The weekly times-record. (Valley City, N.D.) 1912-1922, 1912-11-21
weather Conditions
Further Explained
WINDS AND NEUTRALITY-SUSPICIOUS.
SECOND THEME. OF GEO.
GRAHY INSTRUCTOR

Continued from last weeks Elk
tension by Prof. j. e. Switzer.)
In the issue of last week attempted
to show what were some of the fact
ors which control temperature. In
this article 1 wish to bring to mind
some of the factors concerning winds,
their cause, direction and force.
The pressure of the atmosphere,
about fifteen pounds per square inch
at sea level. decreases with altitude
above the sea, because the higher up
one goes, the less there is above
weighing down. At any given height
above the sea we may expect to find
a surface OF air, all parts of which
have the same pressure; but less than
fifteen pounds per square inch. Still
higher we find other surfaces of
equal pressure but still less, depend
ing upon the elevation.
i The immediate result of increase of
temperature upon the atmosphere IS
to cause it to expand, or occupy
more spare. This expansion tendancy
is in all directions, but it meets with
less resistance upward than toward
the sides, hence the greater expan-
sion is upward. As result OF this
expansion we may think Of the differ
ent surfaces of equal pressure being
bowed, or pushed up, over the heated
area. More strictly speaking, the air
at different elevations, due to- the
expansion below, becomes more dense
over the heated area that at the same,
level over the surrounding area. This
results in a movement outward in the
upper strata. toward the. regions Of
less density at the same level. The
removal thus of some of the air from
over the heated area decreases the
pressure at the bottom of the heated
portion and increases it at the bottom
away from the heated area by the
portion taken from the upper stratas
OF the heated area. AS a result of
this difference in pressure near the
surface, we get air movement from
the region of higher pressure to the
one of lower pressure, and we call
this movement winds. Hence the
direction from which any wind blows
depends upon the relative position
OF region of higher pressure and one
OF lower pressure at the same level.
This movement will continue just as
long as the differences in pressure
continue, and its force and velocity
will depend upon the amount of diff
ference in pressure within given dis
lance. If the difference shown by
the barometer is one-tenth of an inch
in a distance of approximately seven
ty miles, the wind will have We
locity of thirty miles per hour. If the
difference is two-tenths of an inch
the velocity will be about fifty-fiye
miles per hour.
Applying these principles to the
earth as a whole, we find that from
the equatorial region of constant
high temperature, there is constant
movement poleward in the upper
stratas. Since this belt is about Is.
600 miles long and the poles are but
points, there must be q crowding to-
gether and piling up as soon as it be.
gins Its poleward journey. This is suf-
ficient to produce in q narrow belt
about thirty degrees from the equator.
an area of marked higher pressure
than its surroundings. Hence there
Is q movement poleward and equator.
ward from this region Of high pres
sure. Because Of the effect Of ro.1
tation these winds are DETECTED to
the right from their course in the
northern hemisphere and to the left
In the southern hemisphere.
This gives between about thirty
degrees south latitude and the equa-
tor the southeast trade winds, and
between about thirty degrees north
latitude and the equator the northeast
trade winds. Poleward from these
high pressure belts Of thirty degrees
latitude are the prevailing Westerlies,
more southeast in the northern hemi-
sphere and northwest in the southern
hemisphere. This does not explain
the various shifting Of the winds in
North Dakota, however, and the at
tendant changes in temperature and
precipitation. That viii be the theme
for another article.
Ito be continued)