Wind observations of the terrestrial bow shock: 3-D shape and motion

Between late 1994 and early 2001 the Wind orbiter, generally targeted to st ay in the solar wind, passed through the Earth's magnetosphere similar to 5 0 times. About 450 distinct bow shock crossings were collected during the i nbound and outbound bracketing each Wind perigee. These crossings and corre sponding vectorial upstream solar wind measurements by the Wind MFI and SWE instruments are used to study the 3-D shape of the bow shock and its motio n. Mapping of bow shock crossings to the Sun-Earth line and to the terminat or plane is realized using a recent analytical model of the planetary bow s hock. The asymmetry of the terrestrial bow shock in the terminator plane is studied as a function of Friedrichs diagram anisotropy. Analysis of the su bsolar bow shock position as a function of Alfvenic Mach number M-a during intervals of magnetic field aligned solar wind flow shows that the shock te nds to approach the Earth when M-a is decreasing, while for non field-align ed flows bow shock moves from the planet.