Reversal of unified polarization of low-frequency magnetic field
variation was found by Kaguya at equator crossings in the lunar wake
under the condition of dawn-dusk directed background magnetic field. The
polarization was left-handed over a frequency range from 0.01 to 0.3 Hz
in the southern hemisphere of the lunar wake in the dawnward-directed
magnetic field. It turned to be right-handed when the spacecraft entered
the northern hemisphere of the wake. In the duskward-directed magnetic
field the polarization reversed. The same configuration by 90 degrees
rotated was observed in northward-directed magnetic field, too. The
sense of rotation was alike that of surface waves generated by
Kelvin-Helmhlotz instability, but it was not likely because the waves of
unified polarization were not always accompanied by velocity shear. They
penetrated into the very center of the wake, suggesting that they were
not propagating along a surface of wake boundary. The polarization was
highly elliptic except for high frequency component. The magnetic field
variation was predominantly perpendicular to the background magnetic
field, suggesting that they were shear Alfven waves. The mechanism of
unifying the polarization is not yet understood.