Modulation of underground muons from 1800-GV primaries by the heliomagnetic dipole moment

We study a correlation between the solar magnetic dipole moment and the amplitude of the diurnal variation of underground muons from cosmic ray primaries of mean rigidity ≅ 1800 GV. The time series investigated was recorded at Artyomovsk, in the Soviet Union, at a vertical depth of 570 hg/cm2. Our results indicate that both diurnal and semidiurnal variations in the muon intensities correlate well with the variations of the solar magnetic dipole. At the time of the maximum amplitude of the heliomagnetic dipole moment (summer 1982) the vector of the diurnal variation shows an increase in amplitude by a factor of /similar to/3.5 relative to the average value for the remaining period, and a phase shift from the direction of /similar to/18 hours toward /similar to/12 hours. These results suggest that during the enhancement of the magnetic dipole field of the Sun the 1800-GV cosmic rays stream preferably along the radially outward direction, and consequently the mechanism of solar convection dominates over that of diffusion. copyright American Geophysical Union 1989