In article , Torsten Brinch wrote:
On Sun, 23 May 2004 14:01:37 GMT, (Phred)
wrote:

In article , Torsten Brinch
wrote:
On Sat, 22 May 2004 14:58:47 GMT, "Steve Young" wrote:
[...]
"They" say things like, That was a 100 year flood, expected to occur only
every 100 years. (or snow, drought, whatever) But I have doubts about how
they calculate that.

We do not need to get into the detail, but from a solid observation
series (preferably many hundreds of years :-) one can of course make a
good statistical estimate of what magnitude the event must have to
have only a 1 % chance of occurring in any given year. The problem
with some estimated 100 year events is that they do not have that kind
of solid base in observation. Say, if you have only 20 years worth of
data, you are thrust into making an extrapolation resting on a set of
assumptions, which reality may very well see fit to overturn in time.
[...]

Yeah. I recall sitting by a motel pool drinking beer late one evening
several decades ago and discussing "rainfall cycles" (you know the
sort of thing, the 11/13/whatever year "solar cycle" etc.).

No I have never heard of that., Phred. I do recall sitting by a pool
at Uluru camp drinking beer with a friend decades ago too. But we were
talking about a girl... :-)

And a very appropriate topic in such circumstances too. :-)

The local
mathematical statistician pointed out that you would need a minimum of
300 years of annual data to "see" such cycles with any confidence. As
he said, humans are always looking for patterns in things and are very
good at finding them, even if they are not real ones.

Funny, my friend had seen a pattern in things too. He said don't be
stupid, I've seen how she looks at you, just go'fer her.... er,
and he was right :-)

You mean it was a recurring pattern?
(I suppose most patterns are. 8-)

(Incidentally, I don't know if that "300 years" was just a figure
plucked out of the XXXX ambience, or whether he had some knowledge of
the distributions when he made the claim. As he was supporting a
large team of scientists working on pastoral systems at the time, it's
quite possible it was the latter.)

I recall reading an article by someone who had studied a lamination
series in sediment rock (I think the site was down somewhere in the
Flinders Range, but perhaps it is a mix-up in memory with a rather
strange regular lamination I've seen there myself, north of Wilpuna)

Anyhow, in that article the author had meticulously mapped and
measured the laminations in the rock bed laid down over a period of
many hundreds of years, and he indeed linked the patterns in them to
the solar cycle you mention. Of course lamination in _sediment_ rock
could only be linked to the solar cycle by the cycle itself being
linked to rainfall. Another startling thing I remember about his
observations was, that if true, that would mean that our fat old Sun
had very much the same activity cycle when that sediment ws layed
down, many hundreds of thousands of years ago, as it has to this day.

Except that it seems to be wearing out lately:
http://www.chron.com/cs/CDA/ssistory.mpl/nation/2566165
(FWIW).

See also:
http://www.jmccanneyscience.com/notes29.htm
which actually has some sensible discussion and reputable references.
[In fact the sun is not dimming, we're just getting less light from
it here on the surface of Earth.]


Cheers, Phred.

--
LID