Re: Leaves turning over...

[rgrandy@ruf.rice.edu (Richard Grandy)]

I don't see that it is an *explanation* of why leaves turn over before a
storm to  say that the prevailing winds change direction.  Why should that
turn leaves over?  Change of direction is as likely, on average, to turn
fewer leaves rather than more.  Given the roughly random distribution of
leaf orientations, it is most likely to produce no noticeable change.

Since I  observed the change personally before being "taught" it in Boy
Scouts, I believe in the phenomenon.

An alternative, not unrelated, possible explanation is that when a front
moves in the local ground wind speed *increases* and that an increase in
wind speed is likely to turn over a greater proportion of the leaves.

Crude Argument:
Limiting cases:  Wind speed=0, no leaves move.  Hurricane, all leaves
gyrate wildly.    Our case is an interpolation.

I will post an exact mathematical demonstration on my web site anon.  ;-)

Richard E. Grandy
Philosophy & Cognitive Sciences
Rice University


At 8:39 PM 8/24/97, Prof. John P. Ertel (wizard) wrote:
> It's good to hear that some folks remember what they learned in Scouting.
> I checked with a friend (also in Scouting) that was trained as a
> forester/dendrologist and now works for the Maryland State Agriculture
> Dept.  He says that this is the explanation that is still being given in
> the appropriate courses for these professions.  He had just (within the
> two years) audited a course at University of MD in which this explanation
> was given.  Thankfully, some (probably most) of the "old wives tales" that
> we were taught as kids in Scouting are still thought to be correct!
>
>
> ERTEL SENDS.          _____________________
>                     / Prof. John P. Ertel \
>                    /   jpe@nadn.navy.mil   \
>                   /   veteran Eagle Scout   \
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>       | Annapolis, MD 21402-5026     Home : 410-757-6618 |
>       +==================================================+
>
>
> On Sat, 23 Aug 1997 mccaslin@pscosf.peru.edu wrote:
>
> > This is from my recollection of Boy Scout training, but it still
> > seems to make a certain amount of sense.  We were told that the
> > leaves turned over due to a change in the prevailing wind direction,
> > and this change in wind direction often preceeded storms.
> >
> > Stanley J. McCaslin                   Inet: mccaslin@bobcat.peru.edu
> > Assistant Professor, Computer Science Phone:402/872-2208
> > Peru State College, Peru, NE  68421     Home: 402/872-7595
> >
> > On Sat, 23 Aug 1997 dsouder@juno.com wrote:
> >
> > > Date: Sat, 23 Aug 1997 00:08:03 EDT
> > > From: dsouder@juno.com
> > > Reply-To: phys-l@mailer.uwf.edu
> > > To: phys-l@atlantis.cc.uwf.edu, physhare@PSUVM.PSU.EDU,
> > >     sbrauner@ashland.edu
> > > Subject: Leaves turning over...
> > >
> > >     Greetings.  I'm not sure if this is worth sending or not, but it
> > > has been a question that has been bothering me for quite some time and
> > > I'm not sure who else to ask.
> > >     Is it true that leaves turn over right before it rains?  Here in
> > > Ohio with all of the deciduous(sp?) trees, I've notice that the lighter
> > > colored bottoms of the leaves are more visible right before it rains.
> > > I've always thought it was more related to the winds rather than an
> > > approaching storm.  If it is true, what is the cause of the leaves
> > > turning over?
> > >     Sorry for the inconvenience.
> > >
> > > Dwight Souder
> > > dsouder@juno.com

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