The Twin Falls times. [volume] (Twin Falls, Idaho) 1905-1916, 1912-03-12
RIVERS IN The AIR
Curious Play of the Winds In the
Yosemite Valley.
EBB AND FLOW WITH TIE SUN


parent as are the waterfalls you have
SO often viewed with admiration and
delight because of their natural beau
ty? In the famed Yosemite valley the
most interesting feature is, to the sci
enlist perhaps, it's winds.
The winds there are seldom more
than light zephyrs, moody and capri
cious to the ordinary tourist, but when
rightly understood one Of the wonders
of the valley. These interesting facts
are told by Professor F. e. Matthes of
the United States geological survey in
xthe Sierra Club Bulletin.
In no other place in the entire world
perhaps are the air currents more sys-
tematic and regular than in the Yosem-
lite valley, he says. In the first place,
the sun naturally heats the ground
more rapidly than it does the air.
Thus every hillside basking in the sun
becomes heat radiator and gradually
warns the air above it, so that the air,
becoming lighter, begins to rise.
But under these. conditions the air
does not rise vertically because the air
directly over tits still cool and is press
ing downward. Therefore up the sides
of the warm slope the heated air makes
its way. That is why the tourist max
ing his way up the mountain slope
dust travelling upward with him in a
choking cloud
But on coming down the same trail,
when the face Of the slope is in the
shadow, the dust ever descends with
the traveller in the same irritating
cloud. When the face of the mountain
is in the shade the air is cooling from
the face of the slope and is pressing
its way down into the valley.
just as sooh as the sun leaves the
slope of the mountain the earth be-
gins to lose its heat by radiation and
in very short time is really cooler
than the air. The layer Of air next
the face Of the hillside chills by con-
tact with the earth and, becoming
heavier as it condenses, begins to press
down along the slope. Thus there are
normally the warm. up draft on the
sunny slope and the cold down draft
on the side in the shadow. In wind
less region like the Yosemite this rule
may be depended upon at almost any
time
But in the Yosemite, with its bold
cliff topography, these upward and
downward air currents are somewhat
interrupted. On every sunny slope
q o1iN - cAoI
Quently there are downward air cur
rents or local breezes daily at regular
hours as the shadows come and CO.
Glacier Point is one place in particu,
lar in which Professor Matthes says
this shadowy effect on the air cur
rents may readily be tested by casting
small bits Of paper into the air. As
the afternoon wears on and the shad-
ows in the valley gather the cold draft
in the hills pours downward, forming
the valley like great river and flow
ing on to the plains below. Every side
canyon and valley sends its reinforce
ments, like the tributaries of great
river, to this general air current flow
ing onward to the plain.
With the return of the morning sun
the earth at the tops Of the hills is
warmed and the downward current In
the air is suspended. The up draft soon
begins as the sun shines into the val
legs. The air currents are so regular
that they may almost be timed.
Few realize. says the author of the
paper, that it is on these reversing air
currents that one of the chief attrac.
tons of the Yosemite depends. Mir
ror lake, to be viewed at it's best. must
be seen in the early dawn, when the
reflections are most perfect.
The lake is stillest and it's surface
most mirror-like when the cold night
currents have ceased and the uprising
day currents of air have not yet be
gun. Yet unless one is punetual he
will miss the chief beauty Of the place
for this perfect stiffness is as brief as
the turn of the tide.
In the evening and during the night
when the down draft OF air from the
mountain sides is strong, the stream
of cool air pressing down the slope
plunges over cliffs. just as water Il
seen to fall from similar heights Or
either the Yosemite falls or the Neva
da falls trails this air fall curiosity II
readily encountered in the evening.
During the daytime, on the othe
hand, the air rises vertically along tn
cliffs and up into the hanging valleys
taking part of the spray from the fall
along with it. A pretty example o
the air carrying the spray from tn
fall upward may be seen at Brida
Veil falls, where two little combs o
Apray, one on each side Of the stream
steadily curve upward over the brink
AS soon as the sun Is OF the clif
these spray combs cease to exist.
An Attraction.
II hear your new minister IL YER
IN