Whistler Waves in Upstream Region of Interplanetary Shocks

Whistler waves are considered to play an important role in the electron dynamics for the collisionless shock formation process at interplanetary shocks (IPSs). In this report, we analyze IPS events observed by GEOTAIL on 21 February 1994 and 15 July 2000, focusing on whistler wave properties in their upstream region extending the previous work of Shimada et al. (1999). In both events, we have identified the existence of whistler mode waves in the upstream region of the IPS as well as the tendency of the intensity increase toward the shock front. At the same time we have found the detailed features differing between these events: While the intermittent but clear wave bursts were found on 21 February 1994 event, the waves were more or less continuous on 15 July 2000 event.