[en] The solar diurnal variation of cosmic rays was considered to be fully explained by the diffusion-convection theory. Recently, however, it has been found that the geographic latitude distribution of the yearly averaged diurnal variations observed with the neutron monitors and the muon telescopes on the ground does not agree with that expected from the theory. The difference between the two distributions is observed almost every year, and it is especially remarkable in the solar activity minimum period in the positive polarity state of the solar polar magnetic field, when the diurnal variation reduces its magnitude and shifts its phase towards the morning side. It is shown that such a difference is produced by the seasonal variation of the sidereal heliotail-in and helionose-in anisotropies with respective right ascensions of 6 h and 18 h according to the following process. Generally, if any sidereal anisotropy from the right ascension α is subject to the seasonal variation with its maximum and minimum at the times when the earth is closest to and farthest from the source of the anisotropy, respectively, located through its direction at the boundary of the HMS, it produces a yearly averaged residual flux from 0 h LT in solar geographic polar coordinates regardless of its direction (α). This residual flux from 0 h LT produces the difference mentioned above. (author)