海洋环流模式中不同近似假设下的海表高度

Sea Level Height on Different Approximations Assumptions in Ocean Circulation Models

Boussinesq近似是现代海洋环流模式中经常采用的假设,但随着海洋模式的不断发展完善以及气候研究应用的需要,有必要估算Boussinesq近似造成的模式误差。分别利用一个非Boussinesq近似的海洋模式与另一个结构相同且采用Boussinesq近似的模式计算海表高度,并同时利用模式预报的温度、盐度资料计算了比容异常高度。分析结果显示,这3种不同定义的海表高度无论空间结构,还是时间演变,都基本类似,尤其在热带海区最接近,差值≤1cm。Boussinesq近似意味着在模式中以体积守恒代替质量守恒,通常的做法是对其进行简单的质量补偿来保持质量守恒。比较说明,以质量补偿方法进行的高度订正对减小Boussinesq近似带来的误差没有本质的意义。

The Boussinesq approximation is a common assumption used in the modern ocean circulation models, and it is necessary to estimate the model errors caused by the Boussinesq approximation along with the development of ocean model and the application of ocean model to the climate studies. In this paper, two sea level heights are computed by an ocean model without the Boussinesq approximation and a parallel model with the Boussinesq approximation, respectively, and the steric anomaly heights are computed by (using) the temperature and salinity data predicted by the two models. It is shown from the analysis results that 3 kinds of sea level height are basically similar to each other both in spatial structure and time-dependent variation, and especially in the tropical sea area, the mean differences between 3 kinds of sea level height are no more than 1 cm. The Boussinesq approximation implies that volume rather than mass is conserved in the model, so the common practice is to make a simple mass compensation to achieve the mass conservation. It is shown from the comparison between the compensation results that the correction of height by making a mass compensation has no essential significance for reducing the error caused by the Boussinesq approximation.