内蒙古东部春季三类沙尘天气气溶胶散射系数及其与PM10、能见度相关性分析   总被引：3，自引：0，他引：3  

王天舒  牛生杰 《大气科学》2017,41(1):121-131

利用内蒙古东胜、锡林浩特两站2004~2006年春季（3~5月）积分浊度计的观测资料,结合同期PM10质量浓度、大气能见度等资料,分析了背景、扬沙、沙尘暴、强沙尘暴等不同强度沙尘天气气溶胶散射系数的分布特征,讨论了不同强度沙尘天气过程中散射系数、PM10、能见度的日变化规律,以及不同强度沙尘天气过程中散射系数与PM10质量浓度、散射系数与能见度的相关关系。结果表明:散射系数能够很好地反映沙尘天气强度;随沙尘天气强度增强,散射系数日变化从双峰型向单峰型转变;沙尘天气强度较弱时,PM10与散射系数的日变化不相似,强沙尘暴过程中PM10与散射系数的日变化有一定的相似性;能见度与散射系数日变化趋势相反;散射系数与PM10质量浓度呈正相关性,沙尘天气越强,相关性越好,背景、扬沙、沙尘暴、强沙尘暴相关系数分别为0.201、0.809、0.898和0.953;散射系数与能见度有指数相关关系,随沙尘天气强度增强二者相关性逐渐增强,背景、扬沙、沙尘暴、强沙尘暴相关系数分别为-0.773、-0.870、-0.918和-0.940。  相似文献   

冬季蒙古反气旋和伊朗反气旋的年代际变化特征     

智协飞  田笑  朱丹  宋斌  侯美夷 《大气科学》2017,41(5):999-1009

根据NCEP/NCAR再分析资料,采用客观判定和追踪方法,研究了1948~2013年欧亚地区冬季温带反气旋的年代际气候变化的活动特征。结果发现,反气旋的高频分布区也是反气旋气候变化最大的区域,其中蒙古高原和伊朗高原的反气旋最活跃。反气旋的频数和强度既有长期趋势也有年代际变化。蒙古高原和伊朗高原的反气旋频数具有明显的年代际变化特征。反气旋频数具有2~6年和16~30年周期,且具有变频特征。EOF分解发现蒙古高原和伊朗高原的反气旋频数分布均在较高纬度和较低纬度地区呈现显著相反的偶子极态分布形式。蒙古高原的反气旋强度的变化基本可以体现欧亚大陆反气旋强度的变化。反气旋分布和强度的年代际变化可以用对流层低层经向温度梯度表示的斜压锋的位置和强度的年代际变化来解释,但斜压锋对欧亚反气旋的影响具有区域性。蒙古高原的反气旋在1960~1975年50°N以北较多,1990~2005年50°N以南较多的偶极子态变化与80°~120°E区域的斜压锋纬度位置自55°N南移到45°N有密切关系,30°~80°E区域的斜压锋纬度位置变化不能单独解释伊朗高原反气旋偶极子态年代际变化。自21世纪00年代中期斜压锋偏强对反气旋强度偏强有重要影响。  相似文献   

GPM双频降水测量雷达对降雪的探测能力分析     

吴琼  仰美霖  窦芳丽 《气象》2017,43(3):348-353

以双频降水测量雷达为主载荷的GPM卫星于2014年2月发射升空。由于轨道倾角以及仪器通道的设置,大大提升了对弱降水和降雪的探测能力。通过四次降雪个例,分析比较了双频降水测量雷达的三种扫描模式(Ku,KaMS和KaHs)对降雪探测能力的差异。结果表明:DPR相态产品和地面实际观测结果比较一致,固态降雪温度-0.5℃并且降雪发生时的风暴顶高度大多6 km。Ku波段雷达由于仪器灵敏度的大幅提高.对降雪的综合探测能力最强,而KaMs和KaHS也具有特定的作用。此外,为了保证衰减订正的精度,和非降雪部分的衰减相比,需要主要提高降雪衰减尤其是混合相态湿雪的衰减订正精度。  相似文献   

An assessment of land cover change as a source of information for conservation planning in the Vhembe Biosphere Reserve     

