A LARGE STATISTICAL STUDY OF THE ENTRY OF INTERPLANETARY MAGNETIC-FIELD Y-COMPONENT INTO THE MAGNETOSPHERE

We used 5 years of GOES-6 and 6 years of GOES-7 data to correlate the y-component of the geosynchronous magnetic field with the y-component of IMF. One motivation is that the subsolar merging model and the anti parallel model predict distinctly different patterns for B-y in the ma gnetosphere as a function of IMF B-y. Although both models predict tha t nightside magnetospheric magnetic field will tilt in the direction o f the IMF B-y, the antiparallel merging model predicts that magnetosph eric magnetic field lines in the vicinity of local noon will tilt in t he direction of the IMF, where as the subsolar model does not. The cor relation coefficients between the geosynchronous data and the IMF B-y peak at both noon (0.61) and midnight (0.50), favoring the antiparalle l model. These results were obtained with 1789 (noon) and 1312 (midnig ht) data points. The slopes of the regression lines indicate 29% IMF B -y entry at noon and 79% at midnight. The local-time distribution of t he slopes varies smoothly from midnight peak to a broad minimum near n oon.