The Geographical Journal (Journal of the Royal Geographical Society): Volume XII, No. 2 [‎294r] (90/154)

UNITED STATES DAILY ATMOSPHERIC SURVEY.
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later, Loomis, Dove, and Ferrel reviewed these theories and added much to our
knowledge ; but at this late date no one has been able to satisfactorily co-ordinate
the forces operative in cyclones, or to assign quantitative values to the horizontal
temperature and pressure gradients, to the surface resistances and internal frictions
of convection, to the latent heat of condensation, and to the effect of hemispherical
circulation. Probably the only components of cyclonic force that are well under
stood and accurately computed are the centrifugence and the deflection due to the
•earth’s rotation.
Our early investigators studied only the storms of low levels and humid airs,
where convection only needed to carry the moist air-currents to a slightly higher
elevation, when cooling by expansion produced condensation, and an immediate
acceleration of the cyclone by the liberation of latent heat. They had never seen
the whirling cyclones of the arid northern Rocky mountain plateau dash down
upon our great lakes with rapidly increasing energy, notwithstanding the fact that
there was little or no condensation, and hence no addition of the latent heat which
Espy supposed was absolutely essential to a continuation of storms.
The great diversity in elevation, topography, temperature, and aridity of the
broad region under our observation, constitute conditions unequalled anywhere in
the world for the advantages which they present to the physicist to study the
mechanical phases of storm development and progression, or, at least, so far as they
can be profitably studied by means of observations taken only at the bottom of the
great aerial ocean surrounding the Earth.
Here we see summer cyclones formed under the intense insolation which beats
down through a cloudless atmosphere upon the arid waste of the Rocky mountain
plateau; or winter cyclones, which, if they form in the northern part of the plateau
region, move eastward to our lakes, and thence to the St. Lawrence, with scant
rainfall; cyclones which, if they have their origin farther south, on the warmer
plains of Colorado, move into the Ohio valley, and thence into New England, with
considerably more precipitation; and cyclones which, if they have their inception
on the high plains of Arizona and New Mexico, can always be expected to give
abundant rainfall when they reach the Lower Mississippi valley, and later, as they
pass over the Middle Atlantic states. All of these conditions can be studied during
their inception at an average altitude of 5000 feet above sea-level, and under
conditions of extreme aridity ; they can be viewed later, as they come down nearly
to sea-level in the Mississippi valley and reach a more humid atmosphere, 1000
miles from the place of their birth; and, finally, they are seen as they reach the
extremely humid air of the Atlantic ocean, 1500 miles farther east.
The great winter cyclones, which originate south of the Japanese islands and
cross the Pacific ocean, come under our vision as they successfully surmount the
formidable Rocky mountain barriers with but little diminution of energy, sweep
across our continent with increasing force and heavy precipitation, and, within
three days, pass beyond our meteorological horizon at the Atlantic seaboard, only
to be heard from three days later as borean ravishers of Northern Europe.
The great anti-cyclones, or high-pressure eddies, which constitute the American
cold-waves, drift into our territory from the Canadian North-West Provinces, and,
by means of our charts, are studied under rapidly changing conditions during 3090
miles of their course. The high-pressure eddy, with all the convectional principles
of the cyclone reversed, may be said not to depend upon the land of its birth for
the cold it brings; for a strong vortical and anti-cyclonic motion at the centre is
continually drawing down the cold air from above. In the cold wave it must be
conceded that the loss of heat by radiation to a cloudless sky is much greater than
that dynamically gained by compression, or else it must be assumed that the
No. II. —August, 1898.] N