副热带急流向极地移动及其对中国北方气候的影响

The topical belt is widening in warming climate because of the poleward expansion of hadley circulation and poleward shift of subtropical jets, resulting in a poledward expansion of subtropical dry zone. This expansion has important implications to regional climate anomalies, increased weather and climate extreme events, and a greater potential for midlatitude droughts. Following our pioneering research in this area, we propose to further study the poleward shift of subtropical jets and its impact on the climate change in northern China. We will fist reconcile the trend differences from various observational analyses by examining the extent to which these differences are related to the data quality for trend analyses versus details of tropical width definitions using various physical variable as well as the relationship among them so that we can quantify the magnitude of the tropical expansion and poleward shifts of subtropical jets. We will then examine and document the subtropical jet positions in East Asia in terms of their interannual variability and long-term trends as well as their seasonal dependences. We will explore the relation between subtropical jet position and weather system and examine the impact of the poleward shift of subtropical jets on the breakout and development of dust storm, droughts, and cold waves in northern China, and examine the underline mechanisms. These studies will lead to a new scientific basis for improving our understanding of the relationships among the above-mentioned important scientific issues as well as the mechanisms.

针对全球气候变暖背景下，Hadley环流向两极扩展，副热带急流向两极移动，使得热带地区快速变宽，导致亚热带干旱区域也向两极扩展，由此引起了相关地区气候异常、极端天气气候事件增加、干旱荒漠化加剧等一系列重大问题，在我们已有开创性研究工作的基础上，进一步研究副热带急流向极地移动及其对中国北方气候的影响。首先仔细对比各种用于分析趋势变化的资料的质量，检验各种不同的物理量对热带宽度的定义及其之间的内在关系，研究揭示各种资料计算的副热带急流移动幅度不一致的原因，进而更合理地确定热带展宽幅度和副热带急流移动幅度。其次，探析东亚副热带急流位置移动幅度、年际及年代际变化特征、长期变化趋势及其对季节的依赖性。最后，探明副热带急流向北极移动及其与其它天气系统相互作用对我国北方沙尘暴、干旱和寒潮发生、发展的影响及其机理。以期为深化对上述一系列重大问题之间关联性和影响机制的认识提供新的科学依据。

本项目经过4年的执行，在项目组成员共同努力下，共发表论文21篇，其中SCI/EI论文14篇。我们详细分析了副热带急流北移对我国西北地区干旱和寒潮的影响，研究了东亚副热带西风急流的变化特征及其与中国沙尘天气的关系；率先在国际上利用陆地干燥度的变化描述干旱化过程；揭示了陆地干燥度对气溶胶和温室气体辐射强迫的响应机制，开展了过去千年到未来百年陆地干燥度的数值模拟；明确了将潜在蒸散引入水文循环气候和气候变化领域的重要性；开展了塔克拉玛干地区夜间低空急流的研究工作，揭示了低空急流是影响塔克拉玛干沙漠夏季起沙的一种重要机制。