排序方式： 共有44条查询结果，搜索用时 647 毫秒
21.
22.
Although many studies relevant to snow cover and permafrost have focused on alpine, arctic, and subarctic areas, there is still a lack of understanding of the influences of seasonal snow cover on the thermal regime of the soils in permafrost regions in the mid-latitudes and boreal regions, such as that on the western flank of the Da Xing'anling(Hinggan) Mountains, northeastern China. This paper gives a detailed analysis on meteorological data series from 2001 to 2010 provided by the Gen'he Weather Station, which is located in a talik of discontinuous permafrost zone and with sparse meadow on the observation field. It is inferred that snow cover is important for the ground thermal regime in the middle Da Xing'anling Mountains. Snow cover of 10-cm in thickness and five to six months in duration(generally November to next March) can reduce the heat loss from the ground to the atmosphere by 28%, and by 71% if the snow depth increases to 36 cm. Moreover, the occurrence of snow cover resulted in mean annual ground surface temperatures 4.7–8.2 °C higher than the mean annual air temperatures recorded at the Gen'he Weather Station. The beginning date for stable snow cover establishment(SE date) and the initial snow depth(SDi) also had a great influences on the ground freezing process. Heavy snowfall before ground surface freeze-up could postpone and retard the freezing process in Gen'he. As a result, the duration of ground freezing was shortened by at least 20 days and the maximum depth of frost penetration was as much as 90 cm shallower. 相似文献
23.
The impacts of four teleconnection patterns on atmospheric circulation components over Eurasia and the Pacific region, from low to high latitudes in the Northern Hemisphere (NH), were investigated comprehensively in this study. The patterns, as identified by the Climate Prediction Center (USA), were the East Atlantic (EA), East Atlantic/Western Russia (EAWR), Polar/Eurasia (POLEUR), and Scandinavian (SCAND) teleconnections. Results indicate that the EA pattern is closely related to the intensity of the subtropical high over different sectors of the NH in all seasons, especially boreal winter. The wave train associated with this pattern serves as an atmospheric bridge that transfers Atlantic influence into the low-latitude region of the Pacific. In addition, the amplitudes of the EAWR, SCAND, and POLEUR patterns were found to have considerable control on the “Vangengeim–Girs” circulation that forms over the Atlantic–Eurasian region in winter or spring. The EA and EAWR mainly affect the westerlies in winter and spring and the POLEUR and SCAND, respectively, in summer and winter. Strong westerlies confine the extension of the North Polar vortex, which generally results in a small weak vortex and a shallow East Asian trough located in a position further east than normal. Furthermore, the North Polar vortex presents significant connections with the patterns during winter and summer. Analyses in this work suggest that the teleconnection patterns in summer could be driven, at least partly, by the Atlantic Multidecadal Oscillation, which to some degree might transmit the influence of the Atlantic Ocean to Eurasia and the Pacific region. 相似文献
24.
兰州1960—2003年大气气溶胶光学厚度和太阳辐射变化特征 总被引：5，自引：4，他引：1
利用兰州站1960—2003年的太阳辐射资料以及据此反演的气溶胶光学厚度数据,分析了近44 a来兰州气溶胶光学厚度（AOD）、地面能见度和太阳辐射的变化特征。结果表明,20世纪70年代初气溶胶光学厚度增加很快;70年代中期至80年代中期,光学厚度处于较高水平,平均为0.568;90年代以来,光学厚度有波动下降趋势,年下降0.006,且季节间差异有减小趋势。能见度夏季最好,冬季最差;80、90年代能见度有明显变好趋势,年增长为0.340 km;2000年以来又有下降趋势。总辐射和直接辐射的变化可以分为两个时期,1992年之前为下降期,1992年以来有显著上升趋势。 相似文献
25.
内蒙古雨养农业区土壤水分动态监测模式 总被引：3，自引：0，他引：3
文章根据多年实际观测资料,在土壤水分平衡参数模拟方法的基础上,利用初始土壤有效水分贮存量、降水量和实际蒸散量3要素,建立了0～50 cm土层的土壤水分动态监测模式,确定了各项参数的计算方法。通过11个站点两年的检验和试用,对主要农作物春小麦和春玉米农田的水分状况监测准确率达80%以上。同时,对两个站点的土壤水分进行了预报,准确率平均为92%。 相似文献
26.
Landsat 8地表温度反演及验证—以黑河流域为例 总被引：1，自引：0，他引：1
地表温度是区域和全球尺度地表物理过程的一个重要参数,目前已有的地表温度产品空间分辨率较低,缺乏高空间分辨率的地表温度产品。Landsat系列卫星提供了大量免费的高空间分辨率遥感数据,然而对应的高空间分辨率地表温度产品还未见到,为了获取长时间序列的高空间分辨率地表温度数据,针对Landsat 8 TIRS数据提出了一个物理单通道地表温度反演算法。该算法首先利用ASTER全球地表发射率产品(ASTER GED)结合Landsat 8地表反射率产品计算Landsat 8影像的地表发射率,然后利用快速辐射传输模型RTTOV结合MERRA大气廓线数据对热红外影像进行大气校正,最后利用物理单通道地表温度反演算法得到地表温度。利用黑河流域HiWATER试验2013年—2015年15个站点的实测地表温度数据对本文方法和普适性单通道算法进行了验证,同时对验证站点的空间异质性进行了分析。结果表明,本文方法和普适性单通道算法估算的地表温度整体精度均较高,能够获取高精度、高空间分辨率的地表温度数据,可以服务于城市热岛效应、地表蒸散发估算等相关研究。 相似文献
27.