《Applied geography (Sevenoaks, England)》2017

Determining changes in land use/land cover (LULCC) can be used to assess and monitor habitat loss as one of the five global priority causes of biodiversity loss. In South Africa, two national land-cover (NLC) datasets have been developed from satellite imagery obtained in circa 1990 and 2013/2014. The Vhembe Biosphere Reserve (VBR), designated in 2009, is located in the north of the Limpopo Province in South Africa and has a surface area of 30,457 km². The aim of biosphere reserves is to provide a landscape-scale framework for conservation and sustainable development of an area. The area within a biosphere reserve is prioritised by designating it into one of three zones 1) Core, 2) Buffer, and 3) Transitional Zones. Two national parks and six provincial reserves (PAs) are the current and form part of the proposed updated core areas (pCAs) of the VBR. Intensity analyses was used to assess LULCC in the VBR. The pCAs cover 39.7% of the surface area of the VBR. The PAs cover 39.7% and only 15.8% of the surface area of the pCAs and VBR respectively. Based on the NLC 2013/2014 a majority of the VBR, pCAs and PAs consisted of indigenous vegetation dominated by Woodland/Open bush, Grassland, and Thicket/Dense bush. The extent of transformed land in the VBR declined from 1990 to 2013 by 1697.7 km². The total amount of change and mean annual change in the VBR was 53.1% and 2.31% respectively. The overexploitation of fuel wood by rural communities in rural areas of the VBR, was partly responsible for the targeted loss of Woodland/Open bush to Thicket/Dense bush and Grasslands. The unquantified presence of novel vegetation and alien invasive plants means that the NLC 1990 and 2013/2014 overestimates the quantity and distribution of the remaining indigenous vegetation in the VBR. In order to address this the distribution of alien and indigenous invasive plant species in the VBR needs to be determined and used to update future NLCs. Assuming a worse-case-scenario of all the coal deposits in the VBR, including the Kruger National Park, being mined it would amount to 24.7% of the surface area of the VBR. Only 6.8% of the area of all the coal deposits in the VBR was transformed with 93.2% currently remaining untransformed. It is recommended that transformation of indigenous vegetation to one of the seven transformed land cover categories and more specifically from coal mining should be restricted to the VBR's Transition Zones.  相似文献   

2020年5月17日和6月1日山东强冰雹风暴双极化特征分析          下载免费PDF全文

刁秀广 《山东气象》2021,41(1):68-81

利用济南、青岛和烟台S波段双偏振多普勒天气雷达资料和常规观测资料以及天气实况,对2020年5月17日和6月1日两次强对流天气过程的关键环境物理量和风暴低层强冰雹区偏振量、三体散射、强冰雹衰减等偏振特征等进行了分析。结果表明:1)两次强对流天气都具有大的温差和强垂直风切变,中层较干。5月17日山东半岛0～6 km垂直风切变更强,低层湿度更大,湿球0 ℃层高度较低,是产生多个超级单体风暴并出现特大冰雹的关键物理量。2)5月17日城阳风暴低层强冰雹区具有适中的差分反射率（ZDR）和偏小的相关系数CC及偏大的差分相移率（KDP）。ZDR多在0.30～2.60 dB之间,平均为1.50 dB;CC多在0.900～0.965之间,平均为0.931;KDP多在2.0～6.3(°)·km-1之间,平均为4.1 (°)·km-1。少量融化的冰雹粒子和大的雨滴导致适中的ZDR和偏大的KDP。3)6月1日长清风暴低层强冰雹区具有偏小的ZDR和偏小的CC及大的KDP。ZDR多在-0.12～1.50 dB之间,平均为0.68 dB;CC多在0.925～0.970之间,平均为0.950;KDP多在4.0～7.6 (°)·km-1之间,平均为5.8 (°)·km-1。高浓度的液态雨滴和融化的小冰雹粒子导致大的KDP。4)三体散射、旁瓣回波、衰减及波束非均匀填充(nonuniform beam filling,NBF)等特征可作为冰雹识别判据。衰减特征在ZDR产品上表现较为明显,风暴核后侧较长径向上出现负值区,显著衰减可作为特大冰雹的判据。NBF仅在CC产品上有明显特征,风暴核后侧较长径向上CC明显较小。  相似文献   

