The persistence barrier of sea surface temperature anomalies(SSTAs) in the North Pacific was investigated and compared with the ENSO spring persistence barrier.The results show that SSTAs in the central western North Pacific(CWNP) have a persistence barrier in summer:the persistence of SSTAs in the CWNP shows a significant decline in summer regardless of the starting month.Mechanisms of the summer persistence barrier in the CWNP are different from those of the spring persistence barrier of SSTAs in the central and eastern equatorial Pacific.The phase locking of SSTAs to the annual cycle does not explain the CWNP summer persistence barrier.Remote ENSO forcing has little linear influence on the CWNP summer persistence barrier,compared with local upper-ocean process and atmospheric forcing in the North Pacific.Starting in wintertime,SSTAs extend down to the deep winter mixed layer then become sequestered beneath the shallow summer mixed layer,which is decoupled from the surface layer.Thus,wintertime SSTAs do not persist through the following summer.Starting in summertime,persistence of summer SSTAs until autumn can be explained by the atmospheric forcing through a positive SSTAs-cloud/radiation feedback mechanism because the shallow summertime mixed layer is decoupled from the temperature anomalies at depth,then the following autumn-winter-spring,SSTAs persist.Thus,summer SSTAs in the CWNP have a long persistence,showing a significant decline in the following summer.In this way,SSTAs in the CWNP show a persistence barrier in summer regardless of the starting month.
利用1951—2010年逐月的HadISST海表温度资料、SODA次表层海温资料和NCEP/NCAR再分析资料等,对比分析了东太平洋(EP型)La Nia和中太平洋(CP型)La Nia的海气耦合特征在季节演变过程中的差异。EP La Nia海表温度异常中心在发展年夏季出现于南美沿岸,随后向西移动,盛期最大海表温度异常中心位于赤道东太平洋,而CP La Nia海温异常中心少动,基本维持在160°W附近,其强度更强,持续时间更长。受海温分布形态影响,热带大气对两类La Nia的响应非常不同,成熟期间CP型在中太平洋偏旱的强度和范围比EP型大,且略偏西。发展年夏、秋季,北半球位势高度响应较弱;冬季,负PNA位相易伴随两类La Nia出现,但异常活动中心的位置和强度不同,在北大西洋其大气响应几乎相反,这些差异会引起显著不同的区域气候异常。
