the weapons industry modelling for the
most part not weapons, but high energy laser interactions with matter.
We were driven by the sudden and unanticipated end to testing into a
much greater reliance upon simulation, thus the rush in the 90s to
massively parallel codes, all of which had to be rewritten entirely and
benchmarked against codes that had been around since the 60s.

We were able, as we moved to 3D codes, often with far less physics than
the older 2D codes, to "observe" much greater detail, but it was not
always clear that what we were observing was "real" or some artifact. I
would suggest that this always true of simulations, esp. when they get
divorced from experimental campaigns.

It was the opinion of most of the oldtimers (I'm not quite old enough to
be considered one) than numerical simulations were interpolation
routines, not simulation routines. And in order to interpolate you
something to interpolate between, that is, you need experimental
results. I have long suggested that the same is true of the climate
simulation models, which is why I have little confidence in their
forecasting, esp. long terms forecasting, computations. It is
especially as you add increasing complexity of nonlinear, interrelated
physics packages, that you begin to realize the necessity of a smart
code user and developer who learns to tweek the code, ignore certain
complexities. Some purists believe that the greater detail and more
physics we can add to the code, the better off you are. This is by no
means clear. The more you do this, the more chaotic the code becomes
and the more sensitive to the smallest of variations, including
roundoff.

Anyway, just my 2 cents.

bill

On Sun, 30 Aug 2009, Dave Wallace wrote:

> Rich Blinne wrote:
>> http://www.nasa.gov/topics/earth/features/climate_computing.html
>>
>> Climate Simulation Computer Becomes More Powerful
>> 08.24.09
>> Remember the day you got a brand-new computer? Applications snapped open,
>> processes that once took minutes finished in seconds, and graphics and
>> animation flowed as smoothly as TV video. But several months and many new
>> applications later, the bloom fell off the rose.
>>
>> Your lightning-fast computer no longer was fast. You needed more memory and
>> faster processors to handle the gigabytes of new files now embedded in your
>> machine.
>>
>> Climate scientists can relate.
>
> IMO this is flat wrong. Climate scientists need faster computation, as the
> later text says, to perform finer grid simulations or to model more of the
> physics. Most users of home pcs do not suddenly add applications (except
> possibly something like Photoshop or a video editing package) that demand a
> great deal more processor and memory capacity. Typically machines slow down
> for other reasons eg for Wintel pcs the registry gets large and corrupted,
> the hard disk gets fragmented... Viruses etc and small applications that
> users see on the web also tend to slow things down. The inevitable crashes
> also seem to leave junk in the registry, startup directories etc that slows
> things down. My machine crashed in late May and I rebuilt but over June
> July and August it has gotten noticeably slower. I think you would find
> that most users machines do likewise. By the way I have not added any new
> programs and run both a firewall and virus protection and obtain the latest
> patches from software vendors when I have high speed network access.
>
> Making this kind of error in the introduction creates an initial unfavorable
> attitude to read the rest of the article. Having spent most of my career at
> large corporations, I realize that such articles are likely written by hacks
> and can discount the falsity however, it does create a poor image.
> I would also hope that the climate community is spending a larger amount of
> their funding on basic climate science and improving data accuracy than on
> modeling and modelers. Glenn's review shows that the accuracy of ground
> stations leaves something to be desired and makes one wonder if the whole
> effort is as shoddy as the ground station data.
> Glenn's analysis can be seen at: http://themigrantmind.blogspot.com/ If
> Glenn's data analysis can be shown to be wrong I would be most interested.
> Comments can be added to Glenn's blog entries.
> Dave W
>
>
>
>
>
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Received on Sun Aug 30 09:13:45 2009