北冰洋次表层暖水形成机制的研究

THE THERMODYNAMICS OF SUBSURFACE WARM WATER IN THE ARCTIC OCEAN

分析了北冰洋加拿大海盆上层海水温度结构特征,针对在海冰覆盖区域普遍发生的次表层暖水现象,建立了冰海耦合的一维柱形模式,成功模拟了次表层暖水的垂向结构和形成机制,证明了太阳辐射加热和表层冷却是次表层暖水的成因。通过数值实验定量分析了形成次表层暖水各因子的作用,表明太阳辐射是形成次表层暖水的能量来源;长波辐射、气温和比湿等其他大气因子对次表层暖水强度有较大影响;在厚冰区不能形成次表层暖水,海冰越薄,水道面积越大,则冰下次表层海水温度升高得就越快,薄冰和冰间水道是形成次表层暖水的主要能量通道;通过模式的拟合给出湍扩散系数垂向变化的估值,冰下表层海水垂向湍扩散系数为5.0×10-3m2/s左右,而次表层垂向湍扩散系数却快速降低到1.0×10-6m2/s,表明跃层导致的稳定性增大是形成次表层暖水尖峰的关键因素。

Subsurface Warm Water （SWW） is a phenomenon frequently observed in the most part of Canadian basins, which presents a temperature peak under sea ice at the depth of 20 m. A thermodynamically coupled sea ice-upper ocean column model was developed in this paper to examine the thermodynamics of SWW. Using this model, the SWW was nu- merically simulated and proved successful. The result is consistent with the observed results. The mechanism of the SWW formation was proved able to generate by both solar radiation heating and surface cooling. It is verified that the solar radiation is the dominant energy source. Meanwhile, long-wave flux, air temperature, and atmospheric humidity play important roles in determining the relative intensity of SWW. As the solar energy would be obstructed from thick ice, SWW is formed on the areas of thin ice, leads, and still open water. The sumulation result of typical sharp peak of SWW agrees well with the observational ones. The variation was about 5.0×10^-3m^2/s beneath the sea ice, and dropped sharply to 1.0×10^-6m^2/s in subsurface layer, indicating that the peak of SWW was caused by the stratification of halocline.