韓国ウールムゴルにおける夏季氷結現象の数値実験 A Numerical Simulation of Summertime Ice Formation in the Ice Valley in Milyang, Korea
A numerical simulation was carried out to examine the mechanism of summertime ice formation at the Ice Valley in Milyang, Korea. The Ice Valley's ice is different from ordinary perennial cave ice in that the ice is formed at the surface of the talus, exposed to hot air during summer, and disappears during winter. The talus consists of sedimentation of large boulders about 100cm in diameter along the mountain slope and has sufficient open space between the boulders for cold air to penetrate during winter.<br> The author attempted to simulate the Ice Valley's ice based on a theory of convective ice formation. This theory explains ice formation by an effective drainage flow of cold air penetrating into the talus during winter, since the air temperature above is colder than the temperature of the talus. The wintertime ice may be preserved by the extremely stable stratification of the air within the talus until the next summer.<br> A numerical model was developed based on a system of the equation of motion for air, the continuity equation for air, and the thermodynamic energy equation for both air and talus. The physical processes considered in the model are: 1) buoyancy; 2) Rayleigh friction, 3) adiabatic heating; 4) Newtonian cooling; 5) diffusion of air; and 6) thermal conduction of the tales. The governing equation is integrated in time by controlling the air temperature from -5°C in winter to 25°C in summer to examine the ice distribution and the stream function in the talus.<br> The result of the simulation appears to support the theory of convective ice formation under suitable model parameters. We confirmed that cold air can penetrate deep into the talus to form ice in winter and that the wintertime ice is preserved untill the next summer. During winter, the penetration of the cold air starts from the top region of the talus, a moderate downward motion occurs inside the talus, and an upward motion dominates along the slope of the talus surface. Conversely, in summer a descending motion along the talus slope develops to create a typical cold air flow, as observed. A moderate ascending motion is induced inside the talus to compensate for the strong cold air descending motion. The Ice Valley's ice melts fast at the region of the warm air intake at the foot of the talus slope. Hence, the coldest region appears slightly above the foot of the talus slope, which is consistent with observations.<br> It was found in this study that the ice itself plays an important role in preserving wintertime coldness owing to its abundant solidification heat. Without the existence of ice, rocks in the talus alone are inadequate to maintain the freezing temperature during summer because of its their specific heat capacity. The results of this study suggest that the moisture supply from the underground water table at the bottom of the talus is a necessary condition to form the Ice Valley's ice.
- 地理学評論. Ser. A
地理学評論. Ser. A 70(1), 1-14, 1997