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 antiparallel model predict distinctly different patterns for B y in the magnetosphere as a function of IMF B y . Although both models predict that nightside magnetospheric magnetic field will tilt in the direction of the IMF B y , the antiparallel merging model predicts that magnetospheric magnetic field lines in the vicinity of local noon will tilt in the direction of the IMF, where as the subsolar model does not. The correlation coefficients between the geosynchronous data and the IMF B y peak at both noon (0.61) and midnight (0.50), favoring the antiparallel model. These results were obtained with 1789 (noon) and 1312 (midnight) 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 the slopes varies smoothly from midnight peak to a broad minimum near noon.