Comment on “ionospheric signature of plasma sheet thinning prior to a substorm” by J.R. Dudeney and A.S. Rodger

Abstract

In a recent paper, Dudeney and Rodger (1988) have presented a study of a substorm expansive phase which they use to attempt to distinguish between the near-Earth neutral line model for substorms (cf. Hones, 1984) and the boundary layer model for substorms proposed by Rostoker and Eastman (1987). One of the features of the event studied by Dudeney and Rodger is a Pi2 pulsation which, the authors contend, is not accompanied by a substorm expansive phase. The purpose of this Comment is two-fold. In the first place I wish to demonstrate that the evidence that the Pi2 pulsation alluded to by the authors is not accompanied by a substorm expansive phase is far from compelling. In the second instance, reasons for rejecting the boundary layer model as an explanation for the event under consideration are shown to be without foundation. which is connected to the magnetosphere by fieldaligned currents at its eastern and western edges (viz. a current wedge). In this case, it is clear that to the equatorward side of the ionospheric electrojet, the magnetic signature is a negative Z-component bay. A 10 nT Z-component bay is quite consistent with the development of a westward electrojet of peak strength 150 nT whose center is 10” poleward of the observing station (e.g. Halley). (Note that Fig. 1 shows a westward electrojet for the Northern Hemisphere, so that the corresponding signature for a negative Z-component bay would be a positive Z-component bay at the Southern Hemisphere station of Halley.) Based on these considerations, I would suggest that the authors have no strong reason to believe that their 00: 50 U.T. pulsation is not accompanied by an expansive phase onset or intensification.