SIMULTANEOUS 2-HEMISPHERE OBSERVATIONS OF THE PRESENCE OF POLAR PATCHES IN THE NIGHTSIDE IONOSPHERE

The presence of polar patches as observed simultaneously in the same m agnetic meridian of opposite nightside ionospheres by coherent and inc oherent scatter radars art described. The patches appear to be related to variations either in the B-z or B-y component of the interplanetar y magnetic held which cause transient merging on the dayside magnetopa use. The passage and characteristics of polar patches as they traverse the polar cap into the nightside auroral oval an not significantly af fected by the occurrence of small substorms. This study illustrates ho w the observations of polar patches in the nightside high-latitude ion osphere could be of great value in determining their formation process .