The new air world

by Willis L. Moore

In the Southern Hemisphere there is not such a pronounced shifting of the Highs and the Lows from oceans to continents and back again, with change in the seasons, as there is in the Northern Hemisphere, because of the small area of land in comparison with that of water; but in the midst of the southern summer, which occurs in January ([Chart 2]), Lows are shown over South America, Africa, and Australia. Note how the winds blow out of all the Highs and into all the Lows. Also observe that the winds generally blow from about latitude 30° north and south towards the equator, due to the great heat of the tropics, which causes the air to rise and in the high levels to flow northward and southward, settling down to the earth again through the belts of high pressure that irregularly encircle the earth at latitudes 30° north and south.

In the interior of continents the temperature falls lower at night and rises higher during the day, and falls lower in winter and rises higher in summer than on any of their coasts. On the coast of central California, for instance, the ocean is so cool in summer and the winds blow so steadily from it that the thermometer ranges between 55° and 70°, even when there are temperatures of over 100° but a few hundred miles away in the great interior valleys, or on the broad plateaus of the mountains. New York and Boston, in nearly the same latitude, also have their summer temperatures modified by ocean influence, but they are on the east side of a broad continent, where the prevailing westerly winds give to them more the character of a continental climate than one marine; but occasionally the east wind, for a short time, gives to them the modifying influence of the ocean. In the winter the influence of the oceans is to modify the extremes of cold, the same as they do the excessive heat of summer.

Chart 12.—Average Maximum Temperature for July (Henry).

[Chart 8] (page 129) showing the lowest temperatures ever recorded at Weather Bureau stations, and [Chart 12], presenting the average of the highest daily temperatures of July, graphically show, clearer than any text can describe, the influence of continents and oceans on climate. On the Atlantic the average maximum of day varies from 70° on the Maine coast to 85° on the coast of North Carolina; while on the Pacific, where the marine influence is stronger, the average is from 65° on the Washington coast to 80° on the coast of southern California. But near the center of the United States where the continental influence predominates, the average of the highest daily temperatures varies from 85° to 90°. On [Chart 8], showing the lowest temperatures, the line of 20° below zero passes through Boston, southwest to Chattanooga, west to Flagstaff, Arizona, and then irregularly north to Seattle, showing the influence of both oceans in carrying the line northward.

Chart 13.—Ocean Currents.

Because of the vast extent of the Eurasian (Europe and Asia) continent the difference between continental and marine climates is more marked than in the Western Hemisphere. Huntington and Cushing, in their splendid work on “Principles of Human Geography”,[3] make a comparison between the southern Lofoten Islands, off the coast of Norway, and Verkhoyansk in Siberia, which probably furnish the greatest contrast to be found anywhere between places of the same latitude. Although both are inside the Arctic Circle, the influence of the Atlantic Ocean with its warm-water currents coming all the way from the tropics ([Chart 13]) protects the Lofoten Islands from the extreme cold that otherwise would come to them; vegetation remains green and cattle are pastured every month in the year. But the ocean retains nearly the same temperature in summer as in winter, and as a result the Islands are too cold to grow trees or many crops. Verkhoyansk is so different that one can scarcely believe that both places are in the same latitude. At the Siberian town the winter temperature falls to 70° or 80° below zero every winter, and has been known to register 90° below zero. It is said that steel skates often will not “take hold” but slip sideways as well as forward on the surface of the excessively cold ice. This doubtless is due to the fact that under ordinary winter cold the weight of the skater melts a thin film of water under the edge of the skate, which freezes instantly when the skate passes and relieves the pressure. But here the cold is so intense that the weight of no skater is sufficient to lubricate his movements with water molecules. Remarkable to relate, the summer at Verkhoyansk is warmer than in the islands off the Norwegian coast, due to the rapidity with which the land surface warms up under the action of the solar rays in the midst of a continental area remote from water, 75° to 80° frequently being recorded during the long summer days. The ground never thaws for more than a foot or so, but a number of crops are successfully grown.

In the interior of a continent like that of Siberia or of North America not only the changes from season to season but from day to night are extreme; while in mid-ocean the diurnal and the annual range of temperature is small, day and night, winter and summer being much the same. A place is influenced by the ocean in proportion to its distance from the sea, the presence or the absence of hills or mountains between the place and the water, and by the fact that the prevailing winds come from or go to the ocean. Cities as far inland as Baltimore and Philadelphia have their extremes of temperature somewhat modified by the Atlantic Ocean, and if it were not for the Coastal and the Sierra Nevada Mountains the influence of the Pacific Ocean would be felt at least as far inland as Denver, and the great Rocky Mountain plateau would be one of the garden plots of the world. The influence of the Pacific would reach inland farther than now does the Atlantic because of the prevailing westward drift of the atmosphere in all middle latitudes.

Exaggeration of the Forest Influence on Climate. [Chapter XIII], on Change of Climate, shows more in detail the process whereby the sun lifts up the water vapor from the Gulf of Mexico and the Atlantic Ocean and how cyclonic storms draw this vaporous atmosphere northwestward far into the interior of the continent, the Alleghany Mountains not being high enough to offer serious obstruction.