澳门人地关系研究   总被引：5，自引：0，他引：5  

胡兆量  李燕茹  阮学金 《地理学报》1999,54(6):481-486

从１６世纪中叶到２０世纪末叶,澳门的城市性质和城市功能发生多次急剧变化。人地关系一些要点在澳门的发展和变化中都有反映。澳门在浙、闽、粤沿海众多的港口中脱颖而出反映自然环境是社会是社会发展必不可少的条件。澳门成为东西方交流的桥梁反映自然环境在人地关系的演变,澳门经济转型艰难反映人文资源在人地关系中的地位呈上升趋势。澳门的城市形象和空间格局有抹不掉的自然印记,反映人地关系的发展是利用自然和利用自然规律  相似文献   

Attenuation behaviour of tuffaceous sandstone and granite during microfracturing   总被引：1，自引：0，他引：1  

Angelika-M. Wulff  Toshiyuki Hashida  Kimio Watanabe  & Hideaki Takahashi 《Geophysical Journal International》1999,139(2):395-409

Laboratory measurements of ultrasonic wave propagation in tuffaceous sandstone (Kimachi, Japan) and granite (Iidate, Japan) were performed during increasing fracturing of the samples. The fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the specimen using a constant low strain rate. The observed variation of wave velocity (up to 40 per cent) due to the development of micro- and macrofractures in the rock is interpreted by rock models relating velocity changes to damage and crack density. The calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite. Using the estimated crack densities, the attenuation behaviour is interpreted in terms of different attenuation mechanisms; that is, friction and scattering. Rayleigh scattering as described by the model of Hudson (1981 ) may explain the attenuation qualitatively if the largest plausible crack dimensions are assumed in modelling.  相似文献   

Numerical simulation of the propagation of P waves in fractured media   总被引：1，自引：0，他引：1  

Sylvie Kelner  Michel Bouchon  & Olivier Coutant 《Geophysical Journal International》1999,137(1):197-206

We study the propagation of P waves through media containing open fractures by performing numerical simulations. The important parameter in such problems is the ratio between crack length and incident wavelength. When the wavelength of the incident wavefield is close to or shorter than the crack length, the scattered waves are efficiently excited and the attenuation of the primary waves can be observed on synthetic seismograms. On the other hand, when the incident wavelength is greater than the crack length, we can simulate the anisotropic behaviour of fractured media resulting from the scattering of seismic waves by the cracks through the time delay of the arrival of the transmitted wave. The method of calculation used is a boundary element method in which the Green's functions are computed by the discrete wavenumber method. For simplicity, the 2-D elastodynamic diffraction problem is considered. The rock matrix is supposed to be elastic, isotropic and homogeneous, while the cracks are all empty and have the same length and strike direction. An iterative method of calculation of the diffracted wavefield is developed in the case where a large number of cracks are present in order to reduce the computation time. The attenuation factor Q ⁻¹ of the direct waves passing through a fractured zone is measured in several frequency bands. We observe that the attenuation factor Q ⁻¹ of the direct P wave peaks around kd = 2, where k is the incident wavenumber and d the crack length, and decreases proportionally to ( kd ) ⁻¹ in the high-wavenumber range. In the long-wavelength domain, the velocity of the direct P wave measured for two different crack realizations is very close to the value predicted by Hudson's theory on the overall elastic properties of fractured materials.  相似文献   

区域介质品质因子对地震动参数衰减的影响   总被引：5，自引：0，他引：5  

杜修力  崔江余 《地震工程与工程振动》1999,19(1):15-20

本文考虑介质环境表观品质因子,根据美国西部强地震动记录确定了地震动衰减模型中的参数,在不考虑震源机制细节差异的条件下,分析比较了八个地区由于表观品质因子Ｑ值不同导致的地震动加速度傅里叶幅值谱和均方根强度衰减关系的差异。  相似文献   

华北地台东部古生代与新生代岩石圈地幔特征及其演化   总被引：28，自引：0，他引：28  

郑建平 Orei.  SY 《地质学报》1999,73(1):47-56

古生代含金刚石及捕虏体的金伯利岩和新生代含捕虏体的玄武岩先后共同侵位于华北地台东部,提供了研究自古生代以来板内岩石圈地幔特征及其演化的深源岩石探针。通过对古生代与新生代,新生代时郯庐断裂带内与带外岩石圈地幔物质之间岩相学,岩石和矿物的主元素,微量元素,地幔热状态的对比研究,结合现代地球物理资料,建立了以新生地幔物质对古老岩石圈置换作用为主的华北地台东部地幔减薄模型。该模型强调,古老岩石圈地幔业已成  相似文献