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The plasma density enhancements recently observed by the Large-AngleSpectrometric Coronagraph (LASCO) instrument onboard the Solar and HeliosphericObservatory (SOHO) spacecraft have sparked considerable interest. In ourprevious theoretical study of the formation and initial motion of these densityenhancements it is found that beyond the helmet cusp of a coronal streamer themagnetized wake configuration is resistively unstable, that a travelingmagnetic island develops at the center of the streamer, and that densityenhancements occur within the magnetic islands. As the massive magnetic islandtravels outward, both its speed and width increase. The island passively tracesthe acceleration of the inner part of the wake.  In the present paper a few spherical geometry effects are included, takinginto account either the radial divergence of the magnetic field lines and theaverage expansion suffered by a parcel of plasma propagating outward, using theExpanding Box Model (EBM), and the diamagnetic force due to the overallmagnetic field radial gradients, the so-called melon-seed force. It is foundthat the values of the acceleration and density contrasts can be in goodagreement with LASCO observations, provided the spherical divergence of themagnetic lines starts beyond a critical distance from the Sun and the initialstage of the formation and acceleration of the plasmoid is due to the cartesianevolution of MHD instabilities. This result provides a constraint on thetopology of the magnetic field in the coronal streamer.

Diamagnetic and Expansion Effects on the Observable Properties of the Slow Solar Wind in a Coronal Streamer