Corotating and transient structures of IMF at Venus and Earth orbits

Magnetometer data obtained from the Pioneer Venus orbiter (PVO) provide a unique data base for studying interplanetary magnetic field (IMF) structures at 0.7 AU. Comparison of the same structure observed at 0.7 and 1 AU provides information about the effects of stream interactions between these two distances. Besides, the PVO observations provide solar wind conditions at various longitude separations from the Sun-Earth line, because the orbital motion of Venus is about 0.6 deg/day faster than that of Earth. Thus, it is possible to examine the effects of time variations in the coronal conditions on the solar wind conditions by comparing corotating structures observed at Earth and those from the PVO at different longitude separations. Some results obtained so far are as follows. We have found several transient structures observed at both 0.7 and 1 AU, when the Sun, Venus, and Earth are closely aligned. Each event exhibits magnetic field variations very similar to each other between Venus and Earth, implying that the effects of stream interactions are small. The IMF sector boundaries were compared between the Venus and Earth orbits as typical examples of corotating structures. We have found both well-correlated and poorly-correlated structures depending on the longitude separation between the Earth and Venus, and on the persistence of the sector structures.