Internal Variability and Regional Climate Trends in an Observational Large Ensemble
Internal Variability and Regional Climate Trends in an Observational Large Ensemble
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DOI：
10.1175/jcli-d-17-0901.1
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发表时间：
2018-09-01
影响因子：
4.9
通讯作者：
Deser, Clara
中科院分区：
文献类型：
--
作者：
McKinnon, Karen A.;Deser, Clara
最近观察到的气候趋势是外部辐射强迫和内部产生的可变性共同作用的结果。为了更好地了解这些趋势并预测未来的趋势，有必要对内部可变性的时空特性进行适当的建模。这里，基于1921-2014年的月度网格观测数据集，建立了一个关于地球温度和降水以及全球海平面气压的统计模型。该模型用于生成一个合成集合，其中每个成员具有唯一的内部可变性序列，但具有类似于观测记录的统计特性。这一合成集合与气候模型对外部强迫响应的估计相结合，产生了一个观测大型集合(OBS-LE)。东大西洋公约组织的1000个成员在其50年的区域气候趋势上表现出相当大的多样性，这表明在几十年的时间尺度上内部变化的重要性。例如，与北环型相关的非强迫大气环流趋势可以引起欧亚大陆冬季温度趋势，其幅度与过去50年的强迫趋势相当。同样，在全球大部分地区，内部变化对冬季降水趋势的贡献很大，导致幅度和在某些情况下50年趋势的迹象在区域上存在很大的不确定性。OBS-LE提供了与初始条件模型集合相对应的真实世界。该方法可以扩展到使用古替代数据来模拟较长期的变异性。
Recent observed climate trends result from a combination of external radiative forcing and internally generated variability. To better contextualize these trends and forecast future ones, it is necessary to properly model the spatiotemporal properties of the internal variability. Here, a statistical model is developed for terrestrial temperature and precipitation, and global sea level pressure, based upon monthly gridded observational datasets that span 1921-2014. The model is used to generate a synthetic ensemble, each member of which has a unique sequence of internal variability but with statistical properties similar to the observational record. This synthetic ensemble is combined with estimates of the externally forced response from climate models to produce an observational large ensemble (OBS-LE). The 1000 members of the OBS-LE display considerable diversity in their 50-yr regional climate trends, indicative of the importance of internal variability on multidecadal time scales. For example, unforced atmospheric circulation trends associated with the northern annular mode can induce winter temperature trends over Eurasia that are comparable in magnitude to the forced trend over the past 50 years. Similarly, the contribution of internal variability to winter precipitation trends is large across most of the globe, leading to substantial regional uncertainties in the amplitude and, in some cases, the sign of the 50-yr trend. The OBS-LE provides a real-world counterpart to initial-condition model ensembles. The approach could be expanded to using paleo-proxy data to simulate longer-term variability.