LAUSR

The present study investigates the persistence of summer sea surface temperature anomalies (SSTAs) in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time (approximately 8–14 months) around the Kuroshio Extension (KE) region. This long persistence may be strongly related to atmospheric forcing because the mixed layer is too shallow in the summer to be influenced by the anomalies at depths in the ocean. Changes in atmospheric circulation, latent heat flux, and longwave radiation flux all contribute to the long persistence of summer SSTAs. Among these factors, the longwave radiation flux has a dominant influence. The effects of sensible heat flux and shortwave radiation flux anomalies are not significant. The persistence of summer SSTAs displays pronounced interdecadal variability around the KE region, and the variability is very weak during 1950–82 but becomes stronger during 1983–2016. The changes in atmospheric circulation, latent heat flux, and longwave radiation flux are also responsible for this interdecadal variability because their forcings on the summer SSTAs are sustained for much longer after 1982.摘要大尺度海温的持续性可以影响大气环流和天气的变化. 海表温度异常(SSTAs)的持续性具有很强的季节依赖. 对于北太平洋, 人们已经对冬季SSTAs的持续性进行了较为全面的研究, 取得了一致的结论. 但是, 对夏季SSTAs的持续性特征及机制的研究却存在相互矛盾的观点. 前人主要是针对人为选取区域的SSTAs或是某一海域SSTAs主模态的持续性进行研究, 而这两种方法会对结果产生不确定性影响. 因此, 本文对每个空间格点SSTAs的持续性都进行了分析和计算, 从而明确给出了中纬度北太平洋夏季SSTAs持续性的空间分布, 并对其物理机制及年代际变化进行了分析讨论. 结果表明, 中纬度北太平洋夏季SSTAs可以持续较长的时间, 黑潮延伸体区域的持续时间可以达到8-14个月. 因为夏季中高纬度海洋混合层太浅这使得表层海温很难受到深层海洋变化的影响, 所以黑潮延伸体区域SSTAs较长的持续性主要与局地大气强迫密切相关. 大气环流, 潜热, 长波辐射通量的变化都对SSTAs较长的持续性有所贡献, 其中, 长波辐射通量是主要因子. 而潜热通量和短波热射通量的影响并不显著. 黑潮延伸体区域夏季SSTAs的持续性还存在显著的年代际变化, 其持续性在1950–82很弱, 而在1983-2016显著增强. 大气环流, 潜热, 长波辐射通量的变化仍然是影响这一年代际变化的主要因素, 三者对SSTAs的强迫作用在1982年以后显著增强.