Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771

On May 5, 1996, the Interball-1 and IMP 8 spacecraft crossed the bow shock boundary. The upstream conditions were special in two factors: (1) the interplanetary magnetic field was anti-parallel to the solar wind flow within 15°; (2) the conditions were stable for a prolonged period (~9 hours). At the nose of the magnetosphere, the Interball-1 data revealed that the magnetopause was farther outward by ~2 R_E than model predictions and the subsolar magnetosheath was unusually thin, at most 10% of the magnetopause standoff distance. Both results stand in contrast to predictions of existing magnetopause/bow shock models. Assuming a hyperboloidal (paraboloidal) shock wave, the calculated shock's standoff distance was 13.7 (13.6) R_E and the focus was located on the X-axis at 4.5 (4.2) R_E. Based on the IMP 8 observation, the bow shock flares significantly less than MHD simulations predict for a field-aligned bow shock at the magnetospheric flanks. This study discusses differences between the observations and existing MHD bow shock simulations for field-aligned upstream flow. Furthermore, it is suggested that the flow-aligned IMF orientation causes a significant change of the magnetopause shape into a bullet-like obstacle.

AGU Preprint, paper number 10.1029/2002JA009697, 2002