对流层增暖热带放大现象:基于FGOALS-g3的模拟研究

Tropical Amplification in Tropospheric Warming Simulated using the Flexible Global Ocean–Atmosphere–Land System Version 3 Climate System Model

热带地区的湿绝热过程会放大地表的增暖幅度,在约200 hPa高度上产生增暖峰值,该现象被称为“热带对流层放大”。热带对流层放大是气候变化的显著特征之一,是检验气候模式性能的重要指标。本文基于RSS4.0卫星数据和ERA5.1再分析资料,系统分析了FGOALS-g3模式对气温变化特别是热带对流层放大的模拟能力,并通过新旧版本模式(FGOALS-g3与FGOALS-g2)的比较指出了新版本模式模拟技巧的提升;通过比较FGOALS-g3历史模拟试验与GAMIL3单独大气模式AMIP试验结果,研究了海气耦合过程对模拟结果的影响。结果表明,FGOALS-g3能够合理再现观测中的全球对流层显著增温趋势,但模拟的增温趋势偏强,这与气候系统内部变率以及两代气候系统模式所使用的历史气候外强迫差异有关。其对于观测中热带平均增温廓线以及热带对流层放大的空间分布均表现出良好的模拟性能,模拟的热带对流层放大现象的量值大小存在正偏差,与模拟的对流层低层温度变化偏强有关。FGOALS-g3较FGOALS-g2在性能上有一定提升,主要表现为增加了对于火山气溶胶强迫的响应,并在热带对流层放大的空间分布及平均气温趋势廓线的刻画方面更加合理。由于缺少海气耦合过程,GAMIL3 AMIP试验无法有效体现外强迫变化对于对流层增温趋势的作用,故在长期趋势的模拟上存在结构性偏差,但由于受观测海温驱动其在年际变率方面表现合理。

Moist adiabatic processes in the tropics amplify the surface warming, producing a warming peak at approximately 200 hPa, known as the “ tropical tropospheric amplification”. Tropical tropospheric amplification, as a remarkable feature of climate change, is an important metric in evaluating model performances. In this study, based on RSS4.0 satellite data and ERA5.1 reanalysis data, we systematically assess the ability of the Flexible Global OceanAtmosphere-Land System Version 3(FGOALS-g3) model in simulating temperature change, especially the tropical tropospheric amplification, and reveal improved simulation skills in the latest version, FGOALS-g3, compared with those in the previous version, FGOALS-g2. By comparing the results of the historical simulation of FGOALS-g3 with those of the simulation from its atmospheric component, the Grid-Point Atmospheric Model of LASG-IAP(GAMIL3), the role of air–sea coupling is studied. The results show that FGOALS-g3 can reasonably reproduce the observed significant global tropospheric warming, but with a stronger trend that is related to internal variability of the climate system and the differences in historical external forcing used by the two generations of climate system models. FGOALS-g3 has also appropriately simulated the observed vertical profile of mean tropical warming and spatial distribution of the tropical tropospheric amplification. This model has shown a positive bias in the simulated magnitude of the tropical tropospheric amplification, resulting from a greater temperature change in the lower troposphere. Compared with FGOALS-g2, the improvement in FGOALS-g3 is mainly manifested as an enhanced response to volcanic aerosol forcing, a more reasonable spatial pattern of the amplified tropical troposphere and the vertical profile of the mean temperature trend. The GAMIL3 simulation fails to influence the external forcing changes on the tropospheric warming trend because of a lack of the air–sea coupling, leading to biases in the long-term trend simulation. However, the GAMIL3 simulation reasonably captures interannual variability because it is driven by the observed sea-surface temperature.