Evening star., 1935-05-21
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
BY THOMAS r. HENRY.

The Great Plains area of the United
States, stripped bare by drought and
duststorms during the past year, has
a much more favorable outlook for the
coming Summer.
The meteorological deadlock which
was threatening to create an American
Sahara appears to have been broken
during the past two months, says J. B
Kincer, principal meteorologist Of the
United States Weather Bureau, and II
the great air masses over the cont.
nent continue to behave there should
be normal rainfall for the rest of the
year.
The conditions fundamentally re-
sponsible for the drought have
changed. The masses of air from the
North Pole once more are spilling out
of the Arctic basin through the low
lying valley Of the Mckenzie River
in Northwestern Canada and sweeping
southwark just east of the Rocky
Mountains over the Dakotas and
Kansas. Last year there was very
little cold air coming down west OF
the Mississippi. 1t was as If the Nc
Kenzie Valley had been plugged. The
Arctic highs" escaped southwark by
way Of Hudson's Bay and the Great
Lakes.
Great masses Of cold air everything a
region are absolutely essential for rain
Cold air must come from the Arctic
1t breaks out along the Arctic Circle
at points Of least resistance, such as
low waterways. There are two such
north of North America-the Nc
Kenzie Valley and Hudson's Bay
Sometimes the "highs" come through
both. Sometimes, for no known rea-
son, they come through only one.
Once such q process has started, II
tends to continue until something
happens to break it up.
The Winter of 1933-34 was one OF
the coolest ever known east of the
Mississippi and one Of the warmest
to the westward because all the cold
air was coming through the Hudson's s
Bay break in the Arctic basin. The
region west Of the Mississippi, conse-
quently, was covered with great masses
of tropical air. It contained moisture
enough, but it had a monopoly
There were no cold waves coming
down to disturb it. Consequently il
remained stagnant.
Now, as Mr.. Kincer explains, the
one requisite for rain is that a tropical
air mass and polar air mass shall
bump against each other. The colder
air, of course, is heavier and hugs the
nty
over it, just as If it we're mountain
in the way. As it climbs it Is cooled
and the cooling process squeezes the
moisture out of 1t. The result Is rain
There will never be precipitation from
tropical air left in undisturbed
possession of an area in the temperate
zone.
There was water vapor enough In
this warm air all the time, Mr.. Kincer
says, to have provided the Great
Plains with normal rainfall. But the
fate of the territory depended on
something that was happening In
Northwestern Canada where the
willow -fringed Mckenzie empties into
the Arctic. Late in February the
change started. The Arctic air masses
started coming down along their ac-
customed path. AS they crossed the
Canadian border they smashed into
the stagnant tropical air which had
been disturbed very little for year or
more. Abundant rains were the re-
suit over the Dakotas and Montana.
During the Spring they have had a
slightly more than normal rainfall, in
striking contrast to the year before
when hardly a drop had fallen on the
parched ranges.
But ths7tropicat air was obstinate.