塔克拉玛干沙漠风蚀起沙观测研究——试验介绍与观测结果初报

介绍了中国气象局乌鲁木齐沙漠气象研究所在塔克拉玛干沙漠开展的风蚀起沙观测试验。对观测试验所获观测资料进行了初步分析,获得了一些有关塔克拉玛干沙漠风沙运动的特征。主要结果为,下垫面状况影响风沙流结构,塔中、若羌0~100 cm高程风沙流结构完全符合指数分布,肖塘则上部偏离指数分布;3地0~100 cm高程风沙流分别有72.4％、47.3%、62.6%的输沙量分布在0~30 cm高程内;3地风沙流输沙的粒径以细沙、极细沙、粉沙为主,其中极细沙可占到输沙量的43.8%~75.5%;风沙流中贴地层风速廓线受风沙相互作用的影响,不再符合对数分布,更加符合幂函数u=azb分布,拟合系数均大于0.93;沙尘撞击颗粒数与2 m高度风速变化趋势一致,塔中、肖塘、若羌3地的临界摩擦速度分别为0.25 m·s-1,0.27 m·s-1,0.21 m·s-1。     

塔里木盆地一次东灌型沙尘暴环流动力结构分析

利用NCEP再分析资料和常规地面观测资料,对2006年4月10日塔里木盆地发生的一次东灌型沙尘暴,从气候背景、环流形势、螺旋度场、锋生次级环流、温度平流等方面进行分析,揭示了此类沙尘暴强盛期的环流动力结构。结果表明：①里咸海脊、乌拉尔脊、新地岛脊同位向叠加,西西伯利亚横槽转竖南下,引导泰米尔半岛强冷空气爆发直插新疆,东灌进入南疆盆地,造成大范围沙尘暴天气;②西西伯利亚地面冷高压爆发性南下并强烈发展是造成此次沙尘天气的根本原因;③盆地前期的干暖形势为沙尘暴的产生提供了有利的热力条件;④沙尘暴区上空螺旋度垂直分布为低层正值、高层负值,构成低空强辐合、高空强辐散的上升运动区,揭示强旋转上升运动是大范围沙尘暴发生的动力条件;⑤高空急流入口区次级环流下沉支导致高层动量下传 ,促使对流层中低层风力加大,冷锋南压,驱动沙尘天气的发生。     

塔中地区土壤风蚀的影响因子分析

以塔中地区为例,利用野外观测数据和通过对比分析,论述了气候、地表粗糙度(包括植被覆盖)以及地表土壤特性等因子对土壤风蚀的影响,并对这些影响因子进行了量化研究。结果表明:塔中地区的年平均风蚀气候因子指数C为28.3,从季节分布上来说,夏季最大为13.9,冬季最小仅为0.7,C值与风速有着密切的指数关系;塔中地区的地表粗糙度Z0平均为6.32×10-5m,地表粗糙度小,加重了该地区的土壤风蚀程度;塔中地区的土壤类型特点、地表土壤平均粒径小、缺乏植被覆盖以及地表土壤含水率低为该地区土壤风蚀的发生提供了良好的条件。塔中地区土壤风蚀的现状是该地区气候、地表粗糙度以及地表土壤特性等因子共同作用的结果。     

气泡混合轻质土试样制备研究

由于气泡消泡的缘故,室内制备和现场浇筑气泡混合轻质土时存在塌陷问题。为分析和解决该问题,以砂土为原料土,开展了不同温差、湿度和掺砂与否条件下3种密度气泡混合轻质土的制备试验,并测定了各试样的高度和强度,基于热力学理论分析了3种因素对试样制备和强度的影响规律。试验结果表明,试样制备时温度与养护温度之间的温差是影响气泡混合轻质土胀缩性的决定性因素,轻质土中的气泡含量越高,受温差影响越大,通过控制温差即可解决塌陷问题;湿度和掺砂与否对气泡混合轻质土的试样制备影响不明显,但是湿度高会延长试样脱模时间以及影响试样的完整性;温差和温度共同影响气泡混合轻质土的早期强度,其中温差主要影响试样密实度,温度主要影响水泥水化反应速率。试验结果可为气泡混合轻质土制备和施工时间点选择提供借鉴。     

Using Landsat images to monitor changes in the snow-covered area of selected glaciers in northern Pakistan

Landsat satellite images were used to map and monitor the snow-covered areas of four glaciers with different aspects(Passu: 36.473°N, 74.766°E;Momhil: 36.394°N, 75.085°E; Trivor: 36.249°N,74.968°E; and Kunyang: 36.083°N, 75.288°E) in the upper Indus basin, northern Pakistan, from 1990-2014. The snow-covered areas of the selected glaciers were identified and classified using supervised and rule-based image analysis techniques in three different seasons. Accuracy assessment of the classified images indicated that the supervised classification technique performed slightly better than the rule-based technique. Snow-covered areas on the selected glaciers were generally reduced during the study period but at different rates. Glaciers reached maximum areal snow coverage in winter and premonsoon seasons and minimum areal snow coverage in monsoon seasons, with the lowest snow-covered area occurring in August and September. The snowcovered area on Passu glacier decreased by 24.50%,3.15% and 11.25% in the pre-monsoon, monsoon and post-monsoon seasons, respectively. Similarly, the other three glaciers showed notable decreases in snow-covered area during the pre-and post-monsoon seasons; however, no clear changes were observed during monsoon seasons. During pre-monsoon seasons, the eastward-facing glacier lost comparatively more snow-covered area than the westward-facing glacier. The average seasonal glacier surface temperature calculated from the Landsat thermal band showed negative correlations of-0.67,-0.89,-0.75 and-0.77 with the average seasonal snowcovered areas of the Passu, Momhil, Trivor and Kunyang glaciers, respectively, during pre-monsoon seasons. Similarly, the air temperature collected from a nearby meteorological station showed an increasing trend, indicating that the snow-covered area reduction in the region was largely due to climate warming.     

