阿拉善高原风力侵蚀和堆积作用强烈，风沙活动频繁，是我国沙尘暴的主要源地之一。其中，黑河下游冲积平原和干涸尾闾湖为主要风蚀区，巴丹吉林沙漠、腾格里沙漠和乌兰布和沙漠为主要风沙堆积区。黑河下游与巴丹吉林沙漠间分布有砾质戈壁、灌丛沙堆、泥漠、盐碱地和干涸湖泊等地表类型，构成了戈壁风蚀区到沙漠堆积区重要的过渡带。

本文主要从不同尺度研究了地表类型对风沙活动的影响。首先，对黑河下游与巴丹吉林沙漠过渡带的砾质戈壁、细砾盐碱地、平沙地、泥质盐碱地、沙质盐碱地5种地表的气象和风沙跃移活动进行长期同步观测，观测内容包括风速、风向、温度、湿度、水汽压、跃移数量和跃移动能，分析了不同荒漠地表间气象因子和风沙活动动力特征差异，讨论了温湿度、水汽压、降雨等因素对不同地表跃移活动的影响。针对古居延泽干涸湖床区域的风蚀堆积特征，分别对该区域的沙丘移动、地表跃移强度以及风蚀速率进行了测量和分析。另外，从大尺度角度出发，结合我国北方土地利用分类、气象站点的沙尘暴及大风频率等数据，分析了我国干旱半干旱区沙尘暴易发性的时空变化特征，进一步探讨了不同地表类型对风沙活动的影响机制。主要结论如下：

（1）通过野外观测，揭示了不同荒漠地表风况、温湿度、水汽压等气象要素的差异性。砾质戈壁和平沙地平均风速相对较高，约为其它地表的1.31-1.43倍。受局部地形影响，各观测点风向频率分布并不一致。不同荒漠地表间月平均气温差异较小，日内小时平均温度差异在日落后逐渐显现，沙质盐碱地温度下降最快，而平沙地温度下降速度较慢。日内小时平均相对湿度与气温呈负相关关系，平沙地地表的相对湿度波动幅度最小，沙质盐碱地最大。除沙质盐碱地水汽压较低外，其它4种荒漠地表间在各季节的日内水汽压和月平均水汽压均差异较小。

（2）沙粒跃移数量和动能的同步观测结果反映出不同地表类型风沙活动频率和强度的显著差异。各观测点风速频率整体呈偏态-Weibull分布，而输沙过程中风速频率呈正态分布。5种地表的输沙日数、累积跃移数量、累积跃移动能由高至低顺序均为平沙地＞砾质戈壁＞细砾盐碱地＞沙质盐碱地＞泥质盐碱地。砾质戈壁、细砾盐碱地和平沙地的跃移数量与动能呈对数关系，泥质盐碱地、沙质盐碱地的跃移数量与动能呈线性关系。砾质戈壁、细砾盐碱地、平沙地、泥质盐碱地和沙质盐碱地起沙阈值分别约为10、10.5、7.5、13和10 m s^-1，起沙风主导风分别为N、NNW 、WNW、WNW和NW，受局部地形影响主导风向有所差异。平沙地合成净跃移数量最多，分别是砾质戈壁、细砾盐碱地、沙质盐碱地合成净跃移数量的12、297和679倍。输沙事件主要发生在日间，持续时间为10-955 min不等，事件持续时长与事件累积跃移数量呈线性正相关。平沙地事件数量最多、平均持续时间最长，事件数量约为其它地表的3.1-10.5倍，平均时长是其它地表的1.5-2.6倍。

（3）温湿度以及降雨等是控制各地表风沙跃移活动强度的重要因素。较高的空气温度、较低相对湿度和水汽压等自然条件更有利于风沙输移活动的发生。砾质戈壁、细砾盐碱地、平沙地和泥质盐碱地4种地表跃移活动主要集中在10-30℃，而沙质盐碱地主要集中在0-20℃。细砾盐碱地跃移活动更多集中在相对湿度20-30%区间，而其它地表多集中在10-20%的相对湿度区间。砾质戈壁和平沙地分别有71.9%和67.9%的输沙记录发生在水汽压为0.2-0.8 kPa的区间内，其它3种地表跃移活动主要集中在0-0.6 kPa区间。结合GSMAP小时降雨数据，分析砾质戈壁和平沙地两种地表不同降雨情形下的输沙过程，结果表明降雨对地表跃移存在明显的抑制作用。与干燥条件下输沙强度对比，不同降雨情形导致砾质戈壁地表沙粒跃移数量平均减少78.4-90%，跃移动能平均减少36.4-62.3%，平沙地地表沙粒跃移数量平均减少74.5-86.3%，跃移动能平均减少49.9-64.6%。

