Mapping of the Earth's bow shock and magnetic tail by Explorer 33

Abstract

The Explorer 33 satellite was launched July 1, 1966 and was injected into a highly elliptical earth orbit. The Goddard Space Flight Center magnetic field experiment onboard the spacecraft consists of a triaxial fluxgate sensor with a maximum dynamic range of ±64 gammas and a sensitivity of ±0.25 gamma along each axis. Because of the initial apogee‐earth‐sun angle of 118° west of the sun, the first 8 orbits of Explorer 33 (July 1 to November 11, 1966) mapped the earth's magnetosheath and magnetic tail from the western flank of the bow shock to the eastern flank. This mapping of the geomagnetic tail out to 80 earth radii established that the tail extends beyond the lunar orbital distance. Explorer 33 has also found that the earth's bow shock is still a detectable boundary between the interplanetary magnetic field and the downstream magnetosheath at a geocentric distance of 75.7 earth radii. The measurements have further suggested that the cross section of the geomagnetic tail is probably not cylindrical and have shown that the magnetic field magnitude in the tail decreases with distance down the tail from the earth.

Geometry of the geomagnetic tail

“…It was found that the field magnitude decreases with distance from the earth, with a gradient that can be described by an inverse power law (Behannon, 1968a;. The initially observed gradient has shown no statistically significant secular change ).…”

“…The early Explorer 33 data further suggested that the tail may not be c.Lrcular in cross-section but rather is elliptical with the major axis in the Z direction (Behannon, 1968a). All of these basic sm features of the tail field topology have been reviewed in detail by Ness (1969) and by Behannon and Ness (1969).…”

“…-2 -It has been suggested that the tail gradient must be the result of either reconnection of field lines across the neutral sheet or an increase in the radius of the tail with distance, or a combination of the two mechanisms (Behannon, 1968a;. The early Explorer 33 data further suggested that the tail may not be c.Lrcular in cross-section but rather is elliptical with the major axis in the Z direction (Behannon, 1968a).…”

Effects of the interplanetary magnetic field on the twisting of the magnetotail: Global MHD results

“…a circle or slightly elongated in the GSM z direction [Behannon, 1968[Behannon, , 1970Fairfield, 1971;Scarf et al, 1977]. Most empirical magnetopause models [e.g., Sibeck et al, 1991;Petrinec and Russell, 1996;Shue et al, 1997;Kawano et al, 1999] also adopted the hypothesis that magnetopause is rotational symmetric about the aberrated Sun-Earth line and has a rounded section at magnetotail.…”

Observations of the geomagnetic tail at 500 Earth radii by Pioneer 8

“…See Ness (1969) for a comprehensive review of the experimental studies of the geomagnetic tail. Existence of an ordered tail and its imbedded neutral sheet was established by Explorer 33 to distances of 80 RE (Ness et al, 1967a, Behannon 1968Mihalov et al, 1968). At larger distances, the measurements by Pioneer 7 (Ness et al, 1967b;Wolfe et al, 1967) at 1000 RE suggested that certain of the observed field lines were connected to the earth in the shape of intermingled filamentary tubes.…”