Magnetotail changes in relation to the solar wind magnetic field and magnetospheric substorms

Substorm activity is known to be associated with changes in the solar wind parameters and the magnetotail configuration. In this paper we investigate whether the magnetotail changes occur only as a consequence of substorms or also as a direct consequence of changes in the solar wind parameters. Using data from several satellites (Ogo 5, ATS 1, Imp 4, Explorer 33 and 35) and 17 ground magnetic observatories, we conclude that the tail responds to both changes in the north-south orientation of the interplanetary field and substorm activity. Specifically, we show the following. (1) A change from a northward to a southward interplanetary field causes a slow increase of the field to be recorded by a satellite within the lobe of the tail, and a thinning of the plasma sheet. (2) A change from a southward to a northward interplanetary field causes the plasma sheet to expand. In contrast, it seems that in the inner magnetosphere the distortion of the magnetic field due to a period of southward interplanetary field is not relieved by an interval of northward field but only through the occurrence of a substorm expansion. (3) A substorm expansion causes a slow decrease of the field within the lobe of the tail and an expansion of the plasma sheet.