Internal distribution of acid materials within snow crystals

We found that river water is acidified not only in the first stage but also in the later stage of the snowmelt season in Japan, which differs from the so called acid shock occurring in the first stage of the snowmelt in the n orthern Europe. The acid shocks depend on the regional characteristics of t he melt-refreeze processes forming the internal distribution of acid materi als within snow crystals under the warm metamorphism. In a warm climatic re gion like the central Japan, there are possibilities to have the complicate d distribution structure of acid materials within granular-snow crystals du e to the repeated melt-refreeze processes even in midwinter. Consequently, the pH value of meltwater does not always increase as the snowmelt proceeds . Then, we showed the possibility by using the X-ray computed tomography th at the domains with the acid materials exist in the inner parts of snow cry stals. So, the acidification of the river water may occur even in the later stage of the snowmelt.