Observations of snow clouds and the number concentrations of aerosol particles were conducted during two winter seasons, at Rebun Island in 1991 and at Ishikari Bay in 1992 on the west coast of Hokkaido, Japan. A significant increase of 1 to 2 orders of magnitude in the number concentration of relatively large aerosol particles was recorded in several 10-min intervals during the observation period. However, there was only a poor direct correlation between the number concentrations of large particles greater than 0.5 ¿m in diameter and wind speed. In contrast, the increase in number concentration was correlated with a convergence field calculated by the velocity azimuth display method using a Doppler radar. These results imply that the large and giant aerosol particles, including sea-salt nuclei which were generated by wind stress near the sea surface under winter monsoon periods, which is known as a typical pressure pattern of west-high and east-low (as shown in Figure 2), were transported and were then gathered under the convergence field of unstable/convective meteorological systems with developing cumulus cloud cells.