Can Interhemispheric Asymmetries in Ionospheric Outflow Wag the Magnetotail?

Abstract:

Ionospheric outflow varies due to diurnal photoionization patterns and is a significant contributor to plasma in the magnetosphere during magnetic storms. The sunlit hemisphere should yield more ionospheric outflow compared to the nightside as a result of the magnetic dipole tilt. Previous studies have suggested that this difference in northern and southern hemisphere outflow may asymmetrically mass load the lobes and affect the tilt of the magnetotail. Recent MHD simulations have confirmed this, finding that the magnetotail is predicted to tilt towards the hemisphere with stronger ionospheric outflow. This study surveys the possible trend between asymmetric mass-loaded magnetospheric lobes and the magnetotail tilt.

Magnetotail crossing events observed by Cluster are tabulated and compared to modeled magnetotail crossing events. Comparisons of Cluster observational data to results from several versions of the Tsyganenko empirical models reveal a time difference between expected crossing through the magnetotail plasma sheet, indicating additional drivers of tail geometry not accounted for in the models. Differences in time between observational data crossing events and model data crossing events is compared to differences in average plasma density in the northern and southern lobes. Positive correlation between time differences and density differences could signify asymmetric mass outflow as a direct cause of magnetotail tilt. Results are analyzed as a function of activity, mass loading, and tangential solar wind velocity to narrow down possible causes of tail tilt. The net result is a full examination of the ability of asymmetric ionospheric outflow to affect the geometry of the magnetotail.