Dynamical plasmapause positions during the July 29-31, 1977, storm period: a comparisons of observations and time-dependent model calculations

The temporal evolution of the plasmapause boundary is studied over a period of three and a half days covering the successive substorm events of July 29 and July 30, 1977. The equatorial plasmapause position in different local time sectors is first calculated as a function of universal time using electric field distributions derived from the models of Volland-Stern and McIlwain, with similar variation of the electric field intensity as a function of the Kp index. Model predictions are then compared with experimental data deduced from a large number of whistlers received at Kerguelen and at General Belgrano. In situ electron density measurements made on board the GEOS-1 satellite, and estimates of low-altitude plasmapause boundaries deduced by Fennell et al. from S3-3 satellite data are also used for this study. From the comparison of the observations and theoretical model calculations, we infer that when the mechanism of plasma interchange motion is taken into account the calculated positions of the plasmapause fit the observations better than in the case of the classical MDH proximation. The time-dependent E3H and Volland-Stern's electric field models respectively describe satisfactorily number of features which are observed. Some of the observation presented can be interpreted in favor of both E-field models. The discrepancies found between the observations and the numerical simulations can be used to correct the empirical E-field models used in model calculations of the plasmapause positions