Subseasonal convection variability over the Intra‐American Seas simulated by an AGCM and sensitivity to CMIP5 SST biases and projections
Subseasonal convection variability over the Intra‐American Seas simulated by an AGCM and sensitivity to CMIP5 SST biases and projections
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AGCM 模拟的美洲内海次季节对流变化以及对 CMIP5 海温偏差和预测的敏感性
DOI：
10.1002/joc.6475
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Lee, Dong Eun
中科院分区：
文献类型：
--
作者：
Vigaud, Nicolas;Lyon, Bradfield;Lee, Dong Eun
利用ECHAM5大气全球气候模式（AGCM）实验的聚类（k -均值）日OLR异常，研究了5 - 11月雨季期间耦合模式海表温度（SST）气候偏差和海温预估对美洲海（IAS）日对流的影响。AGCM首先是由1980-2005年观测到的海温（GOGA）强迫的，然后是由31个CMIP5耦合模式（HIST）的气候、多模式平均月气候海温偏差和在观测值上施加的2040-2059年（PROJ）和2080-2099年（PROJ2）预估海温变化强迫的。确定了7种循环对流类型，包括3种干对流和4种湿对流，其中3种类型的特征是横跨IAS的表面对流细胞与对流层上层的罗斯比波之间的热带-中纬度相互作用，以及ITCZ典型的广泛润湿状态。与早期的观察性研究相比，所有7种情况在HIST试验中都得到了相当好的再现。然而，与GOGA相比，后者表现出更干燥的干燥状态，更少潮湿的类似ITCZ的潮湿状态，以及在其他三个状态中对流异常在IAS上的东南移动，所有这些都导致模拟IAS气候更干燥。PROJ和pro2的ECHAM5投射运行都以抑制广泛的ITCZ样潮湿状态为特征，这表明干旱天气更频繁的显著趋势。与此同时，随着铅的增加，与热带-中纬度相互作用相关的对流异常向加勒比海以东进一步移动。这些结果表明，热带大西洋和美国东南部的极端降雨将更加频繁和强烈，而加勒比地区的部分地区预计将经历更干燥的气候。然而，预估的干燥与历史海温偏差的结果具有相同的数量级，这表明在模式预估中需要考虑后者，这可能低估了未来的IAS干燥。
The influence of coupled model sea surface temperature (SST) climatological biases and SST projections on daily convection over the Intra‐American Seas (IAS) during the May–November rainy season are examined by clustering (k− means) daily OLR anomalies in ECHAM5 atmospheric global climate model (AGCM) experiments. The AGCM is first forced by 1980–2005 observed SSTs (GOGA), then with climatological, multi‐model mean monthly climatological SST bias from 31 CMIP5 coupled models (HIST) and projected SST changes for 2040–2059 (PROJ) and 2080–2099 (PROJ2) imposed on top of observed values. A typology of seven recurrent convection regimes is identified and consists of three dry and four wet regimes, including three regimes characterized by tropical‐midlatitude interactions between surface convection cells across the IAS and Rossby wave in the upper‐troposphere, and a regime of broad wettening typical of the ITCZ. Compared to an earlier observational study, all seven regimes are reasonably well reproduced in the HIST runs. However, the latter exhibit drier dry regimes, a less wet ITCZ‐like wet regime and a southeastward shift of convective anomalies developing across the IAS in the three other regimes, all result in a drier simulated IAS climate compared to GOGA. ECHAM5 projection runs for PROJ and PROJ2 are both characterized by the inhibition of the broad ITCZ‐like wet regime, indicating a significant trend towards more frequent dry weather. Meanwhile, convection anomalies related to tropical‐midlatitude interactions are shifted further east of the Caribbean as lead increases. These results suggest more frequent and intense extreme rainfall over the tropical Atlantic and the southeast US, while parts of the Caribbean are projected to experience drier climate. The projected drying, however, is of the same order of magnitude as results from historical SST biases, suggesting that the latter need to be considered in model projections, which might underestimate future IAS drying.
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