GEOTAIL observations of anomalously low density plasma in the magnetosheath

During the anomalously low density solar wind interval of May 1999, GEOTAIL was in the magnetosheath for similar to 37 hours after making an inbound c rossing of the expanding bow shuck at similar to 8 R-E upstream of its nomi nal position. Comparison among data sets obtained from GEOTAIL (magnetoshea th), WIND (near upstream - bow shock), and ACE (far upstream) reveals sever al unique features: Firstly, during the interval of 1430-1530 UT on 11 May, we observed both in the solar wind and magnetosheath double-peaked protons with a peak separation of 250-300 km/s, which was close to the local Alfve n velocity during the event. Secondly, rye observed extremely strong strahl electrons both in the solar wind and magnetosheath during the interval of 0600-2100 UT on 11 May 1999. We present an overview of the GEOTAIL observat ions, and discuss their physical significance.