Plasma and magnetic field data from 223 orbits in the first nine tail seasons of Pioneer Venus are examined to provide a statistical description of the combined ion and magnetic field properties of the Venus magnetosheath and magnetotail. This description is based solely on instrumental responses, with no a priori assumptions about existing regions or their plasma and field characteristics. Over 22,000 plasma spectra taken from 7 to 12 RV downtail are categorized as to whether they contain shocked solar wind, pickup ions, or no discernible plasma. The magnetic characteristics associated with each plasma spectrum category are examined, and the average two-dimensional cross-tail ion flow and magnetic field structures of the Venus tail are determined at a resolution of 0.25¿0.25 RV. Plasma flows everywhere tailward, slowing from 450 km/s in the sheath to less than 300 km/s at the tail axis. Weak outward deflections of 50 km/s or less are found within the tail.

The magnetotail is found to be highly draped, with a field-reversing current sheet not more than 0.25 RV thick. At these distances the tail is filled with shocked solar wind but also contains pickup ions and a plasma component with fluxes that are not detectable by the Pioneer Venus orbiter plasma analyzer. The bulk flow and field configurations imply a number density of 1.2 cm-3 and a temperature of 9¿106 ¿K for a current sheet composed of 90% protons and 10% O+. These conditions are at or below the limit of instrumental detection. Weak magnetic field asymmetries are associated with the plasma dropouts. The undiscernible plasma component in the tail is consistent with a planetary ion population with fluxes below the instrumental detection threshold. A high E/q plasma population previously interpreted as planetary pickup ions (O+) is found asymmetrically both within the tail and in the adjacent sheath. The undiscernible and pickup ion plasmas (plasmas of Venusian origin) are observed from 5 to 15% of the time within the tail region. This rate depends on solar EUV flux, indicating a photoionization sources. Thus the Venus tail is filled with plasma that is primarily shocked solar wind at sometimes undectable fluxes, which coexists with a photoion population that produces asymmetries in the bulk plasma and magnetic field properties. ¿ American Geophysical Union 1990