Beryllium-7 depositions in Hokuriku, Japan in winter (1991-2021); Factors causing the temporal variation

Yoshida, Keisuke; Kato, Shingo; Okuyama, Shinichi ; Ishimori, Yuu  ; Inoue, Mutsuo*

The factors causing the temporal variation of Be deposition in the Hokuriku region (the Sea of Japan side of central Honshu, the main island of Japan) during winter (November to February) were examined using monthly samples of Be deposition conducted over 30 years, spanning from 1991 to 2021. The predominant factors on Be deposition at a Hokuriku region site were as follows: 1) the amount of Be generated by cosmic rays, 2) the volume of air transported from the Arctic, and 3) the amount of precipitation at the observation site. The contribution of each of these factors fluctuated depending on the sampling period. The temporal variations in Be deposition during the first half of the sampling period (1991-2005) were primarily driven by cosmic rays. In contrast, during the latter half of the period (2006-2021), meteorological factors, particularly snowfall, emerged as significant contributors. This shift in influence was attributed to the effects of climate change in the Hokuriku region.