A SATELLITE STUDY OF DAYSIDE AURORAL CONJUGACY

A study of dayside auroral conjugacy has been done using the cleft/bou ndary layer auroral particle boundaries observed by the DMSP-F7 satell ite in the southern hemisphere and the global UV auroral images taken by the Viking spacecraft in the northern hemisphere. The 22 events hav e been studied on the basis of an internal IGRF 1985 magnetic field; i t is shown that there is a displacement of up to 4 degrees in latitude from the conjugate points with the northern aurora appearing to be lo cated poleward of the conjugate point. No local time dependence of the north-south auroral location difference was seen. The use of a more r ealistic magnetic held model for tracing field lines which incorporate s the dipole tilt angle and Kp index, the Tsyganenko 1987 long model p lus the IGRF 1985 internal magnetic field model, appears to organize t he data better. Although with this external plus internal model some t racings did not close in the opposite hemisphere, 70% of those that di d indicated satisfactory conjugacy. The study shows that the degree of auroral conjugacy is dependent upon the accuracy of the magnetic fiel d model used to trace to the conjugate point, especially in the daysid e region where the field lines can either go to the dayside magnetopau se near the subsolar point or sweep all the way back to the flanks of the magnetotail. Also the discrepancy in the latitude of northern and southern aurora can be partially explained by the displacement of the neutral sheet (source region of the aurora) by the dipole tilt effect.