Ring Current Asymmetry as Observed by Ground Magnetometers, In Situ, and Space-based Remote Sensing Data

During enhanced geomagnetic activity, the ring current is well-known to exhibit a strongly asymmetric structure. Some storm models predict a rapid change to symmetric ring current in early recovery, but this is not always what is seen. In particular, many use the ASY index to characterize the inner magnetospheric ring current morphology, as it is widely available and continuous, though it is not clear how well it represents what is actually occurring in the inner magnetosphere. The increased availability of in situ and remote sensing measurements from instruments on spacecraft such as POLAR and IMAGE, has given physicists the opportunity to re-evaulate the meaning and usefulness of such indices and gain a better understanding of the ring current morphology. The asymmetric index (ASY), in particular, is analyzed to evaluate its usefulness in parameterizing the asymmetry of the storm-time ring current. Data used for this evaluation include POLAR CAMMICE and LANL in situ data and IMAGE HENA data. We analyze the ring current morphology in storm times and discuss whether ASY provides a useful characterization.