（4）结合沙丘移动、地表跃移以及风蚀速率等数据，分析了古居延干涸湖床区域风沙输移动态变化以及风蚀强度特征。古居延泽三角洲干涸湖床区域流动沙丘以新月形沙丘和沙丘链为主，高度约为2.3-10.2 m，平均移动速度为4.4-11.1 m yr^-1，沙丘移动方向与该地区的主导风向一致，介于131.7-143.3°。根据沙丘移动速度和沙丘密度估算，该区域平均输沙通量约为61.3-120.1 t m^-1 yr^-1。选取黑城与天鹅湖附近地表进行风沙跃移和气象观测，结果显示两观测点风沙活动都集中在春季，分别占全年的39.8%和61.4%，主导风向均为WNW和NW。黑城观测点各风速段的单粒跃移动能均高于天鹅湖观测点，约为天鹅湖观测点的1.3-4.5倍，造成这种差异的原因是天鹅湖观测点地表较为松软，而黑城附近地表较为坚硬。风蚀速率测量结果显示，黑城观测点平均风蚀厚度约为天鹅湖的1.78倍，两观测点平均风蚀速率分别为5.74 kg m^-2 yr^-1和3.22 kg m^-2 yr^-1。通过估算，观测期间居延泽干涸湖床区域风蚀量约为3.23-4.30×10⁶ t。

（5）利用102个气象站1971-2007年沙尘暴和大风资料，分析了我国北方干旱半干旱区沙尘暴易发性的空间分布特征。选取耕地、草地、荒漠、戈壁荒漠和盐结皮地表的15个气象站点，分析沙尘暴易发性年际变化，探讨了地表类型对风沙活动的影响机制。在不同地表类型下，沙尘暴频率与大风频率之间均存在正相关关系。根据沙尘暴易发性大小可将5种地表类型分为两类：一是耕地和沙漠，沙尘暴易发性指数分别为0.64和0.53，约为其它3种地表的2.6-10倍，在强风条件下极易产生沙尘暴；二是戈壁沙漠、草地和盐壳地表，平均沙尘暴易发性指数为0.06-0.20，在强风条件下沙尘暴发生的概率较低。新疆塔克拉玛干沙漠周边地区沙尘暴频率明显大于大风频率，即使在正常的侵蚀性风条件下也很容易发生沙尘暴。沙尘暴频率的空间分布与大风频率的空间分布并不完全一致。大风频率高的地区主要分布在青藏高原北部和内蒙古高原中部，而沙尘暴频率高的地区主要集中在沙漠沙地和干旱区绿洲（以灌溉农业为主）附近。近40年来，不同地表易发性总体呈上升趋势，这可能与当地人类活动和气候变暖有关。

The Alxa plateau is one of the main sources of dust storm in China because of its strong wind erosion and accumulation, and frequent blown sand transport. The alluvial plain and dry terminal lake of Heihe river in Alxa plateau are mainly wind erosion areas, while Badain Jaran desert, Tengri desert and Ulanbuh desert are mainly aeolian sand accumulation areas. Gravel gobi, shrub, mud desert, playa are the main land surface types which constitute an important transition zone from Gobi wind erosion area to desert accumulation area.

In this paper, the influence of land surface types on aeolian sand activities was investigated from two aspects. Firstly, year-long in situ aeolian process observation on the surfaces of gravel gobi, fine gravel saline alkali land, sand sheet, argillaceous saline alkali land, and sandy saline alkali land in the transition zone between the lower reaches of Heihe river and Badain Jaran desert was conducted. The observation items include wind speed and direction, temperature, relative humidity, water vapor pressure, aeolian sand particle count and kinetic energy near land surface. Land surface characteristics, meteorological factors, and sand acivities among different surfaces were analyzed, the intensity of aeolian sand transport events, and the refraining effect of rainfall on saltation over gravel gobi and sand sheet surfaces were discussed. Secondly, sand and dust storm and strong wind frequency on different land surface types were analyzed to reveal the spatial-temporal distribution of sand and dust storm susceptibility in arid and semi-arid areas of north China, and the mechanism of different surface types on large scale sand and dust storm activity was discussed. The main conclusions are as follows:

 (1) The differences of meteorological elements such as wind speed and direction, temperature, relative humidity and water vapor pressure were shown among the five surface types according to observation in situ. The daily average wind speed and monthly average wind speed of gravel gobi and sand sheet were were relatively higher about 1.31-1.43 times of other surfaces. Distribution of wind direction frequency at all observation sites were not consistent due to the influence of local topography. Little difference of monthly mean air temperature among various observation sites but the difference of hourly mean air temperature gradually appeared after sunset. The temperature over sandy saline alkali land fell the fastest, while that in sand sheet fell the slowest. The relative humidity was negatively correlated with air temperature, the fluctuation range of relative humidity within day was the smallest over sand sheet and largest over sandy saline alkali land.

