一种冰-海洋模式的热力耦合方案

冰与海洋的热力耦合对冰与海洋环流的模拟有极其重要的影响,是冰-海洋相互作用的一个重要方面.对其精确确定需要详细考虑冰-海洋界面附近的湍流过程,这在长时期的模拟特别是气候模拟中,常受到技术条件的限制.过去的研究常常假设冰下海洋混合层的温度为冰点,特别是在单纯冰模式的模拟中,但考虑海冰漂移和冰点变化的效应时,这一假设是不精确的.因此,弱化冰下海洋混合层温度为冰点的约束,不考虑详细的冰-海洋界面和海洋混合层的湍流过程,根据冰-海洋耦合系统的能量收支关系,设计了一个简化的冰-海洋热力耦合方案.对该方案引起的海洋混合层适应、热力结构和海冰发展的影响进行了分析,并将其用于全球冰海洋耦合模式的数值试验,结果表明,在大气热力强迫下该耦合方案既可使冰区混合层海水温度向冰点适应,又使冰边缘带海水温度与冰点保持明显差异,能够较好地反映冰-海洋热力相互作用.利用该耦合方案构造的全球冰-海洋耦合模式模拟的海冰范围及季节变化与实际观测非常接近.

A thermodynamic coupling scheme for ice-ocean model

Thermodynamic coupling plays an important role in the simulation of sea ice and general oceanic circulation. It is an important factor to represent the ice-ocean interaction. It is necessary to copy with such a process with detailed turbulence model, however, this treatment is limited by computation especially for the climate model. And the temperature of the upper oceanic mixed layer in ice zone was assumed at the freezing point of seawater, which is often set to a constant, in most of the ice models and coupled ice-ocean models. Such an assumption is exact enough for the inner ice zone. But there exist exceptions when ice floe advects to a warmer waters in the marginal ice zone or when the freezing point varies with the salinity of seawater under ice bottom for salt rejection while freezing or for freshening while melting. A new thermodynamic coupling scheme is presented according to the energy balances between the coupled ice-ocean system. The scheme neither keep the temperature of the mixed layer at the freezing point of seawater nor consider the detailed turbulent processes at the ice-ocean interface. The analysis and experiments on the scheme show that the coupling scheme produces more reasonable temperature in the upper ocean mixed layer. The temperature of the mixed layer is close to the freezing point of seawater in the ice zone and is obviously above the freezing point of seawater in marginal ice zone under the atmospheric forcing. The simulated sea ice extents and their seasonal variations in the Arctic and the Antartctic are close to the observations with a global coupled ice-ocean model based on this coupling scheme.