Multipoint Observations of the Large Substorm Associated with the Galaxy 15 Anomaly

Abstract

On April 5, 2010 around 09 UT, the NOAA Geosynchronous Operational Environmental Satellites (GOES) observed a large reconfiguration of the magnetospheric magnetic field in the midnight to dawn local time sector. Specifically, near midnight, the GOES-11 Hp (north-south) magnetic field increased by approximately 100 nT in 15 minutes. This is one of the largest dipolarizations of Earth:s field ever observed by GOES. At the same time, there were large increases in the flux of energetic electrons and protons and large ground magnetic perturbations. While the auroral electrojet index (AL) was extreme, being less than -2000 nT during this event, the preliminary, real-time Dst storm index was only on the order of -30 nT during the event (although it reached somewhat more intense values during the following day). The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) monitored currents at low altitude during this event, and these observations can be used to place the localized measurements at geosynchronous orbit in a global context. Additional measurements were made by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft just tailward of the GOES satellites. Minutes after the initiation of this intense substorm, at 0948 UT, Galaxy 15, located at geosynchronous orbit, just a few degrees away from GOES-11, suffered a serious anomaly and to date, contact has not been restored. At the time, it was reported that this anomaly was likely related to the solar generated event; however, the anomaly is still under investigation. The purpose of this presentation is not to evaluate the anomaly, but rather to describe the large response of the magnetosphere and ionosphere system to the solar and solar wind conditions that caused this extremely large substorm.