Production and behavior of beryllium 7 radionuclide in the upper atmosphere

We calculate the 7Be production rate in the atmosphere assuming the galactic cosmic ray and solar proton spectra in 2002-2004. The global average production rate is 0.043 7Be/cm2 s that is in agreement with the previous ones within a factor of ∼2. Although intense protons associated with an extraordinary large solar event (X17/4B) on Oct. 28, 2003 produce 7Be in the polar region, the effect of solar protons is not significant because the solar proton spectrum is soft. The latitudinal production rate at geomagnetic latitude 20-30° (Japan) is 0.023 7Be/cm2 s, indicating ∼1% of cosmic-ray produced 7Be contributes to the surface 7Be radioactivity. The temporal variations in the surface 7Be radioactivity in Tokyo exhibit the enhancements in spring and autumn. We discuss the possibility of the stratospheric-tropospheric air mass exchange caused by a periodic passage of a pair of a traveling anticyclone and extratropical cyclone in spring and autumn.