Recent results derived from the diurnal‐variation observations of the atmospheric‐electric potential‐gradient on board the Carnegie

Abstract

The Department of Terrestrial Magnetism, in accordance with its director's plans, has for many years been making not only magnetic but also atmospheric‐electric observations aboard its survey vessel, the Carnegie. It is thus contributing the chief data for mapping both the earth's magnetic field and its electric field. Furthermore, since 1915 numerous observations have been made aboard the Carnegie to determine the nature and magnitude of the changes in the electric condition of the atmosphere which take place during a 24‐hour cycle.For the potential‐gradient the general procedure in the diurnal‐variation observations is to make a set of 20 observations during each of 24 consecutive hours. The observations for such a set require about 20 minutes and their mean value is referred to the mean time for the set. From deductions based on the observations made prior to April, 1916, it appeared that the diurnal variation of the potential‐gradient over the oceans probably did not differ much from that which has been found at many land stations; that is, they indicated two rather pronounced maxima and two minima during a 24‐hour period. However, very few data were available from oceans other than the Pacific, and as pointed out in the report just cited, a large percentage was derived from series of observations which were terminated by the advent of unfavorable weather. It should also be noted in passing that Swann a year later in discussing the results of the observations for the year ending February 20, 1917, states that “the effect of the 12‐hour Fourier wave is less important in the present curves than in those already published.”