Configuration and reconnection of the geomagnetic tail

Abstract

A description of certain aspects of the geomagnetic tail is made using data from the Ames magnetometer on the Explorer 33 satellite. The general shape corresponds with earlier findings of Ness and co-workers. The tail is found regular to distances greater than 82 RE. The field values for Kp ≤ 2+ vary from a low of about 4 gammas to a high value of 40 gammas. Generally the values are in the neighborhood of 10–20 gammas. A distinct skewing of the field lines away from the solar-antisolar direction is observed, such that an added component of magnetic field in the direction of planetary motion is present on both sides of the region of field reversal. The skewing appears to be greatest near the region of field reversal. Increase in field magnitude with increasing Kp is observed. The radial gradient can be shown to fit a power or exponential law with near equal validity. A correlation analysis of field magnitude with radial distance, ap, and transverse position coordinates, also is discussed. A radial gradient cannot be detected in the outermost half of the data (beyond 58 RE), although significant correlation with geomagnetic activity remains. No significant cross gradient, apart from a radial gradient, is observed in the tail field. Strong evidence for reconnection of field lines is found, and statistics are presented for a dual mechanism regarding the residual Z field across the region of field reversal. The tail structure seems patchy at the neutral sheet, both near the magnetopause and near satellite apogee.