MAGNETIC-FIELD CONTROL OF THE DAYSIDE ION TEMPERATURES IN THE IONOSPHERE OF VENUS

Ion temperatures measured by the retarding potential analyzer carried aboard the Pioneer Venus Orbiter were sorted according to the ionosphe ric magnetic field conditions. It was found that the dayside ion tempe ratures measured during the first couple of years of operations, corre sponding to solar maximum conditions and while the periapsis was held at low altitudes (similar to 150 km), were basically independent of th e magnetic conditions. This contrasts with earlier studies, which show ed that electron temperatures are significantly elevated when the iono sphere is magnetized. Theoretical studies by Cravens et al. [1980] pre dicted that electron temperatures will depend on fluctuating magnetic fields, but not the ion temperatures. This is consistent with these fi ndings.