The National tribune. [volume] (Washington, D.C.) 1877-1917, 1890-07-10
THE WEATHER.
Honsoons OF North America.
BY LIEUT.. J. P. FINLEY U. s. SIGNAL SERVICE.

Correspondence invited, suggestions desired,
and information chceTfuly furnished. Every ef-
fort employed 10 make this Bureau Of practical use
to the readers OF THE NAuoEAL THiBusE. All
communications should be addressed Weather,
THE NATIoSAL TRIBUNE Office Washington, -. o.
On the continent Of North America we have
monsoon influences similar 10 those OF Asia, but
not nearly so strong. because the extent OF the
continent, aud consequently the annual range
Of temperature, are not so great. They are,
for the most part, not sufficiently strong to
completely overcome and reverse the current
OF the general circulation OF the atmosphere,
aud 50 10 produce a real monsoon, but they
cause great differences between the prevailing
directions Of the Winter aud Summer winds.
IN the Summer the whole interior of the con-
tinent becomes heated up TO temperature
much above that OF the oceans Oh the same
ATTITUDES on each side indeed above that Of
the Gulf Of Mexico aud the Pacific Ocean on
It's southern and southwestern borders. The
consequence Is that the air over the interior of
the continent becomes more rare than over the
oceans, rises up aud flows out in all directions
above, while the barometric pressure is dimin.
ished, and the air from all sides, from the At
lantc on the east To the Pacific Ocean on the
west, the Gulf of Mexico on the south, aud the
Polar Sea on the north, flows IN below 10 sup
ply its place.
On the east the tendency TO flow In Is not
strong enough 10 cOuuteTact the general east
erly motion Of the air at the earth's surface in
the middle latitudcs, aud 10 cause a westerly
current, but it simply Tetards the general
eastefly current aud gives rise 10 10 "a greater
prevalence Of easterly winds along the Atlantic
sea coast during the Summer season.
On the southern aud southeastern coasts the
heating up Of the interior causes the prevail
ing winds TO be southerly and southeasterly
instead OF northeastefly, as they otherwise
would be in these trade-wind lattndes. The
monsoon influence IN the Mississippi Valley
aud westward is much strengthened by the
gradual slope from this valley up TO the high
plateaus east Of the Rocky Mountain range, so
that when this slope becomes heated in Sum
mer the surface air tends 10 flow up IL toward
the mountain range, aud causes winds which
otherwise would be southerly ones to become
more southeasterly, and the s0uthwesterly
winds 10 become southerly ones.
In Winter the thermal conditions over the
continent are reversed. The interior Of the
continent is now the coolest part, and il is
especially colder than the surrounding oceans
at that season. 1t has also very high platcaus
aud mountain ranges.
The air therefore Of the lower strata. and es-
| pecially those next TO the earth's surface, now
tends 10 flow out in all directions TO the warmer
| oceans aud the Gulf of Mexico aud especially
to run down the long slope of plateau from the
| Rocky Mountains into the Mississippi Valley.
| The effect over the whole of the United States
| east Of the Rockies is to cause the winds, which
otherwise would be westerly aud s0uthwesterly,
! 10 become generally n0rthwestcrly winds in
| stead Of southerly and southwesterly ones MS
| in Summer. There is not a complete monsoon
! effect, but simply great change between Sum
mcr and Winter in the prevailing directions OF
the winds In Texas, however. and farther
east along the northern border Of the Gulf, the
effect is somewhat that Of a complete monsoon.
| Ia New England and farther south in the
/ Eastern States the monsoon effect is to cause
the prevailing winds TO be from some point
north of west instead of south of west, as
in Summer Along the west coast OF North
| America, in the middle 1atttudes, there il
"A strong monsoon influence, for the interior
| Of the continent becomes heated in Sum.
mcr TO much higher temperature than
that of the southwesterly ocean, and hence a
strong current is drawn in from this direction
at rightangles to the general trend of the
coast, which, combining with the general
s0uthwesterly winds Of these ATTITUDES in the
general circulation of the atmosphere, causes
| the strong aud steady westerly and south
westerly winds Of this region during the Sum
| mer.
Farther north toward Alaska, the Sum
mer monsoon effect is combined with the cur
rent caused by the detection Of the continent
! as well as the general easterly current Of high