Science: High Heat

Far higher above the earth than any balloon has ever ascended lies a series of curved shells of electrified air which scientists call the ionosphere. From this ionized region of upper space radio waves carom and curl around the earth. For two years Carnegie Institution’s Department of Terrestrial Magnetism has had under way a program of ionosphere research mustering a platoon of scientists and ranging from the tropics to the far North. At the Naval Research Laboratory in Washington, Dr. Edward Olson Hulburt kept track of the work, conferred with the workers. Last week in the Physical Review he put forth some remarkable conclusions:

¶There are three major ionized layers. Their heights were obtained by noting the time required for radio echoes to return to Earth. As the signal frequency is stepped up, a “critical frequency” is usually found at which the signals shoot through a lower layer and bounce back from a higher, or escape into space. By this means density of ionization and fluctuations therein may be charted.

¶The region of the two lower layers, E and F¹ (65 and 130 miles up) are not deadly cold but fairly hot. Their temperature seems to be 80° F., with a daily and seasonal variation above & below that point of about 55°.

¶During a total eclipse of the sun, loss of ionization is sevenfold greater than usual.

¶At night the two top layers, F¹, and F², merge into one.

¶The top layer, F², is “strongly heated” where the sun enters it vertically. From that point winds of heat-expanded air blow out in all directions, carrying tides of dense ionization, like a jet of water pouring over a round ball. But the Earth-ball is also rotating. Where the expanding waves go in the direction of rotation the wave-front is smooth; where they go against it they are like whitecaps in a tide rip.