Ground‐based studies of ionospheric convection associated with substorm expansion

Abstract

The instantaneous patterns of electric fields and currents in the high‐latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground‐based magnetometer observations for October 25, 1981. For this purpose, an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used. These global patterns are unobtainable from any single data set. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE 2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large‐scale potential distributions are indeed of general two‐cell patterns representing the southward IMF status, but the night‐morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively.

Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

“…Of course, the flow pattern is complicated further by smaller-scale perturbations which are imposed by localised changes in the conductivity, however, these are discussed in more detail below. The largerscale, azimuthally extended, Harang flows may actually correspond to the true form of the Kamide et al (1994) equatorward substorm convection cell as postulated by Liang et al (2006). In this case, however, these flows also appear to be intrinsically related to the enhanced auroral and sub-auroral flows described earlier.…”

“…They also found a systematic increase in the transpolar voltage from ∼40 kV 2 min before onset to ∼75 kV 12 min after, and attributed this to the removal of open flux from the polar cap by nightside reconnection. Recently, Liang et al (2006) (following earlier work by Kamide et al (1994)) discussed observations of two distinct systems in the substorm convection pattern. The first is a post-midnight anticlockwise convection vortex (PoACV) at higher latitudes and the second is an azimuthally extended clockwise vortex at lower latitudes.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…Recently, Liang et al (2006) (following earlier work by Kamide et al 1994) discussed observations of two distinct systems in the substorm convection pattern. The first is a postmidnight anticlockwise convection vortex (PoACV) at higher latitudes, and the second is an azimuthally extended clockwise vortex at lower latitudes.…”

Different responses of northern and southern high latitude ionospheric convection to IMF rotations: a case study based on SuperDARN observations

“…Ionospheric convection patterns resulting from reconnection at the Earth's magnetopause have been the object of a vast literature which has studied their dependence on Interplanetary Magnetic Field (IMF) orientation by means of lowaltitude spacecraft (Heppner and Maynard, 1987;Weimer, 1995), ground magnetometers (Kamide et al, 1994;Papitashvili et al, 1994) and, more recently, SuperDARN convection measurements Greenwald, 1996, 2005;Chisham et al, 2007). On the other hand, a detailed understanding of high latitude ionospheric convection has been achieved in the course of years starting, for instance, from the seminal work of Cowley and Lockwood (1992).…”