Gaussian analysis of two hemisphere observations of galactic cosmic ray sidereal anisotropies

We have analyzed the yearly averaged sidereal daily variations in the count rates of 46 underground muon telescopes by fitting Gaussian functions to t he data. These functions represent the loss cone and tail-in anisotropies o f the sidereal anisotropies model proposed by Nagashima et nl. [1995a, b]. The underground muon telescopes cover the median rigidity range 143-1400 GV and the viewing latitude range 73 degrees N-76 degrees S. From the Gaussia n amplitudes and positions we have confirmed that the tail-in anisotropy is more prominent in the southern hemisphere with its reference axis located at declination (delta) similar to 14 degrees S and right ascension (alpha) similar to 4.7 sidereal hours. The tail-in anisotropy is asymmetric about i ts reference axis, and the observed time of maximum intensity depends on th e viewing latitude of the underground muon telescopes. We also find that th e declination of the reference axis may be related to the rigidity of the c osmic rays. We show that the loss cone anisotropy is symmetric and has a re ference axis located on the celestial equator (delta similar to 0 degrees) and alpha similar to 13 sidereal hours. We have used the parameters of the Gaussian fits to devise an empirical model of the sidereal anisotropies, Th e model implies that the above characteristics of the anisotropies can expl ain the observed north-south asymmetry in the amplitude of the sidereal diu rnal variation. Furthermore, we find that the anisotropies should cause the phase of the sidereal semidiurnal variation of cosmic rays to be observed at later times from the northern hemisphere compared to observations from t he southern hemisphere. We present these results and discuss them in relati on to current models of the heliosphere.