Lee-face Airflow,Depositional Types and Its Significance
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摘要: 在腾格里沙漠东南缘对现代沙丘表面气流、沉积过程的野外观测结果表明,由于区域气流、沙丘形态及其相互作用等的不同使沙丘背风坡气流发生变化,在此发现三种背风坡次生气流 :分离流、附体未偏向流和附体偏向流。前者以弱的反向流为特征多发生在横向气流条件下坡度较陡的背风坡;后二者具有相对高的风速,其中附体流多发生在坡度缓和的背风坡,其方向在横向气流条件下保持原来的方向,而在斜向气流作用下发生偏转且其强度为原始风入射角的余弦函数。根据背风坡气流方向及强度,作者阐述了不同区域气流环境中沙丘背风坡沉积过程、层理类型及特征,探讨了交错层产状与区域气流方向之间的关系.Abstract: Field measurement of surface airflow,sand transport and sedimentary processes on the modern dunes(harchan dune) the main ridges and secondary ridges of networks dune)was conducted in southeastern Tengger Desert to refine aeolian cross-strata as an indicator of paleaowind direction. It has been found that the velocity and direction of lee-side secondary airflow varied with dune morphology and primary wind direction and their interactions.Three types of lee-side secondary flow occurred in this example separated flow, attached flow, and deflected flow. These flow is controlled at least two factors, lee-slop morphology and primary wind direction relative to dune crestline.Separated flow, characterized by lower wind velocity typically occurred on the dunes with steeper(>20°)lee-slop in the conditions where primary wind direction is perpendicular to dune crestline.Attached flow with higher velocity occurred on the gentle lee slop(<20°).The attacked flow could he deflected in the oblique primary wind environment but not deflected in transverse flow conditions.The direction of the lcc-side deflected flow is in accordance with the direction of crcstlinc of dunes regardless of the incident angle values of oblique wind.Further analysis has also found that the magnitude of lcc-side secondary wind velocity is the cosine function of primary wind direction relative to dunes which can he expressed by natural log cosine relationship: U1=Uc{K*ln(cos(i)〕+A}.0
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Key words:
- lee-face airflow /
- sedimentary processes /
- aeolian cross-strata /
- paleaowind direction
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