Solar wind control of the tail lobe magnetic field as deduced from Geotail, AMPTE/IRM, and ISEE 2 data

Abstract

A statistical study was made of the tail lobe field response to the dynamical pressure of the incoming solar wind and to the interplanetary magnetic field, as well as its relation to the concurrent level of the Dst field. The study covers a wide range of distances between 10 and 60RE and is based on a large set of tail lobe magnetic field data, compiled from three sources: (1) Geotail magnetometer and low‐energy plasma instrument data for 1993–1997, (2) AMPTE/IRM magnetometer and plasma instrument data for 1985–1986, and (3) ISEE 2 magnetometer and fast plasma experiment data for 1978–1980. The tailward variation of the tail lobe field and of its response to the solar wind and interplanetary magnetic field (IMF) conditions was studied using a regression relationship, including various combinations of the interplanetary quantities, measured by IMP 8 and Wind spacecraft. An investigation of the role of the time lag effects was made by tagging each lobe field measurement by a “trail” of 12 consecutive 5‐min average values of the solar wind parameters and finding best fit distributions of the lagged response amplitudes in the solar wind and IMF‐related regression terms. The goal of the work is to find a set of input variables providing the highest correlation between the observed and predicted magnitude of the tail lobe field, so that their combination could be used for parameterizing the strength of the cross‐tail current in the data‐based magnetospheric models.