FGOALS海洋同化试验对西北太平洋夏季SST—降水关系的模拟评估

评估了耦合气候系统模式FGOALS海洋同化试验对西北太平洋夏季降水和SST相关关系的模拟技巧，并对比了相应的观测海温强迫试验（AMIP）和历史气候模拟试验结果。结果显示，FGOALS海洋同化试验对亚洲季风区大部分海域夏季SST年际变化有较高的模拟技巧，但其对菲律宾以东海域模拟技巧较低。在西北太平洋夏季降水-SST相关关系方面，同化试验部分地再现了南海和菲律宾以东海域降水超前SST变化1个月和同时二者的负相关关系，优于AMIP试验但逊于自由耦合模拟试验。同化试验对SST倾向-降水相关关系的模拟技巧亦介于AMIP试验和自由耦合试验之间。观测中，西北太平洋夏季降水与环流异常受日界线附近和赤道东印度洋海洋大陆地区海温异常的遥强迫，并通过改变到达海表的净短波辐射通量影响局地SST异常，导致局地海温-降水和局地海温倾向-降水的负相关关系。在AMIP试验中，遥强迫导致的西北太平洋地区环流异常较之观测偏弱，由于缺少局地海气耦合过程，在西北太平洋多数地区表现为海温对大气的强迫作用，即SST-降水正相关关系。FGOALS同化试验和自由耦合试验考虑了局地海气耦合过程，虽然低估了遥强迫对西北太平洋地区夏季环流异常的影响，依然部分模拟出局地降水-SST负相关关系但较之观测偏弱。同时，自由耦合试验高估了西北太平洋20°N以南地区海温异常对大气环流异常的强迫，使得其对中国南海和日本岛以南海域SST-降水负相关关系的模拟稍优于同化试验。

Summer Rainfall-SST Relationships in the Western North Pacific Simulated by the FGOALS Model with Ocean Assimilation

This study evaluates the performance of FGOALS (Flexible Global Ocean-Atmosphere-Land surface-Sea ice coupled model) with ocean assimilation in the simulation of summer rainfall-SST relationship during 1979-2005 in the western North Pacific (WNP), and compares the results with corresponding simulations forced by observed sea surface temperature and FGOALS historical simulation. Results show that the FGOALS with ocean assimilation well captures the interannual variability of summer SST over the WNP except that over east of the Philippines. For the interannual variability of precipitation, it barely demonstrates any skill over Asian summer monsoon region, which is comparable to the AMIP (Atmospheric Model Intercomparison Project) simulation. However, for the summer rainfall-SST relationship, the observed negative correlations over South China Sea and east of Philippines are partly reproduced in the FGOALS with ocean assimilation, in particular when the precipitation leads SST by one month and is concurrent with SST. The simulated skill is better than the AMIP simulation, but is inferior to the historical simulation. Based on observations, anomalous convection and circulation in the summer over the WNP are primarily driven by SST anomalies over the area near the dateline and the eastern Indian Ocean-Maritime Continent. The induced anomalous convections affect solar radiation reaching the sea surface, which contributes significantly to local SST anomalies and leads to negative SST-rainfall correlation and SST tendency-rainfall correlation. In the AMIP simulation, the anomalous circulation over the WNP driven by the remote forcing is underestimated. Since the AMIP simulation is forced by observed SST, the anomalous convection and circulation are forced by underlying SST over some places of the WNP, leading to positive rainfall-SST correlation. Although the anomalous circulations over the WNP driven by the remote forcing are also underestimated in both FGOALS with ocean assimilation and historical simulation, weaker than observed negative SST-rainfall correlations are produced since local air-sea coupling is included. In addition, the historical simulation tends to overestimate the forcing from SST anomalies over the WNP south of 20°N, which leads to better simulated SST-rainfall correlation than the FGOALS with ocean assimilation over South China Sea and south of Japan islands.