季節積雪地域の雪氷化学
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概要
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降雪粒子は大気環境情報を記録して降ってくる. 札幌と十日町における降雪試料中のCl-/Na+濃度比は海水中の濃度比と一致しており, これらふたつの成分は海塩を起源としていることがわかる. また, 降雪中のNa+濃度は雪雲の対流混合層の高さと良い相関を示し, さらに, 総観規模の気象条件が降雪の化学的性質に影響を及ぼしている. 冬型の気圧配置時の降雪中では海塩起源物質が優占し, 日本海低気圧や南岸低気圧による降雪では非海塩起源物質が優占する. 降雪中の酸素同位体組成は, 総観規模の気象条件ごとに雲頂気温と良い相関を示し, 同じ雲頂気温でも, 冬型の気圧配置時には南岸低気圧時よりも酸素同位体比が大きくなる. 積雪表面からの融雪が起こらなければ, 化学物質は積雪層中に保存される. しかしながら, 融雪時には, 融雪水中の化学物質濃度は高くなりpH は低下する. 積雪中のクロロフィル-a濃度はアカマツ林内で, コナラ林内・林外に比べて高く, 雪氷藻類の活動も融雪期に活発になる.The snow particle is an indicator of atmospheric environmental information. The ratio of Cl-/Na+ concentration in the snow sample at Sapporo and Tohkamachi is nearly equal to that in the sea water. This result suggests that the origin of Na+ and Cl- in the snow particle is sea water. A good relation is observed between Na+ concentration of the snow and the heights of a convective mixing layer of cloud. It can be seen that Na+ concentration of the snow increased in proportion to the height of the convective mixing layer. The synoptic weather conditions affect chemical properties of snow particle. Sea salt materials are dominated in the snow formed under the winter monsoon pressure pattern. On the other hand, non sea salt materials are dominated in the snow formed by a low pressure system on the Sea of Japan or on the Pacific Ocean. A close relationship is observed between temperature at the cloud top and the oxygen isotopic composition of snow, and the mutual relationships are recognized for each weather condition. Winter precipitation formed during the winter monsoon has a higher value of oxygen isotopic composition than those formed when a cyclone is positioned over the Pacific Ocean near Honshu at the same temperature. If there is no meltwater runoff in the snowpack resulting from surface melting, then chemical substances in the snowpack will be retained in each snow layer. The concentrations of chemical substances increase and the pH value decreases in the meltwater. Concentration of chlorophyl-a in the snowpack is higher at the coniferous forest site than at both the open site and the deciduous forest site. Activity of snow algae is considered to be large during the snowmelt season.
- 2012-03-31
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