Omaha daily bee. (Omaha [Neb.]) 187?-1922, 1915-08-22

mer's afternoon?
Many features of this familiar occur
renee have not been clear even to scien-
lists, and Professor William J. Humphreys,
the well-known meteorological of the United
States Government, has recently furnished
some interesting information on the sub
Ject. The rain of the thunderstorm occurs
because the earth, heated much more rap
idly than the upper air on a hot Summers
day, sends violent current of hot surface
air into the upper region. This current
gathers moisture as II rises, is finally
cooled, and then falls in the form of rain.
Why thunder and lightning accompany
the storm is more obscure matter, and
is explained by Professor Humphreys by
a description of a recent experiment in
which a minute thunderstorm was pro-
duced. The experimenter allowed drops
of distilled water to fall through vertical
blast of air of sufficient strength to produce
spray. From this the following facts we're
ascertained: 1. The breaking of drops of
water is accompanied by the production
of both negative and positive ions (the
particles of which electricity is composed).
2 Three times as many negative ions as
positive are released.
Now this experiment closely reproduces
the conditions that produce a thunder
storm. Such q storm is characterized by
strong upward currents of hot air, and
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breaking up of all rain drops which would
otherwise fall through them. Hence at
the top of the uprushing air current OF the
storm, l. e., within the thundercloud, a
rapid electrical separation goes on, the
first result of which is positively charged
rain drops and free negative particles. The
positive charges of the rain drops are con-
tinually increased by the successive divi.
sion and union of the drops. These posi-
lively charged drops fall to the earth when.
ever the air current becomes weak enough
to permit their passage.
The negative particles are carried up
into the higher part of the cloud where
they unite with the cloud particles and
facilitate their formation into negatively
charged drops. These ultimately fall in
the gentler rain of the storm. The reunion
of the two separated forms of electricity
produces lightning.
Any weather condition in which layer
warm air is beneath a layer of cold air
is likely to give rise to a thunderstorm II
the temperature contrast be strong enough.
Such a situation is unstable and leads to
the violent moving about of different
strata Of the air, which is the essential
feature of thunderstorm.
The storm may arise from intense local
heating OF the earths surface, in which
case it is knows as a local or heat thunder
storm, or from the over-running of one
layer of air by another at a different tenn
perature. ThundeTstorms may also result
from the undermining, and consequent
uplift OF a saturated layer of air by
denser layer.
Non-local types Of thunderstorms are
classified by the weather experts as cy-
clonic, tornado. anti-cyclonic and border
thunderstorms, according TO their position
with respect TO cyclonic and anti-cyclonic
formations IN the atmosphere line or
row Of tornado storms extending from
cyclonic centre constitute the wellknown
cline sGuall."
On land thundeTstoms occur most ire
quently in the early afternoon and in Sum-
mer, and at sea they are most frequent at
night and IN Winter. This is because the
relative temperature Of the air as COM
pared with land and with water at the two
seasons is reversed. Thunderstorms are
more frequent in warm and wet years than
in cold and dry ones. Heat is the deteTm-
lining factor in producing them, and con-
sequently they are most frequent at the
period of minimum sun spots and least
frequent at times OF maximum sun spots.
Professor Humphreys explains the struc-
ture OF a typical thunderstorm in a very
interesting manner. First We have air