The evolution of under-ice melt ponds, or double diffusion at the freezing point
The evolution of under-ice melt ponds, or double diffusion at the freezing point
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冰下融化池的演变，或冰点的双重扩散
DOI：
10.1017/s0022112074002527
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发表时间：
1974
影响因子：
3.7
通讯作者：
P. Kauffman
中科院分区：
文献类型：
--
作者：
Seelye Martin;P. Kauffman
在一项实验和理论研究中，我们模拟了在北极夏季观察到的一种现象，即温度为0°C的淡水层漂浮在冰点的海水层和冰层之下。我们的结果表明，该系统中的冰增长分三个阶段进行。首先，由于淡水密度在过冷时降低，热量相对于盐的快速扩散从淡水向咸水扩散导致密度反转，从而在淡水中产生高瑞利数对流。在这种对流中，过冷水上升到冰层，在那里它成了薄的垂直互锁的冰晶。当这些薄板向下生长到界面时，过冷就停止了。其次，垂直冰盖的存在既限制了温度T和盐度S位于冰冻曲线上，又允许它们在垂直方向扩散。在界面区域，这些过程的组合产生了横向晶体生长，这种生长一直持续到水平冰盖形成。第三，由于该冰盖下方海水的T和S梯度，水平冰盖既向上移动，又增厚。从前两个阶段的一维理论模型中，我们发现热传递速率是经典热扩散计算的5-10倍。
In an experimental and theoretical study, we model a phenomenon observed in the summer Arctic, where a fresh-water layer at a temperature of 0°C floats both over a sea-water layer at its freezing point and under an ice layer. Our results show that the ice growth in this system takes place in three phases. First, because the fresh-water density decreases upon supercooling, the rapid diffusion of heat relative to salt from the fresh to the salt water causes a density inversion and thereby generates a high Rayleigh number convection in the fresh water. In this convection, supercooled water rises to the ice layer, where it nucleates into thin vertical interlocking ice crystals. When these sheets grow down to the interface, supercooling ceases. Second, the presence of the vertical ice sheets both constrains the temperature T and salinity s to lie on the freezing curve and allows them to diffuse in the vertical. In the interfacial region, the combination of these processes generates a lateral crystal growth, which continues until a horizontal ice sheet forms. Third, because of the T and s gradients in the sea water below this ice sheet, the horizontal sheet both migrates upwards and increases in thickness. From one-dimensional theoretical models of the first two phases, we find that the heat-transfer rates are 5–10 times those calculated for classic thermal diffusion.