The average configuration of the geomagnetotail has been deduced from numerous spacecrafts measurements. These lobes are separated by the neutral sheet. The position of the neutral sheet varies with time, and can only be definitely known at the instant a spacecraft traverses the reversal region of the magnetic field. Numerous studies (Fairfield 1980 and references there in) have shown that the annual and diurnal changes of the tilt angle between the earth-sun line and the subsolar point induce significant movements of the neutral sheet away from the solar magnetospheric XY plane.

According to the previous neutral sheet models, there remains a varying discontinuous region between neutral sheet and the equatorial plane of the tilted geomagnetic dipole field. A Standard Equatorial-Neutral sheet (SEN) model (Xu, 1992), a Displaced Equatorial-Neutral sheet (DEN) model (Xu, 1991) and an Analytical Equatorial-Neutral sheet (AEN) model (Xu et al., 1993, Zhu and Xu, 1994 and Wang and Xu, 1994) inside the magnetopause (Sibeck et al., 1991) are developed.

In these three Equatorial-Neutral Sheet models the tilted equatorial plane joints smoothly to the neutral sheet, so that they can be used in the whole magnetosphere regions, including in the near tail region. The SEN and DEN models contain of 3 different complicate equations. The AEN model is expressed by one simple equation and remain approximately the general characteristic of the DEN Model. Based on the AEN model, a normal curve coordinate system is set up, in which the AEN sheet becomes one of the coordinate surface. This coordinate system will change with the Earth's tilt angle,and thus can almost offset the titled effect on the pattern of the geomagnetic field on the Magnetotail (Zhu and XU, 1994).

This packege contains the FORTRAN 77 source codes (*.FOR) of SEN, DEN and AEN. They compute the position of SEN (DEN or AEN) sheet along Zsm, at a given point Xsm and Ysm inside the magnetopause at different dates and times.