Solar Wind Dynamic Pressure Effects on the Terrestrial Magnetosphere.

The average dayside boundary of the magnetosphere is determined from actual crossings of the magnetopause by ISEE-1 and -2, and is found to vary as expected with the solar wind dynamic pressure. We find that the average stand-off distance of the magnetopause is 0.5 R _{rm e} further from the Earth when the IMF is northward than when it is southward. The average stand-off distance of the magnetopause, normalized by the solar wind dynamic pressure, decreases with increasingly negative values of the z-component of the IMF when B _{rm z}<0 nT. However, the average normalized stand-off position is constant for IMF B_{rm z} values greater than 0 nT. There is no observed dependence of the size of the magnetosphere on the intensity of the ring current. There is empirical evidence that the magnetopause shape is influenced by the cusps, even near the magnetospheric equator at times of large dipole tilt. Observed magnetospheric fields are compared with those predicted by a scaled vacuum analytic model of the magnetosphere. In the dayside magnetosphere, Pc 1 waves are rarely triggered in the magnetosphere by the passage of sudden impulses. The shape and size of the average near-Earth magnetotail is derived from pressure balance considerations between the solar wind and magnetotail lobes. The resulting shape and size agrees well with an earlier model of the magnetotail for nominal values of the solar wind dynamic pressure, but is more dependent on the momentum flux than is predicted by this earlier model. The dependence of the tail radius on dynamic pressure does agree well with another empirical study, which examined crossings of the magnetotail by IMP 6 between -15R_{rm e} and -20R_{rm e}. The effect of IMF B_{ rm z} on the size of the magnetotail is also examined; the tail cross section increases for increasingly negative values of IMF B_{ rm z}, but does not vary with positive values of IMF B_{rm z}. When the IMF is northward, there is no change in the level of magnetic flux across the sudden impulse, whereas when the IMF is southward and the passage of the sudden impulse triggers a substorm onset, the magnetic flux decreases.