GEOTAIL Observation of Interplanetary Shock-Magnetic Hole Interaction on 25 September 2001: An overview

Magnetic holes (MHs) in the solar wind are isolated depressions in the magnitude of the interplanetary magnetic field, which have attracted recent observational and theoretical attentions. On 25 September 2001, we observed an interaction event between an interplanetary shock (IPS) and a MH using the GEOTAIL data (plasma and energetic particles, magnetic and magnetic fields, and plasma waves) as well as those from the other ISTP spacecraft (ACE and WIND). What we observed were, (1) within the MH the solar wind plasma density and temperature respectively showed a decrease and increase keeping the pressure balance condition with the dropping magnetic pressure, (2) the solar wind velocity showed a significant decrease in the region surrounding the MH, (3) the nonthermal ions were trapped within the MH structure, and (4) in the MH there were enhancement of magnetic turbulence in the frequency range of 0.1-8 Hz, while no obvious enhancement was seen in the frequency range above ∼10 Hz. We will discuss physical implications of these observations. In addition, we are trying to deduce the evolution history of the MH-IPS system from the multi-satellite data.