表面气温内部变率估算方法的比较研究

本文利用37个CMIP5模式和CESM（Community Earth System Model）包含40个成员的超级集合试验的表面气温预估数据，比较了工业革命前气候参照试验、多项式拟合法和方差分析方法这三种目前在国际上运用较多的方法所估算的表面气温内部变率的异同，分析了内部变率的估算对气候预估中信号萌芽时间（TOE）的影响。结果表明:若采用CMIP5多模式集合，则工业革命前气候参照试验和多项式拟合法都是估算内部变率的合理方法，而方差分析方法则由于包含模式性能自身的影响会夸大内部变率故不推荐使用。内部变率的全球分布呈现出极向强化的现象，中高纬度地区的内部变率幅度远大于热带、副热带地区。内部变率受不同排放情景的影响较小，且随时间无显著变化，但方差分析方法估算的内部变率在热带地区容易受到排放情景的影响。若基于类似CESM这样的单个气候模式的超级集合模拟试验来估算内部变率，三种方法估算的结果相似。不同方法估算的内部变率对TOE的影响主要位于北大西洋拉布拉多海、南大洋威德尔海和罗斯海等邻近海洋深对流区。对于中国区域平均来说，基于CESM超级集合模拟试验，三种方法估算的内部变率与强迫信号之比都小于15%；对CMIP5多模式集合，采用工业革命前气候参照试验和多项式拟合法得到的结果与此接近，但若采用方差分析方法则显著高估内部变率的作用。

A Comparison of Three Methods for Estimating Internal Variability of Near-Surface Air Temperature

The estimated internal variability of near-surface air temperature was compared using three widely adopted methods pre-industrial control (piControl) simulations, polynomial fit method, and analysis of variance method , based on 37 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and 40 large-ensemble simulations from the Community Earth System Model (CESM). The associated influences on the time of emergence (TOE) of near-surface air temperature in future climate projections were also quantified. The results showed that for multimodels from the CMIP5, the estimated internal variability was comparable based on the piControl simulations and the polynomial fit method, while variability estimated by the analysis of variance method was exaggerated in terms of the magnitude because of its inclusion of model uncertainty. Polar amplification was evident in the spatial distribution of estimated internal variability of surface temperature, with considerably larger magnitudes in the mid- to high-latitudes than the low-latitudes. The internal variability of surface temperature did not vary significantly with time or emission scenarios, except for in the tropics, estimated by the analysis of variance method. Moreover, the estimated internal variability showed high consistency among the three methods, based on large-ensemble simulations from the CESM. The different estimated internal variabilities further affected the TOE in future climate projections, mainly in the North Atlantic Labrador Sea and the Weddell and Ross Seas in the Southern Ocean where deep overturning circulations occur. Specifically, the internal variability was estimated to be less than 15% of the forced signals over China based on all three methods in the CESM large-ensemble simulations. This result was comparable to those estimated by the piControl simulations and polynomial fit method based on the CMIP5 multimodels but tended to be overestimated by the analysis of variance method.