ROTATIONAL POLARITIES OF SUDDEN IMPULSES IN THE MAGNETOTAIL LOBE

A sudden impulse (SI) is a sudden change in the magnetic field strength which is caused by a change in the solar wind pressure and is observed throughout the magnetosphere. In this report we have examined the rotations of the magnetic field vectors at times of SIs in the magnetotail lobe, by using IMP 6, 7, and 8 magnetometer data. The following properties have been found: (1) At the time of SI the arrowhead of the magnetic vector tends to rotate in one plane. (2) The plane of rotation tends to include the unperturbed magnetic field vector. (3) The plane of rotation tends to be aligned with the radial direction from the magnetotail axis. (4) The magnetic vectors have a particular rotational polarity: when the plane of rotation is viewed so that the Sun is to the right of the viewed plane and the magnetotail axis is to the bottom, the arrowhead of the vector tends to rotate counterclockwise in this plane. These magnetic vector properties are consistent with those expected when part of an increase in solar wind lateral pressure squeezes the magnetotail axisymmetrically while moving tailward.