 (2) Simultaneous observation results of sand saltation count and kinetic energy reflect the significant differences in the frequency and intensity of aeolian sand activities over different land surfaces. Distribution of wind speed frequency at each observation site was skewed Weibull distribution, while the wind speed frequency during aeolian transport was approximately normal distribution. Sand transport days, cumulative saltation number and kinetic energy are in the same descending order on five land surfaces, which can be ranked by sand sheet, gravel gobi, fine gravel saline alkali land, sandy saline alkali land, argillaceous saline alkali land. Logarithmic relationship was shown between saltation count and kinetic energy over gravel gobi, fine gravel saline alkali land and sand sheet, while linear relationship can be described on sandy saline alkali land and argillaceous saline alkali land. Aeolian threshold on gravel gobi, fine gravel saline alkali land, sand sheet, argillaceous saline alkali land and sandy saline alkali land were about 10, 10.5, 7.5, 13 and 10 m s^-1 respectively, and the prevailing direction of blown sand wind were N, NNW, WNW, WNW and NW respectively. The amount of synthetic sand saltation (sum of vector calculation) on sand sheet was the largest, which was 12, 297 and 679 times higher than that on gravel gobi, fine gravel saline alkali land and sandy saline alkali land respectively. Sand transport events mainly occurred during day time, with duration ranged from 10 to 955 min. A linear positive correlation was shown between the duration of event and cumulative saltation count. The number of sand transport events was the largest and the average duration was the longest on sand sheet, which was about 3.1-10.5 and 1.5-2.6 times of other surfaces.

(3)  Air temperature, relative humidity and rainfall are important factors to control the intensity of surface sand saltation. Natural conditions such as higher temperature, lower relative humidity and water vapor pressure are more conducive to the occurrence of aeolian sand transport. Aeolian transport activities on gravel gobi, fine gravel saline alkali land, flat sand land and argillaceous saline alkali land were mainly concentrated at from 10 to 30℃, while that of sandy saline alkali land was concentrated at 0-20℃. Aeolian transport activities on fine gravel saline alkali land was more concentrated in the relative humidity range of 20-30%, while other surfaces are mostly concentrated in the relative humidity range of 10-20%. 71.9% and 67.9% of sediment transport records on gravel gobi and sand sheet occurred in the range of water vapor pressure of 0.2-0.8 kPa, and the records of other three surfaces are mainly concentrated in the range of 0-0.6 kPa. Combined with the hourly rainfall data of GSMAP, sand transport process at gravel gobi and sand sheet site under different rainfall conditions were analyzed. The results show an obvious refraining effect on surface saltation by rainfall. Compared with sand transport intensity under dry conditions, different rainfall conditions lead to an average reduction of 78.4-90% in saltation count and 36.4-62.3% in kinetic energy on gravel gobi land, while 74.5-86.3% saltation count and 49.9-64.6% in kinetic energy over sand sheet surface.

(4) Combined with the data of dune movement, surface saltation and wind erosion rate, the dynamic changes of blown sand transport and wind erosion intensity ancient Juyan lake bed area are analyzed. The mobile dunes on the dry lake bed area are mainly barchan dunes and dune chains, with a height range from 2.3 to10.2 m and an average moving speed of 4.4-11.1 m yr^-1. The moving direction of dunes is consistent with the dominant wind direction in this area, ranging from 131.7-143.3°. According to sand dune movement speed and sand density, average sediment flux in this area was estimated about 61.3-120.1 t m^-1 yr^-1. Two sites near Heicheng and Swan lake were selected for sand saltation and meteorological observation. Results show that blown sand activities at the two observation sites were concentrated in spring, accounting for 39.8% and 61.4% during sampling period, and the dominant wind directions are WNW and NW. The single saltation energy of each wind speed class at Heicheng site was about 1.3-4.5 times higher than that of Swan lake observation site, due to the surface of Swan lake site is relatively soft, while the surface near Heicheng is relatively hard.Wind erosion thickness at Heicheng site was about 1.78 times that of Swan lake site during sampling period, and average wind erosion rates were 5.74 kg m^-2 yr^-1 and 3.22 kg m^-2 yr^-1 respectively. Wind erosion flux in ancient Juyanze dry lake bed area during the observation period was estimated about 3.23-4.30×10⁶ t。

(5) In this paper, an aerodynamic parameter, defined as the ratio between dust storm frequency (DSF) and strong wind frequency (SWF), was calculated for quantifying dust storm susceptibility (DSS). The characteristic value and temporal change of DSS in five typical land surface areas, including cultivated land, grassland, sand desert, gobi desert, and salt crust, were analyzed with dust storms and strong wind records at 15 weather stations. The spatial distribution of DSS in the arid and semiarid regions of northern China was described using dust storms and strong wind records at 102 meteorological stations. There are positive correlations between SWF and DSF for any identical land surface type. Land surface conditions have a great influence on dust storm susceptibility. According to DSS value, the five land surface types can be divided into two categories: Cultivated land and sand desert, with DSS between 0.64 and 0.53, about 2.6–10 times higher than that of the other three land surfaces, are prone to forming dust storm under strong wind conditions; gobi desert, grassland and salt crust, with average DSS from 0.06 to 0.2, exhibit lower probability of dust storm occurrence under strong wind conditions. The DSF in the surrounding areas of the arid Taklimakan desert in Xinjiang are much larger than SWF, and dust storms take place readily even at normal erosive wind conditions. The areas with high DSF are not spatially consistent with SWF distribution but more coincide with high DSS areas where sand deserts and farmland are concentrated. In the nearly four past decades, the DSS showed an overall increasing trend on different ground surfaces which may be related to local human activities and climatic warming.