A new longitude effect in the geomagnetic solar daily variation

Abstract

The daily variation of geomagnetic vertical intensity (Z) at Koror, Palau Islands, slightly south of the dip equator, is characterized by a positive salient before 1100 hours and a negative one after 1500 hours. This feature, which persists throughout the year, appears to reflect a component of the Z curve that simulates the time derivative of the horizontal-intensity (H) curve. A similar though less pronounced effect may be discerned at Huancayo and at Trivandrum; at Addis Ababa its sign is reversed. This component probably makes inapplicable to Koror (and possibly to some other localities) the suggestion that the day-to-day fluctuations in the ratio of Z and H ranges in western Africa may reflect shifts in the latitude of the electrojet. To account for the observed Z effect it is suggested that there is superimposed on the conventional S/sub q/ pattern of ionospheric currents a north-south flow of current confined to the daylight side of the earth, that this current reverses its sign in a systematic relation with the earth's rotation, and that it may tend to channelize along the paths established by the S/sub q/ patterns, so as to become manifest in the daily- variation curves at stations in highermore » latitudes as well as along the dip equator. On the basis of the relative amplitudes of the eastward and westward salients of magnetic declination curves, the suggestion is strongly supported as regards Europe and the western hemisphere; but equivocal results are obtained for Australasia and the western Pacific, notwithstanding that Koror in this region exhibits the Z effect more strongly than any other equatorial station. Neither the source of the postulated current nor the path by which its circuit is completed is clear. It is conjectured that a persistent leakage of charged particles trapped in the magnetosphere, falling from their mirror points into the upper air, may give rise to vacillating potential differences between the northern and southern auroral zones, and that the phenomena here reported represent the ebb and flow of ionospheric current required to equalize these potential differences.« less