人为气溶胶的直接辐射效应及其对南亚冬季风的影响

运用区域气候模式RegCM4.0(Regional Climate Model Verson 4.0)耦合入一个化学过程,对硫酸盐、黑碳、有机碳这3种人为气溶胶的时空分布特征和直接辐射效应进行了数值模拟,进而研究了气溶胶对南亚冬季风的影响。结果表明:光学厚度和地表短波辐射强迫的时空变化可能主要受硫酸盐气溶胶的影响。在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,大气层顶和地表的负短波辐射强迫分布与气溶胶分布基本一致,地表辐射强迫强度绝对值比大气层顶辐射强迫强度绝对值大得多。相关分析和合成分析表明:在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,南亚人为气溶胶主要分布区中的气溶胶柱浓度含量与南亚冬季风的建立和强度有反相关关系。这与气溶胶吸收太阳辐射,从而引起气温和位势高度的变化有关。

冬季热带印度洋上层流场异常模态分析

利用复经验正交函数(CEOF)分解对冬季热带印度洋海洋上层流场异常做了模态分析和结果讨论,得到以下主要结果:该流场异常前两个模态均呈现赤道俘获波形式,其异常在赤道上最大,向南北两侧迅速衰减,呈现纬向流的形态;第一、二模态的性质分别是大洋赤道波动的半波和1波形态,这表明此时赤道波动异常在大洋流场异常中占有重要地位。冬季第一模态大洋垂直运动所导致的近表层海温异常与春、秋季不同,此时在赤道印度洋呈现正—负—正的经向分布态势,这与印度洋耦极子(Indian Ocean Dipole,IOD)的不同,并是IOD在冬季衰亡的直接原因。第二模态相应的海温异常则在赤道东印度洋呈现北负南正的分布态势。第一模态与南亚冬季风异常密切有关,为印度洋冬季风环流模态。第一、二模态都有明显的年际变化和年代际变化,年际变化均为3~5年,主要的年代际变化则分别为约18、22年,此外两者还均有约13年的年代际变化。本文第一、二模态年代际变化的主周期也是冬季北太平洋和冬季热带太平洋流场异常第二、一模态的主周期。

氧同位素第6期北印度洋的一次重大古海洋学事件

北印度洋赤道海岭的远洋沉积记录在氧同位素第 6期的早期 ,即 16 7～ 16 0ka期间 ,揭示出一次重大的古海洋学事件 .在多项代用指标中 ,浮游有孔虫组合和通量的变化对该事件的反映最为强烈 ,因此将其命名为“第 6期海洋生态环境严重恶化事件” .该事件以广适性种Globigerinitaglutinata的高度发育、凉水种Neogloboquadrinapachyderma和Globigerinabulloides的异常增多、其他有孔虫常见种的普遍减少及有孔虫总量的大幅度降低为特征 .结合其他代用指标和邻区资料 ,认为导致事件发生的主控因素在于超强的南亚冬季风及其所引发的表层水温降低和贫瘠的深层水团上涌 .一般情况下 ,南亚冬季风对研究区环境的影响力远较夏季风弱 ,它的阶段性超常强化似乎总与青藏高原的强烈隆升有关 .可推测 ,发生在第 6期的生境恶化事件很可能是最近一次高原大规模构造抬升的产物 .

AN ANALYSIS OF THE WINTER EXTREME PRECIPITATION EVENTS ON THE BACKGROUND OF CLIMATE WARMING IN SOUTHERN CHINA

Based on daily precipitation and monthly temperature data in southern China, the winter extreme precipitation changes in southern China have been investigated by using the Mann-Kendall test and the return values of Generalized Pareto Distribution. The results show that a winter climate catastrophe in southern China occurred around i99I, and the intensity of winter extreme precipitation was strengthened after climate wanning. The anomalous circulation characteristics before and after the climate wanning was further analyzed by using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data. It is found that the tropical winter monsoon over East Asia is negatively correlated with the precipitation in southeastern China. After climate warming the meridionality of the circulations in middle and high latitudes increases, which is favorable for the southward movement of the cold air from the north. In addition, the increase of the temperature over southern China may lead to the decrease of the differential heating between the continent and the ocean. Consequently, the tropical winter monsoon over East Asia is weakened, which is favorable for the transport of the warm and humid air to southeastem China and the formation of the anomalous convergence of the moisture flux, resulting in large precipitation over southeastern China. As a result, the interaction between the anomalous circulations in the middle and high latitudes and lower latitudes after the climate warming plays a major role in the increase of the winter precipitation intensity over southeastem China.