The fundamentals of the measurement of the earth's magnetic field are described. The general form of the geomagnetic field is approximated to the field of a theoretical dipole magnet. The solar daily type (S) of transient variation in the geomagnetic field depends on the solar activity, the seasons, the geographical latitude, and local time. At Huancayo Magnetic Observatory the abnormally high daily variation of the horizontal component of the geomagnetic field at the magnetic equator was discovered. This variation is confined to a narrow belt around the magnetic equator due to an induced effect of the equatorial electrojet.
This equatorial electrojet is an eastward flowing current in the atmosphere at about 100 km altitude, some 660 km wide, with a measured maximum current density of as high as 140 amp/ km of width, for a given time. The theory of the origin of the electrojet developing from an increase in atmospheric conductivity at the equator and winds at high latitudes is described. Finally, the quiet-day solar daily variation in the vertical component of the geomagnetic field in the magnetic equatorial region in Peru is presented tentatively as a combined effect of the normal upper atmospheric current flow and the electrojet. A bibliography is included.
