Longitudinal modulation of hot electrons in the Io plasma torus

摘要

The longitudinal modulation in the Io torus has been an open question for decades.A major clue was provided by the discovery of the key modulation of the hot electron population, at both the System III and System IV periods. However, very little progress has been made in explaining the origin of these hot electron modulations. We propose that the hot electrons population is powered by the inward motion of empty flux tubes (i.e.related to the outward transport of the Iogenic plasma), which has been observed in the torus. We propose that the System IV and System III modulation of the hot electron population corresponds to modulation of the intensity of the current system and of the efficiency of the electron acceleration, respectively. We build on the latest models of the Io current system to describe the current system associated with the motion of the empty flux tubes, and the associated electron acceleration. The System III modulation of the hot electron population, due to the modulation of the efficiency of the electron acceleration, can then be related to the topology of the magnetic field. We show through calculation and simulation that the electron acceleration related to the inward motion of the empty flux tube may explain the observations. We discuss the energy budget and show that it is in favor of our hypothesis.