塔中涡动资料不同坐标旋转方法比较分析

坐标旋转是涡动协方差(EC)通量观测数据后处理当中必须进行的步骤,本文利用塔克拉玛干沙漠腹地塔中西面标校站自然沙丘上3 m高度和塔中本站32 m高度2009年4—10月湍流通量数据,对比分析了不同坐标旋转方法在塔中通量观测数据中的应用。结果表明,塔克拉玛干沙漠腹地塔中湍流各通量在旋转订正前后差别不显著,不订正造成的通量计算误差1%。塔中32 m和塔中西站3 m通量计算误差,与两个站点的采集仪器架设高度差别较大有关。即使对于相对平坦的下垫面,也必须要进行倾斜校正,以修正地势、仪器振动、安装倾斜等产生的虚假信息。本研究对塔中涡动资料进行旋转时采用了二次坐标旋转方法。此结果为塔克拉玛干沙漠腹地EC通量观测的风速仪倾斜校正提供参考。     

2009年8月－10月塔克拉玛干沙漠北缘地表能量收支特征?

利用塔克拉玛干沙漠北缘肖塘陆气相互作用观测站2009年8-10月探测的资料,对该地区能量收支状况进行了初步分析。结果表明：2009年8-10月的平均能量闭合率为78%,闭合差为22%。夏季白天,感热、潜热、土壤热通量各占净辐射的52%、6%、16%,夜间依次占净辐射的53%、3%、6%。夏季白天、夜间能量不平衡率分别为26%、38%。8月肖塘的总体输送系数CD平均值为4.5×10-3,CH为2.2×10-3。CD、CH季节变化和日变化显著,都是夏季大于秋季,白天大,夜间小。     

Using Portable Gamma-Ray Spectrometry for Testing Uranium Migration: A Case Study from the Wadi El Kareim Alkaline Volcanics, Central Eastern Desert, Egypt

The 300±20 Ma anomalously radioactive trachytes of Wadi El Kareim, central Eastern Desert, are a significant example of U-mineralization related to the alkaline volcanics in Egypt. Extensive portable gamma-ray spectrometric data has been utilized to identify geological factors controlling uranium mobility in the geological units along the three detailed study locations of Kab Al-Abyad, South Wadi (W) Al-Tarafawy and W. Al-Farkhah; their eTh/eU ratios averaging around 4.1, 3.7 and 5.6 respectively. Quantitative analysis with the integration of mobility maps and geological studies suggest two systems controlling U-migration within the geological units (confined system and unconfined system). In the confined system, the syngenetically formed U have experienced mobility after leaching and are redistributed in the presence of an incorporation carrier during transportation (probably as carbonate complexes). Then the retardant for uranium is achieved by sorption or by coprecipitation with the aid of Fe oxy-hydroxide, and finally the formation of immobile secondary U-bearing minerals takes place along a lithogeochemical trap. In contrast to the confined system, the unconfined one is basically lacking the lithogeochemical trap which in?uences the final accumulation of U-bearing minerals. The radioactivity of the trachyte rocks arises from the radioactive minerals uranophane and beta-uranophane with U- and/or Th-bearing minerals samarskite, Th-rich REE silicates, monazite and allanite.     

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers, NW Pakistan

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan. Two grids covering an area of 10x18 m2 and 8x10 m2 were analyzed using a G-858 Cesium Vapor Magnetometer. The anomalous zones obtained were plotted on contour maps, 2D and 3D magnetic intensity maps. Based on the magnetic anomalies, grid-1 of the study area was sampled at three different anomalous zones for geochemical analysis. These zones contain gold concentrations, ranging from 2.11 ppm to 6.109 ppm with an average of 4.01 ppm. Increase in gold concentration in the subsurface within the anomalous zones indicates that magnetometer survey followed by a geochemical analysis can potentially narrow down the gold-bearing anomalous zones.     

新疆东部黑戈壁地表辐射及能量收支演变特征

新疆东部黑戈壁作为气候恶劣、人迹罕至的生态脆弱区，具有丰富的太阳能资源。利用红柳河陆气相互作用观测站2019年4、7、9月观测资料，分析东疆黑戈壁地表辐射及能量收支演变特征。结果表明：（1）地表辐射及能量收支各分量日变化均为单峰型。就不同季节而言，太阳总辐射和净辐射为夏季>春季>秋季，反射短波辐射为春季>夏季>秋季，地表和大气长波辐射为夏季>秋季>春季。（2）能量收支各分量季节变化明显，感热通量为春季>夏季>秋季，潜热通量为夏季>秋季>春季，地表土壤热通量为秋季>夏季>春季；能量分配在不同季节均以感热为主，地表土壤热通量次之，潜热通量极其微弱。（3）地表反照率日变化均为“U”型，在不同季节表现为春季>秋季>夏季，依次为0.29、0.27、0.26。东疆黑戈壁地表反照率整体较高，这是下垫面为黑色砾石所致。