  We study a possible relationships between seasonal distributions of the
visually observed cloudless days (CD) and cloudless nights (CN) at Abastumani
Astrophysical Observatory (41.75N, 42.82E; Georgia) in 1957-1993. The annual
variations of monthly numbers of CD and CN have been observed, with maximum in
August for CD and in September for CN. During geomagnetic disturbances it is
also observed the growth of number of CD in September andMarch (equinoctial
months), and for CN, together with September, in June, April and February. We
assume that this phenomenon indicates an influence of cosmic factors on
cloudiness, as well as the existence of semiannual and possibly
shorter-periodicity variations. This cosmic factor can be the manifestation of
different rates of the galactic cosmic rays (GCRs) flux variations in CD and CN
periods. The influence of GCR flux on ionization of lower atmosphere and
variations of density of cloud condensation nuclei also can be connected to the
annual and seasonal changes of temperature at Earth surface of this region. To
comprehend behaviors of the annual and semi-annual variations of the GCR
intensity and their possible relationships with the seasonal distributions of
CD and CN we compose and numerically solve two dimensional (2-D) time dependent
transport equation including all important processes in the heliosphere. An
analysis of experimentally observed and theoretically obtained results have
been carried out.
