Two Hemisphere Observations of the North-South Sidereal Assymetry at ~1TeV

A new underground moon telescope system installed at a depth of 154 m.w.e. at Liapootah, central Tasmania, has been continuously monitoring cosmic ray intensity since December 1991. In two hemisphere observations, this telescope plays an important roll as a conjugate station to Matsushiro in Japan, which has been operating at a similar depth (220 m.w.e.) since April 1984. In this paper, we analyze data recorded at Liapootah during 33 months from January 1992 to October 1994, to test the north-south asymmetry in the sidereal diurnal variation caused by galactic anisotropy of high energy cosmic ray intensity. We find average sidereal variation (0.041 ± 0.006%, 3.5 ± 0.6 hr) being observed by the vertical component telescope (median latitude of viewing λ e = 36.2°S). Comparison with the sidereal diurnal variation (0.028 ± 0.006%, 2.6 ± 0.8 hr) observed by Matsushiro λ e = 34.5°N) during the same period confirms the existence of a north-south asymmetry in which the amplitude of the variation increases as the median direction of viewing moves southward over the equator. This is the first positive result indicating the north-south sidereal asymmetry by two hemisphere observations. © 1995, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.