average magnetic field configuration of the outer magnetosphere

Over 1500 hours of data from the satellites IMP 1, 2, and 3 have been used to study the configuration of the magnetic field in the outer magnetosphere between 5 and 18 R E . Hourly average field vectors were projected in the solar magnetic equatorial plane and in 24 meridian sections corresponding to each hour of local time. The plots show the sweeping back of the field toward the tail and the dawn and dusk transition from compressed dayside field lines to extended nightside field lines. Constant B contours in the equatorial plane were constructed, and flux conservation was used to establish a quantitative relationship between the equatorial crossing point of an outer magnetosphere field line and the latitude of its earth intersection. A contour diagram in the equatorial plane designating the latitude of field line origin permits the mapping of low‐altitude phenomena to the equatorial plane and vice versa. Auroral oval field lines are found to come from the region of the magnetopause in the day‐light hemisphere but from well within the magnetosphere in the night hemisphere. The outermost closed field line is found to come from approximately 78° throughout the dayside hemisphere.