The influence of the direction of the geomagnetic dipole on the position of the neutral sheet

An analysis of neutral sheet crossings detected by the NASA-Goddard Space Flight Center magnetometer on the Explorer 34 satellite has shown that the diurnal wobble of the geomagnetic dipole measurably influences the position of the neutral sheet at 30 RE. Viewed in the solar-ecliptic coordinate system, the dipole wobble originates from the 11° angle between the earth's spin axis and the dipole axis, has a period of 24 hours, and can be resolved into components of motion perpendicular and parallel to the earth-sun line. The perpendicular component exerts a torque on the magnetotail and causes the neutral sheet to pivot about an axis approximately parallel to the solar wind direction. The parallel component encourages the neutral sheet to move above and below the solar-magnetospheric equatorial plane with an amplitude of 1 RE. This latter motion is consistent with the neutral sheet's being hinged at a geocentric distance of 5.25 RE. Although hinging is not as dominant a feature of neutral sheet motion as pivoting at 30 RE, both are in phase with the 24-hour precession of the dipole axis about the earth's spin axis.