摘要:利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（LASG/IAP）发展的耦合的气候系统模式FGOALS-s2工业革命前控制试验结果研究了大西洋经向翻转流（Atlantic Meridional Overturning Circulation，AMOC）的年代际变率及其物理机制。传统AMOC是利用深度坐标下的质量流函数来表征，本文通过对密度坐标下49.5°N的AMOC指数与其余纬度的AMOC指数作相关分析，发现AMOC的变化有从深水形成区向南传播的过程，且密度坐标下的AMOC变率在北大西洋高纬度明显大于低纬度。分析进一步表明，模式模拟的AMOC具有年代际振荡，周期约为70年。这个低频振荡主要是由与AMOC变化相关的温度和盐度的变化与海表风场之间的相互作用引起，具体机制如下：格陵兰-冰岛-挪威海有异常强的海表风场，导致蒸发增强，继而使海表盐度增加，深水形成增多，从而使AMOC增强。AMOC加强后，会使得向北的热量和盐度输送增加，减弱此处的经向温度梯度，风场随之减弱，从而完成位相的反转。
关键词:气候系统模式/
大西洋经向翻转流(AMOC)/
年代际变率
Abstract:Decadal variability of Atlantic Meridional Overturning Circulation (AMOC) has been studied in the Flexible Global Ocean-Atmosphere-Land System model, version s2 (FGOALS-s2) preindustrial simulation. Traditionally, the streamfunction on depth coordinate is used to represent AMOC. According to correlations between the AMOC index on density coordinate at 49.5°N and AMOC index at all latitudes north of 34°S, the authors find that AMOC variations propagate southward from the deep-water formation region. Furthermore, the AMOC variability on density coordinate is larger at high latitudes North Atlantic than at low latitudes North Atlantic and South Atlantic. Moreover, the AMOC displays a low-frequency variability with a period of about 70 years. The low-frequency oscillation is related to the interactions between temperature and salinity variations that are associated with the AMOC variations and surface winds. The physics of this decadal variability is as follows. Surface winds in the Greenland-Iceland-Norwegian (GIN) seas are anomalously strong, leading to abnormally large evaporation and thus the positive sea surface salinity (SSS) anomalies. The SSS anomalies strengthen the convection in the GIN seas and subsequently intensify the AMOC. This leads to a strengthened northward heat transport and decreases the meridional temperature gradient and surface winds, which completes the phase reversal.
Key words:Climate system model/
Atlantic Meridional Overturning Circulation (AMOC)/
Decadal variability
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