Strengthened African Summer Monsoon in the Mid-Piacenzian

Using model results from the first phase of the Pliocene Model Intercomparison Project （PlioMIP） and four experiments with CAM4, the intensified African summer monsoon （ASM） in the mid-Piacenzian and corresponding mechanisms are analyzed. The results from PlioMIP show that the ASM intensified and summer precipitation increased in North Africa during the mid-Piacenzian, which can be explained by the increased net energy in the atmospheric column above North Africa. Further experiments with CAM4 indicated that the combined changes in the mid-Piacenzian of atmospheric CO2 concentration and SST, as well as the vegetation change, could have substantially increased the net energy in the atmospheric column over North Africa and further intensified the ASM. The experiments also demonstrated that topography change had a weak effect. Overall, the combined changes of atmospheric CO2 concentration and SST were the most important factor that brought about the intensified ASM in the mid-Piacenzian.

Non-uniform spatial difference in the South Asian summer monsoon during the mid-Piacenzian

利用CAM4模拟研究了上新世暖期(3.264–3.025 Ma)相对工业革命前南亚夏季风的差异。模拟结果显示,上新世暖期相对工业革命前,南亚夏季风表现出不均一的空间差异。在~20°N以北,上新世暖期南亚夏季降水更多且西南风更强,而在~20°N以南降水减少并伴有异常的东风。这些差异与两个时期边界条件改变所引起的海表面气压的差异有关。进一步分析发现,两个时期大气CO_2含量和海表温度的差异是导致南亚夏季风差异的主要原因。通过对比发现,模拟得到的上新世暖期印度半岛北部的湿润气候与地质证据定性一致。

Potential impacts of enhanced tropical cyclone activity on the El Ni?o–Southern Oscillation and East Asian monsoon in the mid-Piacenzian warm period

热带气旋不仅是一种严重的灾害性天气事件,其在气候时间尺度也可通过加强海洋上层垂直混合进而调节全球海洋经向热量输送。基于一个海气耦合模式,本文探讨了强热带气旋活动对皮亚琴察暖期(又称晚上新世暖期;约300万年前)ENSO和东亚季风环流的可能影响。模拟结果表明,热带气旋引起的海洋垂直混合加强可造成热带东太平洋显著增温、温跃层加深,但ENSO年际变率减弱。对东亚季风而言,夏季副热带高压南移且西伸,副热带急流减弱并南移,我国南方西南风加强;冬季东亚大槽加深,副热带急流南移,我国北方偏北风加强。上述模拟结果可增进我们对热带气旋气候反馈作用以及晚上新世暖期全球气候特征的认识。