Plasma waves in the magnetotail of Uranus

Abstract

As the Voyager 2 spacecraft left Uranus during its encounter with the planet on January 24, 1986, it passed through the magnetotail over the distance range of about 11 R U to 79 R U . During this interval the plasma wave receiver on board measured only very weak plasma wave intensities. The most remarkable of these waves are found predominantly inside of about 23 R U with an additional event occurring between about 48 and 56 R U . The frequency of these magnetotail plasma waves is generally below about 100 Hz, extending down to the 10‐Hz lower frequency limit of the receiver. In each case the upper frequency limit of the emissions lies below the local electron cyclotron frequency. The plasma waves are found prior to the first neutral sheet crossing and between the second and third neutral sheet crossings, as defined by the Voyager magnetometer investigation. This timing suggests the waves are found only in the negative solar magnetospheric lobe of the tail, corresponding to field lines which intersect the planet near the southern magnetic pole—that which is continuously in the nightside hemisphere during the encounter epoch. The observations are not conclusive as to the mode of propagation of the waves. However, the spectrum is similar in some respects to broadband electrostatic waves observed in similar regions of Earth's magnetotail.