冬季降水中の海塩起源物質濃度と気象条件

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A chemical study of the winter precipitation and the new snow layer was conducted in Tohkamachi and the surroundings area. The relationship between the chemical property of winter precipitation and the weather condition was studied. Samples of daily precipitation were collected in Tohkamachi during winter periods from December 24, 1990 to April 9, 1991, from December 17, 1991 to April 10, 1992 and from December 15, 1992 to April 10, 1993. Samples of the new snow layer were collected at thirteen sites on February 26, 1991 and March 23, 1992. A trench was dug and cores of new snow layer were extracted from a side wall of the trench using a clean plastic pipe 82mm in diameter. The samples were filtered, and conductivity and pH were measured with a conductivity meter and pH meter, respectively. Anions and cations were determined by an ion chromatography (Dionex 2020i/SP). The ratios of Cl-/Na+ and Mg2+/Na+ in the samples of winter precipitation and the new snow layer were nearly equal to those of the sea water. This result suggests that the origin of Na+, Mg2+ and Cl- in the winter precipitation and the new snow was sea water. A relationship was observed between Na+ concentration of the winter precipitation and the height of a convective mixing layer. Cloud droplets containing sea salt particles are believed to be collected by snow crystals through the rain-out process. The higher the convective mixing layer, the larger the rate of collection of the sea salt particles by the snow crystals. The regression relationship between Na+ concentration in the winter precipitation and the height of a convective mixing layer is obtained as C=0.078·e1.38·H where C is Na+ concentration of the winter precipitation (mg/l) and H is the height of a convective mixing layer (km). A relationship was observed between Na+ concentration of the new snow layer and the distance from seashore along an individual ray of the observation. Along the same ray, Na+ concentration of the new snow layer near the seashore was larger than that inland. Na+ concentration of the new snow layer up a steep valley was larger than that at a moderate valley. This result suggests that the orographic condition affects the cumulus convection of cloud and Na+ concentration of snow.

冬季降水中の海塩起源物質濃度と気象条件

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