FGOALS-g3模拟的南亚夏季风:气候态和年际变率

Simulation of South Asian Summer Monsoon Using the FGOALS-g3 Climate System Model:Climatology and Interannual Variability

南亚夏季风的变化决定着印度半岛的旱涝状况,气候系统模式则是研究南亚夏季风变化规律的重要工具。本文基于观测和JRA55再分析资料,系统评估了FGOALS-g3模式模拟的南亚夏季风气候态和年际变率,并重点关注FGOALS-g3与FGOALS-g2以及是否考虑海气相互作用的模拟差异。结果表明,由于局地海温模拟的变化,相比于FGOALS-g2,FGOALS-g3模拟的南亚夏季风在气候态热带印度洋信风和El Ni?o期间沃克环流下沉支上有明显改进。同时,由于对流层系统性冷偏差持续存在并且中心位于副热带300 hPa附近,造成气候态上经向温度梯度减弱,使季风环流减弱,导致FGOALS-g3中陆地季风槽的水汽辐散偏差和降水干偏差仍然存在;在年际变率上,FGOALS-g3模拟的El Ni?o期间赤道西太平洋海温冷异常偏弱,印度洋偶极子偏强,导致印度半岛下沉运动减弱,FGOALS-g3中ENSO—印度降水负相关关系也依然偏弱。研究表明,耦合过程导致的气候态海温偏差通过改变环流和水汽输送,有效补偿了大气模式中印度半岛中部和中南半岛的降水湿偏差;在年际变率上,耦合模式由于考虑了海温—降水—云短波辐射的负反馈过程,能够减小大气模式模拟偏差的强度,但印太暖池区海温模拟偏差导致沃克环流下沉支偏西,使得印度半岛的降水响应出现更大的湿偏差。

In this study,according to observation and reanalysis data,we evaluated the performance of the South Asian summer monsoon(SASM)using the FGOALS-g3 climate system model.We focused on the differences between FGOALS-g3 and FGOALS-g2,and the coupled model and atmospheric model.The results showed that compared with FGOALS-g2,FGOALS-g3 better simulated climatological Indian Ocean trade winds and the sinking branch of the Walker circulation during El Ni?o,owing to the change in local sea surface temperature(SST).The FGOALS-g3 model showed that systematic cold biases persisted in the middle and upper troposphere,which reduced the meridional temperature gradient and weakened SASM,leading to biases in descending motion and moisture divergence,and dry biases occurred over the terrestrial monsoon trough.Meanwhile,the negative correlation between El Ni?o—Southern Oscillation and Indian summer rainfall captured by FGOALS-g3 was weaker than the observation,owing to the weaker descending motion caused by SST biases.The results also showed that climatological SST biases induced by air–sea interactions compensated the wet biases in the SASM region through the change in atmospheric circulation and water vapor transportation.At an interannual timescale,the inclusion of the negative feedback process of SST–precipitation–cloud shortwave radiation in the coupled model effectively improved the bias intensity of rainfall and atmospheric circulation simulated by the atmospheric model;however,the westward biases of the sinking branch of the Walker Circulation caused by SST biases in the coupled model led to greater wet biases in the Indian Peninsula.