New Ulm review. (New Ulm, Brown County, Minn.) 1892-1961, 1912-02-21
IN THE AIR.
Curious Play Of the Winds In the
Yosemite Valley.
EBB AND FLOW WITH THE SUN

EBB AND FLOW WITH THE sun
These Air. Currents Or Air Falls Ars So
Regular That They May Almost Be
1imsd-Mirror Lake and the Spray
Combs at Bridal Veil Falls.
Did you know there are air falls in
the atmosphere just as real and ap.
parent as are the waterfalls you have
60 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. its 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. 3. Matthes of
the United States geological survey in
the Sierra Club Bulletin.
In no other place in the entire world
perhaps an. the air currents more sys-
tematic and regular than in the Yosem-
tie 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 a 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 1t is 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
with the sun on his back finds his own
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 soon 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 abr. The layer of air next
the face OF the hillside chills by con-
tact with the earth and. becoming
heavier Al 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
bold cliffs create shadows. and couse-
quently there are downward air cur
rents or local breezes daily at regular
hours as the shadows come and go.
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 dow-
ing on to the plains below. Every side
canyon and valley sends It's REINFORCE
ments like. the tributaries of a great
river. to this general air current fow-
ing onward to the plain.
With the return Of the morning sun |
the earth at the tops of the hills is
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 its best. must
be seen in the early dawn, when the
reflections are most perfect.
The lake is stillest and its surface
most mirror-like when the cold night
have ceased and the uprising
lay currents Of air have not yet be:
gun. Yet unless one is punctual be
will miss the chief beauty of the place,
'or this perfect stillness Is as brief as
he turn Of the tide.
In the evening and during the night,
when the down draft Of air from the
sides is strong. the stream
4 cool air pressing down the slope
'lunges over cliffs. just as water Is
cen to fall from similar heights. On
ither the Yosemite falls or the Neva-
la falls trails this air fall curiosity Is
eadily encountered in the evening.
During the daytime, on the other !
land. the air rises vertically along the ,
lifts and up into the hanging valleys.
aking part Of the spray from the falls
long with it. A pretty example of |
he air carrying the spray from the {
al npI I~~