On the use of photometer data to map dynamics of the magnetotail current sheet during substorm growth phase

The Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) i s a large-scale ground-based instrument array of remote sensing equipment m onitoring the high-latitude ionosphere from the north central to the northw est portion of North America. It provides realtime coverage of auroral even ts such as magnetospheric substorms. In this paper the variation of magneto tail thickness is estimated during substorm growth phase by using a simple magnetic field model and data from the meridian scanning photometers in the CANOPUS array. An important parameter in the modeling process is the kappa parameter, defined as the square root of the minimum curvature radius to m aximum Larmor radius ratio. Through use of this parameter we are able to gr ossly determine the expected proton precipitation regions in the ionosphere . Two examples presented (February 9, 1995, and March 9, 1995) show that cr osstail current sheet thinning from 2-0.1 R-E can occur during the course o f a growth phase. Within the framework of our model it is demonstrated that the magnetotail field line stretching, associated with thinning of the cur rent sheet, is correlated with the equatorward motion of H-beta auroral emi ssions. Also demonstrated is the Earthward movement of the inner edge of th e plasma sheet to within 6 R-E.