Saturated heat conduction and Joule heating in the Venus ionosphere by 100 Hz fields

The ratio of the Joule heating and conduction cooling terms in the macroscopic energy equation of electrons in an ionized gas is examined under conditions which may include saturation of the heat flux. The saturation flux may be represented in quantity alpha nkT(kT / m)(0.5), where n, T, and m are, respectively, the electron density, temperature, and mass, and alpha may be of the order of 0.1. Consequences of this assumption are developed for application to the question of Joule heating of electrons by 100 Hz electric fields in the Venus ionosphere. When saturation exists, there can be large overestimates of the conduction cooling, and corresponding underestimates of the temperature, if the classical Spitzer-Harm formula is employed. A minimal reduction factor to apply to this cooling rate is presented. Taking into account both the existence of saturation and the burst nature of the 100 Hz fields, it is shown that Joule heating by observed fields may balance conduction cooling in parts of the Venus ionosphere. In particular, this occurs at, and somewhat below, high Venus ionopauses. It is suggested that more research on these regions may add to our knowledge of saturation.