The impulsive penetration model predicts that blobs of solar wind plasma penetrate the magnetosphere by becoming detached from the magnetopause. If so, negative radial density gradients should be common near the magnetopause. We present the results of case and statistical studies of simultaneous Interball 1 and Magion 4 omnidirectional plasma sensors (VDP) plasma observations during magnetopause passes. The spacecraft observe very similar features when their interspacing is small. By contrast, the spacecraft located farther radially outward invariably observes densities greater than or equal to those seen at the spacecraft nearer Earth when the interspacing increases. The observations are consistent with the standard interpretation in which a boundary layer of plasma with intermediate densities often lies sandwiched between the magnetosheath and the magnetosphere proper. Blobs of magnetosheath or boundary layer plasma rarely, if ever, become detached from the magnetopause. ¿ 2000 American Geophysical Union