On the average shape and position of the geomagnetic neutral sheet and its influence on plasma sheet statistical studies


  • J. Dandouras


A geometric model of the average geomagnetic neutral sheet is presented. The average neutral sheet is best fitted by a smooth warped surface that crosses the solar magnetospheric equatorial plane near the tail flanks and that has no slope discontinuities. The geometry is defined to fit a magnetohydrostatic equilibrium model of the magnetotail, and the values of the parameters are determined by minimizing the Rms deviation from zero of the satellite distance to the model position of the neutral sheet when BX polarity reversals are observed. The average neutral sheet position given here is optimized for geocentric distances of the order of 20–22 RE (ISEE orbit). Comparison with the Fairfield neutral sheet model, which is optimum for R = 30 - 40 RE, shows the overall geometric stability of the average neutral sheet and its alignment parallel to the solar wind flow. A small flattening that is observed as a function of the increasing geocentric distance is due to the greater magnetopause radius and the reduced influence of the tilted geomagnetic dipole. The model presented here is used to examine the spatial distribution of the particle flux dropouts observed in the plasma sheet, and it is confirmed that in the central magnetotail (|Y| < 10 RE) the plasma sheet can be completely pinched during substorms.