南海海平面对两类El Ni?o的不同响应

利用ECMWF ORAS4重构数据，分析了南海海平面异常(SLA)对东部型(EP)El Ni?o和中部型(CP)El Ni?o的不同响应特征。南海SLA在两类El Ni?o期间表现出不同的时空演变规律。对于东部型El Ni?o，南海空间平均的SLA在发展年的秋、冬季显著下降，最低可达?2 cm，并在次年开始上升，至次年冬季可达2 cm。空间分布上，在发展年秋、冬季，除越南东南部海域存在一个正异常中心外，在南海绝大部分海域，SLA均表现为显著的负异常；从次年春季开始，SLA负异常减弱，而越南东南部的正异常开始发展，直至冬季南海大部分海域以正异常为主。对于中部型El Ni?o，南海SLA在整个El Ni?o发展和衰退期间均表现为显著负异常，异常值始终维持在?2 cm左右，并且在空间上表现为全海盆一致的负异常模态。相比于传统的经验正交分解(EOF)，季节EOF(S-EOF)能够更好地刻画南海SLA在两类El Ni?o期间的时空演变特征，S-EOF的第一模态表现为中部型El Ni?o模态，而第二模态更多地表现为南海SLA在东部型El Ni?o期间的演变特征。南海海平面在两类El Ni?o期间的不同变化主要是由于海峡通道处的热量平流输运异常所产生的热比容效应导致的，但是比容海平面的贡献主要集中在南海内区和南海东部等深水海域，对于南海西部等近岸海域，海平面的变化机制还有待进一步深入研究。

Different sea level variations in the South China Sea in response to two types of El Niño

Using the ECMWF ORAS4 reconstruction data, the different response characteristics of the South China Sea Sea Level Anomaly (SLA) to the Eastern Pacific (EP) El Niño and the Central Pacific (CP) El Niño were analyzed. The South China Sea SLA showed different spatial and temporal evolution during the two types of El Niño. For the EP El Niño, the average SLA in the South China Sea decreased significantly in the autumn and winter of the developing year, with a minimum of -2 cm, and began to rise in the following year, up to 2 cm in the following winter. In terms of spatial distribution, in the autumn and winter of developing year, except for the existence of a positive anomaly to the southeast of Vietnam, in most of the South China Sea, SLAs are characterized by significant negative anomalies; from the spring of the following year, SLA negatively weakens, while the southeastern part of Vietnam was beginning to develop abnormally until the majority of the South China Sea is dominated by positive anomalies. For the CP El Niño, the South China Sea SLA showed significant negative anomalies throughout the El Niño development and decline, the outliers were always maintained at around -2 cm, and spatially represented as a consistent negative anomaly of the whole basin. Compared with the traditional empirical orthogonal decomposition (EOF), the seasonal EOF (S-EOF) can better characterize the temporal and spatial evolution of the South China Sea SLA during the two types of El Niño. The first mode of the S-EOF is CP El Niño mode, while the second mode is more characterized by the evolution of the South China Sea SLA during the EP El Niño. The different variations of the South China Sea SLA during the two types of El Niño are mainly due to the thermal specific volume effect caused by the thermal advection transport anomaly at the channel, but the contribution of the thermosteric sea level is mainly concentrated in the interior South China Sea. While in the coastal regions, such as the western South China Sea, the mechanism of sea level change needs further study.