On 22/12/2010 14:37, Pete B wrote:
"Alan Murphy" wrote in message
...
"John Hall" wrote in message
...
In article ,
Alan Murphy writes:
The work of Lorenz on the
chaotic nature of weather was to suggest that very small
changes in the initial conditions of a chaotic system could cause
huge and unpredictable variations on the final outcome. Amazing
that his work has fallen out of fashion so quickly :-)

It hasn't.

I don't think that it has done. I've seen it referred to in at least one
TV documentary recently. And isn't chaos believed to be why computer
models can't forecast the weather more than a finite time ahead?

Yes. It is also worth pointing out here that in a chaotic systems some
future paths are more clear than others (less sensitive to the exact
choice of initial conditions). For instance once a blocking high becomes
well established it takes a fair whack to shift it - and medium range
predictability is improved.

Conversely if the atmosphere is hopelessly unstable and the various
ensemble models all diverge then predicting more than a couple of days
ahead becomes difficult. At least these days there is some chance the
forecasters will spot that their predictions are very uncertain.

Exactly so, John. I'm just exploring possible causes and effects.
After WW2 the weather was unsettled for a long time and many
people blamed it on the munitions used. The standard refutation,
prior to Chaos Theory, was that the energy in storm systems was
many orders of magnitude greater than that of nuclear explosions
and that these, therefore, had no affect on the weather.

Alan.

But isn't that part of the confusion?

The effect of munitions (nuclear or otherwise) or other energy/dust
producing sources on the "weather" may mean a localised storm, fog etc
following the weapon(s) detonation but no discernable long term effect
beyond a few hrs. There is no doubt that there were probably small
effects on the localised weather immediately after such events. but how
long did this last?

It does have some nasty short range weather effects. The Japanese
thriller "Black Rain" has this as a part of its underlying back story.

However, to get a truly global effect on weather that persists for a
year or so takes a volcano in the class of Krakatoa (nacreous displays
seen 1884,5,6) or Tamborra (year without summer 1816).

You can see small dips in the CRU data that correspond to a few other
very big volcanic events in the past 150 years. Mount St Helens for
instance barely made a dent whereas Mt Pinatubo (sp?) in 1991 did:

http://denali.gsfc.nasa.gov/research/so2/article.html

Similarly, to say the entire NH circulation in early 1947 following a
couple of nukes in 1945 followed by a couple of further tests in 1946
was in any way linked is very doubtful. Isn't this time distant/area
widespread claim to a link years later becoming a "climate" effect
rather than a "weather" one anyway?

It might have created a radioactive fallout rainstorm somewhere downwind
of the test site but that is about it.

As I said originally, although I'm in no way stating a preference one
way or the other or getting anywhere near politics of it, from a purely
physics point of view, the idea that the introduction of many
GTonnes/annum of a known infra red absorbing 'trace' gas into the
atmosphere affecting the overall global energy in/out balance and
therefore climate is far more plausible.

And this can be tested by Earth orbit satellite observations independent
of ground based temperature measurements.

Regards,
Martin Brown