Wind Observations of an Unexpected Precursor to Flapping of the Distant Tail

Abstract:

This presentation illustrates how observations from an array of spacecraft spread throughout the magnetosphere can provide insight into magnetospheric dynamics. Specifically, we use data from Wind, ACE, Cluster, Polar, DMSP and ground-based magnetometer chains to provide context for Wind observations of distant (R ~ -226 Re) magnetotail flapping on January 10, 2004. Just before the flapping began, Wind observed a plasma and magnetic field structure in which the field strength rises by a factor of 2, and the By and Bz components rotated in a strong, tailward (-900 km/s) and duskward flow burst. Closer inspection reveals a flux rope (plasmoid) containing a hot and tenuous plasma. We try to identify the origin of this precursor by looking at data from the various spacecraft. Working back towards the dayside, we discover several effects occurring at the same tine. We argue that they are set in motion by a solar wind planar structure containing a magnetic depression and sharp density rise, and its interaction with the bow shock. These phenomena include (1) a huge compression of the magnetosphere, (2) a strong sunward flow (3 km/s) in a double vortex-like structure flanked by 2 sets of field-aligned currents at the poleward edge of the oval, and (3) the ground signature of a traveling convection vortex. Clearly, an intertwined set of phenomena is occurring at the same time and further analysis can give us great insight into the response of the magnetosphere to significant transient solar wind changes.