On the Choice of Ensemble Mean for Estimating the Forced Signal in the Presence of Internal Variability
On the Choice of Ensemble Mean for Estimating the Forced Signal in the Presence of Internal Variability
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DOI：
10.1175/jcli-d-17-0662.1
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发表时间：
2018-07-01
影响因子：
4.9
通讯作者：
Steinman, Byron A.
中科院分区：
文献类型：
--
作者：
Frankcombe, Leela M.;England, Matthew H.;Steinman, Byron A.
在本文中，我们研究了气候模式模拟中强迫信号计算的各种选择，以及这些选择对内部变率估计的影响。我们发现，从一个单一的气候模式[一个单一的模式集合平均值（SMEM）]运行的集合平均提供了一个很好的估计，即使是非常少的集合成员的模型的真实强迫信号。然而，在给定模型只有单个成员可用的情况下，其他模型的SMEM通常会被所有可用气候模型模拟的缩放集合平均值[多模型集合平均值（MMEM）]优于。因此，缩放的MMEM可以用作用于观测的强制信号的估计。然而，MMEM方法导致未来误差进一步增加，因为模型中不同的变暖速率导致它们的轨迹发散。因此，我们将SMEM方法应用到具有足够数量的集合成员的模式中，以估计未来强迫情景下内部变率幅度的变化。与以前的结果一致，我们发现，平均而言，在高纬度地区，特别是在海洋沿着海冰边缘的表面空气温度变率降低，而降水的变化平均增加，特别是在高纬度地区。海平面气压的变化在南半球平均减少，而在北方半球则存在区域差异。
In this paper we examine various options for the calculation of the forced signal in climate model simulations, and the impact these choices have on the estimates of internal variability. We find that an ensemble mean of runs from a single climate model [a single model ensemble mean (SMEM)] provides a good estimate of the true forced signal even for models with very few ensemble members. In cases where only a single member is available for a given model, however, the SMEM from other models is in general out-performed by the scaled ensemble mean from all available climate model simulations [the multimodel ensemble mean (MMEM)]. The scaled MMEM may therefore be used as an estimate of the forced signal for observations. The MMEM method, however, leads to increasing errors further into the future, as the different rates of warming in the models causes their trajectories to diverge. We therefore apply the SMEM method to those models with a sufficient number of ensemble members to estimate the change in the amplitude of internal variability under a future forcing scenario. In line with previous results, we find that on average the surface air temperature variability decreases at higher latitudes, particularly over the ocean along the sea ice margins, while variability in precipitation increases on average, particularly at high latitudes. Variability in sea level pressure decreases on average in the Southern Hemisphere, while in the Northern Hemisphere there are regional differences.