Electron density at the subsolar magnetopause for high magnetic shear: ISEE 1 and 2 observations

The ISEE radio wave propagation electron density experiment allowed the determination of the integrated electron density between the ISEE 1 and ISEE 2 satellites at the relatively high rate of 8 or 32 Hz. When the component of the spacecraft separation vector in the direction of the normal to the magnetopause is significantly smaller than the thickness of the current layer, this data set allows the internal structure of the magnetopause to be studied and compared with theoretical predictions. For a particular triple subsolar magnetopause crossing with high magnetic shear, an electron density overshoot is observed in the current layer adjacent to the magnetosheath. The similarity of the three crossings indicates that the internal structure of the magnetopause does not change dramatically during the time interval considered. A superposed epoch analysis of these crossings is consistent with the density profile obtained from kinetic simulations. The general relationship between magnetic field asymmetry, magnetic field rotation angle and electron density overshoot is discussed. It is concluded that a density overshoot could be a typical feature of the subsolar magnetopause with high magnetic shear. This conclusion is supported by two other dayside magnetopause crossings for which high time resolution electron density data are available.