Evening star., 1925-09-13
VERTICAL WINDS
SOLVE SKY PUZZLE
Blasts That Wrecked Shen-
andoah Believed Cause of
Hail and Lightning Bolts.

That winds blow up and down as
well as horizontally was forcibly
brought home to many people for the
first time by the destruction of the
Shenandoah Far from being un-
usual, such vertical winds lie at the
heart of some of our best known
weather phenomena, according to a
bulletin from the headquarters here
of the National Geographic Society.
Every flash of lightning that you
see, or that you hear as thunder, and
every pellet of hail that falls is prob
ably due to a vertical wind says
the bulletin. These are the fruits of
rather violent upward and downward
blasts. If you consider as well the
gentler rising and falling currents
the vertical breezes.' let us say-you
must take pretty much the whole field
of weather for your sphere.
Cause of Highs" and Lows"
Practically every surface wind.
whatever be its direction or speed, is
moving along to replace air which has
risen. Clouds, too, are built by ris-
ing air. The elusive little circles on
weather maps that denote lows and
highs are in final analysis the repre-
sentation of upward and downward
air currents. Where cold air from
the upper regions flows down it COM
presses the surface atmosphere and
produces a high; where the air, be-
cause of heat, is rising, it relieves the
pressure and forms a low Most
weather phenomena are due to the
Interplay of forces between highs and
lows, which bring in their train
changes in wind, temperature and hu-
midity.
The most spectacular of the effects
of vertical winds are thunderstorms.
AS the tracer bullet marks the flight
of projectiles for a marksman, so the
great towering thunder head marks
the upward rush of the invisible wind.
Often these thunder clouds may be
seen growing before ones eye. Sell
dom is the growth slow and orderly.
More. often it is violent, and the up
surging clouds appear to boil madly.
ThunderStorms are usually local af
fairs and the wind that has rushed up
ward must come quickly earthward
again to restore the atmospheric bal
ance. In the rear of thunderstormS,
therefore, strong downward currents
are usually encountered. 1t was such
an upward then downward rush of
air. apparently. that played an impor
tant part in the destruction of the
Shenandoah.
Set Lightning Free.
Until comparatively recently the
origin of the tremendous charges of
electricity in a thunderstorm baff1ed
science. Now it is pretty generally
believed that they are caused by the
upward gusts of air-that these are
in truth the dynamos of the sky. The
building up of the electrical charges
is supposed to be brought about by
the guests blasting raindrops to
pieces. the smaller fragments car
rying negative charges upward while
the large droplets with positive
charges remain behind. Hostile forces
are established and when the strain
becomes too great it is relieved by
lightning flash. When the negatively
charged upper cloud floats away be-
fore the strain is relieved, the flash is
to the earth
Vertical winds are also credited
with the production of hail, and their
onionlike structure bears out the
theory. Raindrops carried upward by
the less violent gusts, according to
this hypothesis, are frozen in the cold
upper air. Sinking in the boiling
cloud they acquire more moisture on
the lower levels and are again carried
TO the freezing region. On the number
of Skyward trips made before they
escape from the boiling cloud and fall
earthward depends the size of the hail
stones"