At 09:45 PM 9/11/2009, you wrote:
Looking at the weather data for the next month were would you fly
from to get your 750KM and 1000km
Mal
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Argentina?
Seriously, it will be summer next month so anywhere from Kingaroy to
Benalla, Gawler, Waikerie is possible.
There's no such thing as a weather forecast a month ahead which leads
to the New Scientist article linked to by Robert Hart yesterday.
Certainly not at the level of detail and delicacy for soaring.
Using fractals may ease the computation problem and make it more
tractable but doesn't change the fact that the atmosphere/land/ocean
system is fundamentally chaotic. Chaotic non linear systems are not
even in theory predictable. Sure there are attractors in the system
probably due to energy balance considerations. They are called
"Winter" and "Summer". Note these are due to astronomy and hence
somewhat predictable regardless of vast computer models of the atmosphere.
It isn't at all certain that even averaging the "weather" produced by
these models for any period in the future ("climate") will bear any
relationship to the actual measured climate for that time period when
it rolls around. This is a glib and at first glance, reasonable,
assumption which doesn't stand up to scrutiny.
A simple one dimensional analogy is if you take an accelerometer, sit
it on the bench and measure the output. It isn't going anywhere so if
you integrate the output the integrated output should be zero
(velocity in the direction of measurement). In reality there is noise
on the output. Integrating noise does not give zero output. The
integrated output wanders off in one direction, may come back and
generally goes all over the place. At any random time period in the
future over any period you select the output will be some velocity.
It may even be close to zero. You just can't tell. This does not
mean it is useless. For short time periods starting at a known
velocity and initialising the output to the known value, reasonable
predictions of veleocity can be made. Some other method is used to
stabilise the output over longer periods (drive it towards a known
value). In jet fighters the inertial platform provides updates 50 to
100 times a second. GPS can be used at one or 10 times a second to
provide stabilisation.
With weather systems that short term is days at best. After that the
models produce outputs that look like weather charts (getting that
far was a major step - they didn't used to to) but bear no
relationship to the actual weather charts as observed.
Note also that little "s" in "models". Recently a physicist pointed
out the problem with that little "s", that's right it is "models" not
"model". If there is nothing but physics there would be only one
"model". That there are many (last count 23 major ones even the BoM
uses 3 different ones) is a result of the "parameterisations"
mentioned in the NS article. Every group has their favourite numbers.
Who is right? They all are - sometimes. They are all wrong sometimes.
This is considered to be better than reading tea leaves or chicken entrails.
Mike
.
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