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有无El Niño影响下热带北大西洋春季增暖的差异及可能成因
叶洋波, 余锦华
南京信息工程大学气象灾害教育部重点实验室/气象灾害预报预警与评估协同创新中心,江苏 南京 210044
摘要:
热带北大西洋(Northern Tropical Atlantic,NTA)海温异常(sea surface temperature anomaly,SSTA)对美洲乃至全球的气候变率有着重要影响。利用再分析资料对NTA的暖SSTA进行诊断,分析有、无El Ni?o影响下春季增暖的差异以及可能的成因。结果表明,与El Ni?o有关的情形中关键区(5~25 °N,10~60 °W)平均春季SSTA为0.55 ℃,无El Ni?o情形是0.37 ℃;前者与冬季的显著正偏差出现在NTA,后者主要发生在NTA的东侧,且正偏差的数值较小。El Ni?o激发的热带外Rossby波活动通过加强北大西洋涛动(North Atlantic Oscillation,NAO)负位相,引起El Ni?o 峰值后NTA海域显著的西风异常,暖Kelvin波加热NTA对流层大气,增强其容纳水汽的能力,减小海-气界面的垂直湿度梯度,两者共同作用使海表蒸发减弱,在NTA春季呈现显著暖SSTA。与El Ni?o无关的情形中,NTA SSTA的变化主要受热带海-气反馈过程的调制,其与热带外NAO的季节内振荡有关,NAO的季节平均负位相较弱,异常西风值较小,同时海-气垂直湿度梯度异常增大,使春季NTA的增暖较弱。
关键词:  NTA  春季SSTA  El Niño  遥相关  NAO
DOI:10.16032/j.issn.1004-4965.2021.012
分类号:
基金项目:
INFLUENCE OF EL NIÑO ON SPRING WARMING IN THE NORTHERN TROPICAL ATLANTIC AND POSSIBLE CAUSES OF THE INFLUEN
YE Yang-bo, YU Jin-hua
Key Laboratory of Meteorological Disaster of Ministry of Education / Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China
Abstract:
Sea surface temperature anomaly (SSTA) in the Northern Tropical Atlantic (NTA) has important effects on climate variation in the Americas and the world at large. Reanalysis data are used to diagnose warm NTA SSTA, and the difference in spring warming with or without the influence of El Ni?o and the possible causes of the difference are analyzed. The results show that the average spring SSTA related to El Ni?o reaches 0.55℃ in the key area (5°N~25°N, 10°W~60°W), while the one without the influence of El Ni?o only reaches 0.37℃; the significant positive deviation between the former and winter occurs in the NTA, while the latter occurs mainly on the east side of the NTA, and the value of the positive deviation is relatively small. The El Ni?o-induced anomalous activity flux of Rossby wave outside the tropics leads to significant westerly anomalies in the NTA by strengthening the negative NAO phase after the mature phase of El Ni?o. The warm Kelvin wave heats the troposphere over the NTA, enhancing its ability to hold water vapor and reducing the vertical humidity gradient at the sea-air interface. Under the combined impact of them two, the evaporation in sea surface decreases, leading to warm SSTA in spring in the NTA. When there is no influence of El Ni?o, the variation of NTA SSTA is mainly modulated by the tropical sea-air feedback process and related to the intra-seasonal oscillation of NAO outside the tropics. The seasonal mean negative phase of NAO is relatively weak, and thus the anomalous westerly wind is small, while the vertical humidity gradient at the sea-air interface increases, leading to weaker NTA warming.
Key words:  NTA  spring SSTA  El Niño  teleconnection  NAO
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