Coordinated analysis of data sets from X ray, energetic electron, ionospheric convection velocity, interplanetary magnetic field (IMF), and solar wind plasma experiments yields a comprehensive picture of the stimulated precipitation of trapped relativistic electrons simultaneously onto both polar caps in response to a sharp northward-dawnward turning of the IMF after initiation of a substorm at about 1200 UT on December 17, 1992. Although several explanations are possible, these observations are consistent with the occurrence of conjugate magnetic reconnection tailward of both geomagnetic cusps caused by the draping of northward and dawnward directed IMF over the dayside magnetopause. ¿ American Geophysical Union 1995