全新世太阳活动对东亚夏季风百年尺度变化影响的模拟研究

太阳活动对东亚夏季风(EASM)变化有着重要的影响。本研究利用通用地球系统模式(CESM)开展了全新世气候瞬变模拟试验, 探究了全新世EASM降水百年尺度的变化特征及其对太阳活动外强迫的响应机理。结果表明: 在变化趋势上, 模拟的全新世以来EASM降水呈减弱趋势, 主要受地球轨道参数外强迫的影响。在百年尺度上, 中全新世以来太阳活动外强迫引起EASM降水出现约430年的周期变化特征, 这与高分辨率重建资料记录的周期相似。这一百年尺度变化的空间主模态呈南北偶极型分布, 北方降水与太阳活动存在显著的同期正相关, 当太阳活动增强时东亚海陆热力差异加强, 陆地海平面气压降低, 引起异常的气旋性环流, 有利于北方降水增多。南方降水与太阳活动呈负相关并滞后于太阳活动, 太阳活动通过调制赤道太平洋类拉尼娜态的海温梯度, 引起西北太平洋风-蒸发-海温的正反馈机制, 触发异常的西北太平洋气旋性环流, 从而导致南方降水减少。

Simiulation of centennial scale change of the East Asian summer monsoon response to solar activity during the Holocene

Solar activity has an important influence on the variation of the East Asian Summer Monsoon (EASM). Using a Holocene climate transient simulation with the Community Earth System Model (CESM), including ORB experiment and TSI+ORB experiment, we first evaluate the ability of the model in producing EASM precipitation and circulation climatical fields, and then investigate the centennial timescale variability of EASM precipitation and its response mechanism to solar forcing during the Holocene. For simplicity, we used TSI+ORB experiment minus ORB experiment to isolate the net effect of solar activity. In this study, the north-south summer precipitation index over Eastern China is used to measure EASM intensity. The results show that the simulated EASM precipitation has been weakening since the Holocene, mainly due to the external forcing of the Earth's orbital parameters. On the centennial timescale, EASM precipitation exhibits a significant 430-year periodicity under solar forcing since the Middle-Late Holocene, which is suggested by high-resolution proxy data. We find that there is a significant correlation between the centennial timescale variability of EASM precipitation and solar forcing. In the peaks of solar activity, the leading mode of the centennial EASM variation shows a north-south dipole pattern, with a significant contemporaneous positive correlation between northern precipitation and solar activity. When solar activity intensifies, the land-sea thermal differences strengthen over Eastern China and sea-level pressure decreases, causing anomalous cyclonic circulation, which is conducive to increased precipitation in the north. Precipitation in the south is negatively correlated with and lags corresponding solar activity by about 80 years. We suggest that solar activity modulates the La Niña -like SST gradients of the equatorial Pacific, causing a positive feedback mechanism of wind-evaporation-SST, inducing the anomalous cyclonic circulation in the western North Pacific and reducing precipitation in the south. As the western Pacific warming reaches its maximum at about 80 years, the intensity of anomalous cyclonic circulation in the western North Pacific is the strongest, so the inhibitory effect on southern precipitation is also the strongest.