THE LUNAR WAKE AT 6.8 R(L) - WIND MAGNETIC-FIELD OBSERVATIONS

We report on WIND magnetic field observations at similar to 6.8 R(L) d ownstream of the moon on 27th December 1994. The moon was in the solar wind during the encounter. IMP-8 observations are used to determine b aseline IMF conditions, and therefore determine those features in the WIND data which are related to its proximity to the moon. Previous Exp lorer 35 observations suggest that the lunar wake is not detectable be yond a downstream distance of similar to 4 R(L). However, despite the distance of WIND from the moon, we observe a slight decrease in field intensity just prior to the spacecraft entering the optical shadow, a slight field strength enhancement whilst in shadow, and perhaps a weak depression once the spacecraft reemerges into sunlight. These signatu res closely resemble, but are weaker than, the previous observations. We conclude that a lunar wake did extend to these distances at the tim e of this encounter. We also note a rotation in field direction some d istance outside of the wake signature which may be attributed to the c rossing of the lunar mach cone boundary. We discuss the observations i n terms of simple models of the solar wind interaction with an insulat ing body.