On modelling the seasonal thermodynamic cycle of sea ice in studies of climatic change
On modelling the seasonal thermodynamic cycle of sea ice in studies of climatic change
复制标题
在气候变化研究中模拟海冰的季节性热力循环
DOI：
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发表时间：
1984
期刊：
影响因子：
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通讯作者：
A. Semtner
中科院分区：
文献类型：
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作者：
A. Semtner
最近在模拟大气中二氧化碳增加引起的气候变化方面的工作表明，由于海冰覆盖的季节性减少，极地地区的变化最大。通常，海冰热力学以一种非常简单的方式建模，其中忽略了冰内感热和潜热的储存，并且也可以忽略积雪对电导率和表面反照率的影响以及海洋热通量对底部消融的影响。本文考虑在定量确定区域气候变化的背景下，忽略这些过程是否合理。一个相关的问题，冰动力学的遗漏是否合理，没有考虑。Maykut和Untersteiner（1966,1971）以及Semtner（1976）已经开发了相对完整的海冰热力学一维模型，并对各种环境条件进行了测试。Semtner（1976）的附录中描述了一个忽略感热和潜热储存的更简单的模型。在该模型中，由于忽视蓄热而产生的年平均冰厚误差可以通过反照率和电导率的增加来补偿。在这里，我们研究了由这种模型预测的冰厚的季节周期，发现在相位（提前一个月）和幅度（高估约50%）上存在显著误差。振幅误差随着降雪和海洋热通量的减小而增大（或被忽略）。这表明，在使用非常简单的海冰热力学公式进行气候模拟时，可能会出现重大误差，即过早和过度融化夸大了海冰的季节性消失。为了说明上述观点，我们配置了两个模型来检验北极海冰对大气二氧化碳增加四倍的局部响应。第一个模型忽略了许多物理过程，并模拟了Manabe和Stouffer（1980）中发现的海冰的行为，包括当前和增加的二氧化碳水平。较完整的第二种模式对目前二氧化碳水平下的北极冰进行了较好的模拟，并显示出相对于Manabe和Stouffer（1980）对二氧化碳翻四倍的响应有所降低。特别是，表面温度的变化减少了两倍。鉴于这一结果，在进一步的气候变化研究中，似乎有必要对海冰热力学进行更全面的处理。只需要稍微增加计算量。
Recent work in modelling climatic changes due to increased atmospheric CO2 has shown the maximum change to occur in the polar regions as a result of seasonal reductions in sea ice coverage. Typically, sea ice thermodynamics is modelled in a very simple way, whereby the storage of both sensible and latent heat within the ice is ignored, and the effects of snow cover on conductivity and on surface albedo and of oceanic heat flux on bottom ablation may also be neglected. This paper considers whether omission of these processes is justified within the context of quantitatively determining regional climatic changes. A related question, whether omission of ice dynamics can be justified, is not considered.Relatively complete one-dimensional models of sea-ice thermodynamics have previously been developed and tested for a variety of environmental conditions by Maykut and Untersteiner (1969, 1971) and by Semtner (1976). A simpler model which neglects the storage of sensible and latent heat is described in the Appendix to Semtner (1976). In that model, the errors in annual-mean ice thickness which would arise from neglect of heat storage can be compensated by increases in albedo and in conductivity. Here we examine the seasonal cycle of ice thickness predicted by such a model and find significant errors in phase (one month lead) and in amplitude (≈50% overestimate). The amplitude errors are enhanced as snowfall and oceanic heat flux diminish (or are neglected). This suggests that substantial errors may occur in climate simulations which use very simple formulations of sea ice thermodynamics, whereby early and excessive melting exaggerates the seasonal disappearance of sea ice.To illustrate the above point, two models are configured to examine the local response of Arctic sea ice to a quadrupling of atmospheric CO2. The first model neglects a number of physical processes and mimics the behavior of sea ice found in Manabe and Stouffer (1980), both for present and enhanced levels of CO2. The more complete second model gives a better simulation of Arctic ice for the present level of CO2 and shows a reduced response to CO2 quadrupling relative to that in Manabe and Stouffer (1980). In particular, the change in surface temperature is cut by a factor of two. In view of this result, a more complete treatment of sea ice thermodynamics would seem warranted in further studies of climate change. Only a minor computational increase is required.