OBSERVATION OF THE NORTH-SOUTH ASYMMETRY OF SIDEREAL ANISOTROPY OF COSMIC-RAYS AT MATSUSHIRO UNDERGROUND

We present the observed results of the cosmic-ray sidereal anisotropy in the primary rigidity range 550-950 GV from the Matsushiro undergrou nd (geogr. 36.5 degrees N, 138.0 degrees E; 220 m.w.e. depth) for the period 1984-1994. The muon telescope used is of multi-directional with 17 channels,which scan simultaneously over the median latitude of vie wings from similar to 60 degrees N to similar to 15 degrees S on the c elestial sphere. We obtain significant sidereal diurnal and semi-diurn al terms in the daily variations with several s.d., being consistent w ith other observations. Most notably, the north-south asymmetry in the diurnal variations is confirmed without solar modulation, in which th e amplitude increases as the direction of viewings of the telescopes m oves southward towards and over the equator.