Three east-west intensity asymmetries in the Jupiter system that would appear to an Earth observer in optical S+, extreme ultraviolet S++ and optical Na emissions are reviewed. The three asymmetries imply that some combination of the plasma torus number densities and electron temperature is, on the long-term average, larger west of Jupiter than east of Jupiter. A small east-to-west electric field, previously proposed to explain the ion intensity asymmetries, is also shown to provide a natural explanation for the sodium intensity asymmetry. A long-term average east-to-west electric field of ~3 mV/m and a corresponding west-to-east offset of ~0.16 Jupiter radii for the plasma torus at Io's orbital distance is implied. On a shorter time scale, the east-west electric field appears to be time variable and may be readily monitored from Earth by observations of the sodium cloud. ¿ American Geophysical Union.