POLAR-CAP CONTRACTION ASSOCIATED WITH THE LEADING-EDGE OF A MAGNETIC CLOUD

In the early hours of 14 January 1988 a large magnetic cloud passed th e earth. In this brief article we show evidence of a sudden impulse as sociated with the leading edge of the main body of the magnetic cloud and we map the evolution of the convection patterns which are indicati ve of polar cap contraction associated with the subsequent, large, nor thward-directed interplanetary magnetic field. We provide a unique, st ep-by-step view of the high latitude events, simultaneously tracing bo th dayside and nightside responses to the solar wind variations. Our m aps provide clear global-scale support for polar cap expansion/contrac tion theory. The final state of convection in the northern hemisphere was one of extreme quiescence with the suspension of both dayside and nightside reconnection and a near total loss of motional electric fiel ds mapping into the ionosphere. We discuss how this state developed.