Interal Distribution of Acid Material within Snow Crystals

我们发现，日本的河水不仅在融雪季节的第一阶段，而且在融雪季节的后期都呈酸性，这与北欧融雪季节第一阶段发生的所谓酸性冲击不同。酸冲击取决于形成雪晶内酸性物质内部分布的融再冻过程的区域特征。在日本南部这样的温暖气候地区，由于暖变质作用下长期反复的融再冻过程，粒状雪中酸性物质有可能具有复杂的分布结构。因此，随着融雪的进行，融水的pH值并不总是增加。然后，我们利用x射线计算机断层扫描（CT扫描仪）明确了雪晶内部酸性物质的微观分布结构，在雪晶内部也存在酸性物质的结构域。因此，即使在融雪后期，当酸性物质集中在雪晶的内部时，河水的酸化也会发生。

We found that the river water turns out to be acid not only in the first stage but also in the later stage of snowmelt season in Japan, which differs from the so called acid shock reported to occur in the first stage of the sonwmelt in the northern Europe.The acid shocks depend on the regional characteristics of the melt-refreeze processes forming the internal distribution of acid materials within snow crystals. In a warm climatic region like the southern Japan, there are possibilities to have the complicated distribution structure of acid materials within granular snows due to the repeated melt-refreeze processes for a long period under the warm metamorphism. Consequently, the pH value of melt water does not always increase as the snowmelt proceeds.Then, we clarified the microscopic distribution structure of acid materials within snow crystals by using the X-ray computed tomography (CT scanner) that the domains with the acid materials do also exist in the inner parts of snow crystals. So, the acidification of the river water occurs even in the later stage of the snowmelt, when the acid materials concentrates in the inner part of snow crystals.