Galactic and heliotail-in anisotropies of cosmic rays as the origin of sidereal daily variation in the energy region <104 GeV

It is shown that the cosmic ray sidereal daily variation in the energy region <E-U similar to 10(4) GeV is due to two kinds of anisotropy, one is a galactic anisotropy from the direction with right ascension alpha(G) = 0 hours and declination delta(G) = -20 degrees and can be observed even in the energy region as low as similar to 60 GeV with the same form and almost the same phase as observed by small air showers with similar to E-U [Nagashima et al., 1989]. The other is a newly discovered directional excess flux confined in a narrow cone with a half opening angle of similar to 68 degrees from the direction (alpha(T) similar to 6.0 hours; delta(T) similar to -24 degrees) and observed only in the energy region less than E-U with its maximum near 10(3) GeV. It is suggested that the excess flux is of solar origin and the direction toward it seems to coincide with the expected heliomagnetotail direction (alpha(TP) = 6.0 hours; delta(TP) = -29.2 degrees) opposite the proper motion of the solar system but does not coincide with the expected tail direction (alpha(TN) = 4.8 hours; delta(TN) = 15 degrees similar to 17 degrees) opposite to the relative motion of the system to the neutral gas. The flux (called the tail-in anisotropy hereafter) shows maximum at the December solstice when the Earth is closest to the magnetotail and almost disappears at the remote side of the Earth's orbit from the tail at the June solstice. Owing to the discovery of the tail-in anisotropy, the observed phase shift of the sidereal diurnal (24 hours) variation from 6 to 0 hours with the increase of energy, which has been one of the unsolved problems, can be explained by the distinctive contributions from the two anisotropies. Finally, it appears that the observed sidereal variations deny the existence of the Compton-Getting effect due to the motion of the solar system at least in the energy region less than similar to E-U. This implies that the solar system drags with it in its motion the surrounding interstellar magnetic field within which the cosmic rays with low energy (less than similar to E-U) are isotropically confined.