On Sep 25, 9:36*am, John Dann wrote:
On Fri, 25 Sep 2009 08:47:53 +0100, "Will Hand"

wrote:
Put simply - chaos in action!

If I might be permitted a small hobby-horse aside here, I do wish this
word chaos had never become associated with atmospheric modelling. To
my way of thinking, this behaviour is not chaotic at all, it's
sensitive, or super/hyper-sensitive if you will (to the starting
conditions). Chaotic - to me - implies irrational or unknowable, which
is not what's happening here. Once you can define the starting
conditions with sufficient accuracy then the models can indeed run
with a rational outcome and so aren't chaotic.

JGD

The term Chaos is quite appropriate to atmospheric
modelling because no matter how accurately the starting conditions are
defined (even down to the molecular level) the detailed state of the
system after a certain length of time is literally unknowable. That
length of time is less than a month, as far as I know. This behaviour
is called deterministic chaos because each successive condition
depends on the previous one but no-one can say which path the system
will evolve along. The individual infinitesimal steps in the process
are rational but the final outcome is not.

Tudor Hughes, Warlingham, Surrey.