The plasmapause position is determined by the innermost equipotential surface which is tangent to the 'Roche-Limit' surface of the ionospheric plasma filling the magnetosphere. When the thermal particles corotate with the Earth's angular velocity, the 'Roche-Limit' equatorial distance is Lc=5.78 [RE]. When the angular convection velocity is evaluated from the quiet time electric field distribution E3 of McIIwain (1972), Lc depends on the local time. Its minimum value is then LC=4.5Near 2400 LT, and the plasmapause shape and position satisfactorily fit the observations. The diffusive equilibrium dnesity distribution appropriated inside the plasmasphere, becomes convectively unstable beyond L = Lc, where the collisions type of model satisfactorily represents the observations. In the intermediate region between the plasmapause and the last closed magnetic field line, contimues ionization fluxes are expected to flow out of the midlatitude ionosphere.