The new air world

by Willis L. Moore

Vast Extent of the Area Brought Under Observation. It is a wonderful panoramic picture of atmospheric conditions which, by the aid of the electro-magnetic telegraph and two hundred simultaneously reporting stations, is presented to the eye of the forecaster. Each day the kaleidoscope changes and a new graphic picture comes into view. Nowhere else in the world can the student of the weather find such opportunities.

Early meteorologists studied only the storm of low levels and humid airs, where convection only needed to carry the moist air currents to but a slightly higher elevation before cooling by expansion would produce condensation and an immediate acceleration of the cyclone by the liberation of latent heat within the region of the upward-moving air in its central area. They never had seen the cyclones of the arid northern Rocky Mountain plateau move down to our Great Lakes with rapidly increasing energy, notwithstanding the fact that there had been little condensation, and hence no addition of the latent heat that Espy supposed was essential to a continuation of storms.

The widely differing elevation, topography, temperature, and moisture of the broad region under observation by the United States Weather Bureau present conditions unequaled for the study of every phase of storm development and translation, or at least such as may be comprehended from data taken on the bottom of the atmospheric ocean; and it is but a matter of a short time when the data for extremely high levels will be added.

Here we see summer cyclones formed under the intense solar radiation that beats down through a nearly diathermanous atmosphere upon the wastes of the Rocky Mountain plateaus; cyclones that, if they form in the northern part of the plateau region, move eastward to our Lakes and thence eastward to the St. Lawrence with scant rainfall; cyclones that, if they have their origin farther south in the region of Colorado, move into the Ohio Valley and thence to New England with considerably more precipitation; and cyclones that, if they have their origin anywhere in our southwest States or Texas, or enter our region of observation from the South Pacific Ocean, can always be expected to cause general rainfall when they reach the Lower Mississippi Valley and later as they pass up through the central portions of the continent.

Here also one may view the great winter cyclones that originate in the Pacific between Hawaii and the Aleutian Islands and come under our vision as they successfully surmount the formidable barriers of the Rocky Mountains 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 several days later as boreal ravagers of Northern Europe.

The great anti-cyclones that constitute the American cold waves drift into our territory from Canadian Northwest provinces, and are studied under rapidly changing conditions during three thousand miles of their course.

West Indian hurricanes, at sea level and in humid air, which are the most violent of all storms except the American tornado, intrude themselves into the domain covered by the weather map at Florida or the East Gulf coast and usually pass off to the northeast with high winds skirting our southern coast stations.

Permanent Highs and Lows in the Pacific Are Great Centers of Action. Near the end of [Chapter XII] reference is made to the fact that there is a barrier in the Pacific Ocean that interferes with the movement of storms from the Orient, but which does not entirely stop their progress. Extensive Highs and Lows, sometimes called “Centers of Action” because they do not migrate like the traveling Highs and Lows that cause the alternations of weather that we experience from day to day, are also called Sub-permanent Highs and Lows. They are the parent systems out of which come many of the Highs and Lows that cross the North American continent, and they act as a bar to the free passage of storms from the Far East. As these Sub-permanent areas shift their centers a little to the north or to the south they change the character and the line of movement of the storms and cool waves that come to us, and they alter the general character of the weather for thousands of miles to the east of them. In the region of Iceland is the center of an extensive Sub-permanent Low that has much to do in controlling the weather of Europe, and there is a Sub-permanent High central at or near Bermuda in the southern part of the North Atlantic Ocean. Whenever the latter is built up by having a migrating High from the North American continent join with it, the whole United States experiences what is called a “hot wave”, and the heat continues as long as this Sub-permanent High remains unusually high and extends its western limits to include our South Atlantic States.

The matter in the foregoing paragraph is so important that it will be restated in slightly different form: Whenever either the High or the Low Center of Action (Sub-permanent High and Low), out of which comes nearly all of the migrating Highs and Lows, shifts its normal seasonal position, then storms are erratic and unusual weather occurs over the North American continent and farther eastward. The reason why much the greater number of the storms that cross the United States, the Atlantic Ocean, and Europe originate either in our Rockies, the Canadian Northwest, or just off the Alaskan coast is due to the fact ([Chart 1], page 99) that the Low center of action is normally over the middle and northern Rocky Mountain plateau in summer, and over the Aleutian Islands ([Chart 2], page 100) in winter. The High that follows the migrating Low in winter either separates from the center of action central over the Canadian Rockies ([Chart 2]), or from the one central at Honolulu; if from the latter, the weather will be simply cooler after the passage of the Low, but if the High separates from the center of action in the Canadian Rockies it will constitute a cold wave as it follows a Low southeastward into the interior of the United States and then eastward to the coast.