A SuperDARN Study of Steady Magnetospheric Convection

Abstract

Intervals of Steady Magnetospheric Convection (SMC) are loosely defined as times when convection in the magnetosphere as a whole is enhanced and there are no substorm signatures. A lack of substorm signatures implies that the large scale structure of the magnetotail is maintained. There have been several quantitative methods developed to detect SMC events. None of these methods are based on observations of convection. The Super Dual Auroral Radar Network (SuperDARN) is a useful tool for studying SMC, because it gives a direct measurement of convection on a global scale. Previous SMC selection methods have made use of ground based magnetometer responses to auroral currents in the atmosphere. These methods resulted in a strong seasonal dependence in SMC occurrence due to seasonal changes in ionospheric conductivity. A new SMC selection criterion was developed to improve upon the previous criteria. This new method identifies all the events found using currently accepted methods plus additional intervals that reduce the seasonal dependence in SMC occurrence. SuperDARN was used to evaluate the old and new selection methods. According to SuperDARN convection observations, the new SMC selection criterion largely eliminated ionospheric conductivity effects. A conceptual model of the conductivity effects on the traditional SMC selection method was developed, and the occurrence of modelled SMC events agrees well with observations. Statistical studies have revealed that the additional SMC intervals have similar properties as events selected using traditional methods. Case studies confirmed the statistical results that SMCs selected by the new criterion have SMC properties. Both SMC events sets have a moderate solar wind driver, enhanced convection, and stable polar cap size. Statistical studies have also shown there was good SuperDARN data coverage during SMC, which is not typical of SuperDARN observations during enhanced and disturbed conditions in the magnetosphere. It is therefore shown to be an excellent tool with which to study SMC.