南极长城站积雪及其消融过程

南极长城站区稳定积雪期始于4月中至6月初,8月中至10月达最大深度。1988年沿海地带一般积雪深度为0.6～0.8m,低洼处及建筑物附近可达1.2～1.6m,甚至超过1.8m;潮汐带雪盖下部温度受海冰影响普遍偏低;11月底至来年1月初的消融过程中,积雪表层常常处于相变区,雪层底部温度比冰点低0.02℃,融水下渗形成雪盖下部潜流;积雪相态及其温度变化与大气-雪感热通量的变化过程相对应,大气-雪感热交换是积雪消融的重要因子之一。

SNOW ACCUMULATION AND MELTING PROCESSES AT THE GREAT WALL STATION, ANTARCTICA

The snow accumulation at the Great Wall Station, Antarctica, starts at the middle of April to the early of June, and ends in the middle of August to October. The maximum thickness of snow cover in 1985, 1986 and 1988 were 1.9 m, 2.2 m and 1.2 m respectively which depends on not only the precipitation of snow, but also the condition of blowing snow produced by strong wind. In common case, the thickness of snow cover in the area was 60 to 80 cm, and it could be 1.2 to 1.6 m or more than 1.8 m in the low-lying land and the place nearby building in the November, 1988. Consequently, the construction sites should be selected carefully and the building structures should be designed for blowing snow passing through freely. The distribution and temperature profiles of snow cover from a top of a hill to the low tide line shows that the thickness of snow cover in the low-lying land or the slope with lower step was much more than that in the others; the thickness in low tide line was 20 cm more than that in high tide line; the temperature at the upper 20 cm part in different profiles was almost the same of-0.10C; the temperature at the bottom of profile 3, 2 to l(Fig.3) was -0.23℃, -1.03℃ and -2.10℃ respectively because of the comprehensive effect of saline and thermal action produced by the general circulation of the sea. It was in the stable melting period after 20 November, 1988, the upper part of snow cover was in phase change in which the melting water ran down to the bottom forming runoff. Generally speaking, the penetration depth of icy air for 1 to 4 days cycle only limited at the upper part, 0.1 to 0.2 cm in depth, but it could be nearby 50 cm if the wind speed was stronger enough, for instance 24.3 m/s in max. The air-snow sensible heat flux could be calculated by: where, CB-drag coefficient which approximate value equals 1X10-3; p-air density in g/cm2; Cp=1.0060 J/(g·K) is the dry air specific heat at constant pressure; Va-wind speed at the height of 10 m, in m/s; Ta and Ts-temperature for air near the surface and snow surface in K; and in which, P-air pressure in hPa; Rd=0.287 J/(g·K) is the specific air constant in dry condition,; e-vapour pressure in hPa. The day-to-day variation of air-snow sensible heat flux SH from 15 November, 1988 to 5 January, 1989 has been illustrarted in Fig.5 which is respondence to the melting process of snow cover well, the melting action would be stopped while SH occuied negative peak and the snow could be melted sharply as SH reach the positive peak with a daily mean air temperature of 4.3C and a wind speed of 18.0 m/s in the direction of quasi- north on 1 January, 1989. As a result, the left snow cover, 40 cm in thickness, was melted in 5 days. The snow density measured in the early of December, 1988 at the depth of 0.05 to 0.10m, 0.23 to 0.28m, 0.33 to 0.38 m and 0.55 to 0.60 m was 0.47 g/cm3, 0.47g/ cm3, 0.51 g/cm3 and 0.50g/cm3 respectively.