The Magnetic-Field Geometry of Jupiter and its Relation to Io-Modulated Jovian Decametric Radio Emission

Observations of the Io-modulated Jovian decametric radio emission have been compared with calculations of the magneti&field line passing through Io. Calculations of the angle between the Earth and the magnetic-field line near Io and both the northern and southern intersections of that field line with the surface of the planet were undertaken. Four emission sources favorable for synchrotron emission were located by presuming that the angle of intersection between the Earth and the north- (or south-) threaded field was near 90 and that the declination of Io was positive. These four sources correspond closely to the three major observed emission regions and to one region infrequently observed. These calculations imply little distortion of the Jovian magnetic field by Io. This assumption is quite reasonable as the Moon, an object similar in size and density to Io, produces little effect upon the interplanetary magnetic field. A mechanism by which Io could stimulate the emission is presented that is consistent with the calculations conducted.