Temporal variation of (7)Be concentrations in atmosphere for 8y from 2000 at Yamagata, Japan: solar influence on the (7)Be time series.

We have been continuously observing the daily (7)Be concentrations in surface air at Yamagata, Japan (38.25 degrees N, 140.35 degrees E) since 2000. The yearly profile of the (7)Be concentration indicates the variation in galactic cosmic rays owing to solar modulation. Over 8y, the (7)Be concentration, cosmic neutrons, and number of sunspots varied by 37.4%, 12.2%, and 92.8%, respectively. The influence of precipitation on the (7)Be variability was approximately 5%. Hence, the yearly (7)Be concentration was mainly varied by the solar modulation of the (7)Be production rates. Based on the production rates found in an EXPACS simulation, the observed variability indicates (7)Be transport from high latitudes. The daily (7)Be concentrations have two significant periodic components of 19d and 36d. The 36-d component implies a relationship between the sun's rotation and the vertical transport of air masses under quiet solar activity.