Influence of Magnetospheric Parameters on Geosynchronous Field Characteristics, Last Closed Field Lines and Dayside Neutral Points

Abstract

The day/night field asymmetry at the geostationary orbit, the Earth intersection points of geostationary field lines, the positions of the dayside neutral points, and the intersection latitudes of the last closed field lines have been calculated in a ‘closed’ magnetospheric B-field model as functions of systematic variations in model parameters. The magnetospheric parameters with most influence are: (i) the stand-off distance, (ii) the tail field intensity, (iii) the ring-current D _st - index, and (iv) the dipole tilt angle.

The dayside polar cusps are defined geometrically by the co-ordinates of the magnetopause neutral points and the Earth intersection latitudes of the last closed field lines at local noon. The cusp position near the magnetopause depends strongly on the ‘stand-off’ distance, the tail field and the dipole tilt angle. The ring current essentially determines the B-field configuration in the middle magnetosphere near the synchronous orbit during the recovery phase after a magnetic storm, but can be neglected at the magnetopause. Local time asymmetries increase with magnetospheric compression, i.e. decrease of stand-off distance. Conjugate points are situated at different geomagnetic latitudes in the northern and southern hemispheres in the case of a tilted geomagnetic axis. Magnetospheric B-field characteristics have been computed in a three-dimensional quantitative field model which is based on solution of the Chapman-Ferraro problem.