Plasma flow pattern in the Earth's magnetosheath

Positive-ion observations made on the twin Vela 3 satellites are used to study the plasma flow pattern in the ‘twilight’ regions (near 90° from the subsolar point) of the earth's magnetosheath. Observations from January to May 1967 reveal a persistent deviation from symmetry about the sun-earth line. Both simultaneous measurements by satellites on opposite sides of the magnetosheath and long-term averages indicate a flow pattern whose line of symmetry makes an angle of 8° ± 1° with the sun-earth line, and ∼6° with the direction of the incident solar wind. This tilting of the flow pattern is in good agreement with Walters' 1964 prediction of the effect of the interplanetary magnetic field on the post-bow shock flow pattern.