巴丹吉林沙漠高大沙山形态特征及其演化过程的数字模拟研究

The processes of formation and development of the giant dunes (megadunes) are quite complex. The morphological features (angles and secondary dunes of stoss and lee sides; length, shape and strike of the dune crests, etc.) of mega-dunes are not only the result of the long-term effects of complex wind regimes, but also strongly impacted by various other parameters. Earlier studies suggested that mega-dunes was potentially formed by wind regimes, climate changes, underlying reliefs and/or availability of groundwater. However, an unambiguous interpretation of the formation and development of the mega-dunes' morphological features is still not available. The research target of this project will be the morphological natures of the magadunes in the Badain Jaran Desert, western Inner Mongolia. Numerical simulation will be applied as the main research method, supported by the analysis of meteorological data, remote sensing data, topographic surveying in the field and sedimentological analysis of sand samples. We plan to focus on the formation processes and development of the mega-dunes' morphological features under the impact of the complex wind regimes and underlying reliefs. This research outcome will be further applied to interpret Quaternary changes of wind regimes and earlier impacts of underlying landforms on the dune stratigraphy. The implementation of the project will not only lead to new understanding and knowledge about the formation and development of the mega-dunes' morphological features, but also provide important evidence for understanding the Quaternary climate changes and paleogeomorphological environment in the Alashan Plateau.

形体巨大的高大沙山的形成、演化过程极为复杂，其形态特征（高大沙山迎风坡、背风坡坡度与次生沙丘类型、沙脊线形状及走向、长度等）不仅是复杂风况长期作用的结果，而且与诸多其它要素密切相关。已有的研究认为风况、气候变化、下伏地形及地下水可能是造成高大沙山形成的主要原因，而有关其形态特征的形成机制及演变规律等仍不清楚。本项目拟以巴丹吉林沙漠高大沙山形态特征为研究对象，以数值模拟为主要研究手段，结合气象资料、遥感数据、野外地形测量和沙样的沉积学分析，深入研究高大沙山形态特征在复杂风况和下伏地形双重因素共同影响下的形成、演变规律，反演巴丹吉林沙漠高大沙山地区的古风况变化及下伏地形特征。该项目的实施，将对高大沙山形态特征形成、演变提出新的观点和认识，为认识阿拉善地区第四纪气候变化历史和古地貌环境提供重要佐证。

位于我国东亚季风系统中夏季风和冬季风相互交替作用区域的巴丹吉林沙漠，具有世界上最高大的沙丘，其特殊地貌景观是在不同的气候背景下，由近地表携沙风与地下水、下腹地形等因素之间经过长时间的相互作用，叠加之后形成的。在国家自然科学基金青年项目的资助下，我们对巴丹吉林沙漠高大沙山的形成发育过程开展了沙丘发育模拟、表沙粒度的空间分布特征等方面的研究工作。沙丘数值模拟示踪了沙粒的移动轨迹，发现了沙粒每次在沙丘背风坡的埋藏深度具有随机性，使得沙颗粒的平均埋藏时间不同于以往计算的更新时间，继而发现新月形沙丘沙平均埋藏时间等于纵向最大剖面面积与其对应单宽输沙率的比值。沙丘表沙粒度的空间分析研究表明，季节性变化的近地表风况作用于沙丘表面的携沙能力也不尽相同，在植被覆盖较好的时期，能够造成表沙粗化的过程，继而加速了沙丘的固化过程。