Low-altitude observations of the conjugate polar cusps

A set of 118 pairs of nearly simultaneous polar cusp observations over opposite hemispheres, taken by two identically instrumented satellites on orbits that are very close to each other, is used to determine the morphology of the conjugate polar cusps. It is found that the general mirror image picture does not extend to the precision of a fraction of a degree in magnetic latitude (MLAT). Only 54% of the equatorial boundary observations and 32% of the poleward boundary observations are within {+-}1{degrees} of the conjugate location. The influences of the Earth's magnetic dipole tilt, of geomagnetic activity, and of the IMF parameters on the cusp asymmetry are investigated; no unique parameter is found to better organize the conjugacy of the two cusps. Rather, all of these parameters appear to have a slight effect on the relative locations of the opposite polar cusps. The difference in the MLATs between boundaries of conjugate polar cusp regions depends on the latitude of the cusp location. Furthermore, the projection of the boundaries of the polar cusp regions onto the ionosphere does not follow the offset circle that describes the configuration of the average auroral oval.