AN INITIAL RESPONSE OF MAGNETIC-FIELDS AT GEOSYNCHRONOUS ORBIT TO PI-2 ONSET AS OBSERVED FROM THE DIP-EQUATOR

Fluxgate magnetometer data recorded at the dip-equator (Huancayo, Peru ; 1.44 degrees N, 355.9 degrees in geomagnetic coordinates; 12.1 degre es S, 75.2 degrees W in geographic coordinates; L = 1.00) with higher accuracy of timing (0.1 s) and amplitude resolution (0.01 nT) were uti lized to survey an onset of Pi 2 pulsations in the midnight sector (21 00-0100 LT) during PROMIS (Polar Region and Outer Magnetosphere Intern ational Study) periods (1 March-20 June, 1986). It is found that chang ing field line magnitude and vector as observed by magnetometer on boa rd the synchronous satellites in the midnight sector often takes place simultaneously with the onset of Pi 2 pulsations at the dip-equator. The field disturbances that follow thereafter tend to last for some ti me both at the geosynchronous altitudes and the dip-equator. In this r eport, we examine the initial response of the field lines in space, an d attempt to classify how the field line vector changed in the meridio nal plane.