上新世暖期和未来增暖背景下亚非夏季风降水变化的模拟对比研究

CONTRASTING THE PLIOCENE AND FUTURE CHANGES OF AFRO⁃ASIAN MONSOON RAINFALL

亚非夏季风降水对当地农业、水资源管理、粮食安全以及生态系统等均有广泛影响,其对全球变暖的响应特征是一个重要的科学问题。本研究基于上新世模式比较计划(PlioMIP2)的15个上新世暖期模式模拟数据和第六次国际耦合模式比较计划(CMIP6)的31个高排放情景SSP5-8.5模式模拟数据,对比分析了上新世暖期和未来增暖背景下亚非夏季风降水变化特征的差异及其成因机制。结果表明:在这两类气候增暖背景下,亚非夏季风降水都呈增加的趋势,然而对应于全球平均1℃升温,季风降水在上新世暖期的强度增幅(0.24 mm/day/℃)明显大于其在未来增暖情景的强度增幅(0.17 mm/day/℃),前者降水异常值约为后者的1.4倍。这种差异主要源于,对应于全球平均1℃升温,上新世暖期中高纬增温幅度显著强于未来增暖情景,而低纬度较小。上新世暖期低纬和北半球中高纬度之间的经向温度梯度减弱幅度更大,有利于亚非夏季风环流显著增强,从而导致亚非夏季风降水强度显著强于未来增暖时期。本研究表明,气候增暖背景下低纬与中高纬度之间的经向温度梯度变化对亚非夏季风具有显著影响,准确衡量暖期南-北半球间经向温度梯度的变化对预估区域季风和水循环变化至关重要。

The change in the Afro⁃Asian summer monsoon(AfroASM)rainfall has a wide impact on local agriculture,water resource management,food security and ecosystems,and its response to global warming is an important socio⁃economic topic.Based on the 15 Pliocene simulations from the Pliocene Model Intercomparison Project Phase 2(PlioMIP2)and the 31 shared socio⁃economic pathway(SSP)5⁃8.5 experiments from the Coupled Model Intercomparison Project phase 6(CMIP6),the present study contrasts the AfroASM rainfall changes and its potential mechanisms between the Pliocene and future global warming climate.The results show that the AfroASM rainfall is increased in both two warm climates,but the intensity of monsoonal rainfall is quite different.The multi⁃model ensemble(MME)mean increase of AfroASM rainfall in the past warm climate is about 1.4 times larger than that in the future warming climate for the same increase of global mean surface temperature(the regional rainfall increase in the MME mean:about 0.24 mm/day/℃in the Pliocene versus about 0.17 mm/day/℃in the SSP5⁃8.5 future projections).Such a striking discrepancy in the AfroASM rainfall intensity is mainly attributed to a dramatically stronger warming over the mid⁃high latitudes during the Pliocene relative to the future warming scenario.The more significant northern mid⁃high latitudes warming during the Pliocene decrease the meridional temperature gradient between the tropics and northern mid⁃high latitudes,which could result in a strengthened monsoonal circulation,inducing increased rainfall.Our results highlight that the meridional temperature gradient changes between mid⁃high latitudes and tropics has a significant influence on the AfroASM circulation/rainfall under warmer climates.And it is important to accurately measure the meridional temperature gradient changes to predict the regional monsoon and water cycle changes under a warmer climate.