The magnitude of the interplanetary magnetic field (IMF) exhibits an enhancement during 1978--1979 relative to all years back to 1963. It is shown that IMF magnitude variations over the 1966--1979 period represent the combined effect of variations in both the radial flux density of the IMF and the degree of spiraling of the IMF, consistent with the theoretical model of Parker. The 1978--1979 IMF magnitude enhancement is due to an enhancement of radial flux which was in turn related to an increase of magnetic flux leaving solar active regions. It is also shown that during the corotating stream dominated years 1973--1976, the IMF was less wound up than it was during other years, and that 1973--1974 were years of enhanced radial flux.