Pramod Singh 《Chemical Geology》2010,269(3-4):220-236
Major, trace and REE compositions of sediments from the upper Ganga River and its tributaries in the Himalaya have been examined to study the weathering in the Himalayan catchment region and to determine the dominant source rocks to the sediments in the Plains. The Ganga River rises in the Higher Himalaya from the Higher Himalayan Crystalline Series (HHCS) bedrocks and traverses over the Lesser Himalayan Series (LHS) and the Himalayan foreland basin (Siwaliks) rocks before entering into the Gangetic Plains. The major element compositions of sediments, reflected in their low CIA values (45.0–54.7), indicate that silicate weathering has not been an important process in the Himalayan catchment region of the Ganga River. Along the entire traverse, from the HHCS through LHS and the Siwaliks, the sediments from the tributaries and the mainstream Ganga River show higher Na2O, K2O, CaO and silica. This, and the higher ratios of La/Sc, Th/Sc and lower ratios of Co/Th, suggest that the source rocks are felsic. The fractionated REE patterns and the significant negative Eu anomalies (Eu/Eu? = 0.27–0.53) indicate highly differentiated source. Moreover, the comparison of the sediments with different source rock lithologies from the HHCS and the LHS for their major elements clearly suggests that the HHCS rocks were the dominant source. Further, comparison of their UCC (upper continental crust) normalized REE patterns suggests that, among the various HHCS rocks, the metasediments (para-gneiss and schist) and Cambro-Ordovician granites have formed the major source rocks. The Bhagirathi and Alaknanda River sediments are dominantly derived from metasediments and those in the Mandakini River from Cambro-Ordovician granites. The resulting composition of the sediments of the Ganga River is due to the mixing of sediments supplied by these tributaries after their confluence at Devprayag. No further change in major, trace and rare earth element compositions of the sediments of the Ganga River after Devprayag up to its exit point to the Plains at Haridwar, suggests little contribution of the Lesser Himalayan and Siwalik rocks to the Ganga River sediments. 相似文献
28.
对1989年7月20—21日内蒙古中西部的大暴雨,进行了诊断分析和数值试验。分析表明,南亚高压东北移在该地区对流层上部形成强辐散流场;西来短波槽诱发切变线北抬,使暖湿空气与干冷空气在该区上空交绥,扰动不稳定发展;暴雨落区与辐合线关系密切。数值试验表明,地形的动力作用和热力作用,是产生地面辐合的主要原因之一。 相似文献
29.
本文以ERA5（ECMWF Reanalysis v5）再分析资料为初始场,利用WRF（The Weather Research and Forecasting）模式对2020年4月19～20日的一次大范围暴雪天气过程进行数值模拟研究。模式采用不同云微物理参数化方案进行敏感性试验,并与实测数据（自动站降水数据、雷达基数据）进行对比,分析了此次暴雪天气过程不同阶段的降水、雷达反射率、动热力和水凝物的时空演变和三维细致结构特征。研究表明:Morrison方案更好的模拟出了本次暴雪天气过程,表现在模拟的雷达回波强度、范围及形态更与实况一致,模拟出的降水量的相关系数和均方根误差都优于其他方案;其微物理细致结构表现为强上升运动和低层正涡度的长时间维持,以及7 km以上高层较多的冰晶、中低层较少的霰粒子和雨水粒子。从热动力场上看,bin（SBM fast）方案在600 hPa高度以下存在明显的涡度波列,这主要是因为bin方案将粒子群分档处理,没有捆绑不同粒子类型运动,更能细致描述出不同粒子的下沉拖曳作用。从云微物理特征上看,不同方案模拟的雪、霰、云水以及雨水粒子的比质量都较为接近,而对冰晶比质量的模拟不管在量级还是在分布范围上都存在很大的差异,这种差异决定了不同微物理方案模拟的雷达回波和降水量级和相态的差异。 相似文献
30.
两种常用的春玉米干旱等级指标在东北区域的适用性检验 总被引：7，自引：2，他引：5
作物干旱等级农业气象指标是开展作物干旱监测、预警和评估的科学依据,其适用性关系到农业气象业务质量和防灾减灾效果。应用东北地区31个春玉米代表站1981 2012年逐日气象资料、土壤湿度资料、玉米生长发育观测资料及产量资料,对东北地区春玉米不同生育阶段土壤相对湿度和水分亏缺指数干旱等级指标进行应用效果检验,比较适用性差异,并利用黑龙江省2013—2016年的资料进行干旱实例分析。结果表明,土壤湿度和水分亏缺指数干旱等级指标均适用于东北区域春玉米不同生长时段干旱识别,且有较好的一致性,两套指标判定的春玉米干旱等级完全相同的占75%左右,相同和基本相同的占95%左右。两套指标对历史和近年玉米干旱事件的判识效果都较好,土壤湿度指标和水分亏缺指数的干旱识别正确率分别在80%和75%以上,土壤湿度指标判定效果更好。两套指标在玉米生育前、中期适宜性略好于后期,在东北三省的应用效果要略好于内蒙古东部,部分干旱年份水分亏缺指数判定的灾情等级偏高,因此,当两套指标判定结果存在差异时,应以土壤相对湿度指标判定结果为准。 相似文献