Relationship between interannual changes of summer rainfall over Yangtze River Valley and South China Sea–Philippine Sea: Possible impact of tropical zonal sea surface temperature gradient
Relationship between interannual changes of summer rainfall over Yangtze River Valley and South China Sea–Philippine Sea: Possible impact of tropical zonal sea surface temperature gradient
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DOI：
10.1002/joc.6169
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发表时间：
2019-06
期刊：
影响因子：
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通讯作者：
Y. Ha;Zhong Zhong-Zhong;Yun Zhang;Jinfeng Ding;Xiangrong Yang
中科院分区：
文献类型：
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作者：
Y. Ha;Zhong Zhong-Zhong;Yun Zhang;Jinfeng Ding;Xiangrong Yang
利用1979 - 2012年夏季（6 - 8月）长江中下游地区（MLYRV）、南海和菲律宾海（SCS-PS）降水的年际变化特征，分析了长江中下游地区（MLYRV）、南海和菲律宾海降水的年际变化特征。结果表明，MLYRV和SCS-PS之间的降水变化存在异相性，这与北方印度洋（NIO; 5°-25 ° N，60°-100 ° E）和赤道中东太平洋（CEP; 5°S-5°N，180°-130 ° W）之间的热带纬向海表温度梯度密切相关。在过去的40年中，该模型可以解释MLYRV和SCS‐PS夏季降水总方差的40%。这远远高于NIO SST（24%），CEP SST（14%）和Niño-3.4指数（16%）单独解释的结果。暖NIO和冷CEP之间的正的负负这两个地区降水的异相变化与北半球北半球一个正的对流层重力场在热带地区引起异常的东风和步行者样环流，导致南海-南海边界层异常下沉和边界层辐散。因此，该地区的夏季降雨量减少。同时，西太平洋副热带高压增强后，其西北侧沿着强烈的西南气流加强了水汽输送，为中尺度区域提供了更多的可降水量。相反地，负的赤道气流则会导致地面西风带及有利的环境条件，令南海-太平洋系统产生降雨。在30°N附近，由局地Hadley环流异常引起的干下降流在MLYRV上发展，这对MLYRV降水是不利的。该机制进一步研究了使用数值实验。这些热力过程共同作用导致了MLYRV和SCS-PS之间降水的异相年际变化，表明MLYRV和SCS-PS对夏季降水的年际变化具有很强的指示性。
This study investigates the interannual variability of rainfall over the middle and lower reaches of Yangtze River Valley (MLYRV) and that over the South China Sea and Philippine Sea (SCS‐PS) during boreal summer (June–August) from 1979 to 2012. Results exhibit out‐of‐phase rainfall variations between the MLYRV and the SCS‐PS, which is closely related to the tropical zonal sea surface temperature gradient (ZSG) between the northern Indian Ocean (NIO; 5°–25°N, 60°–100°E) and the equatorial central and eastern Pacific (CEP; 5°S–5°N, 180°–130°W). The ZSG can explain as much as 40% of the total variance of the summer rainfall over the MLYRV and the SCS‐PS in the past 40 years. This is much higher than that explained by the NIO SST (24%), CEP SST (14%) and Niño‐3.4 index (16%) alone. A positive ZSG between the warm NIO and the cold CEP tends to increase rainfall over the MLYRV and decrease rainfall over the SCS‐PS, whereas a negative ZSG between the cold NIO and the warm CEP is generally favourable for rainfall over the SCS‐PS and unfavourable for rainfall over MLYRV. The close connection between the ZSG and the out‐of‐phase interannual rainfall variation over the two regions can be explained by influences of the ZSG on atmospheric circulation over East Asia. A positive ZSG induces anomalous easterlies and Walker‐like circulation in the tropics, which results in an anomalous subsidence and boundary layer divergence over the SCS‐PS. As a result, summer rainfall decreases in this region. Meanwhile, moisture transport increases due to the anomalously strong southwesterlies along the northwestern flank of the intensified western Pacific subtropical high, providing more precipitable water to the MLYRV region. In contrast, a negative ZSG induces surface westerlies and favourable environmental condition for rainfall over the SCS‐PS. Dry descending flow induced by local anomalous Hadley circulation develops over the MLYRV around 30°N, which is unfavourable for rainfall over the MLYRV. The mechanism further examined using numerical experiments. These thermal‐dynamical processes induced by the ZSG work together to cause the out‐of‐phase interannual changes of rainfall between the MLYRV and the SCS‐PS, suggesting that the ZSG is highly indicative of the interannual change of summer rainfall in the two regions.