1.School of Atmospheric Sciences,Chengdu University of Information Technology;2.The Institute of Atmospheric Physics,Chinese Academy of Sciences
the Strategic Project of Chinese Academy of Science (Grant XDA19070402)
基于1979-2017年数据，利用回归方法和线性模式试验，分析了两类El Ni?o事件（东部型EP和中部型CP）期间，南大洋海冰异常的差异及其可能机制。结果表明，两类事件期间尽管海冰异常定性上类似，但强度和位置存在明显差异；在罗斯海和阿蒙森海，两类事件期间海冰均偏少，但 EP期间海冰减少范围更大,振幅更强；在威德尔海，两类事件期间海冰均偏多，但EP期间增多更明显，而且位置相对CP期间偏西偏北。造成这种差异的主要因素是两类事件期间海温异常强度的不同；EP期间对应的海温偏东偏强，其激发的类太平洋-南美型（PSA）模态在南极边缘海的异常高压中心强度更大、范围更广，使得罗斯海区域为东北风异常控制，有利海冰向高纬输送，海冰范围进而减少，而威德尔海区域则是异常偏南风控制，使得海冰向北输运，有利于威德尔海南部海冰范围减少，北部海冰范围增大。相比之下，CP事件期间，赤道中东太平洋的暖海温异常偏于中太平洋且强度弱，其激发的类PSA在南极边缘海的异常高压偏弱，使得动力作用引起阿蒙森海的海冰减少和威德尔海海冰增加偏弱。进一步的分析表明，CP事件期间威德尔海海冰增多还与该区域更早时间(11月份)的海冰增多，及随后海冰-太阳反照率的正反馈效应有关。本研究结果显示两类事件期间海冰异常的强度和位置的差异，与两类事件期间赤道中东太平洋SSTA强度和位置的差异，二者有很好的对应关系，相比前人的合成分析结果—CP期间海冰异常强于EP期间，物理上更为合理。
Based on the sea ice data from 1979 to 2017, this work used linear regression and a linear baroclinic model to investigate the differences of Antarctic sea ice during two types of El Ni?o events (EP and CP) and its possible physical mechanisms. The results suggest that the amplitude and the spatial pattern of sea ice anomalies are different, although there are some similarities. The sea ice anomalies in the Ross Sea and Amundsen Sea in EP and CP event are negative, but they are stronger in the EP event than CP event. The sea ice anomalies in the Weddell Sea are positive, and they are stronger and northwestward in the EP event relative to the CP event. The difference of sea temperature anomalies intensity between EP and CP events is an important reason for the different amplitude of sea ice. The sea surface temperature anomalies are stronger in the EP event than the CP event, and force a Pacific-South America teleconnection pattern with a stronger high-pressure anomaly. Such atmospheric circulation leads to northeast wind anomaly in Ross Sea in the EP event, which transport sea ice to high latitudes and the sea ice decreases, and causes south wind anomaly in Weddell Sea, which accumulate sea ice on the northern Weddell Sea. Compared to the EP event, the Pacific-South America teleconnection anomaly forced by the CP event is weaker, which induced weaker sea ice anomalies. In fact, the positive anomaly of sea ice in Weddell Sea has appeared in previous November during the CP event, and strengthened due to the ice-albedo feedback in the following spring. Our results suggest that sea ice anomalies are stronger when the sea surface temperature anomalies in the tropical Pacific are stronger. It is different from that indicated in previous studies, but is more reasonable.